Synthesis of thermoplastic chitin hexanoate-graft-poly(ε-caprolactone)

Abstract

Herein, we report that chitin hexanoate-graft-poly(ε-caprolactone) (ChHex-g-PCL) is thermoplastic, as confirmed by the formation of a melt-pressed film. Chitin hexanoates with degrees of substitution (DSs) of 1.4-1.8 and bearing free hydroxy groups were first prepared by the hexanoylation of chitin using adjusted feed equivalents of hexanoyl chloride in the presence of pyridine and N,N-dimethyl-4-aminopyridine in 1-allyl-3-methylimidazolium bromide, an ionic liquid. Surface-initiated ring-opening graft polymerization of ε-caprolactone from the hydroxy groups of the chitin hexanoates was conducted in the presence of tin(II) 2-ethylhexanoate as the catalyst at 100 °C to produce (ChHex-g-PCL)s. The feed equivalent of the catalyst, reaction time, and DS value were found to affect the molar substitution and degree of polymerization of the PCL graft chains. Longer PCL graft chains formed their crystalline structures and the (ChHex-g-PCL)s largely contained uncrystallized chitin chains. Accordingly, these (ChHex-g-PCL)s exhibited melting points associated with the PCL graft chains, leading to thermoplasticity.

Keywords: Chitin esters; Melt-pressed film; Poly(ε-caprolactone); Ring-opening polymerization; Surface-initiated graft polymerization; Thermoplasticity.