Synthesis, characterization and thermalstability of phosphazene terpolymers with2-(2-methoxyethoxy)ethoxy and diacetoneD-glucofuranosyl pendant groupsFF Stewart,* MK Harrup, RP Lash and MN TsangIdaho National Engineering and Environmental Laboratory, Lockheed Martin Idaho Technologies Company, PO Box 1625, Idaho Falls,ID 83415-2208, USA

Abstract: Six different phosphazene polymers have been synthesized with varying ratios of 2-(2-

methoxyethoxy)ethanol and diacetone D-glucofuranose to determine how these pendant groups affect

the physical, chemical, and thermal characteristics of these terpolymers. Diacetone D-glucofuranose

serves as the hydrophobic substituent and 2-(2-methoxyethoxy)ethanol is the hydrophilic substituent

on the phosphazene backbone. Characteristics of the polymers made in this study re¯ect a blend of the

two substituents, ranging from powders to viscous ¯uids. Thermal analysis was used to quantify the

thermal stability and water swellability of the polymers. Additionally, DSC was employed to determine

composition based on the Fox equation. Compositions were then veri®ed by integratable proton NMR

indicating the validity of the Fox equation for predicting Tg transitions in phosphazene terpolymers.

Laser light scattering (LLS) revealed that the weight-average molecular weights were in the 107 gmolÿ1

range with mean square radii between 150 and 200nm.

# 2000 Society of Chemical Industry

Keywords: polyphosphazene; saccharide; synthesis; characterization; thermal analysis

INTRODUCTIONPolyphosphazenes are a versatile group of inorganic

polymers that can be tailored to many applications by

varying the substituents on their backbone structure,

which consists of alternating phosphorus and nitrogen

atoms with alternating single and double bonds.1 They

are thermally stable and chemically resistant to most

harsh environments depending on the pendant groups

attached to the phosphorus atom.2 This paper

describes the synthesis and characterization of

mixed-substituent polyphosphazene polymers con-

taining varying ratios of 2-(2-methoxyethoxy)ethanol

and diacetone D-glucofuranose (see Scheme 1). The

goal of this work was to enhance the thermal and

mechanical stability of water-swellable 2-(2-methoxy-

ethoxy)ethanol-substituted phosphazene polymers

that would have potential uses as membranes in

pervaporation of polar solvents (ie water) from process

waste streams. Polymers were made by nucleophilic

substitution3 in an effort to determine the relationship

between the selected pendant group and macroscopic

polymer hydrophilicity.

Diacetone D-glucofuranose is derived by blocking

the 1,2- and 5,6-hydroxyl groups of a-D-glucofuranose

(sugar) with acetone,4 leaving a single hydroxyl groupScheme 1. Synthetic pathway for 2-(2-methoxyethoxy)ethoxy anddiacetone D-glucofuranosyl phosphazene polymer.

Polymer International Polym Int 49:57±62 (2000)

* Correspondence to: FF Stewart, Idaho National Engineering and Environmental Laboratory, Lockheed Martin Idaho TechnologiesCompany, PO Box 1625, Idaho Falls, ID 83415-2208, USAContract/grant sponsor: US Department of Energy; contract/grant number: DE-AC07-94ID 13223(Received 8 September 1998; revised version received 24 May 1999; accepted 4 August 1999)

# 2000 Society of Chemical Industry. Polym Int 0959±8103/2000/$17.50 57

at the 3 position for attachment to the phosphazene

backbone thus preventing uncontrolled crosslinking.

In previous papers,5,6 the glucosyl substituent was

deprotected by hydrolysis with tri¯uoroacetic acid

yielding a hydrophilic polymer. However, the addi-

tional alkyl component embodied by the acetone

protecting groups provides the polymer with a hydro-

phobic component and had the potential to give high

glass transition temperature materials without crystal-

linity. It was envisioned that the steric bulkiness of the

methyl groups on the protecting moiety would inhibit

ef®cient polymer chain packing.

