4 Army Research Laboratory 

Aberdeen Proving Ground, MD 2 1005-5069 

ARL-TR-2403 February 200 1 

Semipermeable Membrane From 

Ionomeric Self-Assembling Block 

Copolymer 

Dawn M. Crawford, Eugene Napadensky, 

Nora C. Beck’Tan, and Jim Sloan 

Weapons and Materials Research Directorate, ARL 

David A. Reuschle, David A. Mountz, and Kenneth A. Mauritz 

University of Southern Mississippi 

Kenneth S. Laverdure and Samuel P. Gido 

University of Massachusetts 

Weidong Liu and Benjamin Hsiao 

State University of New York 

Armroved for public release: distribution unlimited. 
Morphological studies have been performed on novel polystyrene-polyisobutylenepolystyrene (PS-PIB-PS) triblock copolymer films made by different processes. The PS-PIB-PS 

films are composed of approximately 30% polystyrene end blocks. Small-angle x-ray scattering 

(SAXS) and transmission electron microscopy (TEM) confirm that a self-assembled, segregated 

cylindrical morphology forms in the copolymer. Dynamic mechanical analysis (DMA) is used 

as a tool to investigate the structure-property relationships in these polymers. Fourier-transform 

infrared (FTIR) spectroscopy and solvent-sorption studies have validated the membrane transport 

properties. Modified PS-PBPS copolymers have also been characterized. Modifications of the 

copolymers were carried out by converting approximately 20% of the polystyrene end blocks to 

styrene-sulfonic acid. The presence of sulfonic acid groups disrupts the morphology and 

significantly enhances water transport properties. Morphological features of the copolymers are 

discussed as they relate to mechanical and transport properties. 

ii 
Table of Contents 

Page 

List of Figures . . . . . . . . . . . .._............-....-.-.............-......f__.__. _._._**.._.._____.__..___._____~......_.__..._ V 

List of Tables . . . . . ..~.......f......f.f~......~...~~.ff..f.f.ff._f..........f............f.f..~.........................~~ vii 

1. Introduction .__________._._ . _ . ..*.......f~.*..**..*..f.*______.._...._..._.*._.**..***_.*.f*..~......~...~.............~.. 1 

2. 2 

3. Results and Discussion . . . . . . . . . . . . . . . . . ..f..~~~~~...f.~......f...............~...____...____________~___________f_

3 

3.1 DMA .................................................................................................................... 3 

3.2 Sorption Studies.. ................................................................................................. 9 

3.3 Transport Studies ................................................................................................. 9 

3.4 Characterization of Microstructure ...................................................................... 10 

4. Conclusions . . ..~........ff.f......f.........f...~~f~..~........*~...ff.f......~...........f...........-~~~~..--.----..-.-- 14 

5. References ______ . . ..~...~**f~......*.f.*.*.*......**.........~....*..f...__*f..~f...f*..~*.*..f.~.........f..f............. 17 

Distribution List ~..........~....~.~~.......~..~~~~~..~..~...~~~....~~.~..~..~...~~......~......~........ . . . . . . ..*.*.... 19 

Report Documentation Page _.____-___._...__._._.__________ ___________________ ._._. __._.ff.........f...._... 2 1 

.._ 

111 
. 

iV 
List of Figures 

Figure 

1. 

.! 2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

DMA of Unmodified PS-PIB-PS Copolymer .____,._____..._._..._.._......f.f...f...._...............*. 

E’ of PS-PIB-PS Films Formed by Different Processing Methods .___.____._._._.__..-.-..-. 

E” of PS-PIB-PS Films Formed by Different Processing Methods ._......_..,.._._...-.--.*_ 

Tan 6 of PS-PIB-PS Films Formed by Different Processing Methods . . . . . . . . . . . . . . . ...+... 

E’ of PS-PIB-PS Copolymer and Ionomer . . . ..~.._..___________________.____________f____..._f.._f._

Tan 6 of Unmodified PS-PIB-PS and Ionomer . . . . ..f...f........_..._._..__..-.._____.._.__.__.________ 

E” of Unmodified PS-PIB-PS and Ionomer ..~.....,f._._f_____._________________________~~.~~~~~~

Diffusion of Acetonitrile and Water Through Sulfonated PS-PIB-PS 

Triblock Copolymer ____________________.~...~~..~..~~_...~f...~.f._~,.....__._.._____~~~.~~.~~~.____

Diffusion Curves for Various Alcohols Through Sulfonated Block Copolymer....... 

