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Polystyrenes with molecular weights up to 44 x 10(6) grams per mole have been characterized by light-scattering and equilibrium ultracentrifugation methods. The Mark-Houwink equation, which relates the molecular weight and the intrinsic viscosity of flexible polymers, can be used only if the measurements are made in a theta solvent at the theta temperature.

SynopsisLiquid nitrogen-quenched PBT samples produce much larger spherulites of an optic axis orientation different from that of the air-cooled samples. Optical and scanning electron microscopy show that glass fibers in the glass-reinforced PBT sample nucleate the growth of well-defined spherulites along the glass fiber axis. Fracture studies at temperatures below and above the T, indicate, respectively, brittle and ductile interspherulite boundary fracture. From dynamic mechanical studies, three transitions designated by a (flow transition), j3 (Tg), and y (secondary relaxation) are observed.The magnitudes of the j3 and y transitions are larger for the more amorphous quenched sample than the air-cooled sample, suggesting their amorphous phase origin. Addition of glass fibers raises the dynamic modulus and flow temperature, but suppresses the y transition without significantly affecting the melting and glass transition temperatures.

The effect of glass fibers and some fire retardant additives on the kinetics and mechanism of crystallization of poly(butylene terephthalate) (PBT) has been investigated. Shorter half times of crystallization and higher optimum crystallization temperatures of the filled samples are attributed to the nucleating ability of the additives. Based on the percent crystallinity determined, the efficiency of the different quenching media studied can be arranged in the order: ice water > 25°C water ⩾ dry ice/ethanol > liquid nitrogen. The inefficient quenching of dry ice/ethanol arid liquid nitrogen media is attributed to their poor heat transfer. The Tg of these quenched samples is, however, independent of the percent crystallinity.