The synthesis of polyorganophosphazenes is well

established7±9 largely by the HR Allcock group. Due to

the nearly unlimited variety of pendant groups that can

be attached to the P±N backbone, research into

phosphazene chemistry continues. Potential uses for

these polymers include membranes for pervaporation

of organics from water,10 organics from other organ-

ics,11 and C1±C6 hydrocarbon separations.12 In

addition, speci®c polymer formulations made with

D-glucofuranosyl groups have been pursued as bio-

medical devices, carrier ligands for transition metals,

and af®nity chromatography substrates.6

EXPERIMENTALGeneralSubstitution reactions were done under nitrogen with

standard Schlenk line techniques. All glassware was

oven-dried and cooled under dry nitrogen. Phospho-

nitrilic chloride trimer, 98.5% was obtained from

STREM Chemicals and was puri®ed by sublimation

prior to use. Toluene (Aldrich) was dried by azeo-

tropic distillation and hexane (Fisher), anhydrous

tetrahydrofuran (THF) (Aldrich), and methoxyethyl-

ether (diglyme) (Aldrich) were used as received.

Diacetone D-glucofuranose (Sigma) was used as

received and 2-(2-methoxyethoxy)ethanol (Aldrich)

was vacuum-distilled prior to use. Sodium hydride,

60% suspension in mineral oil (Aldrich), was used to

make the sodium salts of the aforementioned alcohols.

Analytical techniquesA Bruker AC-300P NMR spectrometer was used to

obtain 1H (300MHz) and 31P (121.5MHz) data.

Phosphoric acid (85%, Fisher) was used to reference31P shifts. Residual hydrogen in deuterated chloro-

form was used to reference 1H shifts. Thermal analyses

were performed using a TA Instruments Model 2910

differential scanning calorimeter (DSC) and Model

2980 Thermogravimetric Analyzer (TGA). Milligram

samples were subjected to a temperature ramp of

10°C per minute from ÿ150°C to 200°C for DSC

and a temperature ramp of 10°C per minute from

25°C to 600°C under nitrogen atmosphere for TGA.

Dilute solution techniques were used to characterize

the macromolecular structures of the polymers made

in this study. THF, ®ltered through a 0.02-mm ®lter,

was used as solvent, and all experiments were

performed at 22°C. Solution refractive index incre-

ment (dn/dc) values were obtained using a Rainin

Dynamax RI-1 differential refractive index detector.

The instrument constant was determined via calibra-

tion using known concentrations of polystyrene

standards whose dn/dc values are well known. Laser

light scattering (LLS) measurements were made using

a Wyatt Technologies Dawn-DSP laser photometer,

using polarized light (633nm) to measure scattered

light intensities at 18 angles ranging from 22.5° to

147°. The instrument was calibrated with toluene

(Aldrich), which also was ®ltered through a 0.02-mm

®lter. Dilute solutions in the 10ÿ4 to 10ÿ5gmlÿ1 range

were prepared in scintillation vials for scanning on the

LLS instrument. Debye plots were prepared to obtain

weight-average molecular weights, z-average square

radii (mean square radii), and second-virial coef®-

cients. High Performance Size Exclusion Chromato-

graphy and Detection (HPSEC) was performed using

a Waters Model 2690 solvent/sample delivery system

with a column bank of two Styragel HR 5E (4.6mm

ID�300mm) solvent-ef®cient columns. The columns

were kept isothermal at 22°C and operated with a

solvent ¯ow rate of 0.3ml minÿ1. The polymer

solutions were ®ltered through a 0.45-mm ®lter prior

to injection onto the columns. The polymers were

detected using the Wyatt Technologies Dawn-DSP

laser light scattering detector with the F2 ¯ow cell

which measures scattered light intensities at 16 angles

ranging from 12.3° to 165.1°. The refractive index

detector described above was placed in series with the

light scattering detector as a concentration detector.

Synthesis of polydichlorophosphazene, (PNCl2)n (2)The dichlorophosphazene polymer was made by ring-

opening polymerization13 of phosphonitrilic chloride

trimer, 1, using a previously described method.14 An

average of 40±45% conversion to the linear polymer,

(PNCl2)n (2) was achieved.

Synthesis of [PN((methoxyethoxy)ethoxy)(diacetoneD-glucofuranosyl)] polymer 3In a 3-necked, 1-litre round-bottomed ¯ask, 4.7g

(0.0405mol) of polydichlorophosphazene was dis-

solved in approximately 200ml of anhydrous toluene.

Diacetone D-glucofuranose (13.9g, 0.053mol) and

2-(2-methoxyethoxy)ethanol (4.3g, 0.036mol) were

added together in a 500-ml round-bottomed ¯ask

charged with anhydrous THF (150ml). Sodium

hydride (4.1g, 0.085mol) was slowly added to the

alcohol/THF mixture and stirred until the formation

of the alkoxide salts was complete. The salt solution

was slowly added to polydichlorophosphazene, 2.

