final deva project

8/13/2019 Final Deva Project

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CHAPTERI

INTRODUCTION

Polymers1 are macromolecules built by the linking together of large number of

much smaller molecules. The small molecules that combine with each other to form

polymer molecules are termed monomers and the reactions by which these combinations

take place are called polymerizations.

In 1929 Carothers2 classified the polymerization process into two kinds viz.

addition polymerization and condensation polymerization, whereas classification by

Flory3

is based on the mechanism of the polymerization reaction.

Step (Condensation) Polymerization

In step polymerization, the polymer4 build up proceeds through a stepwise

reaction5 between functional groups of the monomers with the elimination of small

molecules such as H2O, NH3, HCl etc., in condensation reaction the type of product

formed is determined by the functionality of the monomers. Monofunctional monomers

give only low molecular weight products with no plastic property. Bifunctional and

polyfunctional monomers give only linear and branched three dimensional network

polymers respectively. It was Stelle6 who pointed out that the structural unit of a step

reaction polymers are usually joined by interunit functional groups like,

R R

C X C

R R n


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Where X is the polymer matrix. The most important reaction which has been

used for the preparation of linear condensation polymers is that of addition and

elimination of the carbonyl double bond of carboxylic acids.

Chain Reaction (addition) Polymerization

Addition polymerization is the process of formation of addition polymers from

monomers without the loss of molecules. It consists of three major steps, namely,

initiation, propagation and termination. These processes can be brought about by free

radicals, cations, anions, -rays, etc.,

Initiation

H

CH2=CHY R CH2 C

R

Y

Here a free radical R attacks itself to the olefin and produces a new radicalconsisting of radical and the monomer unit.


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Propagation

H H H

CH2=CHY

R CH2 C R CH2 C CH2 C

Y Y Y

CH2= CHY

H H

R CH2 C m CH2 C

Y Y

This step is very rapid and leads to high molecular weight products.

Termination

Termination may occur by several processes. Coupling is termination by

combination of two growing chain radicals.

H H H H

Termination

R CH2 C m CH2 C R CH2 C m CH2 C n

Y Y Y Y


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Free radical chain polymerization

In radical polymerization, the active centers are free radicals. Owing to the

presence of an unpaired electron the free radical can easily react with various monomers.

The free radical chain polymerization involves initiation, propagation, transfer and

terminations steps.

Chain initiation

Chain initiation step is the relatively slow and rate controlled step. The initiation

of the polymer chain growth is brought about by free radicals produced by the

decomposition of initiators. The term chain growth represents a process involving a

continuous and very rapid addition of the monomer units to form polymer chains.

Initiators

Initiators are normally unstable compounds and decompose into products called

free radicals. If R-R is an initiator, and the pair of electrons forming the bond between the

two Rs, can be represented by dots, the initiator can be written as R:R.

When energy is supplied to this compound in the form of heat, the molecule is

split into two symmetrical components, each of them having one of the electron from the

electron pair.

R . . R R

The decomposition of the initiator to form free radicals can be induced by any one

of the following methods.

a) Thermally or by heating


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b) Photo chemically(i) By irradiation with artificial light, sunlight, etc.,

CH2 = CHX h [CH2= CHX]*

(Monomer Molecule) (Excited Monomer Molecule)

2[CH2= CHX]* CH3CHX + CH2= CX

(Monomer free radicals)

(ii) By irradiation with -rays or by high frequency electric current.c) Catalytically.

The free radical Rattacks the double bond in the monomer molecule.

H

R+ CH2=

CH R CH2 C

X X

Chain Propagation

The free radical found in the initiation step is capable of adding successive

monomers to propagate the chain.


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H H H

R CH2 C + CH2= CHX R CH2 C CH2 C

X X X

CH2= CHX

H H H

CH2= CHX R CH2 C CH2 C CH2 C

X X X

H H H H

R CH2 C CH2 C CH2 C CH2 C

X X X X

It is to be noted that the chain growth takes place by the head to tail addition of the

chain radical to the monomer.

Chain Termination

The termination of growing chains results in the final maturation of the polymer

molecules with a net loss of one of the radicals by any of the following process.

Termination of the growing polymer radicals results in the formation of dead polymer7.


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Combination

As a result of collision between the growing chains, the terminal radicals couple to

form a polymer.

H H H H

R CH2 C + C

CH2 R R CH2 C C CH2 R

X X X X

Disproportionation

The polymer chain may get terminated by the combination of two growing

polymer chains producing two polymer molecules.

