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 (XylC6N3-g-PLLAs) were prepared by grafting propargyl-terminated poly(l-lactide) onto di-O-(6-azidohexanoyl)-xylan (XylC6N3) 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. XylC6N3 and propargyl-terminated PLLAs were treated with N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) and copper(I) bromide, and the graft copolymers XylC6N3-g-PLLAs were obtained. DSC measurements revealed that the glass transition temperatures (Tg) 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 XylC6N3-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.