Synthesis of poly(acrylic acid)-block-poly(L-valine) hybrid through combined atom transfer radical polymerization, click chemistry, and nickel-catalyzed ring opening polymerization methods

A new hybrid amphiphilic system between a polyacrylic acid (PAA) synthetic segment, and a hydrophobic P-sheet forming peptide segment, poly(L-valine) (PLVAL) was synthesized using a combination of Atom Transfer Radical Polymerization, Click Chemistry, and Nickel catalyzed ring opening of L-valine N-carboxyanhydride. This is the first reported use of Click Chemistry as an intermediary step for the omega-amino functionalization of polymers to obtain macroinitiators that are free from deactivating or interfering molecules to be used in subsequent Ni-catalyzed ring opening reaction. The efficiency of the end-group functionalization in the macroinitiator is about 90%. Three different PAA-b-PLVAL hybrid copolymers with molecular weight range of 8000-15,000 and M-w/M-n < 1.3 had been prepared by varying the monomer to macroinitiator ratio. In addition, the highest achievable molecular weight in the copolymerization was found to be limited by the solubility of the growing chains. This combined synthetic approach can potentially be extended for the synthesis of a multitude of other peptide hybrid systems, and hence will be of interest in the preparation of peptide hybrid systems. (c) 2007 Wiley Periodicals, Inc.