Selective enzymatic grafting by steric control

Enzymatic grafting of caprolactone was carried out from poly[styrene-co-(4-vinylbenzyl alcohol)] containing 10% hydroxyl functional monomer and compared with the grafting of vinyl acetate. A molecular weight increase due to the grafting of polycaprolactone was observed by size exclusion chromatography. Closer investigation of the grafting density by H-1 NMR revealed an upper limit to the amount of grafting of about 50-60% of the pendant hydroxyl groups leaving unreacted hydroxyl groups on the polymer backbone available for subsequent reactions. The higher grafting density (95%) obtained with vinyl acetate suggests that this is not due to limited accessibility of the backbone but sterical constrains. Moreover, the grafting action of polycaprolactone seems to be a combination of grafting from by monomer initiation and grafting onto by transesterification of polycaprolactone.