A systematic investigation of the effect of side chain branching on the glass transition temperature and mechanical properties of aliphatic (co-)poly(2-oxazoline)s

Abstract

The synthesis of a new branched 2-oxazoline monomer, namely 2-(3-ethylpentyl)-2-oxazoline is described. Microwave-assisted cationic ring-opening polymerization allows the synthesis of well-defined homopolymers as well as copolymers when copolymerized with 2-ethyl-2-oxazoline (EtOx). The systems obtained are investigated with regard to their thermal and mechanical properties. In order to elucidate structure–property correlations, these copolymers are compared to copolymers of EtOx with two other branched monomers, namely 2-(1-ethylpentyl)-2-oxazoline and 2-(3-ethylheptyl)-2-oxazoline comprising a different branching position or length of the main side chain, respectively. It is observed that the influence of the branching position on the glass transition temperature and mechanical properties is significantly higher than the length of the side chain. Furthermore, copolymerizations with EtOx are presented which enable the alteration of the thermal and mechanical properties showing a linear decrease of the glass transition temperatures as well as a decrease of the elastic modulus with increasing weight percentage of the branched monomers.