Melt Blending Modification of Commercial Polystyrene with Its Half Critical Molecular Weight, High Ion Content Ionomer, Poly(styrene–ran–cinnamic Acid) Zn Salt, toward Heat Resistance Improvement

A half-critical weight-average molecular weight ( M ¯ w ) (approximately 21,000 g mol−1), high-ion-content Zn-salt poly(styrene–ran–cinnamic-acid) (SCA–Zn) ionomer was successfully synthesized by styrene–cinnamic-acid (10.8 mol %) copolymerization followed by excess-ZnO melt neutralization. At 220 °C, the SCA–Zn’s viscosity was only approximately 1.5 magnitude orders higher than that of commercial polystyrene (PS) at 102 s−1, and the PS/SCA–Zn (5–40 wt %) melt blends showed apparently fine, two-phased morphologies with blurred interfaces, of which the 95/5 and 90/10 demonstrated Han plots suggesting their near miscibility. These indicate that any PS–(SCA–Zn) processability mismatch was minimized by the SCA–Zn’s half-critical M ¯ w despite its dense ionic cross-links. Meanwhile, the SCA–Zn’s Vicat softening temperature (VST) was maximized by its cross-linking toward 153.1 °C, from that (97.7 °C) of PS, based on its half-critical M ¯ w at which the ultimate glass-transition temperature was approximated. Below approximately 110 °C, the PS/SCA–Zn (0–20 wt %) were seemingly miscible when their VST increased linearly yet slightly with the SCA–Zn fraction due to the dissolution of the SCA–Zn’s cross-links. Nevertheless, the 60/40 blend’s VST significantly diverged positively from the linearity until 111.1 °C, revealing its phase-separated morphology that effectively enhanced the heat resistance by the highly cross-linked SCA–Zn. This work proposes a methodology of improving PS heat resistance by melt blending with its half-critical M ¯ w , high-ion-content ionomer.

Effect of the molecular weight on the lower critical solution temperature of poly(N,N-diethylacrylamide) in aqueous solutions

The molecular weight dependence of the lower critical solution temperature of poly(N,N-diethylacrylamide) was studied with 11 samples of the polymer with a number-average molecular weight (Mn) ranging from 9.6 × 103 to 1.3 × 106 g mol–1 and relatively narrow polydispersity indices from 1.19 and 2.60. These samples were obtained by fractional precipitation of the polymer. LCST values of polymers were measured by turbidimetry and microcalorimetry. An inverse dependence of LCST on the molar mass was found and the LCST of the samples remained more or less a constant above a critical molecular weight of ca. 2 × 105 g mol–1. The enthalpy and the entropy changes as well as the LCST of the polymer depend strongly on the molar mass of the polymer, especially in low molecular weight range.Key words: poly(N,N-diethylacrylamide), LCST, thermosensitive, phase diagram, effect of molecular weight.