Bifunctional and recyclable polyesters by chemoselective ring-opening polymerization of a δ-lactone derived from CO2 and butadiene

When aiming at the direct use of CO2 for the preparation of advanced/value-added materials, the synthesis of CO2/olefin copolymers is very appealing but challenging. The δ-lactone 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), synthesized by telomerization of CO2 with 1,3-butadiene, is a promising monomer. However, its chemoselective ring-opening polymerization (ROP) is hampered by unfavorable thermodynamics and the competitive polymerization of highly reactive C=C double bonds under usual conditions. Herein, we report the chemoselective ROP of EVP using a phosphazene/urea binary catalyst, affording exclusively a linear unsaturated polyester poly(EVP)ROP, with a molar mass (Mn) up to 16.1 kg·mol-1 and a narrow distribution (Ð < 1.6), which can be fully recycled back to the pristine monomer, thus establishing a monomer-polymer-monomer closed-loop life cycle. In these polyesters, the CO2 content reaches 33 mol% (29 wt%). The reasons for the unexpected chemoselectivity were investigated by Density-functional theory (DFT) calculations. The poly(EVP)ROP features two pendent C=C double bonds per repeating unit, which show distinct reactivity and thus can be properly engaged in sequential functionalizations towards the synthesis of bifunctional polyesters. We disclose here a methodology providing a facile access to bifunctional and recyclable polyesters from readily available feedstocks.

Polyester Platform with High Refractive Indices and Closed-Loop Recyclability from CO2, 1,3-Butadiene, and Thiols

α-Ethylidene-δ-vinyl-δ-valerolactone (EVL) is the only intermediate to synthesize copolymers of CO2 with 1,3-butadiene whose ring-opening polymerization (ROP), however, is obstructed by the tiglate group. In the contribution, EVL derivatives are synthesized through a Michael addition reaction to saturate the conjugated double bond as well as introduce various groups to synthesize polyesters with designable molecular weights (Mn = 6.9-12.8 kg·mol-1), narrow dispersities (Đ = 1.08-1.19), tunable glass-transition temperatures (Tg = -45-3 °C), and excellent refractive indices (nd = 1.64-1.79) via living and controlled ROP. The obtained polyesters are able to be recycled to the corresponding monomers, which can prepare comparable polymers with identical side groups, realizing the homorecycling. In addition, the retro-Michael addition reaction is established and employed, realizing heterorecycling, which can alter properties during recycling. We propose a strategy for EVL derivatives and establish the corresponding polyester platform with not only high refractive indices and tunable Tgs, but also the ability to tailor properties during recycling.

Sustainable Copolymer Synthesis from Carbon Dioxide and Butadiene

Carbon dioxide (CO2) has long been recognized as an ideal C1 feedstock comonomer for producing sustainable materials because it is renewable, abundant, and cost-effective. However, activating CO2 presents a significant challenge because it is highly oxidized and stable. A CO2/butadiene-derived δ-valerolactone (EVP), generated via palladium-catalyzed telomerization between CO2 and butadiene, has emerged as an attractive intermediate for producing sustainable copolymers from CO2 and butadiene. Owing to the presence of two active carbon-carbon double bonds and a lactone unit, EVP serves as a versatile intermediate for creating sustainable copolymers with a CO2 content of up to 29 wt % (33 mol %). In this Review, advances in the synthesis of copolymers from CO2 and butadiene with divergent structures through various polymerization protocols have been summarized. Achievements made in homo- and copolymerization of EVP or its derivatives are comprehensively reviewed, while the postmodification of the obtained copolymers to access new polymers are also discussed. Meanwhile, potential applications of the obtained copolymers are also discussed. The literature references were sorted into sections based on polymerization strategies and mechanisms, facilitating readers in gaining a comprehensive view of the present chemistry landscape and inspiring innovative approaches to synthesizing novel CO2-derived copolymers.

The Divergent Reactivity of Lactones Derived from Butadiene and Carbon Dioxide in Macromolecular Synthesis

The catalytic conversion of carbon dioxide and 1,3-butadiene into unsaturated lactone monomers provides an efficient route for converting sustainable carbon feedstocks into novel macromolecules. The chemical reactivity of this monomer is reviewed in order to highlight the many viable mechanistic pathways. Polymerization strategies, monomer alterations, and post-polymerization modifications are covered. The polymerization methods include radical, coordination, conjugate addition, ring-opening, olefin metathesis, and thiol-ene chemistries. Materials derived from these processes possess a wide range of function including responsiveness, degradability, adhesion, recyclability, and self-assembly. These aspects along with the advances in polymer chemistry that make them possible are discussed, along with a perspective on the future directions of the field.

Degradable Polymer Structures from Carbon Dioxide and Butadiene

The utilization of carbon dioxide as a polymer feedstock is an ongoing challenge. This report describes the catalytic conversion of carbon dioxide and an olefin comonomer, 1,3-butadiene, into a polymer structure that arises from divergent propagation mechanisms. Disubstituted unsaturated δ-valerolactone 1 (EVL) was homopolymerized by the bifunctional organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) to produce a hydrolytically degradable polymer. Isolation and characterization of reaction intermediates using ¹H, ¹³C, COSY, HSQC, and MS techniques revealed a vinylogous 1,4-conjugate addition dimer forms in addition to polymeric materials. Polymer number-average molecular weights up to 3760 g/mol and glass transition temperatures in the range of 25-52 °C were measured by GPC and DSC, respectively. The polymer microstructure was characterized by ¹H, ¹³C, FTIR, MALDI-TOF MS, and ESI tandem MS/MS. The olefin/CO₂-derived materials depolymerized by hydrolysis at 80 °C in 1 M NaOH. This method and the observed chemical structures expand the materials and properties that can be obtained from carbon dioxide and olefin feedstocks.

Ring-Opening Polymerization of CO2-Based Disubstituted δ-Valerolactone toward Sustainable Functional Polyesters

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVL) is a disubstituent δ-lactone derived from CO₂ and 1,3-butadiene. In this contribution, we report the ring-opening polymerization (ROP) of EVL with β-butyrolactone (BBL) as the comonomer catalyzed by scandium triflate [Sc(OTf)₃]. The obtained polyester bearing active unsaturated bonds has the weight-average molecular weight (M_w) of 4.1 kg/mol, in which the EVL content is 38 mol % in accordance with the initial ratio of 40 mol %. The copolymers are characterized in detail and the cationic ROP mechanism has been confirmed by kinetic study, chain end analysis and density functional theory (DFT) calculation. The modification of the unsaturated bonds in EVL repeating units via the thio-ene click reaction with mercapto-ended polysarcosine polysarcosine yields the amphiphilic grafting polymers. It is a CO₂ fixation approach toward the functional poly(EVL-r-BBL) that is promising as a degradable polyester precursor for adhesive or surface-coating materials.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.