Approximately 200ml diglyme was added to the

solution and THF was removed via a Dean and Stark

trap until the re¯ux temperature reached 115°C. This

mixture was allowed to re¯ux for a total of 20h after

which time [31P]NMR revealed that the peaks

assigned to (PNCl2)n (ÿ18ppm) and (PNCl(OR))n

(ÿ13ppm) were no longer observable. Puri®cation of

58 Polym Int 49:57±62 (2000)

FF Stewart et al

the product polymer involved precipitation in de-

ionized water twice followed by hexane precipitation

from THF solution. The resulting polymer solid was

dried under vacuum for several days (11.4g, 62%

yield). [31P]NMR (CDCl3) ÿ9.0ppm.

Synthesis of [PN((methoxyethoxy)ethoxy)(diacetoneD-glucofuranosyl)] polymer 4This polymer was synthesized using the same proce-

dure as for polymer 3. Amounts of materials used in

the synthesis were: diacetone D-glucofuranose (14.8g,

0.057mol), 2-(2-methoxyethoxy)ethanol (6.8g,

0.057mol), sodium hydride (5.4g, 0.113mol), and

polydichlorophosphazene, 2 (6.0g, 0.052mol). Iso-

lated yield was 67% (14.6g). [31P]NMR (CDCl3)

ÿ8.8ppm.

Synthesis of [PN((methoxyethoxy)ethoxy)(diacetoneD-glucofuranosyl)] polymer 5This polymer was synthesized using the same

procedure as for polymer 3. Materials: diacetone D-

glucofuranose (11.3g, 0.043mol), 2-(2-methoxy-

ethoxy)ethanol (7.8g, 0.065mol), sodium hydride

(5.0g, 0.104mol), and polydichlorophosphazene, 2

(5.7g, 0.049mol). Isolated yield was 35% (6.8g).

[31P]NMR (CDCl3) ÿ8.8ppm.

Synthesis of [PN((methoxyethoxy)ethoxy)(diacetoneD-glucofuranosyl)] polymer 6This polymer was synthesized using the same proce-

dure as for polymer 3. Materials: diacetone D-

glucofuranose (5.3g,0.020mol), 2-(2-methoxyethoxy)

ethanol (9.8g, 0.082mol), sodium hydride (4.7g,

0.098mol), and polydichlorophosphazene, 2 (5.4g,

0.047mol). Isolated yield was 37% (5.3g). [31P]NMR

(CDCl3)ÿ8.0ppm.

Synthesis of [PN((methoxyethoxy)ethoxy)(diacetoneD-glucofuranosyl)] polymer 7This polymer was synthesized using a modi®ed

procedure from polymer 3. To a solution of diacetone

D-glucofuranose (21.7g, 0.083mol) in THF (100ml)

was added sodium hydride (3.83g, 0.096mol). The

resulting mixture was stirred under dry nitrogen

overnight. This solution then was added to a solution

of polydichlorophosphazene, 2, (22.02g, 0.189mol) in

THF (500ml). The resulting solution was stirred

under dry nitrogen at 55±60°C for 3h. Another

solution was prepared from 2-(2-methoxyethoxy)etha-

nol (40.15g, 0.245mol), sodium hydride (15.3g,

0.383mol), and THF (200ml) and was stirred at

room temperature under dry nitrogen overnight. This

alkoxide solution then was added to the polymer

solution and the resulting mixture was stirred for 2h at

room temperature under dry nitrogen. At the conclu-

sion of 2h, [31P]NMR revealed that the chlorines were

fully displaced. To ensure completion, the mixture

was stirred for an additional 16h. Puri®cation of the

polymer was performed by precipitation into water

twice and hexane twice from THF solution. Residues

were collected and dried under vacuum to give

elastomeric polymer 7 in 56% yield (36g).

[31P]NMR (CDCl3) ÿ7.7ppm.

