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Detecting and understanding the topology freezing transition temperature of vitrimers has been very limited in the past. Here the authors use a sensitive and universal method by doping or swelling aggregation-induced-emission luminogens into vitrimers as probes to monitor the topology freezing transition temperature
We carried out the conventional radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization of di(1-adamantyl) fumarate, bis(3,5-dimethyl-1-adamantyl) fumarate, 1-adamantyl isopropyl fumarate, and 3,5-dimethyl-1-adamantyl isopropyl fumarate. Triblock copolymers consisting of rigid and flexible segments were synthesized by the RAFT polymerization of 2-ethylhexyl acrylate using poly(dialkyl fumarate)s as the macro-chain transfer agents. The excellent thermal stability of the adamantane-containing poly(dialkyl fumarate)s was confirmed by thermogravimetric analysis. The alignment of the rigid poly(dialkyl fumarate)s chains in the solid-state was revealed by X-ray diffraction.
The relaxation behavior of random copolymers of diisopropyl fumarate (DiPF) with 1-adamantyl acrylate (AdA) and n-butyl acrylate with various compositions was investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The β relaxation temperature systematically shifted depending on the glass transition temperature of the counterpart copolymers, and the merging of the α and β processes at an intermediate composition was also observed. Thus, the random copolymerization of DiPF and acrylates enables us to fine tune the properties associated with the β relaxation of DiPF segments.
Thickness changes in polyvinyl acetate thin films, during the temperature cycle across the glass transition temperature (Tg) has been studied in detail. Even after enough thermal treatment done at the high-temperature side of Tg, thickness increase during cooling (negative thermal expansion) is observed. On the other hand, slow thickness decrease is observed with aging at the high-temperature side of Tg. The above interesting phenomena can be well explained by the model considering the presence and changes of the interface layer.
Gas transport properties of novel polybenzoxazole (PBO)—silica hybrid membranes prepared via sol–gel rand different thermal treatment protocols were investigated. The hybrid membranes showed enhancements of CO2 permeability and CO2/CH4 selectivity with increasing silica content and thermal treatment temperature. The excellent CO2/CH4 separation ability might be achieved by free volume holes crated around polymer/silica interfacial area and increased intermolecular chain distance.
The combination of addressable synthetic macromolecules with proteins of precise structure and function often leads to materials with unique properties, as is now shown by the efficient multi-site initiation of polymer growth inside the cavity of a virus capsid.
Two-dimensional polymers can serve to organize chemical functionality periodically over large areas, but their rational synthesis has remained limited. Now, a free-standing, single-layer polymer sheet has been prepared and isolated through a two-step procedure — a photochemical reaction within a layered organic crystal followed by exfoliation.