The dynamic behaviors of vitrimer are influenced by the interaction of crosslink density and density of exchangeable groups, which results in the difficulty of extracting the effect of mono-variation. In this study, the dynamic behaviors of vitrimer were tuned by changing the density of exchangeable hydroxyls alone, while leaving the cross-link density undisturbed. A multi-hydroxy vitrimer network without a loading catalyst was synthesized successfully. Three-armed functionalized polycarbonate, obtained by ring-opening polymerization of 1,3-dioxan-2-one and its derivatives, was treated as a precursor polymer. Afterward, the precursor polymer was converted into vitrimer in a single step by treatment with hexamethylene diisocyanate. When the system with constant cross-link density was established, the accurate effect of the hydroxyl density on the dynamic behaviors could be characterized by stress relaxation. The relationship of essential dynamic behavioral parameters, such as topology freezing transition temperature (T v ), exchange activation energy (E a ), and Arrhenius prefactor (τ 0 ), with the density of exchangeable hydroxyls was quantitatively discussed. The results indicated that T v and E a were negatively correlated with the density of exchangeable hydroxyls, while τ 0 showed a positive correlation. In addition, linear models were developed to describe the relationship between dynamic behaviors of vitrimer and density of exchangeable hydroxyls. It is expected that the findings can be applied to precisely control E a , τ 0 , T v , and characteristic relaxation time (τ*) of vitrimer and can also be used as a model for the synthesis of various vitrimer materials.

The synergistic combination of chemotherapy and photodynamic therapy has attracted considerable attention for its enhanced antitumoral effects; however, it remains challenging to successfully delivery photosensitizers and anticancer drugs while minimizing drug leakage at off-target sites. A red-light-activatable metallopolymer, Poly(Ru/PTX), is synthesized for combined chemo-photodynamic therapy. The polymer has a biodegradable backbone that contains a photosensitizer Ru complex and the anticancer drug paclitaxel (PTX) via a singlet oxygen ( 1 O 2 ) cleavable linker. The polymer self-assembles into nanoparticles, which can efficiently accumulate at the tumor sites during blood circulation. The distribution of the therapeutic agents is synchronized because the Ru complex and PTX are covalently conjugate to the polymer, and off-target toxicity during circulation is also mostly avoided. Red light irradiation at the tumor directly cleaves the Ru complex and produces 1 O 2 for photodynamic therapy. Sequentially, the generated 1 O 2 triggers the breakage of the linker to release the PTX for chemotherapy. Therefore, this novel sequential dual-model release strategy creates a synergistic chemo-photodynamic therapy while minimizing drug leakage. This study offers a new platform to develop smart delivery systems for the on-demand release of therapeutic agents in vivo.

In the current context of sustainable chemistry development and new regulations, aminolysis of cyclic carbonate is one of the most promising routes to nonisocyanate polyurethanes, also called polyhydroxyurethanes (PHU). In this study, a new kind of shape memory PHU vitrimers with outstanding mechanical properties and chemical recyclability is prepared. The monomer employed for aminolysis to form the PHUs is bis(six-membered cyclic carbonate) of 4,4′-biphenol (BCC-BP), which is synthesized by bi(1,3-diol) precursors and CO 2 . The synthetic strategy, isocyanate-free and employing CO 2 as a building block, is environmentally friendly and suits the concept of carbon neutrality. The thermal properties, mechanical properties, and dynamic behaviors of the PHUs are explored. The maximum breaking strength and elongation at break of the resultant PHUs reach 65 MPa and 452%, respectively, exceeding other reported PHU-based materials in combined performance. Such a PHU material can also lift up a load 4700 times heavier than its own weight by a shape recovery process. Finally, the bi(1,3-diol) can be regenerated through the alcoholysis of PHUs to realize chemical recycling. This work provides a feasibility study for a green synthetic approach and for designing a novel PHU material with outstanding properties.