A study of the ring-opening polymerization (ROP) of l-lactide by Ph2SnX2 precursors (X = NMe2, OPri): the notable influence of initiator group

Abstract

Studies of the ring-opening polymerization (ROP) of L-lactide by Ph₂SnX₂ reveal that X (X = NMe₂ or OPrⁱ) influences not only the rate of polymerization but also the nature of the polymer formed. Gel permeation chromatography (GPC), mass spectral analysis and ¹H NMR spectroscopy of the polymers from these reactions revealed that for X = NMe₂, a bimodal molecular weight distribution of polylactide (PLA) is obtained. This is indicative of both cycles and long chains (24 kDa) being formed by both intra- and interchain transesterification. This extensive transesterification results in regeneration of the Ph₂Sn[OCHMeC(O)NMe₂]₂ species as the resting state of the tin(IV) species. Conversely, for X = OPrⁱ only a unimodal molecular weight distribution is observed in addition to Ph₂Sn[OCHMeC(O)OPrⁱ]₂, which is indicative of only interchain transesterification. Similar observations were seen in studies of ROP of L-lactide by Ph₃SnX precursors.