Research On The Synthesis And Fluorescent Property Of Poly(Pyrazoline-ester)

Fluorescent polymers are widely used in people’s production and life,but the traditional fluorescent polymers generally have a large rigid conjugated system,which restricts the flexibility and solubility of molecular chains to a certain extent.Therefore,the design and synthesis of non-traditional fluorescent polymers is one of the important directions in the development of fluorescent materials.As a five-membered nitrogenous heterocyclic compound,pyrazoline and its derivatives are important intermediates in organic synthesis,but also have good fluorescence properties,so they are widely used in the field of fluorescent materials,such as fluorescent dyes,fluorescent brighteners,chemical sensors,biological imaging,etc.In this paper,two kinds of non-traditional fluorescent polymers with pyrazoline ring structure in the main chain were designed and synthesized by two methods,and their reaction conditions and fluorescence properties were studied.1.Using methyl diazoacetate（MDA）and methyl acrylate（MA）to perform 1,3-dipolar cycloaddition reaction in one pot under different feeding ratios at room temperature,the five-member heterocyclic compound 3,5-dimethoxycarbonyl-2-pyrazoline monomer was synthesized,and the feeding ratio of the two compounds was proved to be 1:1.2（compared with 1:1）.The yield of the reaction increased significantly,reaching 86.3%.The same was true when ethyl diazoacetate（EDA）was used to react with MA.MDA and EDA did not react with vinyl acetate,styrene and methyl methacrylate at 35℃.These results indicate that the 1,3-dipole cycloaddition reaction of diazo compounds is more likely to react with alkenes with strong electron-absorbing groups and low steric hindrance.Then,under the pressure reduction and catalysis of different catalysts,the above 2-pyrazoline monomer was used for polymerization at a certain temperature.Through the condensation reaction of losing one molecule of methanol between monomer molecules,the polypyrazoline ester oligomers were obtained.The results of GPC showed that:The number average molecular weight（M_n）and weight average molecular weight（M_w）of the polymer reached 883 g/mol and 1178g/mol,respectively.The catalytic effect of stanyous isocapylate（Sn（Oct）₂）was better among the catalysts used.NMR,FTIR and MALDL-TOF-MS results confirmed that the repetitive structure unit was derived from the polycondensation of 3,5-dimethoxycarbonyl=1-2-pyrazoline monomer to release one molecule of methanol.DSC analysis showed that the glass transition temperature（Tg）of pyrazoline ester was up to 122.63%under the condition of 180℃,reduced pressure（550 Pa）and Sn（Oct）₂,and PL analysis showed that:The fluorescence properties of the polymer are better than that of the 3,5-dimethoxycarbonyl-2-pyrazoline monomer.The relative fluorescence quantum yield of the polymer is up to 28%under the excitation light of 355 nm.2.When the feeding ratio of diazoacetate to diolefin is 2:1,dipyrazoline with two pyrazoline rings can be synthesized.Diazoacetate and dipyrazoline can undergo N-H insertion reaction under the catalysis of three different catalysts（palladium chloride,rhodium acetate,ruthenium dichloride dimer）,and pyrazoline ester can be obtained,which confirms that N-H insertion reaction can occur between them.The reaction of double azo-carbonyl compound and dipyrazoline to obtain pyrazoline ester by N-H insertion reaction was further explored.The results of GPC showed that:The catalytic effect on the ruthenium dichloride dimer catalyst was the best,and with the increase of reaction time,the polymerization degree of the obtained polypyrazoline ester was higher,the number average molecular weight of the polypyrazoline ester reached 4587g/mol,and the highest yield was 89.25%.The composition of the polymer was confirmed by NMR,FTIR and MALDL-TOF-MS analysis.The repeating structural unit is the double nitrogen carbonyl compound with N2 inserted into the N-H bond of the dipyrazoline.The DSC analysis results show that when the weight loss of the polymer is 10%,the temperature of the polymer is above 270℃,and the temperature of poly（1a+2b）is 291℃,which indicates that the polymer has good thermal stability.The results of PL analysis showed that the fluorescence property of polypyrazoline ester was better at the excitation wavelength of 344 nm.Compared with dipyrazoline monomer,the fluorescence property of polypyrazoline ester was significantly enhanced.The relative fluorescence quantum yield of the polymer could reach 26%,which has good application and research value.