H H

R CH2 C + R CH2 C

R CH = CH + CH2 CH2 R

X X X X

Chain transfer

The premature termination of the growing polymer chain may occur by the

transfer of a hydrogen atom or other atoms or species between the monomer and the

polymer radical, initiator, polymer, solvent or added modifier.

H

R (CH2 CH )n CH2 C+ R H R (CH2 CH )n CH2 CH2+ R

X X X X


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The radical R can initiate the growth of another polymer chain if it is reactive

enough under the polymerization condition.

Reaction with another free radical

CH2 CHX + CH2 C

HX CH2 CH2 X + CH=CHX

Reaction with solvent

H H

CH2 C + CCl4 CH2 C Cl C

Cl3

X X

Reaction with monomer

H H

CH2 C + CH2 C CH2 CH2 + CH2 C

X X X X

Reaction with a macromolecule


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CHX + CH2 CHX CHX + CH2 CH2X

CH2CH

Reaction with an initiator

H

CH2 C + R O OH CH2 CH2 + R O O

X X

Inhibitors

Substances which affects the rate of polymerization are termed inhibitors or

retarders according to whether the rate is reduced to zero or to a finite value.

Mi + A MiA

Where, A represents a molecule of inhibitors or retarders.

Atmosphere, oxygen is a good inhibitor. The initiating action of oxygen is due to

its biradical nature.

P+ O

O

P O O

(Inhibitor)

P . O O + P P O O P

Where, P is a growing polymer chain.


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So the radical polymerization is carried out under the nitrogen atmosphere.

Redox Initiated Polymerization

Normally an initiator to start the polymerization reaction at a satisfactory rate is

frequently used with an activator. When a reducing activator is used with an oxidizing

initiator, the system is called as a Redox System8. A survey of literature on radical

polymerization of vinyl monomers reveals that redox systems have received wide

attention in recent years as initiators of vinyl polymerization.[9-13]

Initiator can also be induced to decompose into free radicals by making use of

suitable catalysts. The electron transfer mechanism resulting in an oxidation reduction

(redox) is involved. The redox reactions which involve low activation energies (Ea) (12-

20 k cal/mole compared to ca. 30k cal/mole in thermal initiation). This enables the

polymerization to be carried out at low temperatures, the possibility of side reaction will

decreasing, which may change the reaction kinetics and the properties of the resulting

polymer.

Gowariker et.al14

have presented the advantages of redox reactions as:

a) The radical production occurs at reasonable rates at room temperature.b) Polymers with specific end groups can be prepared andc) Extraction of monomer with the oxidizing agent is minimized avoiding any

branching or cross-linking in the polymers.

RATE OF REDOX POLYMERIZATION

Depending upon the termination mode, there are two kinds of kinetics of redox

polymerization15. They are propagation and termination steps. Many of the redox

polymerization follow the same manner as other polymerizations, the only difference

being the source of radicals for the initiation step. In these polymerization where


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termination is bimolecular reaction of propagating radicals the initiation and

polymerization rates will be given by the equations.

Ri = kd [Reductant] [Oxidant]

Rp = kp[M] (kd) [Reductant] [Oxidant]

2kt

Where,

kd= disproportionation constant

kp = propagation constant

kt - termination constant

Some polymerizations involve a change in the termination step from the usual

bimolecular reaction to monomolecular termination involving the reaction between the

propagation radicals and a component of the redox systems. This leads to kinetics which

are appreciably different from those previously encountered.

Thus in the alcoholCe(IV) systems16termination occurs according to

Mn + Ce(IV) Ce(III) + H+ + polymer

At high ceric ion concentration. The propagating radical loses hydrogen to form a dead

polymer molecule with an olefinic end group. The rates of initiation and termination are

given by

Ri = kd [Ce(IV)] [alcohol]

Rt = kt [Ce(IV)] [M]

By making the usual steady state assumption, the polymerization rate may be

obtained as

Rp = kd kp [M] [alcohol] / kt

In many redox polymerizations, monomer may actually be involved in the

initiation process17.


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CHAPTERII

REVIEW OF LITERATURE

I. Polymerization of acrylonitrile

Saccubai and Santappa1have studied the polymerization of acrylonitrile by V(V)

lactic acid system in aqueous sulphuric acid medium. From the results it is concluded that

the polymerization reaction is initiated by an organic free radical arising from the V(V)

lactic acid reaction with termination by V(V) ions. Mutual termination of active polymer

radicals does not appear to operate under the conditions studied. The various rate

parameters are evaluated.

