Natural rubber-graft-methyl

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

These groups can then be used to initiate grafting by any of the methods already discussed. Latex phase grafting is generally favored for its simplicity natural rubber grafts with methyl methacrylate styrene, acrylonitrile, and vinyl chloride have been made in this way (Cockbain et al., 1959). 

The properties of, say, natural rubber grafted with poly(methyl methacrylate) cannot be evaluated unless the copolymer is isolated from either homopolymer species. The methods used are based on fractional precipitation, selective solution, or a combination of these basic techniques. For details, refer to Chapter 3. In many cases, though, technologists are concerned with the materials as manufactured, so we consider in this context also the properties of the block and graft copolymers without homopolymer removed. 

When block and graft copolymers are dispersed in solvents, the solutions have properties that depend on whether or not the copolymer is eventually fully solvated. If the solvent is a good solvent for both sequences—for example, chloroform in the case of natural rubber graft copolymerized with poly(methyl methacrylate) (Halasa et al., 1976)—then both segment types are expanded and films cast from dilute solutions will usually be intermediate in properties to the... 

Meier [23] has derived equations relating block copolymer morphology to thermodynamics using lattice models. His model explains quantitatively the observations of Merrett [24] on the influence of preferential solvents on the mechanical properties of graft copolymers. Merrett found that, depending on the solvent used in casting films of a natural rubber/poly(methyl methacrylate) graft copolymer, he could obtain either a hard stiff film characteristic of poly(methyl methacrylate) or a soft, flexible film typical of natural rubber. He interpreted these results as follows a solvent for poly(methyl methacrylate) collapsed the... 

The preparation of natural rubber-gra/t-methyl methacrylic acid has been reported by Lenka and coworkers. The vanadium ion was used as an initiator, which initiated the creation of free radicals on the backbone of natural rubber and this increased the interaction between the natural rubber and the methyl methacrylate surfaces. The coordination complexes derived from the acetylacetonate of Mn(III) ions could also be used as an initiator to form the natural rubber-gra/t-methyl methacrylic acid. Under different conditions, silver ions could be used as a catalyst to produce natural rubber-gra/t-methyl methacrylic acid with different concentrations of methyl methacrylic acid monomers, and potassium peroxydisulfate as an initiator. Consequently, these methods were successful in the preparation of compatible blended natural rubber and methyl methacrylic acid by graft copolymerization. This compatibility was confirmed by nuclear magnetic resonance and infrared spectroscopy techniques. The interaction between natural rubber and methyl methacrylic acid was significantly increased and was useful for further blending with other polyacrylate molecules or different polymer types. 

The poly(methyl methacrylate) molecules were dispersed in the natural rubber matrix, or vice versa, to form spherical droplets, as observed by optical photographs or scanning electron microscopy. The compatible natural rubber/poly(methyl methacrylate) blends had been made by the addition of the graft copolymer of natural rubber-gr t-poly(methyl methacrylate) as the compatibilizing agent due to its ability to enhance the interfacial adhesion between the two homopolymers. Moreover, Nakasorn and coworkers reported that natural rubber-gr i -poly(methyl methacrylate) could be blended with poly(methyl methacrylate) via a dynamic vulcanization technique with a conventional sulfur vulcanization system. The natural rubber-gra/t-poly(methyl methacrylate) was synthesized by a semi-batch emulsion polymerization technique via different bipolar redox initiation systems, i.e. cumene hydroperoxide and tetraethylene pentamine. ... 

Figure 13.5 Fracture scanning electron micrographs of grafted natural rubber/poly-(methyl methacrylate) blends at the ratios of (a) 70/30 (b) 60/40 (c) 50/50 in low (top) and high (bottom) levels of grafting amount.

The Mooney viscosity value of the maleated natural rubbers/poly(methyl methacrylate) blends increased with an increased concentration of maleic anhydride used in the grafting copolymerization. The shear flow property of the... 

From these studies, it was concluded that several natural rubber/poly(methyl methacrylate) blends were compatible when the interactions between the immiscible phases such as graft copolymer as the compatibilizer was increased, and their viscosity behaviour also changed. 

Coextrusion of chloroprene and EPDM rubbers has given graft copolymers containing 7% chloroprene units [141a]. Mastication of extracted natural rubber with methyl methacrylate in an extruder gives a relatively high conversion of monomers, more than 60%, and the formation of a modified rubber [141]. 

Natural Rubber Grafted with Methyl Methacrylate (Heveaplus MG)... 

Oommen Z, Groeninckx G, Thomas S. Dynamic mechanical and thermal properties of physically compatibilized natural rubber/poly(methyl methacrylate) blends by the addition of natural rubber-graft-poly(methyl methacrylate). J Polym Sci B Polym Phys 2000 38(4) 525-36. 

ATBN - amine terminated nitrile rubber X - Flory Huggins interaction parameter CPE - carboxylated polyethylene d - width at half height of the copolymer profile given by Kuhn statistical segment length DMAE - dimethyl amino ethanol r - interfacial tension reduction d - particle size reduction DSC - differential scanning calorimetry EMA - ethylene methyl acrylate copolymer ENR - epoxidized natural rubber EOR - ethylene olefin rubber EPDM - ethylene propylene diene monomer EPM - ethylene propylene monomer rubber EPR - ethylene propylene rubber EPR-g-SA - succinic anhydride grafted ethylene propylene rubber... 

The polymerization of vinyl monomers in the presence of natural rubber, which is also an unsaturated polymer, has been examined initially by Le Bras and Compagnon (67, 740, 141). Jacobson (118) described graft copolymers of rubber latex with methyl methacrylate, styrene, acrylonitrile, etc. 

Similarly Cooper and Vaughan described high yields of graft copolymer, even at relatively high monomer concentration, in the system natural rubber-methyl methacrylate (70). It was found that nearly all... 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Menon, C. C., and S. L. Kapur Graft polymerization of methyl methacrylate with natural rubber in emulsion. J. Appl. Polymer Sci. 1, 372 (1959). 

The direct radiation grafting of vinyl monomers to natural rubber latex was studied by two groups of workers. Cockbain et a . (1958,1959) grafted methyl methaciylaie using both y radiation and a chemical redox system. 

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