Nanospheres prepared from poly(?-malic acid) benzyl ester copolymers: evidence for their in vitro degradation

• Published in: Journal of materials science. Materials in medicine 1996-03, Vol.7 (3), p.161-166
• Main Authors: Stolnik, S., Garnett, M. C., Davies, M. C., Illum, L., Davis, S. S., Bousta, M., Vert, M.
• Format: Article
• Language: English
• ISSN: 0957-4530; 1573-4838
• DOI: 10.1007/BF00121255

The in vitro degradation of nanospheres prepared from three benzyl ester derivatives of poly (beta-malic acid) containing 80, 90, and 100 percent of benzylated malic acid units was studied. The progressive decrease in the molecular weight of the copolymers was observed as the nanospheres degraded, demonstrating that the degradation under the experimental conditions occurred by a simple hydrolytic cleavage of the ester bond between the monomeric units. The degradation was slow, with the weight average molecular weight decreasing to about 70 percent of the initial value in 5 mo for all the nanosphere systems. A comparison of degradation rates for benzyl ester copolymers with the degradation rate of poly (beta-malic acid) homopolymer demonstrated a decreased degradation rate of benzylated copolymers which suggests that the introduction of a pendent benzyl ester function in proximity to the ester bond in the main chain reduces the rate of the bond cleavage. No significant difference in the degradation behavior of highly benzylated copolymers, containing 90 and 80 percent of benzylated malic acid units, and fully benzylated polymer could be detected to prove an autocatalytic role in the degradation of the free pendent carboxyl group in the former two copolymers. (Author)