Kinetics of vinyl polymerization of acrylonitrile initiated by the redox system

V(V) tartaric acid have been investigated by Mohanty et.al.2 From the results it is

concluded that the polymerization reaction is initiated by an organic free radical arising

from the V(V) tartaric acid reaction with termination by V(V) ions. A suitable kinetic

scheme has been proposed and the various rate and energy parameters were evaluated.

The vinyl polymerization of acrylonitrile by the V(V) glycerol redox system in

sulphuric acid perchloric acid have been investigated by Rout (Et. al.)3 The rate of

polymerization and the rate of V(V) disappearance were measured with respect to their

dependence on time, monomer, metal ion, glycerol, acid and ionic strength. Experimental

evidences provide support to a mechanism involving initiation by a free radical produced

by the decomposition of the acylic complex between V(V) and glycerol. The various rate

and activation parameters are evaluated and an appropriate reaction scheme is proposed.

The polymerization of acrylonitrile initiated by Ce(IV) with Glycerol have been

studied by Rout et.al4. The initiation was effected by the Ce(IV) and the radical produced

from the reaction of Ce(IV) with glycerol. At lower concentrations of Ce(IV), the rate of

monomer disappearance was proportional to [M]1.5, [G]0.5and [Ce(IV)]0.5and the rate of


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Ce(IV) disappeance was directly proportional to [Ce(IV)] and [G]. The results were

explained by a kinetic scheme involving the oxidation of substance by Ce(VI) to give the

primary radical and further reaction of the latter with Ce(IV) to give the final product.

The termination step is postulated to be mutual at lower concentration of Ce(IV) andlinear at higher concentration of Ce(IV).

The kinetics of polymerization of acrylonitrile initiated by the Mn3+

-

thioacetamide redox system was studied by Samal et.al5. The rate of polymerization and

the rate of manganic ion disappearance have been measured. The effect of the various

additions such as water-miscible organic solvents, neutral electrolytes, complexing agents

and surfactants on the rate has been thoroughly studied. A mechanism that involves the

initial complex formation between the thiol form of the thioamide and Mn3+

, whose

decomposition yields the initiating free radical with the polymer chain terminated by

mutual combination of growing radicals, has been suggested.

The polymerization of acrylonitrile initiated by the redox system 2,2

thiodiethanol-Ce(IV) in dilute sulphuric acid was investigated by Jayakrishnan( et.al)6.

The reaction involves the formation of an intermediate complex between the metal ion

and the promoted species of the reductant, whose decomposition gives rise to the

initiating free radicals. Mutual interaction of the growing macro radicals accounts for the

termination of polymerization. A suitable kinetic scheme has been proposed , rate and

equilibrium constants were evaluated.

The aqueous polymerization of acrylonitrile initiated by ascorbic acid

(peroxodisulfate redox system at 350C in the presence of air was studied by Mohamed

Ariff (et.al)7. Molecular oxygen was found to have no effect on the polymerization

reaction. An increase in ionic strength slightly increased the rate. The overall rate ofpolymerization, showed a square dependence on [Monomer] and a half order dependence

on [peroxodisulfate]. A first order dependence on [ascorbic acid] at low concentrations

followed by a decrease in rate of polymerization at higher concentrations of ascorbic acid

was also noted. Addition of catalytic amounts of cupric ions decreased the rate whereas


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ferric ions were found to increase the rate. The added sulphuric acid decreased the rate of

polymerization.

The polymerization of acrylonitrile, initiated by the free radicals formed in situ in

the manganese (III)glycine redox system, was studied by Rai and his co-workers.

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therate of polymerization and the rate of manganese (III) disappearance have been

measured. The effects of water miscible organic solvents, surfactants, and complexing

agents on the rate of polymerization were investigated. The temperature dependence of

the rate was studied and the activation parameters were computed. The chain termination

step is by mutual interaction of the free radicals.

The kinetics of polymerization of acrylonitrile initiated by K2S2O8-Ag+ - EDTA

redox system was studied by Bajpai and R.Dengre9

. The rate expression for Rp

[Monomer]0.45, [K2S2O8]0.42, [Ag+]0.46, [EDTA]0.80 has been studied. The effect of

varying concentrations of monomer and redox components, temperature, added salts,

solvents, H+ions and surfactants in the polymerization kinetics have been studied.

Polymerization of acrylonitrile initiated by the free radicals formed in situ in the

V(V)thiocyanate redox system have been studied by Rai and his co-workers.10

The rate

of polymerization and the rate of V(V) disappearance have been measured. The

temperature dependence of the rate has been studied and the activation parameters are

computed.

