Polylactic acid is an interesting material due to its biodegradability and bioabsorbability  and is produced from lactic acid, either by direct polycondensation of lactic acid or via ring opening polymerization of lactide. Conventional chemical polymerizations of lactic acid or lactide require extremely pure monomers and anhydrous conditions as well as metallic catalysts which must be completely removed before use. To avoid these difficult restrictions for the polymerizations of lactide by chemical methods, enzymatic polymerization may be one of the feasible methods to obtain polyesters. 

The kinetics of the enzymatic ring opening polymerization (ROP) of lactide was investigated in the present study. Polymerization reactions were performed using Candida antarctica lipase and Candida rugosa lipase as catalysts. The reactions were found to be approximately first order with respect to monomer with conversion up to 80%. By the evaluation of semi-logarithmic graphs of the data collected at 80 and 100^oC, reaction rate constants were determined as  k = 1,85.10^-6 s^-1  and  k= 1,34.10^-7 at 80^oC for Candida antarctica lipase and Candida rugosa lipase respectively,  same values were recorded as k = 1,43.10^-6 s^-1 and          k = 7,2.10^-7s^-1  at 100^oC.

The activation energy of the reaction was determined as 13800 J/mol for enzymatic ROP of lactide using  Candida antarctica lipase as catalyst and 92030 J/mol Candida rugosa lipase as catalyst.