CHAPTER

Introduction

T he field of polymer science and technology has undergone an enormous

expansion over several decades primarily through chemical diversity. In

earlier days dilute solution behaviour, rubber elasticity, tacticity, single

crystal format~on, ~iscoelastic behaviour, etc., had their day of peak interest. The

concept of physically blending two or more existing polymers to obtain new

products is now attracting wide spread interest and commercial utilisation. Recent

polymer research and development have been centred less on new polymer

composltlons, but rather on the modlficat~on of exlstlny polymers These I

modlficat~ons Include compos~tes, graft, block or random copolymers, polymer

blends and lnterpenetratlng polymer networks. The progress in the area of polymer

blends during the past few decades has been tremendous and is motivated by the

knowledge that new molecules are not always requ~red to meet the needs for new

mater~als

The objective of polymer blendlng 1s a practical one of ach~eving

comrnerc~ally v~able products havlng e~ther unlque properties or Low cost in

cornpanson with borne other methods The property profiles of polymer blends

are superlor to those of component homopolymers Blendmy also provides

tremendous opportunltles for reuse and recycling of polymer matr~x

The physlcal and chemical properties of polymers vary from one to the

next so that the cho~ce of a given polymer for a particular appl~cation is often a

question of compromise.

1.1. Blending techniques

Depending on the technique employed in preparing the blends, one may

have different types of polymer blends such as ( I ) mechanical blends,

(2) mechanochem~cal blends, (3) chemical blends, (4) solution cast blends and

(5) latex polymer blends.

I. 1 . Mechanical blend

A mechanical blend is made by the melt blending of the component

polymers. While mixing two amorphous polymers the processing temperature

must be above the glass transition temperature of the components and in the case

(of semi-crystall~ne polymer, temperature must be hgher than the melting point of

the constituent polymers. Melt mixing is employed in systems where thermal

degradation is insiynlficant.

I. 1.2 Mechanochemical blends

In this method of blending, two polymers are mixed by melt mixing and

then crossl~nked using a co-crosslinker. This intercrosslinking between the two

polymers improves the phase morphology by the proper control of domain size

and distribution thereby providing resistance to phase separation.

f 3 Chemical blends

It1 , r / z r polymerisatlon and crossl~nklng of the constituent polymers make a

chemcal blend The resultant polymer blend is an interpenetrating polymer

network (LPN) rhese blends possess w q u e properties such as Improved

mechanical strength, thermal stability, chemcal resistance etc In comparison w ~ t h

conventional blends

11.4 Solution cast blends

In solutton blending a diluent is added, which reduces the effect of

temperature and sheanng forces and provides satisfactory mixing without

degradatton But the removal of the diluents may often lead to changes in the

phase morphology of the blend and in extreme case, complete phase separation

may occur Such phase separation may lead to sudden failure of blends in service

condition.

1.1.5 Latex blends

T h ~ s 1s one of the most important techniques for the preparation of

commercial polymer blends Latex is m the form of a suspension and mixing of

two latttces will lead to a random suspension of dissimilar particles, unaffected by

each other Matertal formed this way is an mtlmate mlxture of the two constituent

polymers

1.2. Compatibility of polymer mixtures

Very often the term compatibility is used synonymously with miscibility.

However, in materlal technology compatibility is a more general term. In a strict

technolog~cal sense, compatibility is often used to describe whether a desired or

beneficial result wcurs when materials are combined together. Miscible polymers

yleld property behaviour distinctly different from two phase polymer mixtures in

that miscible blends exhibit a single T, or properties similar to that expected of a

single phased system. Miscibility can ultimately be defined only in

thermodynam~cs term Whether two polymers are thermodynamically miscible or

not is governed by the Gibbs' free energy of mixing, AG,,. According to

elementary thermodynamics the change in free energy of a process is given by

A G = A - TAS., ( 1 . 1 )

If AG, 1s poslt~ve, the blend will undergo phase separation, while in the case of

miscible blends AG,, will be negative and the second derivative of AG,, with

respect to volume fract~on of component 2 (Qz) must be greater than zero.

Frorn the exper~mental evidence it is indicated that most of the polymer

pairs are imm~scible '.' Polymer miscibility is limited to those blend system with

an exotherm~c or mildly endothermic heat of mixing. Thls explains the miscibility

of blends w~th H-bondmg, dipole-dipole interaction or charge transfer

complexation between the two polymers.

1.3. Properties of polymer blends

The ultlmate behaviourd pattern of blends would depend upon factors such

as (a) extent of phase separation, (b) properties of the two phases, (c) composition

of the blend, and (d ) mteraction between the component polymers.

1.3.1 Physical properties

The physlcal properties of miscible blends follow the arithmetic semi-

empirical rule.'-"

where P is the property of interest, Q is the concentration and 1 is an interaction

term that can be positive, negative or zero. If I is zero, the rule of mixtures

(additivity principle) is observed. If it is positive, the property would be better

than the average of' the constituent polymers and the components are said to be

synergistic w~th each other. If I is negative, the blend property could be below the

simple average and the system is non-synergistic.

In i m s c i b l e blends, hawng a contmuous phase and a d~spersed phase,

another seml-empirical equatlon explms the physlcal properties

where 42 is the concentration of the dispersed phase constituents. The value of A

varies from 0 to and B depends on the relative values of the properties, PI and P2

and BX 1s a reduced concentration term that is a function of the maximum packing

fraction It was found that when A + 0, the dispersed phase is soft and when

A -+ m, the dispersed phase is hard. All physical properties other than the failure

and toughness of immiscible blends can be analysed by this equation.

1.3.2 Glass transition behaviour

Attempts have been made to describe glass transition behaviour by

different models that have been thermodynamic, kinetic or molecular in outlook.'

A miscible blend exh~bits a single glass transition peak intermediate between those

of the constituent po lymers .~e te rogeneous blends exhibit two separate T,s

representing each individual polymer present, though some shifting and

broadening are observed in most of the cases. The T, method is not reliable when

the T,s of the component polymers differ by only 20°C or less.

The equations commonly used to express T,-composition relationships for

miscible polymer blends are:

where T, and T,,, represent the glass transition temperatures of the undiluted

polymer components. W, and Wb are the respective weight fractions.

61) (;ordon-7uylor equation

T = [W,'1', + k(l -W.)T,b:I / [W. + k(l-W,)] ( 1 6 )

where k is the ratio of the thermal expansion coefficients between the rubbery and

glassy states of the component polymers, i.e., (alb-agb) / (al,-,;,)

The Kelley-Bueche equation is similar to the Gordon-Taylor equation

except that the volume fraction 4, is used instead of the weight fraction.

As a,%, has been proposed to be constant for all polymers, k = 1 and the

Gordon-Taylor and Kelley-Bueche equations reduce to the linear form.

The glass transition behaviour of polymer blends can be studied by the

following methods

(a) Dynamic mechanical analysis

The elastlc and viscoelastic properties of polymer derived by subjecting it

to small-amplitude cyclic deformation can yield important information concerning

transitions occurrlny on the molecular scale. In a highly phase separated polymer

blend, the transltlonal behaviour of the individual components will be unchanged.

Likewise, in a m~scible blend, a single and unique transition corresponding to the

glass transit~on of the blend will appear.

The dynamic properties are specified by means of two basic quantities.

One of these quantltles, the dynamic storage modulus (E'), provides a measure of

the effective stiffness of the material and is proportional to the energy stored and

received dunng each cycle of deformation. The other quantity known as the loss

factor or dampmy factor (tan S), is proportional to the ratio of net energy

dissipated per cycle as heat (E") to the peak energy stored (E'), i.e.,

tan 6 = E " E ' (1.10)

(b) Dielectric methods

The dlelectrlc loss factor (&") and the dissipation factor tan 6 (E"/&'), are of

primary interest as they are commonly used to ascertain polymeric transitions such

as the glass trans~tion. The experimental advantage of obtaining transition data

from electrical measurements over dynamic mechanical testing is in the ease of

changing frequency. However, the major disadvantage is the diff~culty in

determining the transitions of non-polar polymers.

