Advances in the Synthesis of Chemically Recyclable Polymers

Abstract

The development of modern society is closely related to polymer materials. However, the accumulation of polymer materials and their evolution in the environment causes not only serious environmental problems, but also waste of resources. Although physical processing can be used to reuse polymers, the properties of the resulting polymers are significantly degraded. Chemically recyclable polymers, a type of polymer that degrades into monomers, can be an effective solution to the degradation of polymer properties caused by physical recycling of polymers. The ideal chemical recycling of polymers, i. e., quantitative conversion of the polymer to monomers at low energy consumption and repolymerization of the formed monomers into polymers with comparable properties to the original, is an attractive research goal. In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the "polymerization-depolymerization" equilibrium and closed-loop recycling under mild conditions. This review will focus on the following aspects of closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymer, illustrate the challenges in this area, and provide an outlook on future directions.

Degradation of poly(1,3‐dioxolane). Depolymerization versus hydrolysis

“…Although high molecular weight PDXL has not been commercialized until now, there are opinions that this polymer may demonstrate tensile strength comparable to some commodity polyolefins and therefore may be considered for packaging applications as a recyclable polymer 6,7 . PDXL shows high tensile strength, with σ B = 40.4 ± 1.2 MPa and ε Β = 720 ± 20% 8 …”

“…Depolymerization of PDXL blocks using a strong acid catalyst returns monomer in near‐quantitative yield and occurs even within a commodity plastic mixture 6 . When PDXL is mixed with common commodity plastics such as poly(ethylene terephthalate), polyethylene, polystyrene or poly(vinyl chloride) it can be selectively depolymerized 8 …”

“…6,7 PDXL shows high tensile strength, with ⊞ B = 40.4 ± 1.2 MPa and ε Β = 720 ± 20%. 8 In fact, the tensile strength of PDXL is comparable to the two most prevalent commodity plastic materials, isotactic polypropylene (⊞ B = 26 MPa and ε Β = 420%) and high-density polyethylene (⊞ B = 30.2 MPa and ε Β = 900%). 6,9 DXL is also used as a comonomer in the cationic polymerization of 1,3,5-trioxane for the production of commercialized polyformaldehyde (so-called acetal resin).…”

“…6 When PDXL is mixed with common commodity plastics such as poly(ethylene terephthalate), polyethylene, polystyrene or poly(vinyl chloride) it can be selectively depolymerized. 8 Mechanisms of poly(1,3-dioxolane) degradation PDXL is introduced as a degradable block into polymer gels (thermosets) which are designed for use as commodity plastic materials but also into three-dimensional gels intended for biomedical applications, e.g. as controlled delivery drug carriers.…”

cis-Fused cyclohexane promoted the chemical recycling of polycarbonate to monomer

“…[1][2][3][4] The strategy of chemical recycling to monomer via depolymerization to pristine monomers and repolymerization without loss in properties represents a circular polymer economy with closed-loop life cycle. [5][6][7][8][9][10] This ideal recycling concept has propelled the synthesis of thousands of new polymer structures for fundamental studies and potential practical applications. Recent advancements in monomer design have demonstrated various polymer systems, including polyesters, polyacetals, polycarbonates, and others suitable for closed-loop chemical recycling via ring-opening polymerization (ROP) and ring-closing depolymerization (RCD).…”