Guiding The Design Of Metalloporphyrin Heterogeneous Catalytic System For Cascade Polymer Syntheses

With the development of science technology,synthetic polymer production processes and technologies are becoming more and more mature.But there are still problems such as low production efficiency,complex purification process,heavy metal catalysts are not easy to recover and pollute the environment.The above problems can be alleviated by two means,one is to use high-efficiency and low-pollution highperformance catalysts to eliminate adverse effects from the source;the other is to optimize and design production processes and simplify them.As a new polymerization technology,photoinduced electron/energy transfer reversible addition-fragmentation chain transfer(PET-RAFT)has excellent performance in terms of low energy consumption,small catalyst dosage,wide applicability of monomers and oxygen resistance.Although PET-RAFT polymerization has obvious advantages,there are also problems such as difficult catalyst recovery,complex purification,and narrow solvent selection range.In order to achieve high catalytic efficiency,it is also necessary to develop photocatalysts that are compatible with monomers,chain transfer agent,and light source wavelengths.In this study,porphyrin copolymers were used as photocatalyst units,and they were introduced into membrane reactors and flow reactors to prepare heterogeneous catalytic systems,respectively,to explore the feasibility and separation effects in PET-RAFT polymerization.The specifics of this study are as follows:(1)The combination of membrane technology and polymer synthesis can make the polymerization process more efficient,economical and environmentally friendly.Membrane reactors not only retain the benefits of PET-RAFT polymerization,but also make full use of their separation capabilities to simplify the production process.In this study,heterogeneous catalytic membrane reactor was prepared by covalent bonding of active groups from polydopamine-coated layer with zinc porphyrin copolymers.Moreover,the separation and purification of the products was realized by using the high selectivity of membrane reactors for reactants and products.The polymerization reaction study found that the heterogeneous catalytic membrane reactor prepared by this institute helps to accurately control the polymerization time,and the purpose of regulating the reaction process can be achieved through the “on/off” of the light source,so that the molecular weight of a variety of polymerization products is adjustable and the molecular weight distribution is narrow((?)_ < 1.2).Further,the addition of a small amount of ascorbic acid to the reaction system can improve the oxygen tolerance of the reaction without reducing the rate of polymerization reaction,which can eliminate the time-consuming and labor-intensive deoxidation step.At the same time,the synthesis and separation of aqueous two-block copolymerization products were carried out in this study,and after the polymerization was completed that the products were purified by membrane reactors.The result was better than traditional dialysis purification that 99% of impurities could be removed after only 4 ～ 5 separation volumes,showing the application potential of membrane reactors in the cascading process.Due to the versatility of the porphyrin zinc membrane reactor,it is easier to add or subtract modular units,perform cascade treatment,and obtain well-structured macromolecular products without intermittent purification.(2)Polymer synthesis is carried out in a flow reactor,which can greatly improve safety risks caused by excessive solvent and monomer residues and inefficiency caused by invalid time.At the same time,the tubular spiral design increases the light receiving area of reaction system,which can improve the utilization rate of light.In this study,PETRAFT polymerization was combined with a flow reactor and the porphyrin-based catalyst was fixed on chitosan to prepare heterogeneous catalytic thread for reducing catalyst leaching and recycling heterogeneous catalysts conveniently.The reactor device was designed and assembled,and the effects of PET-RAFT polymerization in the flow reactor were investigated for monomer concentration,catalyst dosage and retention time.The monomer conversion rate can reach up to 95.8% under the following conditions: retention time is 5 h,N,N-dimethylacrylamide monomer concentration is 20 v/v% and molar ratio to the catalyst is 400:0.01.Porphyrin zinc chitosan thread has excellent photocatalytic activity,long service life,and after 5 cycle reactions still has 87.5% monomer conversion rate.