Synthesis of poly-bis-2-(2-methoxyethoxy)ethoxy-phosphazene (MEEP) (8)This polymer was synthesized according to literature

procedures15 but was isolated and puri®ed via a novel

route exploiting the lower critical solubility tempera-

ture (LCST) behaviour of this material in aqueous

solution (Harrup MK and Stewart FF, unpublished)

2-(2-Methoxyethoxy)ethanol (44.2g, 0.368mol) was

added to 360ml anhydrous THF under dry lightly

¯owing argon. Freshly cut metallic sodium (7.02g,

0.306mol) was added to the ¯ask and the mix stirred

at re¯ux until all the sodium was consumed. A solution

of poly(dichlorophosphazene) (12.0g, 0.102mol) in

250ml dry THF was slowly added by cannula and the

reaction mixture stirred for 15h at re¯ux under argon

and allowed to cool to room temperature. The crude

polymer was recovered by precipitation into 500ml

hexanes and the resulting cream-coloured solid was

then dissolved in 200ml de-ionized water resulting in a

solution of pH 12. The solution was neutralized with

4M H3PO4 (®nal pH of 6.5) and gently warmed above

the LCST point to induce precipitation of the

polymer. The polymer was collected while still warm

and immediately placed in a separate container of de-

ionized water at room temperature to dissolve the

polymer. After four sequential cycles of this treatment,

the recovered material was dried in a vacuum oven

(50°C, 70 Torr Ar) for two days to yield a clear gum

(19g, 66%): [1H]NMR (D2O) d (ppm) 3.3 (3H), 3.5

(2H), 3.7 (4H), 4.1 (2H); [31P]NMR d (ppm) ÿ6.6.

Analysis: Calcd:C, 42.4; H, 7.8; N, 4.9. Found:C,

42.5; H, 7.5; N, 4.8.

RESULTS AND DISCUSSIONThe observed physical properties of the polymers

synthesized in this work varied from powders to

viscous ¯uids. [1H] and [31P]NMR spectroscopy was

used to characterize the polymer and results consistent

with data previously reported.5 Resonances in the

proton NMR spectrum were used for integration and

determination of relative ratios of pendant groups on

the phosphazene backbone. Table 1 shows the

measured relative ratios of pendant groups for these

polymers in addition to the `target' ratios used during

the syntheses. Some deviations are noted and expected

from `target' values due to the fact that a 10% excess of

each pendant group was used to ensure complete

substitution of all chlorines on the parent dichloro-

phosphazene polymer. Failure to achieve complete

substitution of all chlorines leaves the polymer open to

hydrolytic decomposition processes. The fact that the

error between the measured and `target' values is

much less than 10% for all polymers suggests that the

relative nucleophilicities for the two pendant group

Polym Int 49:57±62 (2000) 59

Thermal stability of phosphazene terpolymers with pendant groups

alkoxides are similar, with competition between them

minimal.

Analysis of these materials by Differential Scanning

Calorimetry (DSC) revealed a broad spread in Tg from

21°C to ÿ57°C [see Table 1]. This is a re¯ection of

the differing ratios of pendant groups. Poly-bis(diace-

tone D-glucofuranosyl)phosphazene is a high Tg

(87°C)6 amorphous powdery polymer. MEEP is a

viscous ¯uid polymer with a low Tg at ÿ84°C.15

Combination of the responsible pendant groups would

be expected to give Tg values for the terpolymers

between these extremes. Reference to these polymers

as terpolymers is a re¯ection of the fact that two

pendant groups on a phosphazene give rise to three

possible monomers; bis-2-(2-methoxyethoxy)ethoxy

(PN(OR1)), bis-diacetone D-glucofuranose

(PN(OR2)), and the mixed substituent

(PN(OR1)(OR2)). In an earlier work,16 this terpoly-

mer behaviour was investigated by [31P]NMR and it

was shown that three separate monomers could be

observed in a phosphazene polymer with a binary

mixture of pendant groups. Unfortunately, this type of

analysis was not possible on the polymers in question

due to the fact that the 31P resonances for the three

possible monomers were not clearly resolved.

