Selective degradation in aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase

Abstract

Controlling the course of the degradation of aliphatic polyesters is a key question when designing new degradable materials. It is shown herein that it is possible to predetermine the degradation path of aliphatic block copolyesters by controlling the heterogeneity of the amorphous phase, which in turn regulates the availability of the hydrolyzable groups in the polyester backbone. To demonstrate these processes, we synthesized a set of degradable materials based on poly(L-lactide) (PLLA), poly(ε-decalactone) (PεDL) and poly(ε-caprolactone) (PCL) with varying compositions. The materials were subjected to hydrolysis for a six months period. The materials composed of PLLA and PεDL exhibited a heterogeneous amorphous phase, whereas the materials composed of PCL and PεDL presented a more homogeneous phase. The kinetics of the degradation indicated that the slowest degradation rate was observed for the more homogeneous compositions. The degradation path of the heterogeneous amorphous phase materials was driven by a random chain scission process, whereas the more homogeneous composition presented a degradation path driven by a more selective chain scission. The confinement of the amorphous phase by the more hydrolytically stable PεDL permitted a selective degradation of the available hydrolyzable groups. The random and more selective chain scission processes were further verified by using previously determined molecular modeling based on Monte Carlo procedures. Topographical images and thermal analyses of the materials under different degradation periods correlated with the proposed degradation paths. Detailed insights and the ability to predetermine the degradation pathways of aliphatic polyesters will continue to expand the great potential of renewable materials and their use in specific applications for a future sustainable society.

Turning natural δ-lactones to thermodynamically stable polymers with triggered recyclability

“…Aliphatic polyesters are hydrolytically degradable and potentially biodegradable. [3][4][5][6] In addition, ROP is an equilibrium reaction, hence having a built-in reversibility which opens for the possibility of chemical recycling. Lactones can be man-made, like lactide (LA) and ε-caprolactone (εCL), but nature also serves us with a large library of bio-derived natural lactones.…”

Amphiphilic tri- and tetra-block co-polymers combining versatile functionality with facile assembly into cytocompatible nanoparticles

“…9,10 Accordingly, there remains a focus on aliphatic polyesters for pharmaceutical applications, as there are many flexible routes for their synthesis, and the metabolites produced upon their breakdown in the body are largely known and are removed via natural excretory pathways. [11][12][13] Poly(lactide)s (PDLLA), poly(caprolactone)s (PCL) and poly(glycolide)s (PGA) and their copolymers are the most widely used polyesters in the health care sector, owing to their accessibility from readily-available monomers, favourable mechanical properties, hydrolytic degradation and biocompatibility. [14][15][16][17] Of particular interest are poly(lactide)s and associated copolymers which can be easily synthesised via ROP of D,L-lactide (LA), a natural recurring cyclic ester.…”

Forecasting linear aliphatic copolyester degradation through modular block design

“…semicrystallinity or amorphousness of the polymer [38]. Furthermore, we have previously shown that the heterogeneity of the amorphous phase plays a significant role in copolyesters degradation, leading to a more selective chain scission when having a more homogeneous amorphous phase [19]. Based on the previous results, it could even be said that the morphology of the modules had a bigger effect on the hydrolysis behavior of the copolymers than the C/O ratios of the polymer structures when having similar hydrophobicities.…”

“…Specifically, fast hydrolyzable block modules of either poly(1,5-dioxepan-2-one) (PDXO) [13] or poly(-but-2-ene-1,4-diyl malonate) (PBM) [20] have shown gradual or rapid hydrolysis profiles, respectively. In contrast, slow degrading blocks of either poly(ε-caprolactone) (PCL) or poly(ε-decalactone) (PDL) have been demonstrated to severely reduce the hydrolysis rates of the triblock materials [19]. It was observed that PLLA-based triblock polymers with different central block modules showed general hydrolysis rates in the following order: PLLA-PBM-PLLA > PLLA-PDXO-PLLA > PLLA-PCL-PLLA > PLLA-PDL-PLLA.…”