A technique in which the change of dielectric loss is measured under a

definite temperature program, termed 'the thennodielectric loss measurement' has

been used for estimat~ng polymer-polymer miscibility. This technique is claimed

to be more sensit~ve for measuring the degree of miscibility than other methods.

(c) Dilujometric meihods

Polymer glass transitions have many characteristics similar to a second

order themodynarn~c transition. With respect to volume change, a discontinuity is

observed in the rate of volume change with temperature in the region of the glass

transition. In a blend of two distinctly different polymers, two phase behaviour can

be determined by two discontinuities in the derivative curve dv/dT corresponding

to the T,s of the respective phases. Dilatometric techniques are less sensitive than

dynamic mechan~cal methods.

(d) Culorimetric meihods

In calor~metr~c methods, the specific heat of polymers exhibits a change

when passing through the glass transition, generating a maximum in the value of

dC,/dT. The most common instrument used for this study is the differential

scanning calorimeter (DSC). Through sophisticated instrumentation, controlled

rates of heat~ng and cooling are possible with high accuracy of heat input or output

to small specimens.

(e) Thermo-optical analysis

Thermo-opt~cal analysis (TOA) has been employed by Shultz el a/.' to

investigate the misc~bility of polymer blends. This technique involves scribing

scratches onto a polymer or blend surface with a steel stylus. Light transmitted

through the film placed between crossed polariser and analyser 1s converted into

voltage and plotted against temperature. Single transition temperatures

monoton~cally lncreaslng w~th the content of the hlgher T, component are

charactenst~c of the mlsc~ble blend whereas two transltlons corresponding to the

blend const~tuents are observed for the ~mmlscible blend The results obtained by

t h ~ s technique were ~n good agreement wlth the more common techn~ques

fl Radioluminescence spectroscopy

T h ~ s unique method has been successllly utilised by Zlatkevich and

N ~ k ~ l s l u i . ' ~ Irradiation (electron or y ray) of the polymer or blend in the glassy

state results in trapped secondary electrons which are rapidly released, yielding

luminescence, once the sample temperature reaches the glass transition.

Maximum luminescence is observed at a temperature quite close to T, values. For

two phase blends, two distinct peaks can be observed in luminescence versus

temperature plots, corresponding to the respective T,s The resolution of the T, of

the minor phase (as low as several volumes percent) is quite good, thus proving

equal or superior sensitivity to mechanical or calorimetric methods.

1.3.3 Morphology

In majorlty of ~mmiscible blends, a hstinct minor phase is observed. The

size, shape and slze distribution of the minor phase has profound influence on the

polymer blend property.

Many researchers have turned to microscopy to determine the presence and

continuity of the two phases in a blend. In some blends one phase may be

dispersed as small spheres in the matrix phase. On the other hand, the dispersed

phase may exist as fibrils or platelets of varying aspect ratios. Another important

morphology is that in which both the phases are c o n t i n u ~ u s . ~ ' ~ ~ ~ The domain size

and phase morphology are important and influences the ultimate blend property

remarkably. ".I4 The morphology of polymer blends can be investigated by the

following techniques.

( i ) Optical mlcroscopy is a powerful technique for the morphology studies of

polymeric materials that transmit a reasonable portion of the light that is

incident upon them.

(ii) Scannrng electron microscopy (SEM) offers the simple procedure to study

the surface feature of a specimen. It is capable of generating high

magn~fication Images with a resolution better than 5 nm as well as low

magnification lmages even from rough surface samples, as a result of the

instruments ~nherently large depth of field." Since SEM reveals surface

features only, the internal structure of polymer blends is investigated by

viewing the fracture surface created at ambient or cryogenic temperature.

(111) Transmlss~on electron mcroscopy (TEM) constitutes a very powerful

instrument for the study of morphology. It offers high-resolution images,

together with ability to form small diameter probes. The sample should be

thin enough to transmit the electron beam through it. Staining technique is

employed to develop good contrast between the phases. Of all the

available staining agents osmium tetroxide ( 0 ~ 0 ~ ) is of particular

importance. The Os04 reacts with C-C double bond and therefore it is

widely used as a means of enhancing phase contrast in unsaturated

(iv) Atomic force mlcroscopy (AFM) has the advantage that i t can be used for

imaging of both conductive and insulating surfaces at ambient conditions

and is therefore, suitable for analysing polymers. The samples are prepared

by cryosectloning without any staining and the cut surface of the specimen

is analysed. The techmque of force modulation creates images that are

based on var~at~on in elastic modulus at the surface. The AFM has the

advantage of hgher resolution, simplicity of specimen preparation and

greater versatility in ach~eving image contrast, compared to other

microscopical techniques.

1.4. Crosslinking of polymer blends - - -

In two component polymer blends, phase separation is usually observed

due to small entropy of mixing and the heat of mixing. Though limited phase

separation is necessary for proper balancing of properties, unlimited or gross phase

separation is undesirable. Recent research on polymer blends suggests that the

domain size is important in determining the ultimate properties and performance

of the elastomer-plastomer blends. The efforts to control the size and distribution

of the domains led to a new type of blend with chemical crosslmking.

Interpenetrating polymer networks (IPNs) is a good example of chemical

polymer blend. The lPNs are relatively a novel combination of two or more

crosslinked polymer networks held together, mostly by permanent entanglements

(catenation) rather than by mutual covalent bonds (i.e., grafting).

1.5. History of IPN development

It is difficult to pinpoint the origin of interpenetrating polymer network.

Goodyear's work of vulcanisation,l8 development of polymer blends,I9 graftsz0 and

b~ocks,~' all led to the development of interpenetrating polymer networks. The

first interpenetrat~ng polymer network known was invented by Aylsworth in

1914.22 This was a mixture of natural rubber, sulphur and partly reacted phenol

formaldehyde reslns The term, interpenetrating polymer network, was coined by

Millar in 1960, who made a series of scientific study on PSRS interpenetrating

polymer networks, whlch were used as ion exchange resin mat rice^.^'.^^ Frisch

and coworkers conce~ved of the interpenetrating polymer networks as the

macromolecular analogue of ~ a t e n a n e s . ~ ~ Sperling and Thomas investigated finely

divlded polyblends usmg electron microscope to understand the phase structure

and correlated the mechanical and viscoelastic behaviour with the phase

Meyer considered the use of semi-interpenetrating polymer networks

as adhesivesz7 The interpenetrating polymer network field is not explored much

and it inspires yet more research. The history and development of LPN and related

materials are given in Table 1 . 1

Table 1.1. History of 1PNs and related materials - Event First investigators Year