Unmodified PS-PIB-PS Film Formed Under Fast Evaporation Conditions.............. 

Sulfonated PS-PIB-PS Film Formed Under Fast Evaporation Conditions _........._.._.. 

SAXS Intensity vs. Scattering Vector, Q, for PS-PI&PS Triblock, Slow Casting 

Condition . +. . . . . . . . +.. . . . . . . . . . ..+, _ ._.. ++.. . . . .+. . . . . . . . . . . . . . . . . . . . . . . . . . .._. . . . . . . . . . , . . +.. .._. _. __. ._ . . ._ .. ._. . 

SAXS Intensity vs. Scattering Vector, Q, for PS-PIB-PS Triblocks at Different 

Casting Conditions . . . . . . . . . ..f................f.....fffff__f..................f...f..f.......f......................... 

SAXS Intensity vs. Scattering Vector, Q, for Sulfonated and Unsulfonated 

PS-PIB-PS Triblocks, Slow Casting Conditions. ..f..,...f.__.._._.,_.__.._______.._._._.._._-..._._.. 

m 

4 

5 

5 

6 

7 

7 

8 

11 

11 

12 

12 

13 

14 

15 
vi 
List of Tables 

Table PaRe 

1. Sorption and Permeation of PS-PIB-PS and Ionomer .~..~.~......f..f_.__.._.._...__.___.... + .. . . . . . 9 

vii 
JNENTIONALLYLEFTBLANK. 

. . . 

Vlll 
1. Introduction 

The U.S. Army requires that all fielded systems be survivable in a chemical-warfare 

environment. Butyl rubber is currently used in standard protective clothing because it provides 

good protection from chemical and biological agents. However, garments made from butyl 

rubber are bulky and nearly impermeable to air and moisture, resulting in unbearable levels of 

heat inside the garments during use. One challenge at the U.S. Army Research Laboratory 

(ARL) is to develop and characterize advanced polymeric materials for soldier protective 

clothing that can block entry of harmful chemicals and simultaneously allow transport of water 

vapor from the soldier. To address this problem, research has been directed toward developing a 

flexible, triblock copolymer with “membrane-like” characteristics, formed via molecular selfassembly. 

Self-assembled morphologies occur in block copolymers that are composed of 

thermodynamically immiscible constituent blocks. Ordered microstructures including spheres, 

cylinders, or larnellae can be observed, depending on the chemical composition of the blocks, 

sample preparation, interactions between the blocks, or by the addition of diluent [ 11. Block 

copolymers in which an amorphous block is present as a major constituent and a glassy block 

exists as a minor component typically exhibit the solid-state properties of thermoplastic 

elastomers. When a portion of the polymer chain contains an ionic group, the block copolymer 

is classified as an ionomer. Association of ion-rich domains occurs in ionomers, providing 

‘physical” cross-links that affect the block copolymer morphplogy and the thermal and 

mechanical properties [2]. This paper addresses the structure/property relationships observed in 

a polystyrene-polyisobutylene-polystyrene (PS-PIB-PS) block copolymer as a result of 

ionomeric modification in the PS end blocks. 

A commercially available triblock copolymer formulation consisting of a PS-PIB-PS 

backbone was studied. The polymer comprised approximately 30% (molar) polystyrene. The 

thermoplastic elastomers exhibit physical properties of rubber at low temperature and 

melt-processable thermoplastic at temperatures above the glass transition temperature (Tg) of PS. 

