CRYSTALLIZATION BEHAVIOR OF POLY(P-PHENYLENE SULFIDE) - EFFECTS OF MOLECULAR-WEIGHT FRACTIONATION AND ENDGROUP COUNTERION

The crystallization behaviour of poly(p-phenylene sulfide) (PPS) has b een studied. Two PPS samples with [M(W)] = 44 K and [M(W)] = 64 K were fractionated by a process which selectively removes a portion of the low molecular weight species yielding fractionated PPS samples with [M W] = 56K and [M(W)] = 104K respectively. The fractionated samples were then treated with an ion exchange process to allow control over the n ature of endgroup counter-ion, i.e. to introduce Na+ and Zn2+ ions. Us ing a Hoffman-Weeks analysis, the equilibrium melting temperature of t hese polymers was estimated to be 320 degrees C irrespective of endgro up counter-ion or polymer molecular weight. The nucleation density was observed to increase as a function of molecular weight by small-angle light scattering (SALS). The spherulitic growth rates and nucleation densities were studied as a function of the chemical nature of endgrou p counter-ion for PPS with [M(W)] = 56 K that had been fractionated to remove low molecular weight species. Additionally, isothermal rates o f bulk crystallization were analysed as a function of molecular weight of PPS and chemical nature of the endgroup counter-ion. It was found that as a function of endgroup counter-ion, crystal growth rates and o verall crystallization rates decreased in the following order: H+ > Zn 2+ > Na+. The order of decreasing crystal growth rates corresponded to a similar increase in melt viscosity as a function of endgroup counte rion, suggesting that the reason for decreasing growth rates could ori ginate from increasing secondary interchain interactions. Optical micr oscopy studies showed the nucleation density decreased in the order H > Na+. The ion-exchange reactions were shown to be reversible by diff erential scanning calorimetry (d.s.c.) and optical microscopy studies. Crystallinity determinations by wide angle X-ray diffraction (WAXD) a nd measurements of the heats of melting illustrated that higher molecu lar weight PPS attained lower levels of crystallinity than PPS of lowe r molecular weight when crystallized under identical conditions. Copyr ight (C) 1996 Elsevier Science Ltd.