Rubber polymer-bound

Radiation chemistry in polymer research, 168-169 Reactive macroalkyl radicals, formation, 409 Reactive modifiers addition of reactive antioxidants on rubbers, 417 adhesion, 420,422 demanding applications, 414,416 improving additive performance during melt processing, 412 polymer bound antioxidant, 418-419/ Reduced poly(vinyl chloride),... 

Bound rubber - The bound rubber content was measured with toluene as solvent [48,49]. The nonvulcanized samples (0.2 g) were cut into small pieces and put into a steel-wire basket of very fine mesh, which was immersed in 100 mL of toluene at room temperature for 72 h. The solvent was renewed after 24 h. The extracts were collected and left for 24 h in air and 24 h in vacuo at 105°C to evaporate the solvent. The amount of bound rubber (BdR) is expressed as the percentage of the total polymer content in the compound. 

PB. Sulekha, R. Joseph, and K.E. George, Studies on polyisobutylene bound paraphenylene diamine antioxidant in natural rubber, Polym. Degrad. Stab., 63(2) 225-230, February 1999. 

Propellants include both rocket and gun propellants. Most rocket propellants are either Hazard Class 1.3 composites, which are based on a rubber binder, and ammonium perchlorate (AP) oxidizer, and a powdered aluminum (Al) fuel or Hazard Class 1.1 composites, which are based on a nitrate ester, usually nitroglycerine (NG), nitrocellulose (NC), HMX, AP, or polymer-bound NC. If a binder is used, it usually is an isocyanate-cured polyester or polyether. Some propellants contain combustion modifiers, such as lead oxide. 

Reactivity With Nitroso Compounds. Functionalization of diene based rubbers with aromatic nitroso compounds bearing aminic or phenolic moieties 174, like with iV,A-diethyl-4-nitrosoaniline, 4-nitrosodiphenylamine, 4-nitrosodiphenylhy-droxylamine or 4-nitrosophenol represents an effective way for the synthesis of polymer-bound antioxidants [233], The respective nitroso compound can be mixed with rubbers during compounding or with concentrated rubber latexes. The chemical attachement of stabilizing active moieties takes place during subsequent... 

Testing procedure. Small pieces of uncured rubber are immersed for several days at room temperature in a large excess of good solvent such as toluene. The sample in contact with solvent becomes divided into three parts polymer solution, mpi, solvent-dispersed filler particles with absorbed polymer chains, mpu, and solvent-swollen gel of filler particles connected through polymer chains, mpm. The fraction of polymer bound to filler is determined from the equation B = ( m 4- m m p where mp is total mass of polymer. The fraction of polymer not dispersed by solvent is given by the following equation G = m / m p. 

It is concluded that the modification of rubbers after manufacture with chemically reactive antioxidants offers the most promising procedure for producing concentrates of polymer-bound antioxidants that can be used as conventional additives. 

Reactions of Antioxidants with Polymers During Processing. One of the earliest polymer-bound antioxidants was obtained by reaction of nitroso antioxidants (ANO) with rubbers during vulcanization (29). The chemistry of this process is complex, but its discoverers proposed an "ene" reaction with the unsaturation in the polymer. 

Table 11 compares the effectiveness of a synergistic UV stabilizer (BHBM-B + EBHPT-B) with some commercial stabilizing systems for ABS added conventionally. The exceptional activity of the polymer-bound system is believed to be due to the fact that it is confined to the rubber phase of the polyblend (18), which is known to be more sensitive than the thermoplastic phase to the effects of both heat and light (36). This finding, if confirmed in other multiphase systems, could be of considerable importance for the stabilization of heterogeneous polymer blends. 

Macromolecular stabilizers are immobile in the polymer matrix [284], This is unfavourable for applications where surface concentration of stabilizers in thick-walled products should remain high. It was reported [34] that rubber-bound derivatives of PD provide only very poor antiozonant protection. Their antioxidant efficiency was only comparable with that of conventional HMW PD. This indicates that application of polymer-bound amines in rubbers has the prospect of exclusive long-term use in extracting media. 

Polymer-bound amines are of specific importance in multiphase systems where partitioning of migratable stabilizers may diminish the stability of more sensitive phases. System 193 representing a matrix and rubber-phase bound amine in acry-lonitrile/EPDM/styrene terpolymer is an example [297]. The superior performance was obtained when the migratable monomer 192 was melt-blended into the HAS-functionalized multiphase system 193. 

The effect of the solid body surface on the structure of the polymer boundary layers has been considered in detail in a great number of publications and we will not consider this issue in detail. We point out only that a number of publications have reported correlation between the structure of the bound lIy layer and the adhesion strength for couples such as metal-polycapro lmide coating [33], fluoroplastic-steel [34], and epoxy rubber polymers-metals [35]. 

This issue of specific surface area hints at how one might change the nature of reinforcement. In typical micro- and macrocomposites, the properties are dictated by the bulk properties of both the matrix and the flUer. This relationship between the properties of the composite and the properties of the filler is what leads to the stiffening and degraded elongation mentioned earlier. In the case of nanocomposites, the properties of the material are instead tied to the interface. Terms like bound polymer, bound rubber, and interphase have been used to describe the polymer at or near the interface, where significant deviations from bulk structure and properties are known to occur (Fig. 6.2). 

Polymerizetble in emulsion, solution, and bulk/suspenslon systems. Functions in all free radical polymerizations. AZO initiators are preferred. May be incorporated at conventional levels in the total polymer, added as a masterbatch when polymerized at a high concentration, or grafted into polymers. Masterbatches may be used for dry rubber or latex compounding. Synergizes with secondary antioxidants. When polymer bound, it is non-volatile, non-extractable, non-migratory, and non-staining. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

The new interface model and the concept for the carbon black reinforcement proposed by the author fundamentally combine the structure of the carbon gel (bound mbber) with the mechanical behavior of the filled system, based on the stress analysis (FEM). As shown in Figure 18.6, the new model has a double-layer stmcture of bound rubber, consisting of the inner polymer layer of the glassy state (glassy hard or GH layer) and the outer polymer layer (sticky hard or SH layer). Molecular motion is strictly constrained in the GH layer and considerably constrained in the SH layer compared with unfilled rubber vulcanizate. Figure 18.7 is the more detailed representation to show molecular packing in both layers according to their molecular mobility estimated from the pulsed-NMR measurement. 

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