The Fox17 equation, eqn (1), allows for the predic-

tion of Tg in a statistical copolymer based upon relative

amounts of each constituent. However, this relation-

ship is valid only for copolymers in which there is no

phase separation. This equation has been successfully

applied to phosphazenes in previous reports.18

1=Tg � �W1=Tg1� � �W2=Tg2� �1�

The variables W1 and W2 refer to the weights of each

homopolymer in a copolymer matrix and Tg1 and Tg2

are the corresponding Tg values for the homopoly-

mers. In cases where the heat capacities of the

individual monomers are similar, eqn (1) may be

simpli®ed to:

Tg �M1Tg1 �M2Tg2 �2�where M1 and M2 are the percentages of each

monomer in the copolymer. Application of eqn (2)

to these phosphazene terpolymers, where M1 and M2

are the measured percentages of each pendant group

as determined by [1H]NMR, gives good agreement

with the measured Tg values as shown in Table 1. The

expected linear relationship was demonstrated by a

linear regression of the measured Tg values for the ®ve

polymers synthesized in this work plus literature values

for the homopolymers. The R2 value was measured to

be 0.9997 suggesting a good linear ®t to the data (see

Fig 1). This calculation also suggests that the heat

capacities of the three possible monomers are similar

and that the thermal behaviour of these terpolymers

can be described by relationships valid for statistical

organic copolymers.

Application of the Fox equation to previously

reported data5 revealed a poor correlation between

measured Tg and published composition. Calculation

of the polymer composition from the reported Tg

values revealed that the reported data are approxi-

mately 10% low for the diacetone D-glucofuranosyl

component for both polymers reported. The reported

compositions, 60% diacetone D-glucofuranosyl:40%

2-(2-methoxyethoxy)ethoxy and 40% diacetone

D-glucofuranosyl:60% 2-(2-methoxyethoxy)ethoxy,

were calculated to be 50:50 and 28:72, respectively,

using the Fox relation validated for the terpolymers

above. In an attempt to explain this deviation, the

experimental section of the paper was examined,

where a representative synthesis is reported. A

sequential addition methodology was employed in

these syntheses where the 2-(2-methoxyethoxy)ethoxy

pendant group was added to the parent polymer prior

to the diacetone D-glucofuranosyl group. The reported

synthesis should produce a 50:50 polymer, as con-

®rmed by the calculations presented here, but were

reported either as a 60:40 or a 40:60. Further clari-

®cation was not possible.

The laser light scattering (LLS) weight-averaged

molecular weights, Mw, as determined by the batch

mode without ®ltration of the polymer solutions were

all in the 107 to 108g molÿ1 range with sizes (RMS

Table 1. Measured ratios of 2-(2-methoxyethoxy)ethoxy: diacetone D-glucofuranosyl (MEE:DADG) pendant groups as determined by [1H]NMRSpectroscopy and Tg data measured and calculated from the measuredcompositions

Polymer

Target

composition

(MEE:DADG)

Measured

composition

(MEE:DADG)

Observed

Tg (°C)

Calculated

Tga (°C)

3 40:60 39:61 21 20

4 50:50 49:51 6 3

5 60:40 62:38 ÿ19 ÿ19

6 80:20 83:17 ÿ57 ÿ55

7 80:20 81:19 ÿ52 ÿ52

a Calculated using eqn (2) where the measured compositions from [1H]NMR

were employed.

Figure 1. Measured Tg Values vs % diacetone D-glucofuranosyl pendantgroup as measured by proton NMR spectroscopy.

60 Polym Int 49:57±62 (2000)

FF Stewart et al

radii) in the 143 to 156nm range (see Table 2).

Additionally, the second virial coef®cients and the dn/

dc values are included in Table 2. The dn/dc values are

of particular interest due to the fact that they are

unusually low, testifying to the nature of this type of

phosphazene polymer; they do not scatter light nearly

as much as phosphazenes containing other pendant

groups such as phenoxides.

The Debye formalism was used to plot the LLS data

from which the molecular weights and sizes were

extracted. Under the HPSEC conditions used, sensi-

tivity for the polymers was relatively low. However,

number-averaged (Mn) and weight-averaged (Mw)

molecular weights were obtained for polymer 7,

1.1(�0.2)�107 and 1.6(�0.2)�107, respectively,

yielding a polydispersity index of 1.4. The Mw of a

0.45-mm ®ltered HPSEC analyzed polymer was an

order of magnitude lower (106g molÿ1) than the

corresponding un®ltered batch mode analysis. The

RMS radiius moment for this polymer also decreased

by a factor of 1.5. This was attributed to removal of the

highest molecular weight fraction by the ®ltration

process. It should be noted that all of these materials

were completely soluble in toluene, acetone, tetra-

hydrofuran, and chloroform despite the high molecu-

lar weight. The magnitudes of these molecular weights

are proposed to originate from the ring-opening

polymerization process. Owing to the hydrolytic

instability of the precursor polymer, polydichloro-

phosphazene, the molecular weight of this parent

polymer was not measured.

