Study On Brominated Mechanism Of Natural Rubber Latex

Brominated natural rubber(BNR),as a new type of functional polymer materials,is an important raw material for paint,however the poor solubility in common organic solvents for BNR products confines theirs widespread applications.Fourier transform infrared spectroscopy(FTIR)?NMR?TG and high-resolution pyrolysis gas chromatography-mass spectrometry(HRPyGC-MS)were used to investigate the structures of several BNR samples from latex,explore the brominted reaction mechanism,so as to control the structure of the BNR products,improve product overall performance,and accelerate the adoption.BNR from latex lose the rubber properties gradually with the increasing of bromine content,from the gum into fine powder finally.The introduction of the bromine atom had a significant impact on the NR molecular chain conformation,thereby changing the appearance of BNR product.The thermal degradation of BNR samples was completed in two steps;the mass loss rate in the first step was basically equal to the bromine content of the BNR sample,the thermal stability decreased with the increasing bromine content.When the level of bromine content was low,the bromine content of BNR samples prepared at 15°C was slightly lower than the samples at 25 °C,it contrasted when the level' were middle and high.When the adding amount of bromine was small(the molar ratio was 0.5 or less),the bromine content of the product was no more than half of the theoretical content;with the increment of the reaction time and the bromine dosage,the bromine content of the product gradually approached to the theoretical bromine content,which indicated that the bromide substitution reaction dominated in the early bromide reaction process of NR,the addition reaction was synchronized happened with the increase of reaction time.The solubility of BNR samples in acetone,toluene,chloroform and dimethylsulfoxid decreased gradually with the increasing of the bromine content and increased in ethanol.In the low temperature,the gel content was high;the generating of gel was gently.Based on the difference of dissolve situation between the acetone and cyclohexanone,the exiting of ring in the molecular chain can be conjectured.The results of HRPyGC-MS showed that the pyrolysis products of the BNR samples contain benzene homologues and polycyclic aromatic hydrocarbons(PAHs),but no bromobenzene.With the increasing of bromine content,the 2-methyl-1,3-butadiene content in the BNR cleavage product is gradually reduced until it disappears;the content of cyclic olefins and aromatic compound increase gradually.When the temperature rises,in the system,the content of toluene and benzene homologues increases,and PAHs was greatly reduced.The main chain structure of NR changed in the brominated process,and may be accompanied by the cyclization reaction,six-membered ring may present in the BNR molecular chain.The results of FTTR and 1H-NMR indicated that the bromide substitution reaction and the addition reaction were happened in the bromide reaction process of NR HBr,which was a substitution product,was the main addition reactant;and because of the high reaction rate,the bromide substitution reaction happened preferentially;because of the amount of HBr was large,the addition reaction was happened largely.The fact that Br2 react with the double bone in the NR molecular chain was not found.The active intermediate of substitution and addition reaction can involve in the formation of the ring,which lead to the increasing of the gel content.Carboxyl wasn't existed in the molecular chain of BNR sample.The reaction order of bromine reaction at 15? was 0.9564;the reaction rate constant was 2.0788.The reaction order of bromine reaction at 25 ? was 0.9639;the reaction rate constant was 1.0957.The reaction activation energy of the system was-45.7kJ/mol.The low temperature appropriate was good for the proceeding of the bromine reaction at high degree of bromine content.The gel content of bromine products,which were prepared from low molecular weight natural latex,was dramatically declined at high degree of bromine content,solubility property was improved greatly.The complexity of the gel content reflected the complexity of the bromine reaction.