Synthesis, characterization and degradation of hexa-armed star-shaped poly(l-lactide)s and poly(d,l-lactide)s initiated with hydroxyl-terminated cyclotriphosphazene

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene was prepared by the reaction of hexachlorocyclotriphosphazene with the sodium salt of 4-hydroxybenzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. The hydroxyl-terminated star-shaped compound was studied as initiator for the synthesis of star-shaped poly(l-lactide)s and in the presence of stannous octanoate. Effects of molar ratios of monomer to initiator on polymerisation were investigated. The results indicated that the molecular weight of star-shaped poly(l-lactide)s and poly(d,l-lactide)s increased linearly with the molar ratio of monomer to initiator. Thermal analysis demonstrated that star-shaped poly(l-lactide)s possessed lower melting point, crystallinity and onset decomposition temperature but higher maximum decomposition temperature. Analysis of hydrolytic degradation of linear and star-shaped poly(d,l-lactide)s and poly(l-lactide) showed that star-shaped poly(d,l-lactide)s possessed the best degradability, while linear poly(l-lactide)s possessed the poorest degradability. Moreover, the star-shaped polylactide was degraded in two steps.