Lipase Catalyzed Synthesis and Thermal Properties of Poly(dimethylsiloxane)-Poly(ethylene glycol) Amphiphilic Block Copolymers

Resin immobilized lipase B from Candida antarctica (CALB) was used to catalyze the condensation polymerization of two difuctional siloxane and poly(ethylene glycol) systems. In the first system, 1,3-bis(3-carboxypropyl)tetramethyldisiloxane was reacted with poly(ethylene glycol) (PEG having a number-average molecular weight, M-n = 400, 1000 and 3400 g mol(-1), respectively). In the second system, alpha,omega-(dihydroxy alkyl) terminated poly(dimethylsiloxane) (HAT-PDMS, M-n = 2500 g mol(-1)) was reacted with alpha,omega-(diacid) terminated poly(ethylene glycol) (PEG, M-n = 600 g mol(-1)). All the reactions were carried out in the bulk (without use of solvent) at 80 A degrees C and under reduced pressure (500 mmHg vacuum gauge). The progress of the polyesterification reactions was monitored by analyzing the samples collected at various time intervals using FTIR and GPC. The thermal properties of the copolymers were characterized by DSC and TGA. In particular, the effect of the chain length of the PEG block on the molar mass build up and on the thermal stability of the copolymers was also studied. The thermal stability of the enzymatically synthesized copolymers was found to increase with increased dimethylsiloxane content in the copolymers.