II. Polymerization of acrylamide

Redox polymerization of acrylamide initiated by the system V(III) (acac) 3-

hydroxylamine in dimethyl formamide was studied by Vara Prasad and Mahadevan.11

They reported that oxidation is a second order process with polymerization being initiated

and terminated by the amino radicals. Rate and thermodynamic parameters have been

calculated.

The polymerization of acrylamide in aqueous sulphuric acid medium initiated with

ceric ammonium sulphate-malic acid redox pair was investigated by Misra( et.al)12.From

their studies, it is inferred that the rate of monomer disappearance was proportional to the


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first power of malic acid, Ce(IV) and monomer concentrations at lower Ce(IV)

concentration. However, at higher Ce(IV) concentrations the rate was independent of

[Ce(IV)]. The rate of Ce(IV) disapperance was proportional to [MA] and [Ce(IV)] but

independent of [M] at lower Ce(IV)] concentrations. Molecular weights increased withincreasing [M] and decreasing [Ce(IV)]. The activation energy was found to be 57.74

KJ / mol.

The polymerization of acrylamide initiated by Ce(IV) citric acid redox system

was studied by Misra(et.al)13.The rate of Ce(IV) disappearance is directly proportional

to [Ce(IV)] but independent of [acrylamide]. Initial rate and maximum conversion

increase with increasing temperature from 30 to 500C. Increase in pH increases the rate

and maximum conversion. The molecular weight of polyacrylamide increases with

increasing [acrylamide] and decreasing [Ce(IV)].

Kinetics and initiation mechanism of acrylamide polymerization using persulfate /

aliphatic diamine systems as initiator have been investigated by Xin Qio Guo (et.al)14

. It

was found that diamines with two amino groups separated by an ethylene unit possess

higher promoting activities than those with two amino groups linked by methylene or

propylene. The methyl group is preferred substituent at the amino groups of the diamine,

being faster oxidized by persulfate than the methylene groups.

The polymerization of acrylamide initiated by K2S2O8-EDTA-Ag+ redox system

have been investigated by Bajpai(et.al)15. The rate of polymerization varies with the first

power to the monomer and half power to the three components comprising of the redox

system. The termination of growing macro radicals takes place via mixed termination,

(both trimolecular and unimolecular). The rate of polymerization is significantly affected

by the presence of inorganic salts and surfactants, pH and temperature.

Bera and Saha16have investigated the polymerization of acrylamide by Ce(IV)

EDTA redox couple have been studied by loading Ce(IV) ions in the interlayer space of

montmorillonite. Linear termination by Ce(IV) ions in controlled resulting in the

considerable enhancement of chain growth.


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III. Polymerization of methyl methacrylate

The kinetics of aqueous polymerization of methyl methacrylate by Ce(IV)

thiourea initiator system in moderately acid solution was studied by Pramanick and

Chatterjee17. The rate of polymerization was proportional to 0.41 power of Ce(IV)

concentration, 0.32 power of thiourea concentration and 1.18 power of monomer

concentration. The degree of polymerization was smaller than expected form the rate of

polymerization.

The kinetics of polymerization of methyl methacrylate initiated by potassium

peroxodisulfate malonic acid redox system catalysed by Ag(I) was studied by Basha

(et.al)18

.The rate of polymerization was proportional to [MMA]1.4

, [K2S2O8]0.27

, [MA]0.23

and [Ag+]

0.5. The overall energy of activation was calculated to be 13.5 k cal. K

-1. mol

-1

between 20 and 450C.

Aqueous polymerization of methyl methacrylate initiated by the redox system

Ce(IV)isopropyl alcohol was carried out by Fernandez and Guzman19. They suggested

that the rate of polymerization and the rate of Ce(IV) consumption increase with rise in

temperature. A short induction period was observed, as well as the attainment of a

limiting conversion and the total Ce(IV) consumption with reaction time.

Polymerization of methyl methacrylate initiated by ceric ammonium nitrate

maltose in nitric acid have been investigated by Fernandez and Guzman20. The

dependence of the initial rate of polymerization and the initial rate of Ce(IV)

consumption on maltose, Ce(IV), and monomer concentrations has been determined. The

reaction orders were found to depend on Ce(IV) concentration. At a moderately high

Ce(IV) concentration (1 x 10-3

mol litre-1

) the orders were 0.5 and 1.5 with respect to

maltose and monomer concentration respectively and independent of Ce(IV)concentration. But at a low Ce(IV) concentrations (4 x 10

-4mol litre

-1) the orders with

respect to monomer and Ce(IV) changed to 1 and 0.5 respectively. The average

molecular weight, as determined by size exclusion chromatography, was found to

depend on maltose. Ce(IV) and monomer concentrations, as well as on temperature.


