Rational Design of an Amorphous Poly(2-oxazoline) with a Low Glass-Transition Temperature: Monomer Synthesis, Copolymerization, and Properties

A new poly(2-alkyl-2-oxazoline) having a branched side chain, namely, 2-(3-ethylheptyl)-2-oxazoline (EHOx), was synthesized. The microwave-assisted homopolymerization as well as the copolymerization with 2-ethyl-2-oxazoline (EtOx) are reported, whereby the determination of the reactivity ratios indicates the occurrence of a random polymerization. Further studies were performed regarding the thermal and the surface properties. p(EHOx) showed a glass transition of −6 °C, whereas no melting temperature could be detected, representing the amorphous poly(2-oxazoline) with the lowest reported Tg to date. Furthermore, the systematic random copolymerization with EtOx in the range from 0 to 100% EHOx revealed a linear dependence of Tg with composition as well as a complex dependence of the surface energy on the composition showing two plateau regimes.