Effect of side chain length on the glass transition of copolymers from styrene with n‐alkyl citraconimides and with n‐alkyl itaconimides

Equimolar copolymers of styrene with a series of N‐n ‐alkyl citraconimides where the alkyl group varies from methyl to octadecyl were synthesised and the dependence of the glass transition on the length of the alkyl chain examined. Over the series N ‐methyl to N‐n ‐octadecyl only a smooth monotonic decrease in the value of the glass transition temperature T g was found. Any increase in T g at high alkyl chain lengths that might arise from ordering effects was not detected. However, by viewing the copolymer structure as comprising a main chain unit and a series of methylene side chain units of varying length, then plotting the data according to the Gordon‐Taylor equation, a deviation from linearity is revealed that may be interpreted as due to incipient crystallisation of the longer side chains. A similar examination of a series of copolymers of styrene with N‐n ‐alkyl itaconimides proved impracticable due to the inability to prepare isomerically pure itaconimide monomers. Comparisons of the citraconimide series were thus drawn with literature data on copolymers of styrene with N ‐alkyl maleimides.