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The kinetics of polymerization of methyl methacrylate (MMA) with

triethanolamine (TEA) and carbon tetrachloride has been investigated in the presence of

RuCl3 and in dimethyl sulphoxide (DMSO) medium by employing a dilatometric

technique at 60

0

C was studied by Pachauri ( et.al)

21

The rate of polymerization of methylmethacrylate has been found to proportional to [MMA] [TEA]1/2, [CCl4]

1/2and {K + K

[RuCl3]1/2

} where K and K are rate constants for uncatalysed and catalysed

polymerization respectively. The rate of polymerization has been inhibited by

hydroquinone, suggesting a free radical mechanism. The kinetic data indicate the possible

participation of the charge transfer complex formed between [TEA RuIII

] and CCl4

during the polymerization of MMA. In the absence of either TEA or CCl 4, no

polymerization of MMA has been observed under the experimental condition.

IV. Cyclopolymerization of divinyl monomer

The kinetics of polymerization of the symmetrical non-conjugated divinyl

monomer N-N methylenebisacrylamide using Ce(IV) thiourea redox system as

initiator has been studied by Paulrajan (et.al.)22 They reported that the rate of

polymerization, Rp is proportional to [Ce(IV)]1/2

, [Thiourea]1/2

and [Monomer]3/2

. A

cyclopolymerization mechanism fits in with the experimental results.

Gopalan (et.al)23 studied the polymerization of the symmetrical non conjugated

diolefin N, N methylene bisacrylamide initiated by peroxo disulphate ion Fe2+

redox system. The rate of polymerization was found to depend on [M]3/2and [S2O82]1/2

and independent of [Fe2+

] over a range. A polymerization mechanism involving

cyclopolymerization in the propagation step was suggested.

V. Polymerization of acrylic acid

Kinetics of polymerization of acrylic acid initiated by Mn3+

- isobutyric acid redox

system have been studied by Elayaperumal ( et al)24.They reported that the overall rates

of polymerization (Rp), disappearance of manganic ion (-Rm), and degree of

polymerization (Xn) were measured with variation in [monomer], [Mn3+], [IBA], [H+], ,

[Mn2+] and temperature. The polymerization is initiated by organic free radical that


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develops from the Mn3+- isobutyric acid oxidation reaction. The various rate parameters

were evaluated.

The kinetics of polymerization of acrylic acid initiated by a Hexavalentchromium

Organic sulfur compounds reducing agent system have been studied by Lenka andNayak25. The rates of polymerization were measured. Chromic acid alone did not initiate

the polymerization under deaerated and un-deaerated conditions. On the basis of the

experimental observation of the dependence of the rate of polymerization (Rp) on various

variables, a suitable kinetic scheme is proposed.

VI Polymerization of methyl acrylate

Polymerization of methyl acrylate initiated by picolinium p-

chlorophenacylide in CCl4 was studied by Shukla (et.al)26

. Reaction proceeds rapidly

upto 14.18% conversion after which the system becomes highly viscous due to

autoacceleration. The overall energy of activation and the average value of Kp2/ K1for

this system are 27.0 kJ mol-1

and 3.98 x 10-3

respectively.

The polymerization of methyl acrylate in water using ammonium, potassium and

sodium persulphates with sodium bisulphate as redox initiation system was studied by

Badran and his co-workers27. It has been found that ammonium persulphate had the least

activity on the rate of polymerization and resulted in the formation of the highest

viscosity average molecular weights for the obtained polymers. The rate of

polymerization was found to increase with sodium bisulphate concentration in the redox

system, but the viscosity average molecular weights were found to decrease with increase

of sodium bisulphate concentration. Addition of some inorganic silicon compounds

(containing the same weight equivalent of S iO2) resulted in increasing the rate of

polymerization and decreasing the induction period.

VII. Polymerization of methacrylamide

The polymerization kinetics of methacrylamide initated by S2O82-

ion in the

presence and absence of the metal ions Ag+ and Cu2+ has been studied by Manickam

(et.al)28. The rate laws have been established and are compared with those of acrylamide.


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The result indicate that steric hindrance from the methyl group affects the initiation

reaction. Cu2+

ions are found to reduce the rate of polymerization.

The aqueous polymerization of methacrylamide initiated by the glycolic acid

Ce(IV) redox system was studied by Misra et.al

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. The rate of monomer disappearancewas found to be proportional to [MA]1, [Ce(IV)]1/2, [GA]1/2 and the rate of Ce(IV)

disappearance was proportional to [GA] and [Ce(IV)] but independent of [MA].

