Surface-initiated ring-opening polymerization of poly(2-methyl-2- oxazoline) from poly(bromoethyl methacrylate/methyl methacrylate) microspheres and modification into PEI: Immobilization of α-Amylase by adsorption and cross-linking

Bromide-functionalized microspheres were prepared by the suspension polymerization of bromoethyl methacrylate (BEMA), methyl methacrylate (MMA), and ethylene glycol dimethacrylate (EGDMA). The microspheres were employed as a solid macroinitiator for the ring-opening polymerization of 2-methyl 2-oxazoline. The surface brushes were then converted into poly(ethylenimine) (PEI) by simple hydrolysis with HCl and then NaOH as inferred from chemical analyses and FTIR spectra. The microspheres were used for the immobilization of α-Amylase through adsorption and covalent cross-linking. The optimum pH for free enzyme was 6.0 and shifted by about 1.0 unit to the acidic pH range upon immobilization. Compared to free α-Amylase, the immobilized enzyme preparations were found to exhibit better tolerance to variations in pH and temperature, as well as improved storage stabilities. The activity retentions of the adsorbed and cross-linked enzyme preparations were found to be 69% and 53%, respectively. Furthermore, the cross-linked enzyme was reused for six consecutive cycles without any activity loss.