Synthesis of xylan-graft-poly(L-lactide) copolymers via click chemistry and their thermal properties

Di-O-(6-azidohexanoyl)-xylan-graft-poly(L-lactide)s (XylC6N(3)-g-PLLAs) were prepared by grafting propargyl-terminated poly(L-lactide) onto di-O-(6-azidohexanoyl)-xylan (XylC6N(3)) via click chemistry. Di-O-(6-azidohexanoyl)-xylan (XylC6N3) was prepared via two steps from xylan extracted from eucalyptus kraft pulp with aqueous sodium hydroxide solution. Propargyl-terminated poly(L-lactide)s (PLLA) with three different molecular weights were synthesized via ring-opening polymerization of L-lactide using propargyl alcohol as initiator and tin (II) octanoate (Sn(Oct)(2)) as catalyst. XylC6N(3) and propargyl-terminated PLLAs were treated with N,N,N',N',N ''-pentamethyldiethylenetriamine (PMDETA) and copper(I) bromide, and the graft copolymers XylC6N(3)-g-PLLAs were obtained. DSC measurements revealed that the glass transition temperatures (T-g) of the copolymers decreased compared to that of XylC6N3, suggesting that the grafted PLLA side-chains act as an internal plasticizer for xylan. TGA measurements revealed that XylC6N(3)-g-PLLAs had higher decomposition temperatures than those of XylC6N3 or PLLA, and that the decomposition temperatures of the copolymers increased with decrease in the number of PLLA side-chains grafted to the xylan main-chain. (C) 2011 Elsevier Ltd. All rights reserved.