No abstract

A d,l-lactide–δ-valerolactone–d,l-lactide triblock copolymer, synthesized by sequential ring-opening polymerization, showed a nanolamellar morphology and was fabricated into microspheres for drug delivery.

Hydrolytic degradation of BAB terpolymers with δ-valerolactone as the central (A) block and D,L-lactide as the terminal (B) block was studied by 1 H NMR and Raman spectroscopic techniques. The following variations were investigated: (i) the ratio of δ-valerolactone to D,Llactide, (ii) replacement of D,L-lactide with cis-lactide or glycolide, keeping A constant, and (iii) replacement of δ-valerolactone with ε-caprolactone, keeping B constant. The intensity of the characteristic peaks for the D,Llactide segment almost disappeared, and the intensity of the characteristic signals for δ-valerolactone decreased after 30 days. As evident from quantitative analysis of 1 H NMR, 97% of the D,L-lactide segment degraded within 30 days, and the value was 35% for the δ-valerolactone block (both based on the initial value). Upon degradation of the triblock, a significant increase in water uptake and decrease in molecular weight and bulk weight were observed. Crystallinity of the triblock increased after degradation due to removal of the amorphous D,L-lactide from the system. An enormous increase in the ΔH m value after degradation was observed, supporting the increase in crystallinity. Replacing the middle segment with ε-caprolactone resulted in only 0.64% degradation of the middle segment in 30 days. The degradation of terminal segment was reduced using cis-lactide or glycolide in place of D,L-lactide. The disappearance of Raman signal at 870 cm −1 assigned for υC−COO stretching of DLL segment along with a decrease in CO stretching region (1725 cm −1 ) indicated cleavage of the ester linkages. Lower biodegradability of the triblock containing ε-caprolactone was also apparent from 29% degradation in the CO region compared to 55% degradation for the triblock with δ-valerolactone. Strong peaks at 1776, 1247, and 996 cm −1 were observed after 30 days due to remaining crystalline domains of polyglycolide in the triblock.

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 1 H 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 13 C 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-CH 2 , C=O and C-O-C stretching showed characteristic shift in FTIR on copolymerization. The presence of different blocks as middle segment and terminal segment was confirmed from CH/CH 3 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 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 nanofibrills was retained in triblock having ε-caprolactone, which was disturbed for δ-valerolactone based triblocks.

The current work focuses on the influence of microstructure of different lactone‐based triblock copolymers on drug delivery, where the middle segment was δ‐valerolactone or ɛ‐caprolactone and the terminal segment was d,l‐lactide or cis‐lactide. Microspheres were fabricated from the triblocks using salicylic acid as the model drug. The microsphere formation and drug release were investigated by scanning electron microscopy, ultraviolet–visible spectroscopy, X‐ray diffraction, and thermogravimetry. The size of the microspheres ranged from 2 to 20 µm in diameter. The diffusion coefficient values showed that replacement of the middle segment, δ‐valerolactone with ɛ‐caprolactone, retarded the diffusion of the drug molecules. The diffusion coefficient was lowered when d,l‐lactide content was decreased in the triblock. Mathematical models were used to predict the drug release from the microspheres of different triblocks. The modeling study on drug release profiles revealed that the biodegradable nature of the triblock played a crucial role in determining the drug release kinetics. The diffusion and degradation reaction justified the drug release from microsphere. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45284.

Bionanocomposites were prepared using D,L-lactide-d-valerolactone-D,L-lactide triblock and unmodified and modified cellulose nanowhiskers (CNs) at different loadings (0, 2, 4, 8 wt %). Poly(d-valerolactone) chains were grafted on CNs for modification. These were characterized by various techniques. The broadening of OH (hydroxyl) stretching region and the presence of low-intensity peaks at 1064 cm 21 for CAO/CAC stretching vibration and 1426 cm 21 for bending vibration of CH 2 group , were evident in Fourier transform infrared spectra of the nanocomposites. The increase in crystallinity was noticed as the amount of nanowhiskers was increased. The nanowhiskers having the width in the range of 80-300 nm were uniformly dispersed in the triblock matrix. The tensile strength and modulus increased by 130% and 50% respectively at 8 wt % of filler loading. The storage modulus, loss modulus, complex viscosity, and tan d values increased with increased filler loading. Further improvement in mechanical properties was observed with the modified CNs. The modulus mapping from atomic force microscopy confirmed the effective reinforcement behavior of the nanowhiskers. Scaffold fabrication using the bionanocomposite exhibited porous nature, having a homogeneous dispersion of CNs on the surface of the scaffold. The 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay confirmed the suitability of the composite material for scaffold application.Till date, different polymer matrices have been investigated to prepare cellulose-based bionanocomposite. 17-21 Free sulfate groups were introduced on the surface of CNs by sulfuric acid hydrolysis. 22 These negative charges facilitated the formation of Additional Supporting Information may be found in the online version of this article.