Synthesis Of Highly Branched Polylactide Copolymers

In this article we demonstrated, in the Sn(Oct)2catalyzed bulk copolymerizationof L-lactide (LLA) and a large amount of branching comonomer2,2-bis(hydroxymethyl)butyric acid (BHB) activated by aliphatic tertiary amine, lowmolecular weight of copolymers with inhomogeneous structure were generated.Meanwhile the mechanism of the highly branched PLA copolymers was proposed.In the experiment, we controlled the temperature of the reaction was135oC andthe molar ratio of LLA, BHB and Sn(Oct)2was5:1:0.05. Without the addition ofaliphatic tertiary amine to this polymerization system, MALDI-TOF mass spectrumdemonstrated that the lower molar mass fraction was dominated with the BHBhomo-polycondensation products; whereas the higher molar mass fraction wasmainly composed of linear chains of poly(L-lactide)(PLA) bearing one BHB unit.The addition of aliphatic tertiary amine to this polymerization system couldeffectively enhance the molecular weight of the obtained copolymers, whereas,aromatic tertiary amines and aliphatic primary and secondary ones were not soeffective.The obtained PLA copolymers were characterized by GPC,1H NMR,13C NMRand MALDI-TOF MS, which verified that they were composed of LLA and BHBunits and had the highly branched structure. The degree of branching was about0.23-0.30. Thermal analyses by TGA and DSC demonstrated that the resulting highlybranched PLA copolymers were amorphous. Compared with linear PLA, the highlybranched PLA copolymers were thermally more stable and had lower Tg.