Synthesis of Poly(L(+) Lactic Acid) by Polycondensation Method in Solution

In this work. the results of the synthesis of high molar weight poly(L(+) lactic acid) (PLA) which is able to thermally crystallise have been described. Such PLA can be used in fibre formation. The synthesis of poly(L(+) lactic acid) was carried out in a solution of o-dichlorobenzene, p-xylene, o-chlorotoluene, and diphenyl ether. As a monomer, L(+)lactic acid purified by distillation was applied. Stannous chloride and metallic tin were used as catalysts in a quantity of 1.0 wt% calculated on the monomer. Polycondensation was carried out over a period from ten to over 20 hours. The resulting poly(L(+) lactic acids) were characterised by DSC, and the molar masses were measured by the GPC method. Their melting points, thermostabilities, inherent viscosities, and flow indexes were also determined. The poly(L(+) lactic acid) with the highest molar mass was obtained in the synthesis carried out in diphenyl ether under vacuum.