IPN type structure

Graft copolymers

Interpenetratrny polymer networks

Block copolymers

Homo-IPNs

Sequential IPNs

Latex IENs

Simultaneous lPNs

IPN nomenclature

Thermoplast~c IPNs

Aylsworih

Ostromislensky

Staudinger & Hutchinson

Dunn and Melville

Millar

Sperling and Friedman

Frisch, Klempner & Frisch

Sperling and Amts

Sperling

Davison and Gergen

Ref, 26

1.6. Relationships among Mends, grafts and IPNs

Polymer blends are materials with two or more components mixed together

and exhibiting phase separation to a greater or lesser extent. The blends can be of

two types: those with primary bonds between the two polymers and those without

primary bonds. The most important group of blends without primary bonds are

mechanical blends.zx Introduction of some degree of chemical bonds between the

polymenc components gives rise to graft copolymer.29 When the chains of two

polymeric components are joined in an end to end fashlon, it is called block

copolymer.'0 Another class of blends are those in which one of the polymeric

phases or both the phases may be crosslinked. When both the polymeric phases

are crosslinked the material is called a full interpenetrating polymer network or

full-IPN" When one phase alone is crosslinked semi-IPN will result.32 If

polymer I is crosslinked and polymer I1 is linear the product is called a semi-IPN

of the first kind or semi-1. If polymer 1 is linear and polymer 11 is crosslinked a

semi-11 results. The different types of blend systems are schematically represented

in Figure I I

Figure 1.1 Schematic representation of different types of blends (aIMechanica1 blends (b) Grafts (c] Blocks (d)Semi-interpenetrating polymer networks (ejFull-interpenetrating polymer networksz6

Since most IPNs involve the polymerisation of one monomer in the

immediate presence of the other, they are also called graft copolymers. They form

a special class due to the crossllnking of one or both the polymers. The interesting

and unique properties of lPNs emerge when the deliberately introduced crosslinks

outnumber the accidentally introduced grafts. Some amounts of grafts are still

present in IPNs and usually contribute to the IPN behaviour in a favourable

manner. The IPNs and graft IPNs are schematically shown in Figure 1.2.

I Gratea chain

( b )

Figure 1.2. Schematic representation of (a) interpenetrating polymer network and (b) graft -interpenetrating polymer network3'

The two characteristics features of IPN which distinguishes itself from the

rest of the polymer~c mixtures are that ( i ) IPN swells but does not dissolve in

solvents and (il) creep and flow are suppressed.26

1.7. Mode of IPN synthesis

Accord~ng to the mode of synthesis, IPNs are distinguished into five

different types, viz., sequential interpenetrating polymer networks, simultaneous

Interpenetrating networks, interpenetrating elastomeric networks, thermoplastic

lPNs and gradient lPNs.

(I) Sequential Interpenetrating polymer network where polymer I is

crosslmked ~nit~ally followed by the swelling of polymer network 1 with

monomer 11 plus crossllnker and initiator and subsequent polymerisation of

monomer 11, m .siru.""'

(ii) S~multaneous ~nterpenetrating polymer networks SIN):^"' where a mutual

solutlon of monomer 1, monomer 11, crosslinker I, crosslinker 11 are taken

together and then polymerised simultaneously by non-interfering modes.

The above two types of synthesis are represented diagrammatically in

Figure 1 3

Figure 1.3. Schematic representation of synthesis of IPNs through (a) sequential and (b) simultaneous methodsa6

(iii) There 1s a th~rd mode of synthesis where two latices of linear polymers are

mixed and coagulated and both the polymers are crossl~nked

simultaneously. They are called interpenetrating elastomeric network

(IENs) 39

(iv) In the case of thermoplastic IPNs, physical crosslinks are present rather

than chemical covalent crosslmks. Frequently, the polymers exhibit some

degree of phase continuity. In all such cases, the thermoplastic IPNs behave

as thermoset at ambient temperature and as a thermoplastics at elevated

temperature

(v) In gradient IPNs the composition is varied within the sample at the

macroscopic level. This is carried out by swelling the network in monomer

for the requ~red time and polymerising rapidly, before equilibrium sets 40 tn .

Though these types of systems are termed mterpenetratmg polymer

networks, true ~nterpenetratlon occurs only at phase boundaries and most

mterpenetratlng polymer networks phase separate to some extent Molecular level

mterpenetratlon occurs m the case of total mutual solubtl~ty only

1.8. Properties of lPNs

The propertles of blends, grafts and mterpenetratmg polymer networks are

dependent on the two-phased nature, phase contmulty, doman slze and molecular

mixtng at phase boundar~es A study of morphology, glass trans~t~on temperature,

modulus, etc , explams the pecullar propertles of any two component systems

8 I Physical and mechanical behaviour

The properties of IPNs depend on (i) properties of the component polymer,

(ii) phase morphology and (iii) interaction between the phases.

As in the case of any other two component materials, some properties of

IPNs are approximately simple averages of the properties of the component

polymers. Sometimes the values are higher than that expected. The density

measurements on PU-PS simultaneous IPNs showed a density higher than

expected. This was due to the partial interpenetration of chains of the rubbery and

glassy polymer

1.8.2 Glass transition and viscoelastic behaviour

When two polymers form a phase separating mixture, each retains its T,.

In general transition may be broadened or shlfted by mixing and in the case of

mutual solub~lity only one transition is observed. Generally 4 situations are

observed.

(a) Two dlstlnct T,s corresponding to each network 42

(b) Two dlstlnct but Inwardly shlfted T,s 43

(c) One broad T, Intermediate to the T,s of each network 44

(d) One sharp 7., lntermed~ate to the T,s of each network 45

An mward shlft or a merglng of T,s can be considered as partial evldence

to ~nterpenetratlon

In many cases IPNs do not exhibit a single, broad glass transition

temperature. Two distinct transition, due to phase separation may be observed.

The loss and storage moduli for PEAlPS and PEAlPMMA IPNs showed that the

exchange of PMMA for PS, led to more compatibility because of increased

attractive force In the case of acrylic-urethane IENs, two dlst~nct transit~ons are

observed The sl~ght shlftlng and broademng of the peaks ~nd~cate moderate

degree of molecular r n ~ x ~ n ~ . ~ '

Fay, Murphy, Thomas and sperlin$' evaluated effect of morphology,

crossl~nk dens~ty and miscibility on IPN damping properties, for a number of

acrylic, methacryl~c, styrene and butadiene based copolymers and IPNs. The DSC

curve of 50150 composition showed a narrow T, for copolymer IPNs and a broader

T, for multiphase IPNs. Dynamic mechanical spectroscopy studies revealed that

multiphase IPNs had a broad transition. The glass transition behaviour of lPNs

depends on then morphology.

Kim elal.'\tudied the glass transition behaviour of PUPMMA and

PUPS IPNs Two glass transition temperatures were observed in both lPNs

showing phase separatlon. However, an inward shift in T,s is observed showing

some intermixing The pseudo lPNs and linear blends did not show this inward

shift.

Sartor el studied the DSC curve of IPN of composition 25% PU/75%

PMMA. In contrary to usual observation, T, increased over a very broad

temperature range, whch is due to the hstribution of relaxation time. Dynamic

mechanical properties of semi-IPNs based on poly(styrene-co-maleic anhydride)

and poly(2,6-&methyI-l,4-phenylene ethers) (PPE) was studied by Rosch e t ~ l . ~ '

Chen eta^.^' studied pseudo IPNs of linear poly(carbonate urethane) and

crosslinked polychloroprene. The single phase morphology of this pseudo lPNs

has been confirmed by DSC measurements. The glass transition temperature of

the linear PCU, crosslinked CR, linear blends PCUICR and pseudo IPNs are

shown in Table 1 2 Llnear blends showed two T,s, which are in between the T,s

of the component polymers.

Table 1.2. Glass transition temperatures in PCU/CR system -. - - . -- .~-

Polymer sample Composition (wt %) 'r&5 .~~ .~ -- PCUICR ("C) - ~ . -

Linear PCU 10010 -24.6

Crosslinked CK 011 00 -32.2

Linear blend PCUICR 50150 -30.6, -24.9

PlPN 50 50150 -33.7

PlPN 30 30170 -33.6

PlPN 10 10190 -32.4

Ref. 52

1.8.3 Ultimate behaviow

A large number of IPNs exhlbit considerable toughness as measured by

stress-strain curves or Impact strength. The main features required for this are:

(i) elastomeric domain size of 500-5000 A and (ii) a T, of elastomeric phase below

-40°C. The appearance of cellular-type morphology and dual phase continuity

contribute to toughening process.

