Morphology and biodegradability of poly(ε-caprolactone)/poly(vinyl alcohol) block copolymers

Poly(e-caprolactone)-block-poly(vinyl alcohol) (PCL-b-PVA) copolymers were prepared by using a bifunctional initiator 4-(2-hydroxyethoxy)-benzaldehyde (4-HEBA), which could respond to both ring-opening polymerization and aldol-type group transfer polymerization. Morphological changes along with block length ratios were observed with differential scanning calorimeter and polarized optical microscope. Increment of PVA block influenced the crystallizing manner of PCL block. Biodegradability of PCL-b-PVA copolymers, two homopolymers (PCL and PVA), and PCL/PVA blend was evaluated from biochemical oxygen demand (BOD) in the presence of activated sludge. Under the conditions in this study, the biodegradation behavior of PCL-b-PVA copolymer was influenced by shape of sample. Increment of the PVA block in PCL-b-PVA copolymers slowed down biodegradation rates. When the content of PVA block in the block copolymer increased to more than 25 mol %, the biodegradation of PCL moiety was effectively inhibited even after much longer exposure time.