1 
This behavior results from microphase separation of the glassy PS domains that act as physical 

cross-links dispersed in the rubbery PIB matrix. The fraction of PS controls the morphology that 

is formed in the copolymer (cylinders, lamellae, or spheres). Cylindrical morphology exists in 

the PS-PIE3-PS triblock composed of 30% PS. Thus, the morphology formed by the PS fraction 

provides a “channel” by which molecular transport across the film can occur while the PIB 

matrix provides chemical resistance. Ionomeric modification of commercially available 

PS-PIB-PS copolymer was performed by sulfonation. Approximately 20% of the styrene 

monomers were converted to styrene-sulfonic acid. The modified copolymer exhibits 

hydrophilic character that is necessary for transporting water vapor. The polymers were 

characterized in their unmodified and sulfonated form utilizing a number of experimental 

techniques including dynamic mechanical analysis (DMA), transmission electron microscopy 

(TEW, small-angle x-ray scattering (SAXS), solvent-sorption experiments, and 

Fourier-transform infrared (FTIR) spectroscopy transport experiments. 

2. Experimental 

Kuraray, Inc. supplied the PS-PIB-PS triblock copolymers. The copolymers were sulfonated 

in a solution of dichloroethane and hexane at 50 “C with acetyl sulfate, Details of the 

sulfonation procedure are found elsewhere [3]. The copolymers were dissolved in toluene or 

toluene/hexyl alcohol mixtures at a concentration of 1% and were cast into Teflon petri dishes. 

Samples were identified by the rate of solvent evaporation and designated as “fast,” 

“intermediate,” or “slow.” An “ultrafast” evaporation rate was achieved by spraying a solution 

(5% polymer concentration) onto a substrate and allowing the film to form under a hood. 

DMA was performed using an Imass, Inc. autovibron (automated Rheo-200 rheovibron, 

Toyo Instruments). Films of approximately O-01-cm thickness were evaluated between - 130 “C 

and +lOO “C at a heating rate of 1 “C per minute. Data were collected at 1 Hz. 

Solvent-absorption data were collected by submerging dry samples in high-performance liquid 

chromatograph (HPLC)-grade water for specific time intervals. Weight measurements were 

taken until saturation was reached. Weight averages were used to calculate solubility (S) defined 

2 
as weight of liquid absorbed per weight of dry sample. Water-diffusion experiments were 

performed using a HP5890 gas chromatograph (GC). A cylindrical fixture held the sample 

membrane horizontally, while the top surface of the sample was flooded with HPLC-grade 

water. The other side of the sample was swept with dry nitrogen and sent to a split injector of 

the GC oven equipped with a thermal conductivity detector (TCD). 

Transport properties of the sulfonated block copolymer membranes were investigated using a 

Nicolet Research Series FTIR spectrometer with a horizontal attenuated total reflectance (ATR) 

cell and a zinc selenide trapezoidal ATR crystal. The polymer-coated ATR crystal was mounted 

in a flow-through ATR cell. Liquid penetrants are allowed to pass through the cell, flooding the 

polymer-coated ATR crystal. Diftision of the penetrant through the polymer film is detected by 

the infrared (JR) absorbance. Details regarding the experimental apparatus and methodology 

used for the diffusion experiments are discussed elsewhere [4,5]. 

TEM characterization was performed on cast samples coated with a lOO-nm gold layer. A 

JEOL 1OOCX TEM microscope operated at lOO-kV accelerating voltage was utilized. TEM 

samples were prepared by cutting 30- to SO-nm-thick sections using a cryomicrotome, and 

staining in RuO4 vapors for 4 hr. 

SAXS was performed on beamline X27C at National Synchrotron Light Source, Brookhaven 

National Laboratory. Data were collected using a pinhole collimated beam and image plate 

detectors and were reduced by background subtraction and circular averaging. The wavelength 

used was 1.54 A. The sample to detector distance was about 1,000 mm. 

3. Results and Discussion 

3.1 DMA. The tensile storage modulus E’, loss modulus E”, and tan S are plotted as a 

function of temperature and shown in Figure 1. E’ shows a distinct drop at the (T,) of the PJB 

matrix and another decrease that begins at approximately 93 “C associated with onset of the glass 

3 
-50 0 50 

Tern perature “C 

Figure 1. DMA of Unmodified PS-PIB-PS Copolymer. 

transition of the PS domains. The tan 6 curve exhibits a low-temperature shoulder at 

approximately -60 “C that is likely a contribution from less-restricted PIB chains. The T, of 

pure PIE is -70 “C [63. The low-temperature shoulder appears to correspond with the peak of 

E”. The T, is defined as the temperature corresponding with the maxima in the E” data and was 

measured at approximately -63 “C for the PS-PIB-PS copolymers. T, was previously reported 

for noncommercial PS-PJB-PS polymers to be approximately -65 “C using differential scanning 

calorimetry DSC [7], which is in good agreement with the DMA data. 

