Synthesis and characterization of AB‐type copolymers poly( L ‐lactide)‐block‐poly(methyl methacrylate) via a convenient route combining ROP and ATRP from a dual initiator

Diblock copolymers of poly(L‐lactide)‐block‐poly(methyl methacrylate) (PLLA‐b‐PMMA) were synthesized through a sequential two‐step strategy, which combines ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP), using a bifunctional initiator, 2,2,2‐trichloroethanol. The trichloro‐terminated poly(L‐lactide) (PLLA‐Cl) with high molecular weight (Mn,GPC = 1–12 × 104 g/mol) was presynthesized through bulk ROP of L‐lactide (L‐LA), initiated by the hydroxyl group of the double‐headed initiator, with tin(II) octoate (Sn(Oct)2) as catalyst. The second segment of the block copolymer was synthesized by the ATRP of methyl methacrylate (MMA), with PLLA‐Cl as macroinitiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalyst, and dimethyl sulfoxide (DMSO) was chosen as reaction medium due to the poor solubility of the macroinitiator in conventional solvents at the reaction temperature. The trichloroethoxyl terminal group of the macroinitiator was confirmed by Fourier transform infrared spectroscopy (FTIR) and 1H‐NMR spectroscopy. The comprehensive results from GPC, FTIR, 1H‐NMR analysis indicate that diblock copolymers PLLA‐b‐PMMA (Mn,GPC = 5–13 × 104 g/mol) with desired molecular composition were obtained by changing the molar ratio of monomer/initiator. DSC, XRD, and TG analyses establish that the crystallization of copolymers is inhibited with the introduction of PMMA segment, which will be beneficial to ameliorating the brittleness, and furthermore, to improving the thermal performance.