Surface grafting of poly (L-glutamates). 1. Synthesis and characterization

The ring-opening polymerization of N-carboxyanhydrides (NCA) of gamma -benz yl L-glutamate andy-methyl L-glutamate from (gamma -aminopropyl)triethoxysi lane (APS) pretreated substrates such as silicon wafers and quartz slides w as investigated. FT-IR transmission spectroscopy, circular dichroism measur ements, and UV/vis spectroscopy confirmed the pure a-helix conformation of the grafted polypeptide layers. FT-IR spectroscopy also showed that the mos t important part of the polymer growth took place in the first 5 h of tl e polymerization. The average orientation of the rather rigid a-helical polyp eptides, grown during a short period of time, was more perpendicular with r espect to the substrate than the orientation of the polymers grown over a l onger reaction time. For concentrations up to 2.0 M, the polymer growth fro m both NCA monomers showed a pronounced dependence on the monomer concentra tion. Moreover, it appeared that the higher the monomer concentration, the, more perpendicular the average orientation of the helices with respect to t he substrate. The thickness of the grafted polypeptide layers up to 400 Ang strom was determined with ellipsometry and small-angle X-ray reflection mea surements. The absence of chemical chain termination was demonstrated by ad ditional polymer growth in a renewed polymerization.