Spectroscopic and Morphology Studies of Biodegradable Nanolamellar Lactone Based Triblocks

Abstract

Spectroscopic and morphological analysis of a series of lactone-based triblock copolymer was undertaken. In the synthesized triblocks, the middle segment was γ-valerolactone, δ-valerolactone, or ε-caprolactone (5–7 membered rings), while d,l-lactide, cis-lactide, or glycolide was taken as the terminal segment. The specific signals of 1H NMR were shifted depending on the type of monomers present in the copolymer and a peak at 4.3 ppm validated chain extension on addition of the terminal block. In 13C NMR, a sharp peak around 173 ppm and a comparatively low intense peak around 168 ppm due to carbonyl region confirmed the block architecture. The peaks for O-(C═O), O–CH2, C═O, and C–O–C stretching showed a characteristic shift in FTIR on copolymerization. The presence of different blocks as middle segment and terminal segment was confirmed from CH/CH3 stretching and νC–COO stretching regions in Raman spectra. The wide-angle X-ray diffractograms indicated the presence of crystalline domains in the copolymer, but the peak position and intensity were altered as a synergistic effect of crystallographic nature and fraction of the block incorporated in the triblock. The glass transition temperature shifted accordingly. Atomic force microscopy and transmission electron microscopy analysis confirmed the formation of a nanolamellar structure. The lamellar spacing (10–15 nm) calculated from small angle X-ray scattering correlated well with that obtained from atomic force microscopy. Long range array of nanofibrils was retained in triblock having ε-caprolactone, which was disturbed for δ-valerolactone-based triblocks.