Herein, the successful development of a metal‐free, solution [2 + 2] photopolymerization of natural cinnamic acid‐derived bisolefinic monomers is reported, which is enabled by a strategy based on direct triplet state access via energy transfer catalysis. 2,2’‐Methoxythioxanthone has been identified as an effective organic photocatalyst for the [2 + 2] photopolymerization in solution, which can be excited by visible light and activate the biscinnamate monomers via triplet energy transfer. This method features its metal‐free conditions, visible light utilization, solution polymerization, and abundant biomass‐based feedstock, as well as processable polymer products, which is different from the rigid, insoluble products obtained from solid‐state photopolymerization. This solution polymerization method also shows a good compatibility to monomer structures; cinnamic acid‐derived bisolefinic monomers with different linkers, including diamine, natural diol, and bisphenol, can all readily undergo [2 + 2] photopolymerization, and be transformed into colorless, sustainable polymers.
The [2 + 2] photopolymerization of diolefinic monomers
is an appealing
approach for the construction of polymeric materials. Herein, we demonstrate
that the establishment of an effective donor–acceptor conjugation
by introducing electron-donating alkoxy groups at appropriate positions
of the benzene ring could activate p-phenylenediacrylate
(PDA), thus enabling the development of the first solution [2 + 2]
photopolymerization of such monomers under the irradiation of visible
light. Variation on the alkoxy groups and the ester parts could allow
access to a series of linear cyclobutane-containing polymer products
with high molecular weight (up to 140 kDa) and good solubility in
common solvents. Further, temporal control and postpolymerization
modification with preinstalled pendant CC bonds via thiol–ene
click reaction are also demonstrated with this [2 + 2] photopolymerization
system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.