Variation in the solvent evaporation rate did not have a significant effect on dynamic 

mechanical behavior. The most apparent difference was observed between films formed via the 

fastest evaporation rate (spraying) and the slowest evaporation (2 or 3 weeks required for film 

formation). Films formed via slow evaporation exhibited slightly higher values of E’ and 

slightly higher magnitudes of E” and tan scornpared to the sprayed films. These data are shown 

in Figures 2, 3, and 4, respectively. TEM confirmed that slow solvent evaporation rates during 

film formation resulted in better long-range order compared to fast evaporation rates. Cylinders 

formed by the glassy styrenic blocks were oriented with their axes parallel to the f&n plane. 

This morphology is consistent with the E’ shown in Figure 2. An increase in the tensile storage 

4 
l.OOE+lO 

1.cm+oa 

1 .OOE+07 

* Spray 

- Slow 

Figure 2. E’ of PS-PIB-PS Films Formed by Different Processing Methods. 

l.OOE+lO 1 

l.‘JOE+O9 

l.OOE+O7 

* Spray 

l.WE+O6 m 

Figure 3. E” of PS-PIB-PS Films Formed by Different Processing Methods. 

5 
1.2 , 

* Spray 

-slow 

Figure 4. Tan 6 of PS-PIB-P’S Films Formed by Different Processing Methods. 

modulus would be expected when the glassy cylinders exist parallel to the film plane. The 

changes in loss properties shown in Figures 3 and 4 suggest that a more disordered morphology 

caused by Wtrafast” evaporation rates (spraying) may inhibit the microphase separation of the 

PS and PIB domains causing a slight reduction in E” and tan S peak magnitude. This result was 

observed to a much greater extent following sulfonation. Kim and Libera [S, 91 previously 

reported on the effect of solvent evaporation rate on thin film morphology of similar triblock 

copolymers. 

Sulfonation of the PS-PIE!-PS copolymer had the greatest effect on dynamic mechanical 

behavior. DMA results for PS-PIB-PS copolymers and their ionomers are shown in Figures 5-7. 

Figure 5 shows E’ plotted as a function of temperature for the two polymers. Sulfonation of the 

block copolymer resulted in a much higher rubbery E’. The ionomer was observed to be more 

6 
+ PS-PIB-PS 

- Sulfonated PS-PIB-PS 

.,*__ “. 

-1M -100 60 

Temperatere’C ” loo 

Figure 5. E’ of PS-PIB-PS Copolymer and Ionomer. 

+ Sulfonated PS-PIB-PS 

* PS-PIB-PS 

-150 -100 -50 0 

Temperature’C 

50 1m 

Figure 6. Tan S of Unmodified PS-PIB-PS and Ionomer. 

7 
* sulfonatd PSPBPS 

‘tlsPlEH3 

-150 -1CKl -50 0 50 100 

TenT#rature°C 

Figure 7. E” of Unmodified PS-PXB-PS and Ionomer. 

thermally stable with no indication of changes in E’ at 100 “C as was observed for the 

nonmodified copolymer. Figure 6 shows tan S for the two polymers. The sulfonated PS-PIB-PS 

exhibits a greatly reduced tan 6 magnitude. Tan 6 maxima for the sulfonated polymer appears to 

correlate with the low-temperature shoulder of the PS-PIB-PS tan 6 peak. The shape of the tan 6 

curve for the PS-PIB-PS ionomer appears to be reversed from the unmodified copolymer. That 

is, rather than the presence of the low-temperature shoulder preceding the tan S maxima as 

observed for PS-PIB-PS, the sulfonated polymer exhibits the prominent tan S transition at 

approximately -57 “C, corresponding with the low temperature shoulder of the unmodified 

copolymer, followed by a higher temperature shoulder at approximately -45 “C. Similar results 

have been recently reported for copolymer ionomers prepared by sulfonation of the PS blocks of 

PS-poly(ethylene-alt-propylene) (PEP) [lo]. The authors concluded that the enhancement of the 

high-temperature modulus is the result of association and hydrogen bonding of the sulfonic acid 

8 
groups [lo]. The loss modulus of the two polymers is shown in Figure 7. These data indicate 

that sulfonation of the block copolymer does not affect the T, or the magnitude of the glass 

transition (E” maxima). E” of the sulfonated polymer is significantly higher than the unmodified 

polymer at temperatures above 0 “C. 

