Poly(N-vinyl α-amino acid) microspheres: a model—poly(N-vinyl α-phenyl alanine) microspheres: synthesis and characterization

The monomer N-vinyl α-phenyl alanine was prepared by interacting acryloyl chloride with the methyl ester protected α-phenyl alanine. Poly(N-vinyl α-phenyl alanine) was then formed by dispersion polymerization of this vinyl monomer in different mixtures of water/2-propanol. Under these polymerization conditions, an equilibrium between insoluble polymer composed of poly(N-vinyl α-phenyl alanine) microspheres and a soluble polymer was always obtained. The effect of the ratio, by volume, of water/2-propanol on the microspheres, e.g. diameter, molecular weight, molecular weight distribution and yield, was elucidated. Poly(N-vinyl α-phenyl alanine) microspheres were also formed by decreasing the solubility of the soluble polymer, via addition of the soluble polymer solution to pure water. In order to avoid the formation of the soluble polymer, and thus form insoluble polymer only, crosslinked microspheres were produced by a similar dispersion polymeriztion of N-vinyl α-phenyl alanine with the crosslinker monomer: divinyl benzene or ethylenglycol dimethacrylate. The effect of the molar ratio [monomer]/[crosslinker] on the size of the microspheres was elucidated. Carboxylate functional microspheres were formed by basic hydrolysis of the ester protected crosslinked microspheres. The carboxylate functional groups of the microspheres were then used for covalent binding of proteins, e.g. trypsin, to the particles. The stabilization effect of the immobilized trypsin against trypsin inhibitor has been clearly demonstrated. Characterization of the different microspheres was accomplished in a variety of ways, e.g. thermochemical analysis, differential scanning calorimetry, gel permeation chromatography, spectrophotometer and infrared spectroscopy.