Research On Preparation Of Liquid Natural Rubber By Oxidation

Liquid natural rubber(LNR), as a new developing polymer material, is a kind of low molecular weight functional polymer, which is widely used in the fields of industry, agriculture, aviation, aerospace and so on. Now the research of the preparation method of LNR is a hot topic in the rubber industry production.Preparation of LNR by using direct oxidation, phase transfer catalytic oxidation and microwave radiation oxidation respectively was investigated with NR film as raw material and potassium permanganate as oxidant. The influence of heating method, p H, amount of oxidant, reaction temperature and reaction time on molecular weight and yield of LNR was discussed by single factor experiment and orthogonal experiment to determine the optimum reaction conditions. Then, the structure of LNR was analyzed by infrared spectrum and nuclear magnetic resonance. The results showed that the right solvent is toluene and NR concentration is 2.8%. The optimum reaction conditions of direct oxidation were 0.005 mol KMn O4, p H 4, 35 ℃ and 4 h by direct oxidation, the molecular weight of LNR was 4125, and the yield was 77.67%. The optimum conditions of phase transfer catalytic oxidation were 0.004 mol KMn O4, p H 4, 2% CTMAB, 35 ℃ and 3 h, the molecular weight of LNR was 4347 and the yield was 84.36%. The optimum conditions of microwave radiation oxidation were 0.006 mol KMn O4, p H 9, 500 W, and 12 min, the molecular weight of LNR was 5309 and the yield was 85.73%.Infrared spectrum and nuclear magnetic resonance were used for structural analysis of LNR. The results proved that the end group of LNR was carboxyl and carbonyl by direct oxidation, phase transfer catalytic oxidation. However, the epoxy group was existed in the molecular chain of LNR by phase transfer catalytic oxidation and microwave radiation oxidation. Dynamics calculation demonstrated that the mechanism of oxidation of NR film to prepare LNR could be described by secondary dynamic model.The comparative analysis of three oxidation methods indicated that the molecular weight of LNR were 4000~5000. Compared with the direct oxidation, the reaction time of preparing LNR by phase transfer catalytic oxidation shorten 1 h, the potassium permanganate dosage was reduced by 0.001 mol, the yield of LNR raised 6.67%. A further comparison shown that the reaction time was the shortest, only 12 min, and the yield of LNR highest by microwave radiation oxidation. Therefore, the phase transfer catalytic oxidation and microwave radiation oxidation were both the optimal preparation methods of LNR to meet the requirements of the development of green chemistry.