3.2 Sorption Studies. Solvent sorption and permeation studies were conducted to ascertain 

the effect of morphology and sulfonation of PS-PIB-PS on the ability of the polymer to absorb 

and transport water. Details of experimental methods used to measure permeation and 

calculation of diffusion coefficients are discussed elsewhere [ 11, 121. Average solubility and 

diffusion coefficients are shown in Table 1. The hydrophobic nature of PS-PIB-PS is reflected in 

the solubility measurements. The unmodified copolymer exhibited a low value of water 

sorption, and no transport of water vapor through the film was detected. Sulfonation of 

approximately 20% of the styrene monomers resulted in a threefold increase in average water 

solubility. 

Table 1. Sorption and Permeation of PS-PIB-PS and Ionomer 

Polymer/Evaporation 

Rate 

PS-PIB-PS/fasJ 

Ionomerifast 

Xonomer/inter 

Ionomer/slow 

Permeability 

Average Solubility 

Diffusion Coefficient cp) 

(S) 

(grams of water/ @I cm’ x grams of water 

grams of sample) (cm2/s) grams of samples x s 

0.0547 too small to measure too small to measure 

0.1336 3.5024 x 1O-7 4.6793 x lo-’ 

0.1636 8.7838 x lo-s 1.4371 x 1o-8 

0.1211 1.1491 x lo-’ 1.3916 x lo-’ 

3.3 Transport Studies. Transport experiments were conducted using water, acetonitile, 

and a series of alcohols as individual penetrants. Acetonitrile was selected as a penetrant 

because its chemical structure loosely resembles the chemical agent cyanogen chloride, it 

exhibits moderate hydrogen bonding characteristics, and it has a very distinguishing feature in 

9 
the IR spectra. Figure 8 shows the kinetic plot of the JR intensity over time for water and 

acetonitrile. Both diffusion curves show the expected S shape and appear to be Fickian in nature. 

The data clearly show that water transports th.rough the film faster than the acetonitrile. The 

sulfonated block copolymer membrane exhibits a breakthrough time of around 100 min for the 

acetonitrile penetrant. This breakthrough value surpasses the current military quality-assurance 

specification requirement for acceptance testing of chemical/biological protective gloves. Water 

molecules transport through the 8-mil membrane in approximately 25 min. The data show that 

the sulfonated PS-PIB-PS triblock copolymer exhibits superior semipermeable properties for 

chemical protective clothing compared to the currently used butyl rubber. 

Figure 9 shows the kinetic R absorbance data for several alcohols with varying aliphatic 

content. A clear trend becomes apparent as smaller size molecules have higher transport rates. 

Methanol, the smallest alcohol, diffuses very quickly through the membrane, while butanol 

shows no transport at all over the time scale of the experiment (450 min). The per-m-selective 

properties of the sulfonated triblock copolymer membrane is demonstrated by its size selectivity 

characteristics with respect to penetrant. Increasing the aliphatic content of the alcohols by only 

three CH2 groups results in a significant decrease in transport rate. 

3.4 Characterization of Microstructure. The morphology in both modified and 

unmodified PS-PIB-PS triblocks was studied using a combination of SAXS and TEM. TEM 

results, shown in Figures 10 and 11, reveal a microphase-separated morphology in both the 

unmodified and sulfonated PS-PIB-PS triblocks. In the unmodified copolymers, the morphology 

is typical of self-assembled cylindrical systems and displays considerable long-range order 

(Figure 10). The SAXS curves for these materials, shown in Figure 12, show evidence of 

long-range order as well. Scattering peaks occur at positions that are multiples of fi 2, & 

and 3x the position of the primary reflection, indicating that the copolymer forms a hexagonally 

packed cylindrical morphology. The degree of long-range order depends somewhat on the 

processing technique, increasing as the time for film casting increases, as evidenced by sharper 

10 
.- Acetonitrile 

+ Water 

Time (min) 

Figure 8. Diffusion of Acetonitrile and Water Through Sulfonated PS-PIB-PS Triblock 

Copolymer. 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 

-0.2 

Time (min) 

+ Methanol 

-Ethanol 

+ Butanol 

Figure 9. Diffusion Curves for Various Alcohols Through Sulfonated Block Copolymer. 

