<p>The development of new synthetic routes for polylactide and poly(methyl methacrylate) copolymers in the presence of tributylborane is based on the ability of alkylboranes to participate in all elementary steps of radical polymerization. Two approaches were proposed for synthesizing polylactide and methyl methacrylate copolymers in a tetrahydrofuran solution. The first approach involves the simultaneous introduction of polylactide, methyl methacrylate, and tributylborane into the reaction mixture. The alkylborane/oxygen system is presumed to initiate both graft polymerization and methyl methacrylate homopolymerization. Simultaneously, the polylactide is boronated at its terminal hydroxyl group. The resulting boronated polylactide acts as a macroinitiator for the synthesis of the block copolymer. The second approach provides for the synthesis of the macroinitiator in the first stage through the boronation of polylactide at the terminal hydroxyl group. This boronated polylactide macroinitiator dissociates into a carbon-centered radical and a boroxyl radical. The carbon-centered radical initiates the polymerization of methyl methacrylate, yielding a polylactide-poly(methyl methacrylate) block copolymer which was confirmed by MALDI mass spectrometry and NMR spectroscopy.</p>