Study On Microstructure And Regulation Mechanism Of Brominated Butyl Rubber

Brominated butyl rubber(BIIR)has many bromination microstructures and side reactions in the bromination reaction.To adjust these structures to avoid side reactions,we have studied the bromobutyl rubber(BIIR)microscopic structure-activity relationships and methods for regulating different brominated structures by combining quantum chemical calculation methods with experiments.The Gaussian09 simulation software density functional theory was used to study the reaction paths and energy changes during the isomerization and dehydrobromination reactions of butyl rubber bromination.The TS+calcfc method was used to find the transition state of the isomerization reaction and the dehydrobromination reaction.The simulated transition state structure was subjected to the intrinsic reaction coordinate(IRC)operation.The model compounds of different structures were optimized by density functional theory.Its energy and frequency calculations verify the correctness of the transition state.The isomerization reaction was determined to be an advantageous reaction by comparing the transition state with the energy barrier of the reactant.To know the isomerization reaction history by calculating the molecular potential energy map of different structures in the isomerization reaction and the change of WBI bond level and bond length.The highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)of electrons in the course of chemical reaction and the orbital energy level difference(LU-HO)was calculated to find that the primary allyl bromide structure(structure III)is the lowest energy structure and the secondary allyl bromide structure(structure II)is a kinetic stable structure.The solvation effect of the model compound structure optimized by the B3LYP method was simulated using a polarized continuum model(PCM),and increasing the polarity of the solvent facilitated the isomerization reaction.The bromination microstructure and relative composition of BIIR were determined by proton nuclear magnetic resonance spectroscopy(1H-NMR),and bromobutyl rubber was characterized using gel permeation chromatography(GPC)and Mooney viscosity tester.The bromination reaction of IIR was investigated.Since the IIR bromination reaction is an ionic substitution reaction,the bromination free radicals are avoided in the light-proof manner to affect the bromination efficiency.The experiment investigated the factors affecting the bromination reaction,such as bromination reaction time,different bromine amount,different stirring methods,solvent polarity,etc.,and finally realized a brominated product with a bromine content of 1.8 wt%.The vulcanization rates of different brominated structures of BIIR were studied.The vulcanization experiments were carried out on samples containing different ratios of secondary and primary allylic bromide because of different kinetic stability of brominated structures.Experiments show that the sample with higher content of primary allylic bromide has a faster vulcanization rate,and the experimental results are in good agreement with the computer simulation results.