Thermogravimetric analysis revealed that the ther-

mal decomposition behaviour of these polymers in a

nitrogen atmosphere has three major features. Up to

approximately 290°C, all polymers of this series

experience little weight loss, on the order of 2.5% on

average, which may represent loss of any spurious

solvent or small organic molecules. Decomposition

occurs rapidly after 290°C for all polymers with signi-

®cant weight loss observed (see Table 3). This decom-

position was characterized by a sharp weight loss over

a relatively narrow temperature range, approximately

10°C. From approximately 300°C through 600°C,

steady loss of weight is noted corresponding to high-

temperature volatilization of residues. A trend was

observed in the decomposition process between

290°C and 300°C where the polymers with higher

percentages of 2-(2-methoxyethoxy)ethoxy pendant

groups had larger mass losses. This behaviour is

attributed to the increased amount of carbon in the

glucosyl pendant group (12 per molecule) as com-

pared to the 2-(2-methoxyethoxy)ethoxy pendant

group (5 per molecule). The mass loss is primarily

due to a loss of oxygen with loss of carbon being

relatively minor due to the nitrogen atmosphere.

Support for this trend was provided by analysis of a

sample of poly-bis-2-(2-methoxyethoxy)ethoxyphos-

phazene, 8, which had the highest weight loss during

this thermal event due to its lowest relative carbon

content.

An additional use of TGA was to provide quantita-

tion for relative hydrophilic character of these poly-

mers (see Table 3). Samples of the ®ve materials were

soaked in de-ionized water for three days prior to TGA

analysis. The data followed the same general trend, as

did the dry materials with the addition of clearly

observable mass loss of water up to 100°C on all

samples studied. It was initially anticipated that

Table 2. Batch mode LLS molecular weight,refractive index and RMS radii determinations

Polymer

Molecular weight

Mw (g molÿ1�107) dn/dc

Second virial coef®cient

(molmlgÿ2)

RMS radius

(nm)

3 2.02 (�0.3) 0.058 8.2 (�30)�10ÿ6 157.7 (�9.7)

4 3.61 (�0.5) 0.062 1.3 (�1.0)�10ÿ5 157.2 (�8.6)

5 19.8 (�0.8) 0.052 ÿ4.9 (�400)�10ÿ8 142.7 (�4.4)

6 2.34 (�0.7) 0.048 1.5 (�4.0)�10ÿ5 168.6 (�21.9)

7 3.68 (�1.0) 0.054 2.1 (�2.0)�10ÿ5 155.6 (�17.5)

Table 3. Thermogravimetric analysisdata

Polymer

Decomposition

temperaturea

(°C)

Weight loss on

decompositionb

(%)

Water uptake on

immersionc

(%)

Decomposition

temperature of water-

swollen polymera (°C)

3 288 69 131 246

4 287 69 70 252

5 295 73 417 250

6 293 79 Dissolves ±

7 284 79 31 270

8 280 87 Dissolves ±

a Decomposition temperature as measured as the onset of the initial weight loss due to polymer decomposition.b Weight loss measured through determination of mass before and after the event, typically observed from 280 to

300°C.c Measured as loss of mass from ambient temperature to 110°C during the 10°Cminÿ1 temperature ramp up to

600°C. No other losses in this temperature range are attributable to the polymer as observed from dry polymer

measurements.

Polym Int 49:57±62 (2000) 61

Thermal stability of phosphazene terpolymers with pendant groups

polymers with the higher amount of the hydrophilic

polyether would swell more in water than polymers

with a lower amount. In a general sense, this was

observed for polymers 3, 4, 5, and 6 where polymer 5

was swollen to 417% of its original mass and polymer 6

dissolved completely. An anomalous result was pro-

vided by polymer 7 which only swelled 31% in water

(see Fig 2), which indicates that water swellability is

not simply a linear function of pendant group. A re-

examination of the DSC data showed one additional

feature for this and only this polymer, an endothermic

transition at approximately 25°C, suggesting some

degree of crystallinity in the polymer. It is proposed

that this behaviour arises from a non-homogenous

distribution of pendant groups along the polymer

backbone, as observed in other phosphazenes.16 This

leads to a small degree of phase separation that yields a

polymer material with less hydrophilicity and thus a

lower degree of swelling in pure water. This inhomo-

geneity may be the consequence of the sequential

addition method used for the synthesis; it is a known

phenomenon that sodium alkoxides will aggregate in

solution. This would lead to localized populations of a

single nucleophile on the polymer chain, thus leading

to a non-homogenous distribution down an entire

chain.

