On the entanglement density of differently N-substituted alternating styrene-maleimide copolymers

Abstract

Abstract Differently N-substituted maleimides were copolymerized with styrene to yield alternating styrene-maleimide copolymers (SMI-R) with different chain diameters. The polymers were obtained by free radical polymerization and characterized by NMR and size exclusion chromatography / differential viscometry. Glass transition temperatures were measured by differential scanning calorimetry. An increase in chain diameter and chain stiffness is accompanied by a decrease in the entanglement density, reflected in lower values of the plateau modulus, which were corrected for the low molecular weight portion using the Wasserman/Graessley model. Increasing the chain diameter by a factor of two results in a decrease of the entanglement density to one third. SMI-Me showed a much lower entanglement density than polystyrene (PS) although they have the same chain diameter. SMIMe however is more rigid than PS because of the maleimide five-membered ring structure in the main chain. SMI-Me and SMI-PhOPh show the same glass transition temperature. However, because of the larger chain diameter of SMIPhOPh, it has a much lower entanglement density. Thus, both the chain flexibility and the chain diameter, two parameters that are strongly related, affect the entanglement density.