Poly(α-amino acid)-immobilized polymer adsorbents for optical resolution, 2. Effect of crosslinking degree of the support resin on the resolution efficiency

Polymer adsorbents for chromatographic optical resolution were synthesized by grafting poly(N⁵-benzyl-L -glutamine-co-γ-benzyl L -glutamyl) onto cross-linked polystyrene beads. The effects of the crosslinking degree (1,5%, 9%, 30%) and the porosity of the polystyrene matrix on the resolution efficiency of the adsorbent were investigated. Similar resolution efficiencies were observed on 1,5% cross-linked gel (non-porous) and 9% cross-linked porous adsorbents, while a decline in the efficiency was observed on 30% cross-linked porous adsorbent. Studies of transmission electron micrographs of these adsorbent clearly showed the effect of degree of crosslinking on the distribution manner of the incorporated poly(α-amino acid). At a degree of 30%, clustered incorporation occurs mainly on the pore surface and not within the cross-linked polymer matrix. Such incorporation manners are also suggested by the swelling properties of the adsorbents. Pore volumes, pore radii, and specific surface areas of the adsorbents were also measured. It was observed that uniform incorporation of poly(α-amino acid) derives a higher resolution efficiency of the adsorbent.