A decomposition mass loss, as observed for the dry

materials, was observed for water-soaked polymers.

The temperature at which the decomposition initiated

was noted to be signi®cantly lower than for the

corresponding dry materials. Decomposition tempera-

tures were reduced by 14°C to 45°C with no clear

trend correlating this behaviour to composition.

Experiments are under way to understand this

phenomenon fully.

CONCLUSIONSPolyphosphazenes substituted with binary pendant

group mixtures form terpolymers with ®nely tunable

physical structure and physical and chemical proper-

ties differing vastly from those of homopolymers

formed from the respective pendant groups. Diacetone

D-glucofuranosyl incorporation imparts a glass-like

hydrophobic character to the polymer while MEEP

imparts a water-soluble viscous ¯uid nature. As

reported previously, these substituents may be

blended together on a single backbone to give

elastomeric terpolymers with characteristics represen-

tative of both pendant groups. The unexpected result

was the good correlation of the measured Tg with the

calculated Tg using the Fox equation commonly

applied to organic copolymers. This good agreement

extends to the compositional analysis obtained from

[1H]NMR spectroscopy. Additionally, TGA revealed

that these materials are stable up to 290°C and that

some of this stability is lost through the inclusion of

water into the polymer matrix. Water swellability also

appears not to depend exclusively on the amount of

hydrophilic pendant group substitution, but also on

the molecular weight and polymer morphology.

ACKNOWLEDGEMENTThe work described in this paper was supported by the

United States Department of Energy through Con-

tract DE-AC07-94ID13223 and the INEEL Labora-

tory Directed Research and Development program.

REFERENCES1 Zeldin M, Wynne KJ and Allcock HR, (eds), Inorganic and

Organometallic Polymers, American Chemical Society,

Washington DC. p 250 (1988).

2 Peterson ES, Stone ML, McCaffrey RR and Cummings DG, Sep

Sci Technol 28:423 (1993).

3 Mark JE, Allcock HR and West R, Inorganic Polymers, Prentice

Hall, Engelwood Cliffs NJ. p 61 (1992).

4 Schmidt OT, in Methods in Carbohydrate Chemistry, Vol II, ed by

Whistler RL and Wolfrom ML, Academic Press, New York. p

318 (1963).

5 Allcock HR and Pucher SR, Macromolecules 24:23 (1991).

6 Allcock HR and Scopelianos AG, Macromolecules 16:715 (1983).

7 Allcock HR and Kugel RL, J Am Chem Soc 82:4216 (1965).

8 Allen CW, Hybrid Inorganic-Organic Polymers, American Chemi-

cal Society, Washington DC. p 290 (1988).

9 Singler RE, Hagnauer GL, Schneider NS, Laliberte BR, Sacher

RE and Matton RW, J Polymer Sci 12:433 (1974).

10 Peterson ES, Stone ML, Cummings DG and McCaffrey RR, Sep

Sci Technol 28:271 (1993).

11 Peterson ES, Stone MI, Orme CJ, Stewart FF and Cowan RL,

Sep Sci Technol 32:541 (1997).

12 Peterson ES and Stone ML, J Mem Sci 86:57 (1994).

13 Allcock HR, Phosphorous-Nitrogen Compounds, Academic Press,

New York (1972).

14 Singler RE, Schneider NS and Hagnauer GL, Polym Sci Eng

15:321 (1975).

15 Allcock HR, Austin PE, Neenan TX, Sisko JT, Blonsky PM and

Shriver DF, Macromolecules 19:1508 (1986).

16 Stewart FF, Peterson ES, Stone ML and Singler RE, Amer Chem

Soc Polymer Preprints 38:836 (1997).

17 Fox TG, Bull Am Phys Soc 1:123 (1956).

18 Beres JJ, Schneider NS, Desper CR and Singler RE, Macromol-

ecules 12:556 (1979).

Figure 2. TGA of Polymer 7 swollen in water. Loss of water is characterizedas weight loss up to approximately by 110°C. Decomposition is typicallyobserved as a significant loss of polymer mass and was measured as anonset point.

62 Polym Int 49:57±62 (2000)

FF Stewart et al