Glass transition of styrene/n‐alkyl methacrylate copolymers

Abstract

AbstractDependences of the glass transition temperatures (Tg) of copolymers of styrene (ST) with the n‐alkyl methacrylates [methyl, ethyl, butyl and octyl methacrylate (MMA, EMA, BMA, and OMA)] on their overall chemical composition were measured. All the dependences investigated in this study satisfy the dyad approximation suggested earlier for the description of the sequential distribution effect on Tg of the copolymer either (1) using reciprocal Tg's and weight fractions of the dyads (according to Johnston), or (2) by means of Tg's and mole fractions of rotatable bonds corresponding to the respective dyads (according to Barton). It was shown that for copolymers the monomeric units of which did not differ too much in their number of rotatable bonds in the molecule (e.g., ST/MMA), both these approaches are satisfactory; if the comonomeric units differ markedly in the number of rotatable bonds (e.g., ST/OMA), approach (1) yields more realistic results than (2). Extrapolation to zero content of the styrene component in the copolymer ST/OMA gave Tg of poly(OMA) (245 K), which is experimentally inaccessible by the method employed (differential scanning calorimetry).