Linear and star-branched block-copolymer telechelic ionomers: Synthesis, characterization, development and physical properties.

摘要

Using anionic polymerization techniques, a series of telechelic linear and star-branched block copolymers was synthesized, each copolymer was comprised of short polystyrene outer blocks and long elastomeric, poly(ethylene-1-butene) inner blocks. Catalytic hydrogenation was used to render the butadiene-based elastomeric inner block inert to sulfonation. Hexanoyl sulfate was used to place sulfonate groups on the outer blocks; subsequent neutralization with various bases led to elastic ionomers with counterions of Na, K, Li, Cs, Zn, Mg, N(CH{dollar}sb3{dollar}){dollar}sb4{dollar}, and N(C{dollar}sb4rm Hsb{lcub}10{rcub})sb4{dollar}.; Star-branched polymers were formed by linking three arms to a central hub as follows: styrene was oligomerized using sec-buLi; butadiene was added sequentially to produce block copolymer arms; the living arms were linked with methyl trichlorosilane. Linear telechelic polymers were prepared by sequential monomer addition as follows: styrene was oligomerized with sec-buLi; butadiene was added sequentially, forming the center elastomeric block; a second charge of styrene was added, forming the final block; the living triblocks were terminated with degassed methanol.; A new "modular" high-vacuum system was designed that utilizes mechanical agitation in place of magnetic stirring, Teflon Rotoflo{dollar}circler{dollar} stopcocks in place of glass breakseals, and spherical o-ring joints in place of direct glass seals. In this way, a standard reactor was fitted with appropriate reactant ampules, volumetric charging cylinders, etc., to facilitate polymerization, blocking reactions, and linking reactions with minimal effort.; Small Angle X-ray Scattering (SAXS) on ionomer samples revealed that three-arm star-polymers with molecular weights greater than 40,000 g/mole showed an ionic peak corresponding to an inter-domain spacing of 7.0 nm. Lower molecular weight polymers showed cluster spacings greater than the calculated radius of gyration for the corresponding polymer, implying polymer coil expansion due to ionic aggregation.; Dynamic Mechanical Analysis, (DMA) showed a poly(ethylene-1-butene) glass-transition, independent of counterion, at {dollar}-{dollar}55{dollar}spcirc{dollar}C. Hard cations displayed a peak, superimposed on the glass transition, attributed to local ionic reorganization. A second peak, attributed to long range ionic reorganizations, was seen at the end of the rubbery plateau. The onset of terminal flow was counterion dependent; soft counterions showed significant flow, while hard cations resisted flow, at lower temperatures.; Tensile testing revealed that low molecular weight ionomers behaved like perturbed networks and were characterized by low elongation and tensile strength at break. High molecular weight ionomers yielded tough networks with greater elongation at break.