Earlier, the kinetics of polymerization of acrylonitrile initated by various redox

system such as methyl propylketoneCe(IV),30(a)

dimethyl ketone Ce(IV),30(a)

laevulinic

acid - Ce(IV),30(b), 2-methoxy ethanol - Ce(IV),30(b) triethylamine - Ce(IV),30(c), propane

dinitrile trichloroaquo (1, 10 phenanthroline) - Mn(III),30(d)

, laevulinic acid

trichloroaquo (1,10 phenanthroline) - Mn(III),30(e)

, propane dinitrile trichloro

aquobipyridyl Mn(III)30(f)and Ce(IV)citric acid 30(g)systems are has been investigated .

In addition to the above thorough survey of literatures, number of reports related

to redox polymerization kinetics studies initiated by different redox systems have been

reviewed and some of the selected reports are listed below.

Monomer Redox system Reference No.


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CHAPTER III

EXPERIMENTAL PART

POLYMERIZATION REACTION VESSEL

The reaction tubes used for the experiments were pyrex glass tubes, closed by B-

24 cones to which nitrogen inlet and outlets tubes were fused. The longer tube was used

as inlet for passing nitrogen gas through the solution and the shorter one was used as

outlet for nitrogen. After passing nitrogen for the specified time, the tubes were sealed

with rubber gaskets to ensure maintenance of an inert atmosphere.

THERMOSTAT

The thermostat used was a rectangular vessel with a heater, stirrer and

thermometer. The temperature range used for all the experiments reported have were

300C and 350C controlled to an accuracy of 0.10C.

DEAERATION TECHNIQUE

The nitrogen gas used to deaerate the experimental system was freed from oxygen

by passing through several columns of Fiesers solution. The gas after passing through

Fiesers solution was freed from hydrogen sulphide, sulfur dioxide etc., by passing it

through a wash bottle containing saturated lead acetate solution and then washed free of

all vapours by passing it through a wash bottle containing double distilled water. Before

passing the purified nitrogen through the reaction tube, it was passed through a wash

bottle containing the same concentration of monomer solution in order to avoid the lossof monomer during deaeration. For all the experiments the deaer4ation time was 30

minutes.


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PREPARATION OF FIESERS SOLUTION

Fiesers solution1was prepared by dissolving 20g of sodium hydroxide in 100ml

of water and adding 16g of sodium dithionate (Na2S2O4) and 2g of anthroquinone

sulphonate (silver salt) to the warm solution. The mixture was stirred well until a clear

blood red colour solution was obtained. It was cooled to room temperature and then used.

REAGENTS

All chemicals used wee of the purest quality mostly BDH, E.Merck, SDs fine

(AnalaR or G.R.grade) products. Glasswares and the reaction vessels were cleaned with

warm solutions of chromic acid, rinsed frequently with double distilled water and dried in

air oven at 900C.

WATER

Water was distilled in all glass cornery vessel, the second distillation being from

potassium permanganate and the double distilled water was used throughout this study2.

MONOMER

Acrylonitrile was free from phenolic inhibitors by washing with a 5% solution of

NaOH and then with conductivity water. The wet monomers were dried over anhydrous

calcium chloride and distilled under reduced pressure. The monomer was stored in dark

brown bottles at 50C in the refrigerator.

REDUCING AGENT

The reducing agent used in the present work is lactic acid.

ACID

All experiments were conducted in sulphuric acid solution. Solutions of sulphuric

acid were prepared by suitable dilution of concentrated acid with double distilled water

and standardized against sodium hydroxide solution.


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SOLVENT

The organic solvent like ethanol was distilled immediately before use and the

middle cuts of the distillate was used.

OTHER REAGENTS

Sodium hydrogen sulphate were used to maintain the ionic strength.

PURIFICATION OF REAGENTS

To obtain reproducible results and to minimize experimental errors a high degree

of purity of the solvents and reagents is necessary. Therefore only analytical grade

chemicals were used. Commercial sample and laboratory grade reagents were carefully

purified by standard procedure and then purity was checked by melting point

measurements.

ESTIMATIONS

INITIATOR

Ceric Ammonium Sulphate was used as an initiator. The Ce(IV) ion concentration

were determined by cerimetry3. For this an aliquot of Ce(IV) stock solution was run into

a known excess of standard ferrous ammonium sulphate solution. The excess ferrous ion

was back titrated with standard ceric ammonium sulphate solution using Ferroin

indicator.

