Structure−Property Relationships of Copolymers Obtained by Ring-Opening Polymerization of Glycolide and ε-Caprolactone. Part 2. Influence of Composition and Chain Microstructure on the Hydrolytic Degradation

Abstract

A series of glycolide/epsilon-caprolactone copolymers were compression molded and allowed to degrade in a pH 7.4 phosphate buffer at 37 degrees C. Degradation was monitored by various analytical techniques such as (1)H NMR, X-ray diffraction, DSC, CZE, ESI-MS, and inherent viscosity measurements. The results show that the degradation rate depends not only on the copolymer composition but also on its chain microstructure. Generally, copolymers with a higher C-G bond content or a higher degree of randomness exhibit higher degradation rates. Sequences with odd numbers of glycolyl units such as -CGC- and -CGGGC-, which result from the second mode transesterification, appear more resistant to hydrolysis. As a consequence, degradation residues obtained at the later stages of degradation are mainly composed of long glycolyl and caproyl sequences linked by -CGC- and -CGGGC- ones. The degradation rate of the copolymers depends also on the degree of crystallinity of each component which is related to the block length. The caproyl component can be preferentially degraded if it is in the amorphous state and the glycolyl component is semicrystalline.

Novel Pentablock Copolymer-Based Nanoparticulate Systems for Sustained Protein Delivery

“…Several reports suggested that covalent conjugation between PLA and PCL significantly reduces the crystallinity of PCL (21,(30)(31)(32)(33). However, the effects of various isomers of PLA (L or DL) and PGA on the crystallinity of PCL-PEG-PCL triblock copolymers have not been reported previously.…”

Degradation Process of Bioresorbable Copolyesters. Microstructure Investigation by NMR and ESI‐MS

“…The viscosity of the obtained copolymers was determined in 1,1,1,3,3,3-haxafluoro 2-propanol at 25 8C with Ubbelhode viscometer. The concentration of the solutions was 0,002 g/cm 3 . Size-exclusion chromatography (SEC) measurements were performed for the copolymers soluble in chloroform with a Physics SP 8800 chromatograph apparatus equipped with a Shodex SE 61 detector.…”

Application of the lithium and magnesium initiators for the synthesis of glycolide, lactide, and ϵ‐caprolactone copolymers biocompatible with brain tissue

“…The chain microstructure of copolymers has crucial influence for the time and profile of degradation. With the increase of chain randomization, the degradation processes accelerate and short fragments of caproyl chains are removed faster than longer glycolidyl blocks 31,32 from copolymer chain. The in vitro hydrolytic degradation of random glycolide/ e-caprolactone copolymer 10/90 proceeds definitely faster in comparison with hydrolytic degradation of caprolactone homopolymer.…”

“…The in vitro hydrolytic degradation of random glycolide/ e-caprolactone copolymer 10/90 proceeds definitely faster in comparison with hydrolytic degradation of caprolactone homopolymer. 32 A strong immune system response to introduced foreign body is observed in vivo, which certainly causes additional acceleration of polymeric microspheres degradation.…”