Synthesis of 3- and 4- Arm star-block copolypeptides using multifunctional amino initiators and high vacuum techniques

Three- and four-arm star-block copolypeptides, (BL-b-G)₃ and (G-b-BL)₄, of poly(ε-butyloxycarbonyl-L-lysine) (BL) and poly(γ-benzyl-L-glutamate) (G), were synthesized under high vacuum conditions, using three different multifunctional aminoinitiators for the ring opening polymerization of the corresponding α-aminoacid N-carboxyanhydrides. When the initiator contained only primary amine groups {2(aminomethyl)-2-methyl-1,3-propanediamine, AMPDA}, well-defined star-block copolypeptides with monomodal molecular weight distribution were produced. However, if the multifunctional initiator contained both primary and tertiary amine groups {polypropylenimine tetraamine dendrimer, generation 1.0 (DAB); amidoethylethanolamine dendrimer, 1,4-diaminobutane core, generation 0.0 (PAMAM)}, bimodal high polydispersed copolypeptides were formed. The different behaviors are due to the participation of both the primary and tertiary amino groups, each following different polymerization kinetics.