Investigation of local chain dynamics in poly(di-n-alkylitaconate)s

Abstract

13C NMR in solution and molecular dynamics simulations were used to discuss the respective roles of intramolecular constraints and intermolecular contributions in poly(di-n-alkylitaconate)s (PDAI) with various side chain lengths. These polymers exhibit the unusual phenomenon of two distinct glass transitions when the alkyl side chains contain at least six carbon atoms. Nuclear Overhauser enhancement and spin-lattice relaxation time measurements in solution for PDAI’s with different side-chain lengths clearly indicated the existence of a competition between internal plasticization and organization of the alkyl parts of the side chains. This organisation decreases the flexibility of the long side chains and slows down the internal mobility of the main chain and carbonyl groups. Molecular modelling of the relative organization of two polymer chains demonstrates the strong tendency of the long alkyl parts to order and form discrete regions, which can be related to the existence of the second low-temperature glass transition in PDAI’s with long side groups.