Synthesis and degradation of polyesters

Abstract

Copolymers of racemic β-butyrolactone (β-BL) with e-caprolactone (e-CL) P(BL-co-CL) and δ-valerolactone (δ-VL) P(BL-co-VL) were prepared by ring-opening polymerization using a commercial aluminoxane catalyst, tetraisobutyldialuminoxane (TIBAO). The yields, molecular weights, compositions and crystallinities have been determined for both copolymers by gel permeation chromatography (GPC), nuclear magnetic resonance ( 1 H NMR), and differential scanning calorimetry (DSC). The determination of monomer diad sequence distributions was carried out by 13 CNMR. These results and those of reactivity ratios indicate that the copolymers may consist of compatible blocks of BL units and VL units of variable size. Enzymatic degradability of these polymers has been studied in aerobic and anaerobic media. The crystallinity influences the initial degradation rate of copolymers P(BL-co-CL) and P(BL-co-VL) of various feed ratios. All the copolymers synthesized with TIBAO catalyst exhibit a high degree of biodegradation (around 85%) except for those containing a very high portion of unsubstituted CL or VL units. Anaerobic biodegradation of PHB and copolymers P(BL-co-CL) is much lower than aerobic biodegradation, even for bacterial P([R])-HB) and the initial rates follow the same trend.