Synthesis and hydrolytic degradation of aliphatic polyesteramides branched by glycerol

A series of branched polyesteramides (PEAs) were synthesized from adipic acid, hexamethylene diamine, 1,4-butanediol and caprolactam by melt polycondensation using glycerol as branching agent. The obtained copolymers, with glycerol contents of 0-0.9 wt% (LPEA-PEAg10) were characterized by FTIR, 1H NMR, DSC and viscometry. The FTIR and 1H NMR spectra demonstrated the formation of ester and amide bonds. DSC data indicated the melting and crystallization temperatures decrease with increasing glycerol content. Water absorption experiments suggested no distinct difference in hydrophilicity between these branched PEAs. Alkaline hydrolysis of PEA films was conducted in pH 11.0 NaOH solution at 37, 50 or 80 °C, respectively. The tests showed that PEAs degraded quickly in alkali and the degradation rate increased with the medium temperature. PEA films underwent slow degradation in pH 7.0 phosphate buffer saline (PBS) at 37 °C. The degradation was monitored by weight loss, viscometry, DSC, FTIR and 1H NMR analysis. The results showed that branching substantially enhanced the degradation. Structural analyses revealed that ester/amide ratio decreased with incubation time, suggesting the degradation occurs mainly on the ester bonds. During the degradation, the melt temperature and crystallinity of the copolymers increased slightly with the degradation time.