CATIONIC RING-OPENING POLYMERIZATION OF (S)-2-ETHOXY-4-ISOPROPYL-5(4H)-OXAZOLONE TO YIELD POLY(N-ETHOXYCARBONYL-L-VALINE)

A new polypeptide derivative, poly(N-ethoxycarbonyl-L-valine) (2) was prepared for the first time by the cationic ring-opening polymerizatio n of (S)-2-ethoxy-4-isopropyl-5(4H)-oxazolone (1). The polymerization proceeded with a cationic initiator, methyl trifluoromethanesulfonate, BF(3)OEt(2), or trifluoromethanesulfonic acid, in an aprotic non-nucl eophilic solvent such as toluene, chloroform, or nitromethane. The mol ecular weight of the resulting 2 was independent of the feed ratio of monomer to initiator but depended on the polymerization temperature. T he number average molecular weight of 2 prepared at -40 degrees C was 11000. The resulting polymer 2 showed high solubility in organic solve nts, especially in halogenated hydrocarbons.