Synthesis And Characterization Of Natural Rubber Grafted With2-Hydroxyethyl Methacrylate

By grafting polar monomer onto natural rubber (NR), the adhesion between naturalrubber and polar materials such as wood, glass and metal, can be significantly improved, andthe application of natural rubber can be greatly extended. In this paper, natural rubber graftedwith2-hydroxyethyl methacrylate (NR-g-HEMA) was synthesized by solution and emulsionmethod, respectively. Effects of the kind and amount of initiator system, the amount ofHEMA and NR concentration, reaction temperature and time on the monomer conversion,grafting ratio and grafting efficiency were investigated. Effects of mastification time of NR,co-monomer and additive on the grafting reaction by solution method, and effects of themonomer dropping time on the grafting reaction by emulsion method were investigated;respectively.The mechanism of grafting reaction was discussed.When the solution method was used to synthesize NR-g-HEMA, the initiator BPO hadhigher monomer conversion, grafting ratio and grafting efficiency than those of AIBN. Thegrafting ratio increased as the amount of BPO and HEMA increasing, and then became flatwhen the amount of BPO was greater than3%. Reaction temperature significantly affectedthe reaction of HEMA grafted onto NR. The grafting ratio increased when the reaction timeincreasing, and then became flat after the reaction time reached4h. The mastication of NRcould promote the grafting reaction, monomer conversion, grafting ratio and graftingefficiency increased as the mastication time increasing. Since HEMA has the high reactivity,the use of co-monomer St, MMA or VAc and additive TPP, DMF, could not increase graftingratio of the reaction in the solution method. Suitable grafting conditions were as follows: theamount of BPO was3%, the amount of HEMA was30%, the NR concentration was12%,reaction temperature was80℃, reaction time was4h, and NR mastification time was30min,the grafting ratio of NR-g-HEMA reached16%at the condition.When the emulsion method was used to synthesize NR-g-HEMA, the water-solubleredox initiator system KPS/SHS had higher monomer conversion, grafting ratio and graftingefficiency than those of the thermal initiator KPS, oil-soluble redox initiator systemCHP/TEPA and t-BHP/TEPA. The grafting ratio increased when the amount of KPS/SHS andHEMA increasing, then became flat when the amount of KPS/SHS was greater than3%, andthe suitable molar ratio of KPS: SHS was1:1. When the latex concentration or reactiontemperature increased, monomer conversion, grafting ratio and grafting efficiency trended toincrease first and then decrease. When the reaction time or monomer dropping time increased,monomer conversion, grafting ratio and grafting efficiency increased first and then little changed. Suitable grafting conditions were as follows: the amount of KPS/SHS was3%, themolar ratio of KPS and SHS was1:1, the amount of HEMA was10%, latex concentration was30%, reaction time was3h, reaction temperature was50℃, monomer dropping time was1h,the grafting ratio of NR-g-HEMA reached7%.FT-IR and GPC were used to characterize the grafting product, it was confirmed thatHEMA were grafted onto NR chains both throught solution and emulsion method. the relativemolecule weight of the graft product was lower than that of NR, and increased as the amountof HEMA increasing. When used the emulsion method, the degradation of the graftingproduct was lower than that of solution method.