Recent Developments in Lipase‐Catalyzed Synthesis of Polyesters

Abstract

Polyester synthesis by lipase catalyst involves two major polymerization modes: i) ring-opening polymerization of lactones, and, ii) polycondensation. Ring-opening polymerization includes the finding of lipase catalyst; scope of reactions; polymerization mechanism; ring-opening polymerization reactivity of lactones; enantio-, chemo- and regio-selective polymerizations; and, chemoenzymatic polymerizations. Polycondensation includes polymerizations involving condensation reactions between carboxylic acid and alcohol functional groups to form an ester bond. In most cases, a carboxylic acid group is activated as an ester form, such as a vinyl ester. Many recently developed polymerizations demonstrate lipase catalysis specific to enzymatic polymerization and appear very useful. Also, since lipase-catalyzed polyester synthesis provides a good opportunity for conducting "green polymer chemistry", the importance of this is described.

Microwave assisted lipase catalyzed solvent-free poly-ε-caprolactone synthesis

“…This is in agreement with enzymatic ring opening mechanisms where the lipase tends to first ring open the monomer (lactone) to its corresponding hydroxy acid which leads to low M n , however, high PDI (18). Subsequent chain propagation and build up of oligomers lead to higher M n of the polymer while decreasing its PDI (18). Reported literature of lipase catalysis of caprolactones showed that at higher conversions the PDI of the poly-caprolactone formed are about 2 (25,26), however, comparison of use of MW heating and thermal heating of caprolactone polymerization using chemical catalysts showed that the use of MW heating favors chain growth in the initial stage thus limiting the number of polymer chains, whereas thermal heating favors the formation of growing centers (22).…”

“…Figure 1 also indicates that in the region where higher M n chains of PCL are synthesized, the PDI of the polymer is low. This is in agreement with enzymatic ring opening mechanisms where the lipase tends to first ring open the monomer (lactone) to its corresponding hydroxy acid which leads to low M n , however, high PDI (18). Subsequent chain propagation and build up of oligomers lead to higher M n of the polymer while decreasing its PDI (18).…”

“…1, March 2011, 73Á79 remains largely unexplored. Enzymatic polymerizations offer unique advantages such as unique selectivity, avoidance of toxic metal catalyst, and the use of mild reaction conditions (18,19). However, due to the higher cost of the enzymes these processes are not commercially viable.…”

“…Our goal was to systematically investigate the effects of MW process parameters (power, intensity, time, and temperature) on lipase catalyzed polymerizations. Poly-o-caprolactone (PCL) synthesis is the most widely used reaction as a model for enzymatic ring opening studies (18,20). PCL synthesis has also been studied extensively using chemical catalysis in various conditions including bulk (solvent less) conditions (6,20Á22).…”

Enzymatic synthesis and preliminary evaluation as coating of sorbitol-based, hydroxy-functional polyesters with controlled molecular weights

“…The application of enzymes is not limited to their original environment or natural role as such. In fact, their versatility facilitates their use in industrial applications, ranging from the food industry to pharmaceuticals, as well as in organic solvent-based polymerization processes [6].…”