Molecular engineering of chitin based polyurethane elastomers

Biodegradable polyurethane elastomers with potential for biomedical application as non-absorbable sutures with improved hydrophobic properties were synthesized by the reaction of poly(ε-caprolactone) (PCL) and 4,4′-diphenylmethane diisocyanate (MDI), extended with different mass ratio of chitin and 1,4-butane diol (BDO). Their molecular engineering and structural transition due to the changes of hydrogen bonding was confirmed by using FT-IR, 1H NMR and 13C NMR. Involvement of chitin was evidenced by the appearance of new signals in both 1H NMR and 13C NMR spectra, and very strong peak at 1724 cm−1 in FT-IR spectra. From the results, it was concluded that the reaction of the urethane group occurred mainly at C6OH group of chitin in which strong intermolecular and intersheet hydrogen bonds are involved. Contact angle and surface tension measurement of the synthesized polyurethane as a function of chitin contents were investigated. Optimum hydrophobicity was obtained from elastomer extended with chitin in comparison to elastomers extended with BDO. The surface free energy was also affected by chemical composition of the final PU. Structure–property relationship for prepared elastomers showed that the main determining factors were hydrogen bonding, hydrophobicity and content of chitin in polyurethane backbone.