Synthesis And Application Of Cyclic Polymer

After the first discovery of cyclic biomacromolecules in 1960,cyclic polymers have become one of the research hotspots in the field of polymer synthetic chemistry.Initially,the cyclic-linear polymer equilibrium method in stepwise polymerization was used to synthesize cyclic polymer.This method has competition:the terminal functional groups of two different linear polymer precursors are coupled to form undesired dimeric or multimeric linear polymers;terminal active functional groups of the same polymer precursor are coupled with each other to generate the designed cyclic polymer.Although this method is technically simple,the cyclization product only occupies a small amount.Even,after separation or other purification methods,these crude products contain unwanted linear impurities.However,after the initial efforts of polymer scientists on synthetic routes,there are currently three different synthetic routes to generate high-purity cyclic polymers:bimolecular ring closure,unimolecular ring closure,and ring expansion polymerization.In this paper,we use reversible addition fragmentation chain transfer(RAFT)to polymerize functional monomers for generating linear precursors,and then the cyclic polymer was synthesized by photo-induced ring closure.Finally,the thermally induced phase transition behavior and photoluminescence properties of linear and cyclic polymers are compared,and the influence of cyclic topology on the properties of polymers is explored.The results of the study are as follows:1.We synthesized thermoresponsive cyclic PNASME via photo-induced cyclization of anthryl-capped ?,?-homodifunctional PNASME under highly dilute solution.Cyclic PNASMEs show significantly higher lower critical solution temperatures(LCSTs)compared with the linear precursors due to topological interactions.Based on the remarkable increment of LCST stemming from cyclic topology,the LCST of PNASME can be easily and efficiently tuned in a wide range of temperature(32.3-80.9?)by changing the cyclic/linear ratios.This study provides a vivid example for examining the topology effect,and the strategy of tuning the LCSTs can also be a reference to other thermoresponsive polymers.2.We first synthesized the acrylic monomer TPEMA with aggregation-induced luminescence(AIE)properties,and then generated the monodisperse linear polymer PTPEMA by RAFT polymerization.Then,the cyclic PTPEMA was synthesized via photo-induced cyclization of anthryl-capped ?,?-homodifunctional PNASME under highly dilute solution.Due to the ring topology and ring tension,the AIE effect of cyclic polymers is stronger than that of linear counterpart,and they are more sensitive to the water content changing.Linear polymers only exhibit aggregation-induced luminescence properties when the polymer molecules begin to aggregate because that the water content increases to some extent that the polymer does not dissolve.However,due to the existence of ring tension,cyclic polymers can exhibit aggregation-induced luminescence properties when the polymer molecules are not dissolved.The aggregation and conjugation of the luminescent groups among the polymer chain can realize the aggregation-induced luminescence properties.The AIE effect of cyclic polymers is also stronger than that of linear counterpart.