Das and ~hakrabor t~" worked on the mechanical properties of epoxy-

poly(2-ethyl hexyl acrylate) (PEHA) IPNs. The variation of mechanical properties

with respect to blend ratios is

illustrated in Figure 1.4. It was

1 T observed that, as the elastomeric

L J 0 '0 0 I0 4 0 ic compared to epoxy resins

Pfwr.rar w t ~ ~ c ~ r

7%

2 roo I I m z i '"

UX,

Another important fact noticed

PEHA content in the blend is

: b\ increased, the properties like modulus

and tensile strength for both semi- and

full-IPNs decreased, due to the lower -

1 mechanical strength of PEHA

I with epoxy1PEHA lPNs was that the

semi-IPNs have higher modulus and

I tensile strength compared to full-LPNs.

This may be due to the higher

interpenetration of linear PEHA

molecules with the epoxy network

J whlle in full-lPN, PEHA was

0 20 YI 60 5 ) 4WItdT cmrww>PcuL crosslinked earlier to the formation of

epoxy network. Kelley et 01.'' worked Figure 1.4. Variation of mechanical properties with respect to blend on IPNs of PIJ and PMMA. The

for e ~ o x ~ / P E H A IPNs: composition arid presence of la1 modulus and ibl ultimate tensile , ,

crosslinking were found to influence

the thermal and mechanical properties of the solvent-cast films. Table 1.3

shows the effect of composition of the polyurethane/polymethyl methacrylate

composites on mechanical properties,

The SBR'F'S,~~ IPN developed by Donatelli etal. showed that at room

temperature, yield strength and modulus decrease with increasing SBR content,

but increases with the degree of crossllnlung of the rubber phase. Optimum degree

of toughness 1s obtained at an intermediate level of crosslinking of SBR. The

Impact strength was found to be independent of crosslinking in PS.

Table 1.3. Effect of composition on mechanical properties

Composite LPUI Young's Ultimate Tensile type PMMA modulus tensile strain

(MPa) strength (MPa) (%)

LPN (1.0) 1.0 8 3.8

IPN (0.75) 0.75 80 11.3

LPN (0.5) 0.50 500 16.6

IPN (0.25) 0.25 1740 33.8

IPN (0) 0 00 3200 35.0

S-I (1 0) 1.0 8 3.8

S-1 (0.75) 0.75 80 10.5

S-1 (0.6) 0.6 150 14.9

S- l (0.5) 0.5 490 235.0

S-1 (0.4) 0.4 600 29.4

S-1 (0.25) 0.25 1630 38.0

S-1 (00) 0 0 2850 36.2

S-2 (1.0) I 0 - -

S-2 (0.75) 0.75 5 1.2

S-2 (0.6) 0.6 17 4.8

S-2 (0.5) 0 5 80 8.3

S-2 (0.4) 0.4 550 24.1

S-2 (0.25) 0.25 1840 37.0

S-2 (00) 00 3200 35.0 ~

S-1 - semi-I; S-2 - semi-11; Ref. 54

The morphology of

IPNs can be determined by DCD-01 -I.

DVR---n-

electron microscopy. The

morphology has a strong 2

'[

,,4 5 !>

influence on the physical and .-

mechanical behavior of a 4 0 id %, 5o ,. 1 ~ ~ - c 30 I D 5" 6C :j

substance. Physical, mechanical Q.

and morphological behaviour of

PBRJPMMA IPNs are

correlated effectively by Das o I~ d o So 50 lo

1

el The effects of . - 0

0 - - composition and crosslinking 21 of elastomer and plastomer on . -..

.----C-C

properties were studied in + ,, , , , , U U I: 50 tl0 70 2-

detail. Figure 1.5 shows the P M U P CONTENT (w*.!~,

variation he properties with Figure 1.5. Variation of blend properties with

composihon and crosslink composition for PBR/PMMA IPNs~~

density. The morphological

studies showed that full-LPNs had a more ordered, compact and uniform phase

distribution compared to the corresponding semi-IPNs. This can explain the

higher tensile strength, modulus and tear strength of full-IPNs and higher

elongation at break (%) of semi-IPNs.

Frisch and ~ u e ~ ~ used TEM to visualise the network structure in

poly(butadiene)/PS, semi-IPNs. IPNs of PU and epoxy were studied by

Chem et al.58 When the epoxy content is increased, the tensile strength of the

IPNs and graft-IPNs decreased. The tensile strength of IPNs was lower than that

of the graft-IPNs ln the graft-IPNs, some urethane chains are grafted to the

pendant secondary hydroxy group of the epoxy through the reaction with

isocyanates, whlch resulted in hlgher intermolecular force and high tensile

strength

~ater'" used IPN approach to toughen micro cracking resistant high

. temperature polymers, for use in aircraftlaerospace structural components. In this

work he comb~ned crosslinked PMR-15 and linear LaRC-TP1 to form a new

sequentla1 semi-2-IPN called LaRC-RP41. Various techniques were employed to

study the phase morphology and phase stability of LaRC-RP41 neat resin and

composite

1.8.4 Morphology

Most IPNs and related materials show phase separation. The phases,

however, d~ffer in amount, size, and shapes, sharpening of their interface and

degree of contlnu~ty All these aspects control the morphology and thereby

determine the material properties. The factors affecting morphology are chemical

compatibility of the polymers, interfacial tension, crosslink density of the

networks, polymer~sat~on methods and IPN composition.

(u) C'omputibiliiy of IPNs

A degree of compatibility between polymers is introduced by IPN

formation as two polymers are interlocked in a 3-dimensional structure during

synthesis. The phase domains are smaller in hgher compatibility systems. In the

case of systems having low compatibility also the domain sizes are much smaller

than in the case of mechanical blending. Most of the earlier IPN studies were

based on immisc~ble polymers and a small gain in phase mixing was observed.

Fnsch and coworkers prepared IPNs from PS and poly(2,6-dimethyl-l,4-

phenylene oxlde) whch was miscible.60 Several partially miscible polymer pairs

were also made use of6 ' Uempner6' prepared IPNs, which contained opposite

charges, that showed better miscibility than lPNs without charge. olem man" and

co-workers prepared a semi-IPN from the miscible blend of phenolic resln and

ethylene-v~nyl acetate copolymer.

IPNs synthesised from miscible components showed thermally reversible

miscibility. The role of intermolecular interaction such as hydrogen-bonding on

enhancing polymer miscibility has been studied by Kim et al.@ They have

prepared IPNs based on poly(1 -hydroxy 2,6-methylene) phenylene (PHMP) and

PMMA. The H-bonding between -OH group of PHMP and carbonyl group of

PMMA leads to miscibility. Also, the use of copolymers having different amount

of functional groups enhances miscibility. Phase separation occurs during

polymerisation of two components, but the resulting phase domain size is

comparatively smaller for higher compatibility system. The morphology of P U P S

and PU/PMMA was explored by Frisch et al.4',65 PUPMMA pair, which has

close solubility parameter values, showed greater molecular mixing than PUPS

pair. In the sequential TPN with poly(ethy1 acrylate) (PEA) and copolymer of

MMA and styrene, worked out by Huelck et u/.4%ompatibility was studied in

dctail. Figure 1.6 shows the two types of IPN phase domains developed during the

synthesis of PEAPMMA and PENPS IPN synthesis.

(3,) (b)

Figure 1.6. Effect of polymer compatibility on morphology development: (a) microheterogeneous (PEA/PMMA) ,and (b) cellular structure (PEA/ PS)46

PEA and PMMA components are isomeric and almost compatible and the

dispersed phase dommn size was about 100 A giving rise to a fine structure.

