Mechanical behavior elastomers

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Mars, W.V. and Fatemi, A., A novel specimen for investigating the mechanical behavior of elastomers under multiaxial loading conditions, Exp. Mech., 44, 136, 2004. 

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

Hydroxy-terminated PDMS, however, has disadvantages. The monofunctional ends limit the number of connections between the polymer (or oligomer) molecule and the glass network to two. This limitation raises the possibility that some PDMS molecules are not tied at both ends to the glass network if the polycondensation does not go to completion i.e. there may be "dangling" or loose PDMS chains in the final sol-gel material. This occurance of free ends would indeed be anticipated since the extent of reaction most likely is not 100%. Hence, the physical properties, specifically the mechanical behavior of the overall material, would be expected to suffer as a result of loose PDMS chains in the system. Disregarding this potential problem, the mechanical behavior of the sol-gel hybrids are, ultimately, influenced by the mechanical behavior of the modifying elastomer ... 

S.3.2.3 Elastomers. In addition to the numerous ways we have grouped polymers (cf. Section 1.3.2), polymers can also be grouped according to mechanical behavior into the categories plastics, fibers, and elastomers. Though we will not elaborate upon... 

Figure 17 (69) shows the mechanical behavior of different synthetic elastomers. They were found to be generally less efficient than natural rubber in promoting polymerization because of reduced stress during mastication due to greater softening by monomer addition. Nitrile rubber crumbed with methyl methacrylate, styrene and acrylonitrile. 

Predictions of the mechanical response of filled elastomers are further aggravated by the phenomenon of strain dilatation. As soon as dilatation commences, the tensile stress lag behind elongation, the degree of dilatation for a given composite being roughly a measure for the deviation from the expected mechanical response. Dilatation increases with particle size and volume fraction of filler—it decreases somewhat if the filler is bonded to the matrix. Farris (16,17) showed that dilatation can account well for the mechanical behavior of solid propellants and his equation ... 

Their non-linear and often synergistic mechanical behavior which arises from their above mentioned multiphase morphology. Thus, both impact resistant plastics and thermoplastic elastomers have been bom. 

It can be thus summarized that a range of mechanical behavior can be generated by the appropriate choice of processing conditions, filler size, shape and concentration, and elastomer content and its distribution between the matrix and filler. These choices should lead to results predicted by theory. ... 

The relative amounts of the two monomers used in the synthesis determine the relative size of the two blocks or the composition of (BAB)X. This in turn determines whether mechanical behavior resembles that of thermoplastics or thermoplastic elastomers. The greater the polystyrene content, the greater the initial modulus and yield point of the block copolymer. Overall composition thus tends to dominate the parameters discussed above. At a given level of polystyrene the... 

While IPNs can be and have been made extremely tough and impact resistant, many of the proposed applications involve such diverse fields and sound and vibration damping, biomedical materials, and non-linear optics. This is because the presence of crosslinks in both polymers reduces creep and flow, allowing relatively stable materials with a wide range of moduli to be prepared. Thus, those materials with leathery mechanical behavior, combinations of elastomers and plastics, are especially interesting to scientists, inventors, and engineers. 

The ternary polymer blends based on PP, PA6 (or PA66), and elastomers have been studied worldwide during last several decades. Many researchers tried to well understand the compatibility, morphology, and mechanical behavior of such ternary polymer blends. The blend systems studied include PP/PA66/SEBS-g-MA (1-5), PP/PA6/EPR-g-MA (3-5), PP/PA6/PP-g-MA (6), PP/PA6/EPDM-g-MA (7), and so on. Since several years, a research group has begun research work on PP/PA6/ POE-g-MA blends (8-12). 

Mechanical Behavior. The ionomers, - poly[Isobutylene-co-(4-methyl styrenyl, triphenyl phosphonium bromide or tetraphenyl borate)] were found to be different in physical appearance(hard and strong) and tougher than the starting material, the Exxpro elastomer. The mechanical properties of these quaternary phosphonium... 

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