Jon F. Geibel

Crystallization kinetics of poly(p-phenylene sulphide): the effect of branching agent content and endgroup counter-atom

Abstract The crystallization behaviour of poly(phenylene sulphide) (PPS) has been studied as a function of branching agent (trichlorobenzene) concentration in polymerization, and as a function of the chemical nature of the endgroup counter-atom. In both cases, the bulk crystallization phenomena could be described by the Avrami equation with exponent n ≈ 3. An increase of the branching agent concentration in polymerization caused decreases of the linear crystal growth rate, overall rate of bulk crystallization, nucleation density, and heat of crystallization. The effect of branching on the linear crystal growth rate seemed to be more important than that of molecular weight. The chemical nature of the endgroup counter-atom affected the kinetic parameters in different ways. The endgroup counter-atoms considered were hydrogen, calcium, zinc and sodium. In decreasing order, the crystal growth rates were found to be PPSCa > PPSH > PPSZn > PPSNa. However, the overall rates of bulk crystallization and the estimated nucleation densities followed the order PPSH > PPSZn > PPSCa > PPSNa. The nucleation densities accounted for the different rates of bulk crystallization. The crystallinity content of PPSH seemed to be lower than those of PPSZn, PPSCa, and PPSNa. While the lower crystallinity content of PPSH could be rationalized by considering the ionic character of the endgroups, it was not possible to account systematically for the nucleation and growth rate dependencies on the nature of the endgroup counter-atom.

Crystallization behaviour of poly(p-phenylene sulfide): Effects of molecular weight fractionation and endgroup counter-ion

Abstract The crystallization behaviour of poly(p-phenylene sulfide) (PPS) has been studied. Two PPS samples with 〈MW〉 = 44 K and 〈MW〉 = 64 K were fractionated by a process which selectively removes a portion of the low molecular weight species yielding fractionated PPS samples with 〈MW〉 = 56 K and 〈MW〉 = 104 K respectively. The fractionated samples were then treated with an ion exchange process to allow control over the nature of endgroup counter-ion, i.e. to introduce Na+ and Zn2+ ions. Using a Hoffman-Weeks analysis, the equilibrium melting temperature of these polymers was estimated to be 320°C irrespective of endgroup 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 endgroup counter-ion for PPS with 〈MW〉 = 56 K that had been fractionated to remove low molecular weight species. Additionally, isothermal rates of 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 overall crystallization rates decreased in the following order: H+ > Zn2+ > Na+. The order of decreasing crystal growth rates corresponded to a similar increase in melt viscosity as a function of endgroup counter-ion, suggesting that the reason for decreasing growth rates could originate from increasing secondary interchain interactions. Optical microscopy studies showed the nucleation density decreased in the order H+ > Na+. The ion-exchange reactions were shown to be reversible by differential scanning calorimetry (d.s.c.) and optical microscopy studies. Crystallinity determinations by wide angle X-ray diffraction (WAXD) and measurements of the heats of melting illustrated that higher molecular weight PPS attained lower levels of crystallinity than PPS of lower molecular weight when crystallized under identical conditions.