Catalyzed synthesis of poly(l-lactic acid) by macroporous resin Amberlyst-15 composite lactate utilizing melting polycondensation

Efficient and pollution-free catalysts play an essential role in the ultimate biodegradation of products in the synthesis of biodegradable and recyclable poly(l-lactic acid) (PLLA). Therefore, macroporous resin was utilized as the solid acid for the first time, on which lactate that could be absorbed in vivo was composited to catalyze the synthesis of PLLA. It was discovered that macroporous resin Amberlyst-15 showed good catalytic activity in oligomerization and polymerization, and lactate showed different catalytic efficiencies due to the differences in ionic radius and ionic charge. Compared to the traditional catalysts of SnCl₂·2H₂O/TSA, the composite catalyst can improve the quality, yield and optical purity of its product, which can also be recycled without any residual in products. PLLA with molar mass of about 110,000 g mol^-1 was synthesized at the yield of 93%. The product exhibits pure color (white), and its optical purity and crystallinity are 98% and 55%, respectively. A possible catalytic mechanism was proposed. The resulting PLLA products were characterized by GPC, ¹H NMR, DSC, and polarimeter.