11 
Figure IO. Unmodified PS-PIB-PS Film Formed Under Fast Evaporation Conditions. 

PS Phase Was Stained by RuO4 and Appears as the Dark Regions. 

Figure 11. Sulfonated PS-PIB-PS Film Formed Under Fast Evaporation Conditions. 

PS Phase Was Stained by RuO4 and Appears as the Dark Regions. 

12 
100 - 

r 

I I I I I I I 

0.02 0.04 0.06 0.08 0.1 0.12 0.14 

Q (A-’ ) 

Figure 12. SAXS Intensity vs. Scattering Vector, Q, for PS-PIEPS Triblock, Slow Casting 

Condition. Peaks Occur in the Sequence 1, fi 2, fi 3 Times the Position of 

the Primary Scattering Peak, q*. The Primary Scattering Peak Occurs at 

q*= 0.0245 A. 

scattering peaks and more prevalent high-order reflections (Figure 13). The most significant 

change to the morphology occurs as a result of sulfonating the PS block. Mter sulfonation, the 

long-range order of the copolymer is severely disrupted. The electron micrograph, Figure 11, 

shows that the sulfonated triblock forms cylinders that order only locally. The SAXS data also 

show a loss of long-range order, as evidenced by the broadening of the scattering peaks, and the 

lack of clearly defined scattering peaks at higher Q values (Figure 14). The disruption of longrange order upon sulfonation is similar to effects observed in other triblock thermoplastic 

elastomer systems and has been previously reported [l, 131. 

13 
0 Slow 

q Intermediate 

x Fast 

p Spray I c 

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 

Q (A-‘) 

Figure 13. SAXS Intensity vs. Scattering Vector, Q, for PS-PIB-PS Triblocks at Different 

Casting Conditions. 

at q*= 0.0245 A. 

For All Conditions, the Primary Scattering Peak Occurs 

4. Conclusions 

The morphology and viscoelastic properties of PS-PB-PS triblock copolymers were studied 

with respect to film processing and sulfonation of approximately 20% of the styrene monomers. 

TEM and SAXS studies confirmed that the copolymers exhibit phase-segregated cylindrical 

domain morphology and indicated that slow evaporation rates enhanced long-range order of the 

PS domains, while sulfonation greatly perturbed the morphology. Sulfonation of the styrene 

blocks had a dramatic effect on dynamic mechanical properties. Ionomers of PS-FIB-PS 

exhibited a greatly increased rubbery plateau E’ and a dramatic reduction in tan F magnitude. 

These observations are believed to be related to associations of the sulfonic-acid groups that 

14 
c 

0 Unsulfonated 

+ Sulfonated I 

I I I I I 1 I 1 

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 

Q (A-‘) 

Figure 14. SAXS Intensity vs. Scattering Vector, Q, for Sulfonated and Unsulfonated 

PS-PIB-PS Triblocks, Slow Casting Conditions. The Primary Scattering 

Vector in the Sulfonated System, q *s, Occurs at a Lower Value Than for the 

Unsulfonated System Due to Volume Expansion in the PS Block. 

inhibit slippage of the amorphous chains. Sorption and transport studies showed that the ionomer 

exhibited significantly improved water-transport properties and exhibit selectivity between small 

organic molecules. Collectively, the mechanical properties and ease of processing the sulfonated 

PS-PIB-PS triblock copolymer films, combined with their ability to transport water and block 

organic molecules, render these membranes applicable for chemical protective clothing for 

military applications. The unique properties of these polymers would also be useful for 

nonmilitary applications including protective clothing for “first responders” in chemical-threat 

situations or for hazardous materials handling. Future studies are planned to specifically address 

the morphological features in the ionomers with respect to sulfonation levels and counterion 

substitution. 

