On the glass transition temperature of comblike polymers: Effects of side chain length and backbone chain structure

Abstract

Abstract Polymers composed of monomer units that contain n ‐alkyl side chains are characterized by a monotonical decrease in the glass transition temperatures toward a critical value ( T g ) c as the number of C atoms in the side chain increases toward a corresponding critical value n c . Thus the glass transition temperatures of these comblike polymers are for a given backbone chain structure directly related to the molecular weight ( M ) of the monomer unit. This relationship can be represented by the differential equation dT g / dM = − k′M [ T g − ( T g ) c ], which on integration yields T g = (Δ T g ) 0 exp−[ k ( M 2 − M )] + ( T g ) c , where (Δ T g ) = ( T g ) 1 − ( T g ) c , and the subscript 1 refers to n = 1. Values for T g calculated according to this relationship are in good agreement with published data on polybutadienes, polystyrenes, poly(vinyl ether)s, polyacrylates, polymethacrylates, polyitaconates, poly(phenylene ether)s, and poly( N ‐maleimide)s. For these polymers the critical quantities n c and ( T g ) c can be estimated rather well by the simple relationships n c = 1 + 2.8 × 10 −2 ( T g ) 1 and ( T g ) c = ( T g ) 1 − n c ( n c − 1). The T g ( M ) relationship derived appears to be applicable also to copolymers that contain monomer units with alkyl side chains.