Study On The Preparation Of Cyclic Polymer Based On Thiol Click Chemistry

As one of the topological polymers，without the end of the chain，all the units of thecyclic polymer have same physical and chemical properties.Cyclic polymer has manydifferent characteristics compared with the linear polymer,such as lower viscosity,smallerradius of gyration,smaller hyrodynamic volume and higher thermal stability. With thesespecial properties,cyclic polymer become the most important one of the the topologicalpolymers. Now,there are main two methods on the preparation of the cyclic polymer：thering-closure method and the ring-expansion method. Compared with the ring-expansionmethod, the ring-closure method has more advantages,such as we are able to prepare thepolymer with the narrow molecular weight distribution by the ring-expansion. The main workof this paper is that preparing the cyclic polymer with the narrow molecular weightdistribution by the combinaton of reversible addition-fragmention radicalpolymerization(RAFT) and thiol click chemistry.The main content of this paper and the result are as follows:We synthesis successful two kinds of RAFT chain transfer agent with the functionalgroup such as dipyridyl disulfide and bromomaleimides which can reactive with thiol byclick chemistry firstly by the design of the molecular. Then we choose three kinds ofmomomers： mma,nipam and dmam.The latter two are water-soluble monomers. Wesuccessful prepare three kinds of linear polymer the narrow molecular weight distributionby RAFT polymerization. These linear polymers can reactive with thiol by click chemistry.Finally dissolving the polymer in the suitable solvent,the solution is diluted to10-5M and getthe thiol group after removing the ester disulfide group by the reducingagent NaBH4. Cyclic polymer is got by intramolecular reaction in the solution.Cyclic polymer have smaller hydrodynamic volume than the linear polymer.This paper examine the change of the molecular weight distribution curve by GPC. We findthat the molecular weight distribution is not changed,but the molecular weight distributioncurve has move. This result conforms to the characteristic that Cyclic polymer have smallerhydrodynamic volume.It shows that the successful synthesis of the cyclic polymer.A small molecule will be eliminated in the process of the synthesis of the cyclic polymer.This paper examines the change of absolute molecule weight by the MALDI-TOF. We findthat Cyclic polymer has the small molecule weight indeed, and the reduced molecule weightis eaqual with the molecule weight of the eliminated molecular. This result show that wesuccessful prepare the cyclic polymer further. We synthesis of the cyclic polymer in an aqueous solvent and the water avoid the use ofa large amount of the toxic solvent. It is very important for the perparation of the certainfunctional polymer with the feature of green-environment friendly of this method.