**3.1 Direct polymerization**

Since the LA monomer has both –OH and –COOH groups, necessary for polymerization, the reaction can take place directly by self-condensation (Scheme 2):

$$\begin{array}{cccc} \text{In } & \text{CH}\_3 & \text{polymerization} \\ \text{In } & \text{HO}-\overset{\text{C}}{\underset{\text{H}}{\rightleftharpoons}} \text{COOH} & \xrightarrow[\text{catalyst}]{\text{polymerization}} & \text{H} + \underset{\text{H}}{\overset{\text{C}}{\underset{\text{H}}{\rightleftharpoons}}} \text{CH}\_3 + \text{(n-1)} \text{H}\_2\text{O} \\\\ \text{Lactic acid} & & \text{Poly(lattice acid)} \end{array}$$

Scheme 2. Direct polymerization.

Direct polymerization includes solution and melt polycondensation, depending on whether a solvent is used in the reaction to dissolve the PLA or not.
