Alternative synthesis of poly(hydroxymethylsiloxane) for lipase immobilization and use of the adsorbates as esterification biocatalysts

A medium molar mass poly(hydrogenomethyl- siloxane), Me₃Si(O-SiHMe)_nOSiMe₃, (PHMS), has been used for preparing poly(hydroxymethylsiloxane) supports (PHOMS) for lipase immobilization. The procedure involved the conversion of PHMS to the corresponding poly(alkoxymethylsiloxanes). Me₃Si(OSi(OR) Me/_nOSiMe₃ (PHMS), their alkaline hydrolysis to form poly(siloxanolates) which were then converted to PHOMS by neutralization. The effect of different catalysts and alcohols (methanol, ethanol, 2-propanol) on the course of poly(alkoxymethylsiloxanes) formation is reported. PHOMS supports were characterized by BET and Hg porosimetry, and the degree of their crosslinking was determined by solid-phase NMR. Fluorescence spectroscopy was used to assess surface polarity and determine lipase loading. The efficiency of lipase adsorbed on these supports was tested in the esterification of stearic acid with propanol in hexane. It was found that the activity of the adsorbates is controlled by their porosity. The addition of an inert addend (e.g. hydrotalcite) in the step of alkaline hydrolysis of poly(alkoxymethylsiloxanes) increases the adsorption efficiency of the supports as compared to PHOMS. The potential application of the biocatalysts, lipase-PHOMS adsorbates, was extended by their encapsulation into a RTV silicone rubber containing Si-substituted poly(imide) as a swelling modifier.