Donor-Acceptor Covalent Organic Frameworks Films with Ultralow Band Gaps to Enhanced Third-Order Nonlinear Optical Properties

Ring-opening copolymerization (ROCOP) of polyesters may be used to achieve a wide variety of functional polymers using commercial monomer libraries, but primarily make use of metallic catalysts such as tin, magnesium, or cobalt complexes. However, the limitations of such catalysts include toxicity risks and environmental concerns for both the desired application, such as biomaterials, and the end-of-life consideration. There is a need for cleaner, friendlier, and less expensive routes to polymeric materials and devices. Therefore, organobasecatalyzed ROCOP is an intriguing opportunity to improve both the safety and the structural control of the resultant polyesters. Here, organobases with and without supramolecular thiourea co-catalysts are demonstrated for ROCOP of functional polyesters made of cis-4-cyclohexene-1,2-dicarboxylic anhydride and allyl glycidol ether, with ROCOP performed in bulk, open-air conditions. The catalysts resulted in molecular weights of >25 kDa while maintaining controlled polymerization behaviors and a dispersity of <1.3. The role of the thiourea co-catalysts is further explored, with a proposed mechanism for initiation of the ROCOP system. The resultant polyesters are utilized in vat polymerization four-dimensional (4D) printing using thiol-ene cross-linking to manufacture complex prototypes that display shape memory. The role of molecular weight on physical properties, including mechanical and thermal behaviors, is explored along with hydrolytic degradation rates, shape memory responsiveness, and cytocompatibility. Ultimately, the use of organobase catalysis for ROCOP of polyester photopolymer is shown to be an efficient, tunable method of controlling resultant physical properties for improving the environmental friendliness, as well as biomaterial potential.

Automated summary

Ring-opening copolymerization (ROCOP) of polyesters using metallic catalysts can be toxic and environmentally concerning. Organobase catalyzed ROCOP offers a cleaner and safer alternative while maintaining structural control. This study demonstrates the use of organobases with and without supramolecular thiourea co-catalysts for ROCOP of functional polyesters. The resulting polyesters are used in vat polymerization 4D printing, showcasing their shape memory capabilities. Molecular weight is found to impact various physical properties and cytocompatibility.