Synthesis and Properties of Polylactide-graft-poly(methyl methacrylate) Copolymers with Degradable Main Backbone

Graft copolymers of polylactide and oligo(methyl methacrylate) (PLA-g-MMA) were synthesized by atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using PLA containing 10 mol % of acetal units functionalized with bromine or chlorine moieties as a multisite macroinitiator. The ultimate aim was to improve the miscibility of PLA and PMMA by preparing graft copolymers. The MMA was chosen as a model vinyl monomer to investigate whether the presented method allows the synthesis of required copolymers with controlled topology and molecular masses. First, PLA-based multisite macroinitiators (Mn ∼ 10,000 g mol–1) were obtained via the cationic (co)polymerization of l-LA (LA) and functionalized cyclic acetals (2-bromomethyl-1,3-dioxolane─BrDXL or 2-chloromethyl-1,3-dioxolane─ClDXL), carried out in the presence of ethylene glycol as an initiator and triflic acid as a catalyst. Subsequently, PLA-g-MMA with different compositions (containing 60–80 mol % of MMA) were obtained in the presence of the pendant-activated groups (chlorides or bromides) in the catalyst system consisting of copper halides (CuBr or CuCl) and N,N,N,N″,N‴-pentamethyldiethylenetriamine (PMDETA). The size exclusion chromatography (SEC) analysis revealed that the obtained PLLA-g-MMA molar mass was 12,000–23,000 g mol–1. Differential scanning calorimetry (DSC) analysis of all prepared PLA-g-MMA copolymers revealed only one Tg ranging from 55 to 82 °C, which allows us to conclude the miscibility of the components forming the copolymer. Finally, the thermal properties, susceptibility to degradation, and conditions for forming copolymeric particles were investigated.