Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals

Aromatic Poly(dithioacetal)s: Spanning Degradability, Thermostability, and High Refractive Index Towards Eco-friendly Optics

In the quest for eco-friendly optics, high refractive index polymers (HRIPs) with degradability have been one of the desirable optical materials for realizing eco-friendly and efficient lighting technologies. However, it has been challenging for HRIPs to simultaneously realize thermostability, high refractive index (RI), visible transparency, and efficient degradability, all of which are essential for their practical use. In this context, we herein focus on aromatic poly(dithioacetal)s, composed of visible-transparent yet degradable dithioacetal moieties and rigid phenylene sulfide spacers, exhibiting moderately high Tg (> 60 °C), high RI (> 1.7), and colorless film features. In addition, poly(dithioacetal)s can balance (1) high stability under the operating conditions even upon heating and (2) quantitative degradability that can selectively yield cyclic low-molecular-weight products that can be further repolymerized upon further addition of an acid catalyst. These results provide a key concept for high refractive index polymers that allow on-demand degradability and recyclability without compromising their high potential thermal and optical properties.

Cationic polymerization of vinyl ethers using trifluoromethyl sulfonate/solvent/ligand to access well-controlled poly(vinyl ether)s

Cationic polymerization of vinyl ethers to access poly(vinyl ether) polymeric materials has been challenging due to stringent polymerization conditions and inevitable chain transfer. Herein we introduce a protocol using trifluoromethyl sulfonates to catalyze the polymerization of a series of vinyl ethers. These trifluoromethyl sulfonates are fully commercially available and can be stored under ambient conditions. Solvents and ligands have profound influences on the polymerization process, and poly(vinyl ether)s with different molecular weights, molecular weight distributions, and tacticities were obtained. A few combinations of trifluoromethyl sulfonate/solvents/O^O type ligands were explored. They showed high activities and afforded poly(vinyl ether)s with well-controlled tacticity, of which the isotacticity can be up to 81% m. Poly(vinyl ether)s with high tacticities exhibit crystallization behaviors with melting points. We also probed the cationic reversible addition-fragmentation chain transfer (RAFT) polymerization of ethyl vinyl ether employing a RAFT chain transfer agent. Low molecular weight distributions (Đs) around 1.1 can be realized. Since trifluoromethyl sulfonates can be fed at a remarkably low catalyst loading and other chemicals are cheap and easily available, the poly(vinyl ether) polymeric materials are promisingly prepared on a large scale.

An Expedient Route to Bio-Based Polyacrylate Alternatives with Inherent Post-Chemical Modification and Degradation Capabilities by Organic Catalysis for Polymerization of Muconate Esters

The quest for polymers that would be at the same time bio-based and degradable after usage, in addition to offering chemical post-modification options, remains a daunting challenge in contemporary polymer science. Despite advances in polymer chemistry, attempts at controlling the chain-growth polymerization of muconate esters remain unexplored. Here we show that dialkyl muconates can be rapidly polymerized by organocatalyzed group transfer polymerization (O-GTP). O-GTP is conducted to completion at room temperature in toluene within a few minutes, using 1-ethoxy-1-(trimethylsiloxy)-1,3-butadiene (ETSB) as initiator and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2 λ ${\lambda }$ 5,4 λ ${\lambda }$ 5 catenadi(phosphazene) (P4-t-Bu) as catalyst. Chain extension experiments and synthesis of all muconate-type block copolymers can also be achieved. Furthermore, polymuconates are amenable to facile post-polymerization modification reactions. This is showcased through the hydrolysis of the ester side chains leading to well-defined poly(muconic acid), and by epoxidation of the C=C double bonds of the main chain. Last but not least, these internal alkene groups can be selectively cleaved by ozonolysis, demonstrating the upcyclability of polymuconates under oxidative conditions. This work demonstrates that polymuconates constitute a unique platform of bio-based polymers, easily modifiable in addition to being chemically degradable under user friendly experimental conditions.

Selective poly(vinyl ether) upcycling via photooxidative degradation with visible light

Poly(vinyl ethers) (PVEs) have many applications, such as adhesives, lubricants, and anticorrosive agents, thanks to their elastic, nonirritating, and chemically inert properties. The recycling of PVEs remains largely underexplored, and current methods lack generality towards other polymer classes. Thus, the chemical upcycling of PVE into small molecule feedstocks would provide an alternative approach to combat these current issues. Here, we report a visible light-mediated method of upcycling poly(isobutyl vinyl ether) (PIBVE) into small molecules via photooxidative degradation using chlorine or bromine radicals. PIBVE can be degraded to low molecular weight oligomers within 2 h, producing good yields of alcohols, aldehydes, and carboxylic acids. Mechanistic studies suggest that hydrogen atom transfer (HAT) from the backbone or the side chain leads to small molecule generation via oxidative cleavages. Additionally, this protocol was applied to a copolymer of poly(methyl acrylate-co-isobutyl vinyl ether) to demonstrate the preference for the degradation of polymers bearing more electron-rich C-H bonds through a judicious choice of abstraction agent. Ultimately, we show that photooxidative degradation enables the selective chemical upcycling of PVEs as a method of plastic waste valorization.

Living Cationic Ring-Opening Polymerization of Hetero Diels-Alder Adducts to Give Multifactor-Controlled and Fast-Photodegradable Vinyl Polymers

Precise control of multiple structural parameters associated with vinyl polymers is important for producing materials with the desired properties and functions. While the development of living polymerization methods has provided a way to control the various structural parameters of vinyl polymers, the concomitant control of their sequence and regioregularity remains a challenging task. To overcome this challenge, herein, we report the living cationic ring-opening polymerization of hetero Diels-Alder adducts. The scalable and modular synthesis of the cyclic monomers was achieved by a one-step protocol using readily available vinyl precursors. Subsequently, living polymerization of the cyclic monomers was examined, allowing the synthesis of vinyl polymers while controlling multiple factors, including molecular weight, dispersity, alternating sequence, head-to-head regioregularity, and end-group functionality. The living characteristics of the developed method were further demonstrated by block copolymerization. The synthesized vinyl polymers exhibited unique thermal properties and underwent fast photodegradation even under sunlight.