Complexing Blends of an Ionomer and a Rigid Rod Polymer
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COMPLEXING BLENDS OF AN IONOMER AND A RIGID ROD POLYMER L. Shao*, R. A. Weiss* and R. D. Lundberg** *Dept of Chemical Eng. and Polymer Science Program, University of Connecticut, Storrs, CT 06269-3136 **Exxon Research and Eng. Co.; Annandale, NJ 08001 ABSTRACT A unique, molecular architecture was developed based on a hydrocarbon soluble backbone with a liquid crystalline- side group. Lightly sulfonated polystyrene (SPS) ionomer was complexed with poly(y-benzyl-L-glutamate) (PBLG), an amine terminated synthetic polypeptide, by solution blending in either THF or chloroform. Complexation first occurred by proton transfer from the pendent acid to the amine terminal group. A secondary interaction involved hydrogen-bonding between the sulfonic acid and the carbonyl group on the PBLG chain. This material will have the potential as a molecular composite and unusual solution behavior was observed when the interaction occurred. INTRODUCTION The objective of this research was to develop a polymer molecular architecture based on the physical interaction of a rigid rod polymer with a lightly sulfonated polystyrene ionomer. The expected interaction involves a physical association due to an acid-base interaction rather than a covalent bond. The strong attractive interaction can be obtained by complexation of metal sulfonate ionomers and another polymer containing amine groups [1,2]. When the interaction occurs only at the end group of the rigid rod, the structure should be that of comb-like graft copolymer [3]. These materials are expected to associate and possibly orient in a sheared solution, which may yield novel solution behavior. Lightly sulfonated polystyrene (I) and an amine terminated synthetic polypeptide were chosen for this study. Poly(y-benzyl-L-glutamate), PBLG, was the polypeptide (II). The a-helical structure is the preferred conformation of PBLG in the solvents of interest. The a-helix of PBLG exhibits lyotropic liquid crystal behavior. Both SPS and PBLG are soluble in a variety of common solvents. In the blend system, we expect that the ionomeric behavior of SPS will be inhibited by the presence of the bulky PBLG molecule as the conterion [4] and the resulting polymer may have properties similar to a side-chain liquid crystalline polymer, LCP. Characterization by DSC, FTIR and scanning electron microscopy (SEM) was carried out to study the structure of the ionomer/LCP blends. EXPERIMENTAL Various lightly sulfonated polystyrenes with different sulfonation levels were prepared by the procedure described by Makowski et al. [5]. The starting material had a number average molecular weight of about 100,000. Sulfonic acid derivatives containing 1 and 5 mole% of the sulfonated species were used. Poly-y-benzyl-L-glutamate (PBLG) of M, = 20,100 was obtained from Sigma Mat. Res. Soc. Symp. Proc. Vol. 248. 01992 Materials Research Society
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Chemical Co., and PBLG of M, = 3000 was synthesized in our laboratory by the method described by William et al. [6]. BLG anhydride was first prepared from triphosgene and BLG in THF,
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