Lipase-mediated degradation of poly-ε-caprolactone in toluene: Behavior and its action mechanism

Lipase-catalyzed hydrolysis of poly(e-caprolactone) (PCL) in toulene was investigated. PCL with number average molecular weight (M-n) 10,000 g mol(-1) was hydrolyzed using immobilized Candida antarctica lipase B (CALB). The increase in PCL concentration led to a decrease in degradation rate. Enhanced rate was observed when reaction temperature was increased from 30 to 50 degrees C. Enzymatic chain scission of PCL yielded cyclic dicaprolactone, tricaprolactone, tetracaprolactone and oligomers with M-n less than similar to 1000 g mol(-1). Catalytic formation of cyclic lactones via back-biting mechanism in low water content environment was attributed to CALB. Its hydrolysis of PCL displayed consecutive random- and chain-end scission with time from detailed thermal, molecular weight and structural analyses. Apparent activation energy, E-a for hydrolysis was 45 kJ mol(-1) i.e. half of that reverse reaction. Dicaprolactone and oligomers from hydrolysis readily re-polymerized to produce mid-range polymer with M-n 1400 g mol(-1) after 36 h in the same reaction medium. (C) 2016 Elsevier Ltd. All rights reserved.