| Due to its low ceiling polymerization temperature caused by the steric hindrance and conjugation effects, a-methylstyrene (AMS) is unlikely to obtain high molecular weight homopolymer via radical polymerization mechanism. However, the copolymerization of AMS with other monomers can be carried out readily. Copolymers consisting of AMS structural units, such as the copolymers of AMS with butyl methacrylate (BMA) and glycidyl methacrylate (GMA) have been synthesized in this thesis. Based on the thermal decomposition of AMS copolymers, the copolymers containing AMS structural units can be applied as macroinitiators. The results have demonstrated that AMS-containing copolymers could initiate the cross-linking reaction of unsaturated rubbers.In the first part, the effects of AMS molar fraction in copolymer and AMS-containing copolymer content on the gel content of rubber have been investigated in details. With the increase of AMS fraction in copolymer, the gel content of crosslinked rubber increased at the beginning and then decreased. The highest gel content of emulsion polymerized styrene butadiene rubber (ESBR) can be up to about 59.9%with 15.8% AMS structural unit in the copolymer. The results showed that AMS copolymer content can be used to prepare rubbers with different degree of crosslinking. Furthermore, with AMS-containing copolymers as curing agent, different types of rubbers present different curing extent. When AMS-containing copolymer was used as crosslinker,ethylene propylene diene monomer (EPDM) and polyisoprene rubber (IR)could not be crosslinked, natural rubber (NR), cis-polybutadiene (BR),nitrile butadiene rubber (NBR) and ESBR could be crosslinked, and the gel content of crosslinked rubber was 25.7%, 40.1%, 53.1% and 59.9%,respectively. The study indicated that the cross-linking effects of AMS-containing copolymer as curing agent on different fillers were obviously different. With carbon black as filler, the green rubber could not be crosslinked. While silica was used as filler, the green rubber could be efficiently crosslinked. In general, taking AMS-containing copolymer as curing agent, it has simple formula and no small molecular residues while offering the mechanical stability for rubber materials. These merits endow AMS-containing copolymers as a novel type of curing agent in rubber industry.The second part is the preparation of NBR/polypropylene (PP)thermoplastic vulcanizate (TPV) with AMS-containing copolymer as curing agent. Firstly, the NBR/PP TPV was prepared with different processes. Then the properties of the as-prepared TPVs were characterized by mechanical tensile test, differential scanning calorimetry(DSC), swelling test and shore hardness. The study on NBR/PP TPVs prepared by two-step process demonstrated that the curing reaction rate of NBR was accelerated. The phenomenon showed that the tensile strength of TPVs was decreased from 6.75 MPa (NBR/PP=50/50) to 1.09 MPa(NBR/PP=80/20). The elongations at break of the TPVs prepared by one-step process in Haake mixer are higher than that of the TPVs prepared by two-step process. With the increase of NBR/PP ratio, the elongation at break of TPVs rose from 128.6% (NBR/PP=50/50) to 331.1%(NBR/PP=80/20). The NBR/PP TPVs prepared by a twin-screw extruder exhibited high tensile strength and low elongation at break at low NBR/PP ratios. But at high NBR/PP ratios, the TPVs exhibited low tensile strength and high elongation at break. Specifically, with the increase of NBR/PP ratio among all NBR/PP TPVs in this study, the crystallinity of PP and the shore hardness of TPV decreased, the swelling index of TPV increased. |
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