Preparation Of Double Hydrophilic Diblock Copolymers Supported L-proline And Catalysis On Aldol Reaction In Water

L-proline as a common organocatalyst can catalyze the asymmetric Aldol reactions.However,there are some disadvantanges in L-proline catalyzing reactions,such as high catalyst loadings,the difficult recovery and reuse of the catalysts and the use of organic solvents.Immobilizing L-proline can effectively improve the above problems.In many carriers,polymers have a variety of types and their compositions are adjustable.As a carrier,they can effectively solve the problems of small organic molecules catalysts,so they have become a research hotspot.Currently,polymers-supported L-proline have made some progress in Aldol reaction,but common polymer carriers have certain limitations in product separation and catalyst recycling,and most of the catalytic systems still require organic solvents.Hence,it is of great significance to design polymer-supported L-proline catalysts with better properties.In this study,double hydrophilic block copolymers(DHBCs)were used as carriers for L-proline,and thermoresponsive DHBCs supported L-proline and pH-responsive DHBCs supported L-proline were synthesized.These two types of polymers-suppored L-proline can catalyze Aldol reaction in water,where the polymers could assemble into reversible micellar nanoreactors induced by temperature or pH.The specific research content and conclusions are as follows:(1)Thermoresponsive DHBCs supported L-proline P(NIPAm-co-Prol A)-b-POEGA with different POEGA block content were prepared by reversible addition fragmentation chain transfer(RAFT)polymerization.The structure of the polymer was confirmed by proton nuclear magnetic resonance(~1H NMR)and the average relative molecular weight of the copolymer was determined by gel permeation chromatography(GPC).The thermoresponsive properties of the polymer were investigated by ultraviolet-visible spectroscopy(UV).It was found that the phase transition temperature of the polymer increases,as content of hydrophilic POEGA increases.Then the size and morphology of the self-assembled polymer structure is observed by dynamic light scattering(DLS)and transmission electron microscopy(TEM).It was found that these block polymers can self-assemble into micelles at 50°C,but too little POEGA content would influence the dispersion of the micelles.(2)Using mPEG-DDMAT as a macromolecular chain transfer agent,pH-responsive DHBCs supported L-proline(mPEG-b-P(DEA-co-ProlA))were prepared by RAFT polymerization.The structure of each substance was confirmed by ~1H NMR and the average relative molecular weight of the each polymer was determined by GPC.An automatic potentiometric titrator was used to examine the pH-response property of the copolymer with a pKa value of approximately 6.6 at the phase transition point.DLS were used to analyze the size and morphology of the assembled structure of block copolymers at different pH.The results showed that the micelle aggregates with uniform particle size can be obtained at about pH 7.0.(3)Thermoresponsive DHBCs supported L-proline can be used to catalyze the Aldol reaction in water at 50°C.It was found that the catalytic system with a moderate POEGA content(18%)have the best catalytic effect and recycling performance.Because the catalytic system could form stable catalytic system and the product was easy to separate from the system.pH-responsive DHBCs supported L-proline also can be used to immobilize the Aldol reaction in the aqueous phase.The catalytic results of the polymer were not good,when the pH of the catalytic system was too acidic(pH=3.8)or over-alkali(p H=9.2).Only Under the environment of pH=7.0,the catalytic system can form a uniform micellar system and achieve high productivity and selectivity of product.