Moussa and ~ecker~%tudied photopolymerisation of a multiacrylate system. The

wmpatibihty of the two components is essential for ensuring adequate mechanical

and optical properties of the final product. The ultra fast polymerisation, results in

the absence of phase separation in the system.

(b) Effect of crosslinking

IPN based on SBRRS studied by Donatelli el emphasises the control

of morphology by varying the crossldang levels. The degree of crossllnking of

each component, composition and chemical compatibility have been studied. The

polymer syntheslsed first forms the continuous phase and controls the

morphology. In the study, by Mai and Zeng on phase separation and morphology

of high performance semi-IPN based on acetylene-terminated sulphone (ATS-C),

the mechanism of phase separation is d i s c ~ s s e d . ~ ~ SEM observation of the

fractured-etched surface indicates a two phased co-continuous structure. Also

there is a decrease in dispersed particle size with increasing T, of the

thermoplastic. The SEM photograph shows a two-phase morphology of fractured

surface of ATS-CIPSF semi-IPN. In PUPMMA, IPNs, prepared by Akay ef al.

the elastic modulus, hardness and glass transition temperature are influenced by

the phase inversion in simultaneous IPN and dual phase continuity in the

sequential lPNs ''

Crossl~nk~ng of either polymer 1 or polymer 11 leads to phase continuity of

the crosslinked component. In interpenetrating polymer networks where both

phases are crosslmked, two continuous phases are observed. Extent of crossllnking

plays a significant role on the 1PN property.7"

The effect of crossllnking of the two polymer components was studied in

detail in the work by Donatelli el The following are the major conclusion

reached by them. ( I ) Lncreasing the crossldung level of polymer 1 decreased the

domain size of polymer 11. When both polymers are crosslinked the domain sizes

are decreased and dual phase continuity is observed. (ii) If polymer I is not

crosslinked, polymer 11 form continuous phase and polymer 11 attains some phase

continuity. The study on morphology and properties of lPNs of poly(zinc

acrylate) and polyacrylonitrile by Gupta and ~ r i v a s t a v a ~ ~ showed the increase in

wncentrahon of linear polymer and initiator, decreases c r o s s l i h g and increases

incompabbility, wh~le the increase in concentration of crossllnker increases both

crossllnking and phase separation. It was pointed out by Sperling that morphology

of semi- and full-IPNs depends on many factors in whlch crosslinking degree of

the network and mechanism of phase separation are of great importance.72

The crosslmk density strongly controls the morphology of the system as

seen from various In the case of blocks and grafts, the

compatibility 1s improved by the presence of intermolecular bonds. This is also

true in IPN where crosslinks are most prominent. Increased crosslmk density in

the polymer network I in an IPN decreases the domain size of polymer 11.'~ This

is due to the fact that tighter initial network restricts the size of the region in which

polymer 11 can phase separate. Variation of crosslink density of the second

network has little effect on IPN morphology, indicating that the first network is

controlling the phase separation.76 Rajalingam and coworkers77 studied a PVC-PU

based LPN. An increase in NCOIOH ratio increased,the crosslink density causing

increased phase distribution. Investigation of PUPMA sequential lPNs showed

that increase in crosslmk density and thereby the extent of mixing increased with

NCOIOH ratio. The crosslmk density of IPNs can be obtained from equilibrium

swelling studies7"rom swelling data molecular weight between crosslinks and

in turn crosslink density can be calculated. In the papers by Baer el a1.79,80 The

effect of crossltnking in poly(viny1 methy1ether)lpolystyrene system was explored

by small angle neutron scattering.

(c) Effect of composition

The composition of IPN affects the morphology and thereby the properties

of the product An increase or decrease in the percentage of the component

Introduction 25

polymer affects the domain size of the dispersed phase. Yenwo et 01.8"82 studied

the variation of domiun sue with composition and crossl~nk density of polymer I

for castor oil-urethane1PS IPNs. As the wt % of polymer I increases NCOfOH

ratio increases and the NCO/OH ratio has an effect on crossl~nk density,

morphology and properties. As PS concentration is increased, phase domain sizes

decreased. This is because the domain size of polymer I1 is quantitatively

controlled by the crossldung of polymer I. For sequential IPNs of PEAIPS,

Huelck observed a slight increase in domain size when the percentage of PS

mcreased from 25 to In the study of structure-property correlation of PSPE

IPN by Borsig et al. the influence of concentration of PS on the morphology of the

IPN samples was looked into.83 With increase in PS content the PS domain size

increased and a foam-like structure is developed.

The IPN composition determines the relative amount of the two phases

present after polymerisation. Increasing amounts of polymer 11 generally lead to

increasing domam sizes, though it also depends on polymerisation methods.

Verchere er oL8' studied rubber-modified epoxies and the influence of rubber

concent~ation on the morphology was looked upon. lncreasing the rubber amount

leads to an increase in the average size of dispersed phase particles.

7.8.5 Phase continuity in lPNs

Polymer 1 generally form the more continuous phase in IPNs, and this tends

to control the two-phase morphology. The morphology consists of interpenetrating

phase on a scale of 100-1000 A although polymer 11 shows the phase continuity

and sometimes even form a dspersed phase in a matrix of polymer 1. The

morphology may be modified by the degree of compatibility of the two polymer,

the polymerisation method and the IPN composition.

Several yuidel~nes concerning phase continuity may be set down that apply

to lPNs and many two polymer materials.

(i). For simple melt blends the polymer with higher concentration or lower

viscosity tends to form the continuous phase.

(ii). For bulk or solution graft copolymerisations, the first synthesised polymer

forms the more continuous phase. Polymer I1 usually forms cellular domain

in polymer 1.

(iii). Sturing of buk or solution type copolymerisation, especially during the

early stage of the polymerisation of polymer 11, may cause phase inversion

especially ~f polymer 1 is the minor component.

(iv). For emulsion polymerisation, polymer I1 forms the continuous phase after

subsequent mouldmg or film formation. In general, the moulding of shell-

core particulates into macroscopic structures leads to greater continuity of

the shell component.

(v). For d~block polymers, the relative proportion of the two polymers

determines the phase structure and continuity. Mid range composition

favours two continuous phases.

(vi) Crosshnking of either polymer I or polymer 11 tends to promote phase

continuity Materials with both polymers crosslinked (IPNs) tend to

develop two continuous phases.

1.9. Applications of IPN materials

The patent literature reveals that there are many patents utilising an IPN or

closely related materials. Patents mention the production of optically smooth

plastic surfaces, tough plastics, pressure sensitive adhesives, ion exchange resins,

noise and vibration damping materials, impact modifiers, contact lenses, etc.

Besides the patent literature there are number of suggested uses in scientific

literature. predecki8' mentions arteriovenous shunts and Toushaent et suggest

uses as casting syrups. Toughened elastomers, impact resistant plastics,

piezdalysls membrane and wire insulation have also been men t i~ned .~ ' .~~

Hutchinson and coworkers examined a wide range of IPNs, SINS and

semi-IPNs that were useful as reinforced elastomers. PUPMMA s e m i - 1 ~ ~ s ' ~

prepared by bulk polymerisation are used in shaping polymer articles. EpoxyRU

s e m i - 1 ~ ~ s ~ ' are used as adhesives. Ion exchange resins are prepared from

chloromethyl polystyrenetsulphonate polystyrene IPN.~ ' PSIPS IPNs are used to

prepare optically smooth plastic surfaces.92 Poly(ethylmethacrylate)/poly(n-butyl

acrylate) prepared by Sperling el find applications as noise damping coating.

Thermoplastic LPNs have outstandmg resistance to shrinkage and distortion on

heat ageing, ozone resistance and have better mechanical properties.

