Alternating Ring-Opening Metathesis Polymerization Provides Easy Access to Functional and Fully Degradable Polymers

Abstract

Polymers with hydrolyzable groups in their backbones have numerous potential applications in biomedicine, lithography, energy storage, and electronics. In this study, acetal and ester functionalities were incorporated into the backbones of copolymers by means of alternating ring-opening metathesis polymerization catalyzed by the third-generation Grubbs ruthenium catalyst. Specifically, combining large-ring (7–10 atoms) cyclic acetal or lactone monomers with bicyclo[4.2.0]­oct-1(8)-ene-8-carboxamide monomers provided perfectly alternating copolymers with acetal or ester functionality in the backbones and low to moderate molecular weight distribution (D̵ M = 1.2–1.6). Copolymers containing ester and acetal backbones hydrolyzed to significant extent under basic conditions (pH 13) and acidic conditions (pH ≤ 5), respectively, to yield the expected byproducts within 30 h at moderate temperature. Unlike the copolymer with an all-carbon backbone, copolymers with a heteroatom-containing backbone exhibited the viscoelastic behavior with crossover frequency, which decreases as the size of the R group on the acetal increases. In contrast, the glass transition temperature (T g) decreases as the size of the R group decreases. The rate of hydrolysis of the acetal copolymers was also dependent on the R group. Thus, ruthenium-catalyzed alternating ring-opening metathesis copolymerization provides heterofunctional copolymers whose degradation rates, glass transition temperatures, and viscoelastic moduli can be controlled.

Metal-Catalyzed Switching Degradation of Vinyl Polymers via Introduction of an “In-Chain” Carbon–Halogen Bond as the Trigger

“…On the other hand, the development of sustainable polymer materials that can be recycled or disposed without putting a burden on earth is highly required, as the environmental impact of the polymer waste has become more and more serious. − For the global issue, a concept of “switching degradation” has attracted attention for the polymer design, because it could allow on-demand degradation after use while the material stability is ensured. Some researchers have recently reported on switching from “stable use” to “degradation” or “depolymerization” under some stimuli, − and the key is an introduction of the “trigger” into the polymer chain.…”

Progress in Degradation Behavior of Most Common Types of Functionalized Polymers: A Review

“…Interestingly, the degradation rate was dependent on the R group carried out by the acetal function: under mild acidic conditions (pH = 5, 37 °C), H‐carrying acetal‐based copolymer revealed no degradation even after several days, whereas phenyl‐carrying acetal‐based copolymer was fully degraded after 35 h. Moreover, when compared to the all‐carbon backbone polymer, the obtained heteroatom‐containing backbone copolymers had different mechanical properties. [ 79 ]…”

“…Adapted with permission. [ 79 ] Copyright 2020, ACS Publications. a) Dichloromethane, Grubbs third‐generation catalyst (10 × 10 −3 m ), 40 °C.…”

Substituent Effects Provide Access to Tetrasubstituted Ring-Opening Olefin Metathesis of Bicyclo[4.2.0]oct-6-enes

“…However, many alternating copolymerization systems do not strictly alternate due to some degree of homoaddition being present . Alternating ring-opening metathesis polymerization (AROMP) has enabled access to well-controlled architectures by the convenient installation of a precise number of carbon spacers between functional monomers. − Alternating copolymers prepared by AROMP present superior monomer economics and functionalities that are often required in multiple applications such as tunability and degradability. − …”