Nanolamellar triblock of poly-d,l-lactide–δ-valerolactone–d,l-lactide with tuneable glass transition temperature and crystallinity for use as a drug-delivery vesicle

Abstract

A biodegradable triblock copolymer, poly-D,L-lactide–δ-valerolactone–D,L-lactide, was synthesized by the ring-opening polymerization of δ-valerolactone and the sequential addition of the D,L-lactide monomer to the hydroxyl end of a functionalized poly-δ-valerolactone macroinitiator. The copolymer was then evaluated for its suitability as a drug-delivery vesicle. The effect of the monomer ratio, catalyst and initiator concentration on the structure was investigated using ¹H-NMR, ¹³C-NMR and Fourier transform infrared spectroscopy, and gel-permeation chromatography. ¹H-NMR confirmed the presence of the D,L-lactide segment as the terminal segment and δ-valerolactone as the mid-segment. ¹³C-NMR was used to study the block sequencing and extent of trans-esterification. The crystallization of the triblock was retarded compared with the pure poly-δ-valerolactone homopolymer due to the incorporation of the D,L-lactide moiety at the chain end of the poly-δ-valerolactone segment. The glass transition temperatures of the two blocks shifted depending on the ratio of the two monomers. The triblock, with molecular weights between 5000 and 10 000 Da, showed a separated morphology in the nanophase, with alternating stripes of amorphous and crystalline segments (3–6 nm) under transmission electron microscopy. The triblock was then fabricated into microspheres with an average diameter of 17.2 μm and was used to encapsulate salicylic acid. The formation of pores on the surface of the microsphere facilitated the release of the salicylic acid. The release profile displayed the characteristics of a potential carrier.