Chemical Upcycling of Poly(3-hydroxybutyrate) (P3HB) toward Functional Poly(amine-alt-ester) via Tandem Degradation and Ring-Opening Polymerization

Abstract

The upcycling of plastic waste into value-added products is a promising strategy to reduce plastic pollution and create a sustainable style for polymeric materials. We report here the synthesis of a novel N-heterocyclic lactone, 5-methyl-N-Boc-1,4-oxazepane-7-one (MeOxPBoc) and corresponding poly(amine-alt-ester) through upcycling of the poly(3-hydroxybutyrate) (P3HB) biopolymer. Specifically, tens of grams of MeOxPBoc can be easily prepared from P3HB waste in a satisfactory yield. Well-controlled ring-opening polymerization (ROP) of MeOxPBoc was achieved to give an amorphous poly(amine-alt-ester) P(MeOxPBoc) with a targeted molecular weight, narrow molecular weight dispersity, and well-defined terminal groups in toluene using stannous 2-ethyl hexanoate (Sn(Oct)2) as a catalyst. The obtained P(MeOxPBoc) could be depolymerized back to its pristine monomer either in trimethylbenzene at 120 °C using Sn(Oct)2 as a catalyst or in bulk at 150 °C in the presence of ZnCl2 as the catalyst. After simple purification by recrystallization, the recycled MeOxPBoc could be repolymerized to produce virgin-quality polymers. Remarkably, the obtained P(MeOxPBoc) can be converted to the corresponding cationic polymer by simply removing the pendent t-butoxycarbonyl protecting group. This study provides a new insight to address the end-of-use problem of plastic by upcycling the plastic waste to value-added functional poly(amine-alt-ester) with a closed-loop life cycle.

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid‐Based Copolyesters

“…The molecular weight distribution and molecular weight of PSMG are closely related to its physical properties and recoverability. [25] DSC curves show that the glass transition temperature T g increases from 88.6 to 97.9 °C as M n increases from 20.2 to 187.8 kDa (Figure 3 D and E). Similar trends between T g and molecular weight also exits for PSEG (T g = 80.9 °C), PSBG (T g = 94.9 °C) (Figure S36A and B).…”

Continuous Flow Synthesis of Crotonic Acid from Crotonaldehyde

“…Similarly, ethyl 2-butenoate ( 7 ) as the starting material is more expensive than crotonic acid. Additionally, crotonic acid is prepared from allyl alcohol ( 8 ) or poly-3-hydroxybutyrate − ( 9 ) by cleavage at high temperatures in excellent yields. This route is green and renewable.…”

Crystalline Stereoregular Poly(ether-ester) via MeAl[Salen]-Catalyzed Well-Controlled Ring-Opening Polymerization of Enantiopure Cyclic Ether-Ester Monomer

“…Delicately designed closed-loop recyclable polymers have recently witnessed significant advances. Several elegant examples have been reported, mainly including five-, − six-, , and seven-membered monomers. − These monomers with moderate ring strain can achieve “monomer–polymer–monomer” closed-loop life cycles through ring-opening polymerization (ROP) to produce polymers that can be selectively depolymerized back to pristine monomers with high efficiency. Among them, O -heterocyclic lactones are promising candidates to prepare closed-loop recyclable polyesters.…”

“…It is attractive to convert P3HB into new monomers that can be polymerized to produce degradable and recyclable polymers. Recently, we developed a chemical recycling strategy for P3HB toward polymerizable heterocyclic lactones and corresponding poly­(ether- alt -ester) (PEE) and poly­(amine- alt -ester) (PAE) with closed-loop recyclability. , Nevertheless, both polymers are amorphous due to their low stereoregularity, thus hampering their practical applications. The low crystallinity and slow crystallization rate were also observed for most other reported poly­(ether-ester)­s. , Most recently, we addressed this problem by preparing enantiopure bicyclic ether-ester monomers from degraded products of P3HB and obtained closed-loop recyclable crystalline polyesters with a high melting temperature .…”