FERROIN INDICATOR

The Ferroin4indicator was prepared by dissolving 1.485 g of 1,10 phenanthroline

monohydrate (C12H8N2H2O) in 100ml of 0.025M Ferrous ammonium sulphate solution.


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RATE OF Ce(IV) DISAPPEARANCE

Rate of Ce(IV) disappearance (-d [Ce(IV)] / dt) was determined as described

below. At the end of the reaction time, the reaction was arrested with definite amount of

ferrous ammonium sulphate and the excess ferrous ion was determined by cerimetry.

From the amount of unreacted ferrous ion, the Ce(IV) consumed was evaluated and hence

the rate of Ce(IV) disappearance was computed.

ESTIMATION OF MONOMER CONCENTRATION

The concentration of the monomer was determined by the method of addition of

bromine to the double bond. To 10 ml of 0.2 M Winklers solution (11.6 gm of KBrO3and 80 gm of KBr per litre) in an Erlenmeyer flask (250 ml), 3 ml of the stock monomer

solution and 20 ml of 2M H2SO4were added. Tightly stoppered flask was kept in dark

for about 20 minutes with intermittent shaking to allow the liberatd bromine to add on to

the double bonds in the monomer. Potassium iodide solution was then added to the

mixture and the iodine liberated by the excess bromine present was titrated against

standard sodium thiosulphate solution (0.1 N) using starch as indicator. A blank titration

was also made with 10 ml of Winklers solution (withour the monomer) as before and the

difference in the titration was also made with 10 ml of Winklers solution (without the

monomer) as before and the difference in the time value was used to estimate the

monometer concentration and purity.

POLYMERZATION EXPERIMENTS

A solution containing the required amount of monomer, reducing agent, sulphric

acid (to maintain H) NaHSO4 (to adjust the ionic strength), was taken in the reactionvessel and made up to the fixed volume (20ml) with double distilled water. The solution

was then deaerated for 20 minutes with purified nitrogen gas to ensure inert atmosphere

as well as thorough stirring. In order to minimize the concentration of the monomer

during deaeration, nitrogen gas was passed through an aqueous solution containing


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monomer of the same concentration as maintained in the reaction mixture, before

entering into polymerization tube. The tube was thermostated at the appropriate

temperature in thermostat. At the end of 20 minutes, required amount of Cerium

Ammonium solution was added into the polymer tube through a microfunnel which wassubsequently rinsed with 2ml of distilled water. The passage of nitrogen gas was

continued for 5 more minutes. The inlet and outlet tubes were closed to maintain the

nitrogen atmosphere till the end of a fixed reaction time. 10 ml of 0.025 M ferrous

ammonium sulphate solution was then added and air was blown to arrest the reaction.

OXIDATION EXPERIMENT

A typical oxidation experiment is described below. A reaction mixture containing

lactic acid, sulphuric acid, sodiumbisulphate (to maintain the ionic strength) and water (to

maintain total volume constant) was taken in the reaction tube. Nitrogen, freed from

oxygen by passing through Fiesers solution, was bubbled through the solution for 30

minutes and the system was thermostated at the desired temperature. The Ce(IV) stock

solution was added and the tube was sealed with rubber gaskets to ensure maintenance of

an inert atmosphere. The total volume if the reaction mixture was usually arrested by the

addition of a known excess of ferrous ammonium sulphate solution, when the remaining

Ce(IV) was instantly reduced to Ce(III) state. The unreacted Fe(II) was estimated bytitrating with a standard ceric ammonium sulphate solution using Ferroin indicator. The

rate of Ce(IV) disappearance was evaluated from the titre values. The rate of Ce(IV)

disappearance was followed at different substrate concentration, Ce(IV) concentration

and sulphuric acid concentration keeping the constant ionic strength.


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SCOPE OF THE PRESENT PROJECT WORK

Metal ions such as Cr6+, V5+, Ce4+, Co3+, Mn3+ etc. coupled with certain organic

compounds like alcohols, aldehydes, ketones, -hydroxy acids, amines.etc. have been

reported to be useful redox systems for initiating vinyl polymerization. Ce4+ has been

found to be active oxidant in the vinyl polymerization. Hence Ce4+

is chosen as the

oxidizing agent and lactic acid is chosen as the reducing agent for the present

investigation.

Detailed survey of literature reveals that an extensive study has been carried out

on the kinetics of polymerization of various monomer such as acrylonitrile, methyl

methacrylate, acrylamide, etc with organic reducing agents which in combination with

an oxidizing agent constitute a redox pair to initiate the vinyl polymerization.

