Preparation of a natural rubber core/polymer shell in a nanomatrix by graft copolymerization

Abstract

The grafting of a vinyl monomer, methyl methacrylate (MMA) or styrene (ST), onto a natural rubber (NR) exhibited a core-shell structure, with NR as the core and poly(methyl methacrylate) or polystyrene as the shell. The grafting efficiency (GE) of the graft copolymer was determined by a solvent-extraction technique. The synthesized graft copolymer was purified and then characterized by Fourier transform infrared spectroscopy analysis. The effects of the graft parameters, including time, initiator content, and concentration, and the type of monomer, MMA or ST, were investigated. A longer time was favorable for the graft copolymerization. GE first increased and then decreased with increasing concentration of initiator. GE decreased with increasing monomer content, and it was confirmed that the graft copolymerization was a surface-controlled process. The grafting ST monomer had a higher GE compared to MMA under the same conditions. The characterization of the particles by transmission electron microscopy and scanning electron microscopy confirmed the formation of a core-shell structure. From the micrographs, we inferred that at 71% GE, the NR seed particle had a complete closed shell several nanometers in thickness. Therefore, the NR particle was dispersed in a polymer nanomatrix.

From a laboratory to a pilot scale production of natural rubber grafted with PMMA

“…The solid samples of graft copolymers for the analysis of free homopolymers (free NR and free PMMA) and grafting efficiently were obtained by coagulating the graft copolymer latex with 10% CaCl 2 , washing with deionized water until neutral, and finally drying in a hot air oven at 40°C for 24 h. Soxhlet extraction method, which has been widely applied to determine the ungrafted NR and PMMA,11, 18, 21 was used in this work. The Soxhlet extraction of pure NR, which was coagulated from the concentrated NR latex before being used for graft copolymerization, by using light petroleum ether revealed that the NR molecules were completely soluble, i.e., no residue left after the extraction.…”

“…Graft copolymers of NR with various types of vinyl monomers, e.g., styrene,3–5 acrylonitrile,6 dimethylaminoethyl methacrylate,7, 8 and methyl methacrylate (MMA)9–21 have been investigated. Graft copolymerization of MMA onto NR molecule has been performed by free radical polymerization either in solution or in latex states using various initiator systems including thermal initiators, such as benzoyl peroxide,10 potassium persulfate,13 and redox initiators,11, 12, 14, 16–21 e.g. cumene hydroperoxide/tetraethylene pentamine (CHP/TEPA), tert ‐butyl hydro‐peroxide/tetraethylene pentamine ( tert ‐BuHP/TEPA), or potassium persulfate/sodium thiosulfate (K 2 S 2 O 8 /Na 2 S 2 O 3 ).…”

“…cumene hydroperoxide/tetraethylene pentamine (CHP/TEPA), tert ‐butyl hydro‐peroxide/tetraethylene pentamine ( tert ‐BuHP/TEPA), or potassium persulfate/sodium thiosulfate (K 2 S 2 O 8 /Na 2 S 2 O 3 ). The CHP/TEPA was found to be the most effective redox initiating system18 and has been widely applied to prepare the graft copolymers of NR and MMA 16, 19, 21. The graft copolymer of NR and MMA exhibits the improved polarity, hardness, toughness, and oxidation resistance 13, 15, 18.…”

“…The investigations of NR‐ g ‐PMMA in various aspects are normally carried out using the products obtained from a laboratory scale production 9–21. Even though this material is commercialized, such as by Akrochem (USA) and Regitex (Japan), the open discussion on a pilot scale production is very limited.…”

Synthesis of styrene‐g‐polyisoprene nanoparticles by emulsion polymerization and its effect on properties of polyisoprene composites

“…The weight of both the initial samples and the extracted samples were measured for the determination of the grafted PIP (%), free PS (%), and ungrafted PIP (%). The GE (%) was estimated using the following equation: …”