A novel method was applied to study the topological and molecular structures of multicomponent rubber. This method is based on the thermomechanical analysis of a solid polymer. A diblock amorphous structure was found for the studied rubber network. These blocks differ a great deal in their glass transition temperature. The methodology of how to calculate the crosslink density in each block, the molecular weight distribution of the chains between the junctions of the network, and the shares of low-temperature (soft) and high-temperature (hard) blocks in a structure of the rubber network were also shown. Based on these data it is possible to calculate the number-average and weight-average molecular weight and the polydispersity coefficients of the chains between the junctions of the network.
Addition of fullerene in concentration between 0.065 and 0.75 phr increases Schob elasticity, hardness, and modulus of NR-based rubber. There is no substantial influence of fullerene on T g , tan ␦, and G-modulus all evaluated by DMA at twisting within a temperature range Ϫ150 to Ϫ50°C (glassy state). At temperatures between 0 and 150°C (rubbery state) it is different, namely an increase in modulus and some changes in the slope of segments in G(T) curves were observed. It could be resulted from additional strong physical junctions of the rubber network. This suggests the growth of degradation energies of the branching junctions and related rise in the aging resistance as concentration of fullerene increases. Simultaneously, it could be expected some reduction of tire temperature at service. Because of this, introduction of fullerene could be reasonable for tread rubbers in case of reduction of its price. Permittivity and dielectric loss angle are correlated with fullerene concentration. Compounding technology when fullerene dispersed within carbon black is mixed with raw rubber on available machines could be easily implemented in the industry.
A novel method is used to study topological and molecular structure of different kinds of sulfur (mineral and two polymeric types). It is based on thermomechanical analysis of solid (not dissolved) polymer. It was found that a deep difference in their molecular weight distributions and in their crystallinity degrees exist. Both mineral and polymeric sulfur have polymer nature.
Static and dynamic mixers set on the Brabender plastograph were used to investigate the grafting of itaconic acid (IA) onto low-density polyethylene (LDPE) by the reactive extrusion. The initiators of free-radical reactions were monoperoxide 2,5-dimethyl-2-hydroxy-5-tert-butylperoxy-3-hexyne and diperoxide 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane. The reaction mix contained stabilizers of phenolic type as follows: 2,6-ditertbutyl-4-methyl phenol; ester of 3,5-ditert-butyl-4-hydroxyphenyl-propanoic acid and pentaerythritol; 4-alkoxy-2-hydroxy-benzophenone; and 1,4-dihydroxybenzene. The effect of stabilizers, which follow the radical mechanism on the grafting of IA and on the crosslinking, depends on their solubility in the polymer and the monomer. The stabilizers (e.g., 1,4-dihydroxybenzene) with increased affinity toward the monomer reduce the grafting yield and inhibit crosslinking. At 0.3-0.5 wt % of the stabilizer insoluble in the monomer, the grafting yield can be increased, while inhibiting the LDPE-g-IA crosslinking, irrespective of the peroxide used. Hence, classical stabilizers can initiate grafting reactions at raised concentrations, temperatures, and application of the shearing stresses. They also help to obtain a high-grafting yield and a reduced crosslinking degree. A stabilizer, having a close affinity toward LDPE, influences the LDPE-g-IA structure. The stabilizer content of 0.5 wt % transforms the topological structure of LDPE-g-IA into uniblock. Its molecular weight distribution (MWD) may be narrow (M n /M w Ͻ 2) or broad (M n /M w Ͼ 2), depending on the concentration of the initiator used.
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