It could be noticed that lower melt viscosity, notable elongation at break,

high per cent stram to break and high modulus are achieved by chemical blending

or IPN formation. Butyl rubbertphenolic IPNs prepared by Tawney e l ~ l . " ~ ~

exhibited improved high temperature properties over ordinary butyl rubber. The

natural rubber latex was used for synthesising ~bberlplastic IPNs. 96-98 Epoxy

based IPNS"' were found to yield adhesives with high bonding strength to metal.

A hydrophilic/hydrophobic SIN suitable for contact lenses was prepared by

Falcetta el al. loU Hydroxy ethyl methacrylate or similar monomers formed

polymer 1 and a polysiloxane formed the network 11. Natural leatherlmbber IPN

gives rise to improved leather as discovered by Feairheller el al."' Plastic/rubber

lPNs find application in noise dampingp3 as tough plastic, e t ~ . ' ~ ~ Plastic/plastic,

IPNs are useful in preparing optically smooth surfaces? compression moulding

compositions103 and denture base material^."^ Rubbertplastic IPNs are used as

thermoplastic elastomersio5 and impact resistant plastic.106 Rubbedrubber IPNs

could be used as pressure sensitive adhesive.'"

A new application of LPN involves controlled drug delivery. For many

purposes a controlled steady drug delivery is desirable. In general IPNs and semi-

IPNs can be used wherever graft copolymers and polymer blends have been used.

The crossllnks in lPNs allow a new mode of control over two-phase morphology

and hence control their properties. Some commercially used IPN materials are

listed in Table 1.4.

Table 1.4. Commercially used IPNs

Manufacturer

Shell Chem~cal

Inc. lC1 Americas

Inc.

DSM N.V.

Shell Hesearcli B.V Reiohold

Chemical Co.

Rohrn & H w

Monsanto

Eaon

Trade h'nriw Cor~lp~isiliot~ A})plicntio~~

Kraton SEBS-polyester Automotive IPN prt s Rimplat Silicone rubber- Gears or

PU medical ITP PU-polyester- Sheet

styrene molding compounds

Kelburon PP-EP Automotive ~ b b e r - P E - Parts Rubber-PP Tougl~ plastic

TPR EPDM-PP Auto bunipcr parts and wire ar~d cable

- Anionic-cationic Ion exchange resins

Santoprene EPDM-PP Tires. I~oses. bclts, and gaskets

Sornel EPUM-PP Outdoor weathering

Telcar EPDM-PP Tubing, liners. or PE and wire

and cable Vistdor~ EPDM-PP Paintal~le

iluto~nolive parts

Acpol Acrylic-urethane- Sheeting styrene ~c i~ r r lu i~~~r~ l s ~nolding

Trub\-tr Acrvlic-baed Altificid ~iofdrrn teeth - \'il~yl-plienolics Daniping

cornpounds

Rei 108

A poss~ble disadvantage, at least for some appllcatlons, IS due to the

thermosetting nature of these materials However, latex-type formulatron

employing core-shell IEN mode or SIN formation permlts broader potentlal uses

It IS also noticeable that for applications such as adhesives, coatmgs or toughened

elastomers, crosslmked thermoset products are usually requlred

1.10. Objectives of the present work

As discussed m thls chapter, interpenetrating polymer network synthesis is

a novel approach towards achieving new crosslinked materials from polymers with

different property profile. The objectives of this new approach are: (i) to fill

technological gaps between known type of materials, (ii) to overcome important

disadvantages of the basic materials by blending with a second or third polymer,

(iii) to achieve the combined advantages of different polymeric materials, and (iv)

to develop new combination of properties, at times synergistically.

Several researchers have prepared IPNs based on various rubbers and

plastics earlier and evaluated their properties. Recently, Gradwell etal. studied

the morphology and thermal properties of tertiary aliphatic m-tetramethyl xylene

diisocyanate (TMXDI) based polyether urethane/polystyrene 1 ~ ~ s . " ~ Scanning

and transim~sslon electron microscopic studies indicated a grossly phase separated

morphology Structure of interpenetrating polymer network was studied using

neutron scattering technique by Clukina and ~aoud." ' Epoxy resinlanylated

polyurethane semi-IPNs were synthesised by simultaneous method and

characterised by Vabrik et al."' The DMTA studies of these system showed an

inward shift of glass transition temperatures indicating the compatibility of the

semi-LPNs Deb and coworkers studied sequential IPNs based on nitrile rubber-

phenolic resin blend and poiyalkyl methacry~ate."~ These IPNs showed superior

solvent resistant characteristics compared to the blends. The effect of crosslink

density on the physical properties of IPNs of polyurethane and 2-hydroxy ethyl

methacrylate terminated polyurethane was investigated by Hsu e / a/. ' "

L~terature shows that majority of natural rubber based IPNs are from NR

latex. The use of sol~d natural rubber in IPN preparation is not common. Das and

coworkers studied the mechanical properties of NRPS and NRPMMA I P N S . ~ ~ . ~ '

The present work 1s based on solid natural rubber and polystyrene, where they are

intimately m~xed by the sequential method of IPN synthesis. Natural rubber (NR)

is a typical elastomer having good resilience, elongation and elasticity.

Polystyrene 1s an amorphous brittle thermoplastic. The blending of the rubber and

plastic phase will result in a h g h impact resistant plastic or toughened rubber

depenhng on the composition of the blend. This work is an attempt to the

effective utilisation of natural rubber whch is readily available in Kerala. The

solid natural rubber 1s chosen for this study considering the ease of storage, mill

mixing and possibility of different vulcanisation processes.

The work embodied in this thesis concentrates on the preparation and

characterisat~on of sequential interpenetrating polymer networks based on natural

rubber and polystyrene. Such a synthesis of IPN combines the elastomeric

properties of N R and thermoplastic characteristics of PS, which can lead. to

superior property profiles. The material performance is evaluated by studying the

mechanical properties, viscoelastic behaviour, T, swelling characteristics in

various solvents and dielectric behaviour. The effects of blend composition, nature

of initiator on the polymerisation of polystyrene and the crosslink density of PS

phase on the IPN structure and properties have been evaluated.

It may be noted that as the initial step of IPN preparation from NR and PS,

the klnet~cs of' dlffuslon of styrene monomer through crosslinked N R in the

presence and absence of the crossl~nker (divinylbenzene) has been studied in

detail. A close and systematic observation of swelling kinetics facilitates easy

control of the monomer uptake by network I (NR) and thereby providing the scope

for the control of composition, morphology and performance of the IPNs

developed Based on the information derived from swelling studies, NRIPS

interpenetrating polymer networks were prepared by the sequential technique.

The morphology of the IPNs was studled in detail using a scanning electron

microscope. The samples for this study is prepared through the ebonite method.

The morphology of selected samples was further investigated using a transmission

electron microscope. The fracture surfaces are viewed under a scanning electron

microscope to study the mode of failure. The study of mechanical performance

and fractography are important to predict the service life of the IPNs.

The viscoelastic behaviour of IPNS has been investigated using the

dynamic mechanical analysis. This will provide insight into various aspects of

material structure and the transition behaviour of the material. Cyclic stresses

during services w~l l produce heat and hence the studies of dynamic mechanical

behaviour of the IPN systems become important. The viscoelastic behaviour of

hll-IPNs and semi-1PNs have been investigated as a f ic t ion of blend ratio,

initiating system and crosslder content. The variation of tan 6,.,, loss modulus

and storage modulus as a function of temperature has been analysed. Cole-Cole

plots are d r a w to predict the heterogeneity of the system.

