Thermal stability of poly(styrene-b-methyl methacrylate) and poly(styrene-b-ethylene-co-1-butene-b-methyl methacrylate)

Summary

The thermal stability of poly(styrene-b-methyl methacrylate) diblock copolymers (= P(S-b-MMA)) and poly(styrene-b-ethylene-co-1-butene-b-methyl methacrylate) triblock copolymers (=P(S-b-EB-b-MMA)) was investigated. Well-defined high molecular weight block copolymers with narrow molecular weight distribution (MWD) were molded at different temperatures in vacuum and the alteration of the MWD was sensitively monitored by gel permeation chromatography (GPC). Up to 240°C P(S-b-MMA) shows almost no broadening of the MWD. At higher temperatures low molecular weight polystyrene-rich portions are formed. The number average molecular weight (M_n) is strongly reduced. P(S-b-EB-b-MMA) triblock copolymers show broadening of the MWD to higher and lower molecular weights at elevated temperatures, probably caused by chain scission and linking reactions of the EB block. M_n remains approximately constant. Up to 240°C the broadening of the MWD is not very pronounced. In comparison to unhydrogenated P(S-b-B-b-MMA) triblock copolymers, the thermal stability of P(S-b-EB-b-MMA) is greatly enhanced.