( Kinetics of polymerization of methylarylate of initiated by lactic acid - Ce (IV)

redox system is chosen for the present investigation. Mainly, in this work rate of

polymerization is determined. Rate of polymerization in this normal system and rate of

polymerization in the presence of -cyclodextrin is also determined. The rates of

polymerization without -CD and with are compared in this project work.)


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Cyclodextrin

Cyclodextrin are water soluble molecules and are also called cycloamyloses or

cycloglucans & they are composed of - (1,4) linkages of a number of D(+) glucosyl

pyranose units.


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CHAPTER - IV

RESULTS AND DISCUSSION

Kinetics of Oxidation in absence of monomer

The Kinetics of oxidation of lactic acid (LA) by . Ce(IV) in the absence of

monomer was carried at temperature 30oC and 35

oC. The rate of oxidant consumption

(-d[Ce(IV)]/dt) were proportional to [Ce(IV)]. The plots of (-d[Ce(IV)] / dt)-1 against

[LA]-1were linear, with an intercept the complex formation between the oxidant and the

substrate in the redox pair. Double reciprocal plots of (-d[Ce(IV) / dt)-1 vs [H+]-1 were

also found to be linear.

The results of oxidation can be accounted for by the following scheme where

Ce(IV) represents the first species of oxidation.

scheme I

K1

LA + H+ -----------LA - H+ .......................(i)

------

K2

LA - H+ + Ce(IV) - ------- Complex(c) ..........(ii)

C R .+ Ce(III) + H+ ......................(iii)


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K0

R. + Ce(IV) Products ....................(iv)

Where, C represents the complex formation between the substrate and the

oxidant.

The two eqilibrium K1and K

2were treated separately so that,

K1

= ([LA - H+]eq

) / ([LA]eq

[H+]) ...........(1)

and

[LA]T

= [LA - H+]eq

+ [LA]eq

........................(2)

From equation(1),

[LA - H+]eq

= K1

[LA]eq

[H+]

Introducing this value in equation (2),We get,

[LA]T

= K1

[LA]eq

[H+] + [LA]eq

= [LA]eq

(1 + K1[H+]) ........................(3)

Where [LA]eqdenotes the equilibrium concentration of LA also,

[Ce (IV)]T

= [Ce(IV)]eq

+ [C] .........................(4)

From the kinetic step (2)


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= 2Kr[C]

From the equation (5),

-d[Ce(IV)] / dt = 2Kr.K

2[LA-H+]

eq[Ce(IV)]

eq

By using the equation (1),

-d[Ce(IV)] / dt = 2KrK

1K

2[LA]

eq[H+][Ce(IV)]

eq

Applying the equation (3) and (6)

-d[Ce(IV)/dt=(2KRK

1K

2[LA]

T[Ce(IV)]

T[H+]/1+ K

1[H+])x(1+K

2[LA-H+]

eq)

=R0

The above equation explain the dependence of the rate on Ce(IV)

concentration and also variable with substrate concentration. The observation of

Michelis-Menton kineties, i.e., the formation of a complex between the reactants

allow the oxidation data to be treated according to the method of Line Wearer and

Burk.

Thus the above equation can be written as follows:

(2krk1k2 [LA]T[Ce(IV)]T[H+])

-d[Ce(IV)]/dt =

(1+k1[H+])(1+k 2k 1[LA]eq[H

+])

(2krk1k2[LA]T[Ce(IV)]T[H+])

=


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(1+k1k2[LA]T[H+])/(1+k

1[H+])

(2krk1k2[LA]T[Ce(IV)]T[H+])

=(1+k

1[H+]+ k1k2[LA]T[H

+])

]Taking reciprocal rate in given by,

(-d[Ce(IV)]/dt)-1=1/(2kr k1 k2[LA]

T[Ce(IV)]

T[H+])+1/(2k

rk

2[LA]

T[Ce(IV)]

T)

+ 1/(2kr[Ce(IV)]

T) ................................(8)

This equation explains the linear plot of(-d[Ce(IV)]/dt)-1 vs[H+]-1,

(-d[Ce(IV)]/dt)-1 vs[LA]-1

Equation (8) explain the dependence of rate on[Ce(IV)].

Thus Krcould be evaluated from the plots of (-d[Ce(IV)]/dt)-1 vs [LA]-1from the

intercepts of the plots of(-d[Ce(IV)]/dt)-1vs[H+])-1, K2could be evaluated The

value of K1can be determined from the slope of the plots of (-d[Ce(IV)]/dt)-1vs

[H+]-1by knowing the values of krand k

2.

final deva project

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