Transport of various solvents through polymer materials has been a subject

of fundamental interest. The evaluation of dimensional stability of the polymeric

system in presence of aggressive liquids is important from the application point of

view. The sorption, diffusion and permeation behaviour of NRPS lPNs in various

penetrants has been investigated. The influence of blend composition,

temperature, crosslink density and initiator system on the transport properties of

semi- and full-IPNs has been studied in detail. The activation energy of diffusion

and permeahon has been estimated and thermodynamic parameters have been

calculated. The nature of c ross lds present in the N W S IPN system has been

predicted using the phantom and aff111e models. The influence of swelling on

tensile properties has been stuhed by conducting the tensile strength

measurements of dumbbell samples swollen in toluene. The diffusion studies have

been carried out m xylene, toluene and benzene and oils l k e petrol, diesel and

kerosene.

Thermogravimetric analysis is used to study the thermal behaviour of

N W S IPNs. The nature of mode of degradation of IPNs under the influence of

temperature 1s h~ghly important in the processing and fabrication of products.

Thermogravimetry is used widely for determining the thermal stability of

polymeric matenals The loss of weight with temperature is determined from the

TGA curves. The effect of blend composition, crosslinker content and initiating

system on the seml- and full-IPNs has been investigated. The thermal ageing of

the IPNs has been carried out for 72 and 120 h at 100°C. The decrease in tensile

strength on thermal ageing is evaluated.

Only limited studles have been reported on the elechrcal properties of

undoped IPNs The dielectric properties of sequential IPNs from NR and PS were

measured as a function of frequency, initiating system, blend ratio and

crossllnking denslty. The dielectric constant, dissipation factor, dielectric loss

factor, volume resistivity and conductivity of the IPNs were analysed with special

reference to blend ratio and crosslinking of PS phase. T h ~ s study was aimed at

evaluating the possibility of use of NRPS IPNs as insulating materials.

In all the above mentioned investigations the performance of both semi-

and full-IPNs has been evaluated. The properties ehb i t ed by the IPNs have been

wt~elated w~th the morphology.

I I I References

1. R P. Petrich. Polp. Eng. %., 13,248 (1973).

2. R. A Dickie and S. Newman, Aaylae Polymer Partids Comprising a Core and Outershellandan Intermediate Layer, U. S. Patent, 3,787,522, Jan. 22,1974.

3. A L. Bull and G. Holilen, Rubber& Amer. Chem. Soc., April 1976.

4. J. R. Richards, R. G. Mancke and J. D. Ferry, J Po/ym. Su. Part6 2, 197 (1964).

5. L. E. Nielson, Bedidnghehpasition o f f i t u rn , Marcel Dekker Inc., New York, 1978, p. 13.

6. R. Hill. J Me&. Phys. Sobds, 13,180 (1965).

7. M. Grayson (Ed.). Enryclopedia of Chemical Technolw, John Wiley and Sons, New York, 18,458 (1982).

8. N. M. Bikales (Ed.), Encydopedia ofPolymerScience and Technology, Wiley-Interscience, New York, 10,701,703 (1x9).

9. A. R. Shultz and B. M. Beach, J AppL Polym. Su, 21,2305 (1977)

L. Y. Zlatkevich and V. G. Nikokkii, Rubber Chem. Technol., 46,1210 (1973),

L. P. McMaster, Aspets ofLiquid-Liquidhe Transition Phenomena in Multicompnent Polymeric Sptems, Adv. Chem. Ser., No. 142, Amer. Chem. Soc., Washington, M), 1975.

D. Turnbull. SolidStatefip., 3 (1966).

D. J. Houston, F. U. Schafer, J. S. Bath and M. H. S. Gradwell, J /.pL Polym. Su., 67, 1973 (1998).

M. H. Han and S. C. Kim, Poljm. Adv. Technol., 8,741 (1997).

B. J. Hant and M. I. James, Polymer Characteriration, Chapman and Hall, 1993

R A. Weiss, S. Sasonko and R Jerome, Maaomolecules, 24,2271 (1991).

S. Gebiioglu, A. S. Argon and R E. Cohen, Polymer, 26,519 (1985).

C. Goodyear, (/ S. Pat. 3,633 (1844).

T. Hancock. Engl Pat, No., 11,147 (1846).

1. Ostromisbnsky, U S. Pat., 1,613,673 (1927).

A S. Dunn and H. W. Melville, hbture, 169,699 (1952).

J. W. Aylsworih, U S. Pat., 1,111,284 (1914).

J. R. Millar, J Chem. Sot., 1311 (1960).

J. R. Millar, Persona/Communication, Dec. 5, 1978 and Jan. 11, 1979.

H. L. Frisch and D. Klempner, Adv. Maamol. Chem., 2,149 (1970).

L. H. Sperling, lnterpeneh.ating Polymer Network and Related Materials, Plenum Press, New York, 1981

G. C. Meyer and P. Y. Mehrenberger, Eur. Polym. J , 13,383 (1977).

J. E. Wook. Polym. h g Sci, 13.46 (1973).

G. E. Molau (Ed.), Cofoidal and Morphological Behaviour of Block and Grab Copolymers. Plenum, New York, 1971.

M. Szwarc. Po1y11. fi1g Scj, 13, 1 (1973).

J. L. Han, Y. C Chern, K. Y. Li, K. H. Hsiech, J /.pL Polym. Sci, 70(3), 529 (1998).

D. K. Mohapaba. D. Das, P. L. Nayak and S. Lenka, J Appl Polym. Sci., 70(5), 837 (1998).

D. Chakrabrthy. B. Das and S. Roy, J /.pL Polym. Sci., 67,1051 (1998)

A B. Samui, U. G. Suyavanshi, M. Patri, B. C. Chakraborty and P. C. Deb, J AppL Polp . Sci, 68,255 (1998).

Qinmin Chen, Hanhua Ge, Dongzhong Chen, Xiahgdong He and Xachai Yu, J AppL P o l ~ Sci., 54. 1191 (1994).

V. Mishra, P. E. Duprez, E. Cosen, E. J. Grethak and L. H. Sperling, J Appl Polp . Sci, 58,331 (1995).

M. Patri, A. B. Samui, B. C. Chakraborty and P. C. Deb, J Appl P o l p Sci, 65, 549 (1997).

Introduction 31

S. Tan, D. Zhang and E. Zhou, Acta Polpenw, 47,507 (1996).

H. Frisch, D. Klempner and K C. Frisch, Polym. Left., 7,775 (1965).

Y. S. Lipatov, L. V. Karanova, L. A Gorbach, E. D. Lutsyk and L. M. Sergeeva, Polym. ht., 28(2). 99 (1992).

S. C. Kim, D. Mempner, K C. Frisch, H. L Frisch, Mmomolecules, 9.263 (1976)

D. Klempner, K C. Frisch and H. L Frisch, J. Uastoplasti~, 3,2 (1971).

L. H. Sperling, H. J. George, V. Huelck and D. A Thomas, J /.pl Polym. Sci., 14,2815 (1970).

D. R Bradman, H. F. George, M. L. Kirkpahick, L. H. Sperling and D. A. Thomas, J. AppL Polym. &, 14,73 (1970).

K C. Fnxh. D. Klempner, S. Migdal, H. GhiradeUa and H. L. Frisch, Polp. Erg Sci, 14, 76 (1974).

V. Huekk, D. A Thomas and 1. H. Sperling, Macromoldes, 5,340,348 (1972).

D. Klernpner. H. L. Frisch and K C. Frisch, J Polym. Su FhrtA, 28,921 (1970).

J . J. Fay, C. J. Murphy, D. A. Thomas and L. H. Sperling, Polym. bg So'., 31(24), 1731 (1991).

