Macromolecules, Vol.53, No.14, 5857-5868, 2020
Alternating Ring-Opening Metathesis Polymerization Provides Easy Access to Functional and Fully Degradable Polymers
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 (D-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.