15 
16 
5. References 

1. Lu, X., W. P. Steckle, Jr., and R. A. Weiss. Macromolecules. Vol. 26, p+ 6525, 1993. 

2. Weiss, R. A,, A. Sen, L. A. Pottick, and C. L. Willis. PoZymer Communication. Vol. 31, 

p. 220, 1990. 

3. Mountz, D. A., D. A. Reuschle, L. B. Brister, R. F. Storey, and K. A. Mauritz. ACS Polymer 

Preprints. Vol. 39, p. 383, 1997. 

4. Hong, S. U., T. A. Barbari, and J. Sloan. J. Polym. Sci., Polym. Phys. Ed. Vol. 35, p. 1261, 

1997. 

5. Fieldson, G. T., and T. A. Barbari. AICHE J. Vol. 41, p- 895, 1995. 

6. Sperling, L. H. Introduction to Physical Polymer Science, 2nd Ed. New York: Wiley, 

p. 367, 1992. 

7. Reuschle, D. A., D. A. Mountz, B. Brister, C. L. Curry, K. A. Shoemake, R. F. Storey, ad 

K. A. Maurtiz. ACS Polymer Preprints- Vol. 39, p. 381, 1997. 

8. Kim, G., and M. Libera. Macromolecules. Vol. 3 1, p. 2569, 1998. 

9. Kim, G., and M. Libera. h4ucromoZecuZes. Vol. 31, p. 2670, 1998. 

10. Mani, S., R. A. Weiss, C. E. Williams, and S. F. Hahn. Macromolecules. Vol. 32, p. 3663, 

1999. 

11. Billing, C. B., and A. P. Bentz. “PeP;fonnance of Protective CZothing: Second SymposiumASTM STP. ” R. Sager and A. P. Nielsen, Eds., American Society for Testing and Materials, 

Philadelphia, PA, pp. 226-235,1988. 

12. Pauly, S. Polymer Handbook, 3rd Ed. J. Brandrup and E. H. hnmergut, Eds., New York: 

Wiley, pp. 435-439, 1989. 

13. Weiss, R. A., A. Sen, L. A. Pottick, and C. L. Willis. Polymer. Vol. 32, p. 2785, 1991. 

17 
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11. SUPPLEMENTARY NOTES 

l University of Southern Mississippi, 2701 Hardy St., Hattiesburg, MS 39406 

t University of Massachusetts, Amherst, MA 010034530 

’ State University of New York, Stony Brook, NY 11794-3400 

I&I. DISTRIBUTl0N/AVAlLABlLlTY STATEMENT 12b. DISTRIBUTION CODE 

Approved for public release; distribution is unlimited. 

13. ABSTRACT(Maximum 200 words) 

Morphological studies have been performed on novel polystyrene-polyisobutylene-polystyrene (PS-PI&PS) triblock 

copolymer films made by different processes. The PS-PIB-PS films are composed of approximately 30% polystyrene 

end blocks. Small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm that a 

self-assembled, segregated cylindrical morphology forms in the copolymer. Dynamic mechanical analysis (DMA) is 

used as a tool to investigate the structure-property relationships in these polymers. Fourier-transform irmared (FTIR) 

spectroscopy and solvent-sorption studies have validated the membrane transport properties. Modified PS-PlB-PS 

copolymers have also been characterized. Modifications of the copolymers were carried out by converting 

approximately 20% of the polystyrene end blocks to styrene-sulfonic acid. The presence of sulfonic acid groups 

disrupts the morphology and significantly enhances water transport properties. Morphological features of the 

copolymers are discussed as they relate to mechanical and transport properties. 

f4. SUBJECT TERMS 15. NUMBER OF PAGES 

DMA, niblock copolymer, ionomer, sulfonation, microstructure, morphology, solvent 23 

transport 18. PRICE CODE 

17. SECURITY CLASSIFICATION 18. SECURITY CLASSlFlCATlON 19. SECURIW CL4SSlFlCATlON 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL 

NSN 7540-01-280-5500 Standard Form 298 (Rev. 249) 21 Prescribed by ANSI Std. 239-18 298-102 
WTENTIONALLYLEFTBLANK. 

22 
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