Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates

Abstract

Polyhydroxyalkanoates (PHAs) have attracted increasing interest as sustainable plastics because of their biorenewability and biodegradability in the ambient environment. However, current semicrystalline PHAs face three long-standing challenges to broad commercial implementation and application: lack of melt processability, mechanical brittleness, and unrealized recyclability, the last of which is essential for achieving a circular plastics economy. Here we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating α-hydrogens in the PHA repeat units and thus precluding facile cis-elimination during thermal degradation. This simple α,α-disubstitution in PHAs enhances the thermal stability so substantially that the PHAs become melt-processable. Synergistically, this structural modification also endows the PHAs with the mechanical toughness, intrinsic crystallinity, and closed-loop chemical recyclability.

Rapid and Controlled Ring-Opening (Co)Polymerization of Bio-Sourced Alkyl-δ-Lactones To Produce Recyclable (Co)Polyesters and Their Application as Pressure-Sensitive Adhesives

“…27 Chen and co-workers recently presented the ring-opening polymerization (ROP) of α, α-dialkyl substituted β-butyrolactone to produce semicrystalline polyhydroxyalkanoates with enhanced thermal stability, melt-processability, closed-loop recyclability as well as high ductility and toughness that are comparable to commodity polyolefin plastics. 28 However, in contrast to the active research and great advancements achieved in academia, the scalable production in the industry for these closed-loop recyclable polymers proceeds slowly, which greatly hampers their practical applications. One possible reason is the complicated, expensive, and time-consuming scalable process from laboratory to industry for these completely new monomers, especially those with tedious synthetic procedures.…”

“…For example, Lu et al reported the design of 4-hydroxyproline-derived bridged bicyclic thiolactones and their controlled polymerization to produce closed-loop recyclable polythioesters under mild conditions . Chen and co-workers recently presented the ring-opening polymerization (ROP) of α, α-dialkyl substituted β-butyrolactone to produce semicrystalline polyhydroxyalkanoates with enhanced thermal stability, melt-processability, closed-loop recyclability as well as high ductility and toughness that are comparable to commodity polyolefin plastics . However, in contrast to the active research and great advancements achieved in academia, the scalable production in the industry for these closed-loop recyclable polymers proceeds slowly, which greatly hampers their practical applications.…”

Living/Controlled Anionic Polymerization of Glycolide in Fluoroalcohols: Toward Sustainable Bioplastics

“…The activation or deactivation of the initiator is strongly dependent on the type of FAs used (Figure 3f), while all FAs can activate the monomer (Figure 3g; for more discussions, see the Supporting Information, Monomer/ Initiator Activation section, and Figures S28 and S29). The affinity of FA for cyclic esters (simulated by VL rather than GL to avoid polymerization) and polymer main chain esters (simulated by ethyl acetate) was also determined through 13 C NMR titration (Figure S30). The association constant (K ass ) of FA and cyclic ester was measured to be 6.2 M −1 , which is 1.7 times higher than that for main chain esters (3.6 M −1 ), indicating a selective activation of monomers (s-cis esters) over polyesters (s-trans esters) by FA.…”

“…However, ∼82% of plastics on the market are of single use and not recycled, creating extremely negative impacts on the health and the environment. The design and use of biodegradable and chemically recyclable polymers is a promising approach for the circular economy of plastics and for achieving a sustainable world. − This approach has been successfully applied in polyesters, − polythioesters, − polyacetals, polycarbonates, and polyolefins . Among them, aliphatic polyesters are an important class of biocompatible, biodegradable commodity polymers usually obtained by living anionic ring-opening polymerization (ROP) .…”

Facile Fabrication of Photochromic Poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Fibers via a Scalable Melt-Spinning Process

“…For example, Li et al discovered that when more than 10 wt % PHA was added into PLA during melt spinning, the initial modulus of the blended fibers decreased from 78 to 67 cN/dtex. However, current PHAs are intrinsically thermally unstable, with a relatively low degradation temperature (T d , the temperature at 5% weight loss) of ∼250 °C, owing to the presence of α-hydrogens that promote facile cis-elimination via the six-membered transition state to form an internal alkene and a carboxylic acid, causing a large, continuous drop in shear viscosity under melt-processing conditions . Once the PHA is degraded, it will further accelerate the degradation of PLA in the blend system. − Simultaneously, the melt viscosity of PHAs decreases significantly, resulting in decreased melt strength of the PLA/PHA blend system and poor spinning stability of the fibers .…”