Synthetic poly(beta-hydroxyalkanoates) with carboxylic acid or primary amine pendent groups and their complexes

Degradable polyelectrolyte complexes were made by mixing a degradable carboxyl-bearing polyacid, namely poly(beta-malic acid), with a degradable primary amine group-bearing polybase, namely poly(amino serinate), derived from serine. Both oppositely charged polyelectrolytes are functional polymers which belong to the family of poly(beta-hydroxy acid)-type aliphatic polyesters. Poly(amino serinate) polymers were synthesized by a new route starting from the N-carbobenzoxy derivative (N-Z) of DL- or L-serine. These derivatives were allowed to react with mesyl chloride to yield in one step corresponding N-protected derivatives of poly(N-Z-amino serinate) with molar masses in the 20000-40000 range after fractionation. Progressive deprotection of pendent primary amino groups was carried out using a HBr/acetic acid mixture and led to PAS with up to 95% deprotected amine repeat units for less than 15% decrease of the initial molar mass, as shown by N-reprotection with Z groups. Poly(beta-malic acid) and poly(amino serinate) were complexed by mixing aqueous solutions of the two polyelectrolytes: 1-1 neutral precipitates were formed regardless of the respective compositions, provided the molecular weights of both components were high enough. When allowed to age in aqueous media, the solid complexes went rapidly back into solution because of the hydrolytic degradation of at least one of the components. Whether the degradation of one component is affected by that of the other is still unknown.