The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways

Abstract

α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL). Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL) with M up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL). The formation of the three types of polymers, P(MBL), P(MBL), and P(MBL), can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La-X (X = OR, NR, R) group. The resulting P(MBL) is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

Living Coordination Polymerization of a Six‐Five Bicyclic Lactone to Produce Completely Recyclable Polyester

“…Chemically recyclable polymers [1][2][3][4][5][6][7][8][9][10][11][12] have attracted increasing attention in recent years because they allow for recovery of the building block chemicals via depolymerization or creative repurposing through generation of value-added materials,t hus offering af easible solution to the end-of-use issue of polymeric materials and providing ac losed-loop approach towards ac ircular materials economy. [13] However, three key challenges still remain before this approach becomes technologically and economically competitive: energy input, depolymerization selectivity,a nd depolymerizability/performance tradeoff.…”

“…Addressing the depolymerization selectivity issue,weand others have recently discovered that highly stable fivemembered g-butyrolactone (GBL), often considered as "non-polymerizable" due to its negligible ring strain, [14] can in fact be effectively polymerized via ring-opening polymerization (ROP)c atalyzed by either metal-based [6,8] or organic catalysts, [4,7] once appropriate thermodynamic (ceiling temperature,m onomer concentration), kinetic (potent catalyst), and processing (solvent enabling polymer crystallization or precipitation) conditions have been met. [6] Significantly,t he resulting ring-opened polymers such as poly(GBL) (PGBL) and poly(a-methylene-g-butyrolactone) can be selectively depolymerized back to their monomers in quantitative yield, via thermolysis (heating the bulk material about decomposition temperature) or chemolysis (using acatalyst under much milder conditions).…”

“…[6] Significantly,t he resulting ring-opened polymers such as poly(GBL) (PGBL) and poly(a-methylene-g-butyrolactone) can be selectively depolymerized back to their monomers in quantitative yield, via thermolysis (heating the bulk material about decomposition temperature) or chemolysis (using acatalyst under much milder conditions). [6][7][8] To address the more challenging depolymerizability/performance tradeoff issue,w er ecently developed as ynthetic polymer system with intrinsically infinite chemical recyclability and practically useful thermal and mechanical properties of common plastics. [1] That system was based on a trans-cyclohexyl-ring-fused GBL at a,b (or 3,4)-positions,a bbreviated as 3,4-T6GBL, which can be rapidly polymerized using am etal catalyst ([M t ]) under room temperature and solvent-free conditions into highmolecular-weight polymers;t he resulting polymer can be depolymerized back to its monomer in quantitative yield, and purity,e stablishing ac ircular life cycle of such chemically recyclable polymers.…”

Catalyst‐Sidearm‐Induced Stereoselectivity Switching in Polymerization of a Racemic Lactone for Stereocomplexed Crystalline Polymer with a Circular Life Cycle

“…Chemically recyclable polymers [1][2][3][4][5][6][7][8][9][10][11][12][13] have lately attracted growing attention because their building block chemicals,o r monomers,c an be recovered for the production of virgin plastics with the same qualities as the original, thus offering af easible solution to the end-of-use issue of polymeric materials and providing ac losed-loop approach towards acircular materials economy. [14] However, there is aparadox between the ability to depolymerize and performance,where polymers that can be readily depolymerized back to monomers often lack physical properties and mechanical strengths to be widely useful, and vice versa.…”

Functional Polymers and Polymeric Materials From Renewable Alpha-Unsaturated Gamma-Butyrolactones

“…Further decreasing of the temperature (down to the range of −40 to −60 • C) allowed Tang et al (2016) to prepare, as a first, also homopolyester of MBL fully functionalized with pendant vinyl groups. Thus, polyesters with M n up to 21 kg mol −1 and dispersity over 1.4 were successfully prepared by using yttrium or lanthanum-based catalyst in combination with alcohol.…”