S. C. Kim, D. Klempner, K C. Frisch and H. L Frisch, Mauomolecules, 9(2), 263 (1976).

G. Sartor, E. Mayer and G. P. Johari, J Polym. %, Part 6. Polym. &., 32, 683 (1994).

J. Rosch, L. L. de Lucca Freitas and R Stadler, Coloid and PolJnner Science, 272, 261 (1994).

Z. J. Chen, Yongpeng Xue and H. L. Frisch, J P o h . Sci., Part A P o l p Chem., 32, 2395 (1994)

B. Das and D. Chahabrty, Polymer GeIsandNehvork 3,197 (1995).

S. S. Kelley, T. C. Ward and C. Wolfgang, J. &pl Polp. Su., 41,2813 (1990).

A A Donatelli, L. H. Sperling and D. A Thomas, Macromolecules, 9(4), 676 (1976).

B. Das, T. Gangopadhyay and S. Sinha, J AppL Polym. Sci., 54,367 (1994).

H. L. Frisch and Y. Xue, Polymer J , 26(7), 828 (1994).

Y. C. Chern. K. H. Hsieh, C. C. M. Ma and Y. G. Gong, J Mater. Sci. 29,5435 (1994).

R. A. Pater. Polym. fig Sci. 31(1),20 (1991).

H. L. Frisch. D. Nempner, H. K. Yoon, K C. Frisch, Macromolecules, 13, 1016 (1980).

L. H. Sperling, Pure and Applied Research in Interpeneb.ating Polymer Networks and Related Materials, in Po/ymer~endsandMivtum(Eds., D. S. Wakh, J. S. H i d n s and A. Maconnichie), NATO AS1 Series, Series E: Applied Science, No. 89, London, 1984, p. 267.

D. Klernpner, K. C. Frisch, H. X. Xiao, E. Cassidy and H. L. Frisch, Two and Three Component h7lerp~nebating Polymer Nehvorks in Mult~component Pol$meric Materials ( a s . , D. R. Paul and L. H. Sperling), Advances in Chemishy Series, 211,211 (1986).

M. M. Coleman, C. J. Serman and P. C. Painter, Maaomolecues, 20,226 (1987).

H. I. Kim, T. K. Kwei and E. M. Pearce, MauomolecvIes, 22,231 (1989)

S. C. Kim. D. Klempner, K C. Frisch, H. L. Frisch and H. Ghiradella, Porn. hg . Sci,, 15,339 (1975).

K. Moussa and C. Dekker, J Polym. Sci., Chern., 31,2633 (1993).

A. A Donatelli. L H. Sperling, D. A Thomas, Mauomolecules, 9,671 (1976).

K. Mai and H. Zeng, J Appl Polym. Sd., 53,1653 (1994).

M. Akay and S. N. Rollins. Polymer, 34(9), 1865 (1993).

B. Das and T. Gangopadhyay, Eur. Polym. J , 28(8), 867 (1992).

N. Gupta and K. Srivastava. Polymer, 35(17), 3769 (1994).

L. H. Sperling, IPN and Related Materials, Plenum Press, New York, Ch. 6, 1981

B. Das and S. Sinha, T. Gangopadhyay, Eur. Polym. J , 29(1), 57 (1993).

B. Das. T. Gdngopadhyay and S. Sinha, Eur. Pobm. J , 30(2), 245 (1994).

A. A Donatelli, D. A. Thomas and L. H. Sperling, Recent Advances in Polymer Blends, Grab andBlocks (Ed., L. H. Sperling), Plenum Press, New York, 1974.

A. A. Donateh, D. A Thomas and L. H. Sperling, d Appl. Polp . Sci, 21,1189 (1977).

R P. Rajalingam, P. Radhaluishnan and D. J. Feromin, Met. Meter. Roc., 1(3), 197 (1989).

L. F. Gudeman and N. A. Peppas, d 4ppl. Polym. Sci., 55,919 (1995)

R. M. Briber and 9. J. Baer, MaomolemIes, 21,3296 (1988).

B. J. Baer. R. M. Briber and C. C. Han, Po lp . Bepr., 28(2), 169 (1987).

G. M. Yenw~~. J. A. Manson, J. Pulido, L. H. Sperling, A. Conde and N. D. Manjarres, J Appl Poljm Sci, 26,1531 (1972).

G. M. Yenwo. L. H. Sperling. J. A Manson and A. Conde, Chemisby and BoperbPs of Crosslinked Polymers (Ed., S. S. Labana), Academic Press, New York, 1973.

E. Borsig, A Fiedlerova and G. H. Michler, Polymer, 37,3959 (1996).

D. Verchere, J. P. Pascault, H. Sautereace, S. M. Moschiar, C. C. Riccardi and R. J. J. William, J Appl Po&m. Sci., 42,701 (1991).

R. E. Toushaent. D. A Thomas and L. H. Sperling, d Polym. Sci. Part C, 46,175 (1974).

P. Predecki, J &ned Mater. Res., 8,487 (1974).

L. H. Sperling, V. A. Forlenza and J. A. Manson, J Polp. Sci. Po&~n. Lett Ed, 13, 713 (1975).

G. Odian and B. S. Bernstein, Nudeonics, 21,80 (1963).

F. G. Hutchnison, bG. Pat, 1,239, 701 (1971).

J. M. Hawkins. Br. Pat, 1,197,294 (1970).

G. S. Solt. Br Pat., 728,508 (1955).

J. J Staudinger and H. M. Hutchinson, U S. Pat, 2,539,377 (1951).

L. H. Sperling and D. A. Thomas, LI S. Pat, 3,833,404 (1974).

P. 0. Tawney, J. R. Little and P. Viohl, hd Ehg Chem., 51,937 (1959)

P. 0. Tawney and J. R. Little, LI S. Pat, 2, 701,895 (1955).

E. H. Andrew and D. T. Turner, J Appl Polp. Sd., 3.366 (1960).

G. F. Bloomfield and P. Mcl Swift, J Appl Chem., 5,609 (1955).

T. D. Pendle, abck and Grak Copolymerisation, Vol. 7, (Ed., R J. Ceresa), Wiley, New York. 1973

Naamlooze Nennootschap de Bataafsche Petroleum Maatschappij, Br. Pat, 736, 457 11955).

J. J. Falcetta, G. D. Friends and G. C. C. Niu, Ger. Offen. Pat., 2,518,904 (1975)

S. H. Feairheller, A. H. Korn, E. H. Harres, E. M. Rlachione and M. M. Taylor, Lr S. Pat, 3,843.320 (1974).

K. C. Frisch. H. L. Frisch and D. Klempner, Ger. Pat, 2133,387 (1972)

Anonymous (Ciba Lid.), Br. Pat, 1,223,338 (1971).

B. E. Causton, J. Dent. Res., 53(3), 1074 (1974).

W. K Fischer. US. Pat, 3,806,558 (1974).

B. Vollmert. U S. Pat, 3,055,859 (1962).

H. A Clark. Lr S. Pat, 3,527,842 (1970).

L. H. Sperling, Muhcomponent Polymer Matenah (Eds., D. R. Paul and L. H. Sperling). Advances in Chemishy211, Am. Chem. Soc., Washington, DC, 1986.

D. J. Hourston. F. U. Schafer, J. S. Bater and M. H. S. Gradwell. Polper, 39, 3311 (1998).

I. Chikina and M. Daoud, d Polp. Sci. Polym. Php., 36,1507 (1998).

R Vabrik, I. Czajilik, G. Tuy, I. Rusznale, A. Ule and A. Vig, J /.pl Po/ym. Sci, 68, 111 (1998).

A B. Samui, U. G. Suyavanshi, M. PaM, B. C. Chalvabrthy and P. C. Deh, J Appppl: Polp. Sd, 68,255 (1998).

T. T. Hsieh, K H. Hsiech, G. P. Simon, C. Tiu and H. P. Hsu, J Polm. Res. Taiwan, 5, 153 (1998)