Polymer rubber-like

Rubbers exhibit these properties because unlike conventional solids, which are comprised of atoms that occupy fixed positions relative to each other, they are formed from molecules that are arranged to form a flexible, long-chain macromolecule or polymer. While not all polymers are rubber-like, all rubbers are polymeric. The characteristic that makes a polymer rubber-like is its ability to undergo rapid molecular movement, allowing it to deform readily, and the ability of the molecule to return to its original configuration after the deforming forces have been removed. A number of qualities are necessary for attainment of rubber-like properties. 

As it was noted above, the cluster model [18,23] explains two more features of glassy polymers behavior on cold flow plateau. An experimentally observed high values are due to high values v j, which are about of order larger than Vj [23] and glassy polymer rubber-like behavior on the indieated plateau is due to loosely packed matrix rubber-like state. 

An interestii observation has been made in the work (96) to the effect that Kemet s equation is not sufficiently reliable for a complex stem a glass4ike polymer-rubber-like-filler-glass beads. In this case the best results can be obtained if the systems are conridered as a sin phase of a glass-like po mer with rubber in which glass beads are dispersed. Then the modulus of the me m is first calculated as a system filled with a polymeric filler, following which the calculated value is used for the evaluation of the composite material. 

CH = CH — CH = CH — are said to have conjugated double bonds and react somewhat differently from the other diolefins. For instance, bromine or hydrogen is often added so that a product of the type -CHBr-CH=CH-CHBr- is formed. Also, these hydrocarbons participate in the Diels-Alder reaction see diene reactions). They show a tendency to form rubber-like polymers. Hydrocarbons not falling into these two classes are said to have isolated double... 

A typical example is total monomers. 100 sodium stearate, 5 potassium persulfate, 0.3 lauryl mercaptan, 0.4 to 0.7 and water, 200 parts. In this formula, 75 parts of 1,3-butadiene and 25 parts of 4-methyl-2-vinylthiazole give 86% conversion to a tacky rubber-like copolymer in 15 hr at 45°C. The polymer contains 62% benzene-insoluble gel. Sulfur analysis indicates that the polymer contains 21 parts of combined 4-methyl-2-vinylthiazole (312). Butadiene alone in the above reaction normally requires 25 hr to achieve the same conversion, thus illustrating the acceleration due to the presence of 4-methyl-2-vinylthiazole. 

This is because rubber, like many polymers, is composed of long spaghetti-like chains of carbon atoms, all tangled together as we showed in Chapter 5. In the case of rubber, the chains are also lightly cross-linked, as shown in Fig. 5.10. There are covalent bonds along the carbon chain, and where there are occasional cross-links. These are very stiff, but they contribute very little to the overall modulus because when you load the structure it is the flabby Van der Waals bonds between the chains which stretch, and it is these which determine the modulus. 

As pointed out earlier, acrylics differ from the commonly used rubber precursors for PSA formulation in the fact that they often incorporate polar monomers, such as acrylic acid, A-vinyl pyrrolidone, vinyl acetate, or acrylamide. As a result, the solubility parameters of acrylic polymers are typically higher than those of rubbers, like polyisoprenes or polybutadienes. 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives. In the early 1920s, Dr. Nieuwland of the University of Notre Dame synthesized divinyl acetylene from acetylene using copper(l) chloride as catalyst. A few years later, Du Pont scientists joined Dr. Nieuwland s research and prepared monovinyl acetylene, from which, by controlled reaction with hydrochloric acid, the chloroprene monomer (2-chloro-l, 3-butadiene) was obtained. Upon polymerization of chloroprene a rubber-like polymer was obtained. In 1932 it was commercialized under the tradename DuPrene which was changed to Neoprene by DuPont de Nemours in 1936. 

Mark, J. E. The Use of Model Polymer Networks to Elucidate Molecular Aspects of Rubber like Elasticity. Vol. 44, pp. 1-26. 

Synthesis of hydrolytically stable siloxane-urethanes by the melt reaction of organo-hydroxy terminated siloxane oligomers with various diisocyanates have been reported i97,i98) -yhg polymers obtained by this route are reported to be soluble in cresol and displayed rubber-like properties. However the molecular weights obtained were not very high. A later report56) described the use of hydroxybutyl terminated disiloxanes in the synthesis of poly(urethane-siloxanes). No data on the characterization of the copolymers have been given. However, from our independent kinetic and synthetic studies on the same system 199), unfortunately, it is clear that these types of materials do not result in well defined multiphase copolymers. The use of low molecular weight hydroxypropyl-terminated siloxanes in the synthesis of siloxane-urethane type structures has also been reported 198). 

Analytical techniques used in troubleshooting and formulation experimentation available to the rubber compounder were reviewed [90]. Various textbooks deal with the analysis of rubber and rubber-like polymers [10,38,91]. Forrest [38] has illustrated the use of wet chemistry, spectroscopic, chromatographic, thermal, elemental and microscopy techniques in rubber analysis. 

M.J.R. Loadman, Analysis of Rubber and Rubber-like Polymers, Kluwer Academic Publishers, Dordrecht (1999). 

Triblock copolymers, as shown in Fig. 5.8 d), comprise a central homopolymer block of one type, the ends of which are attached to homopolymer chains of another type. As with other block copolymers, the components of triblocks may be compatible or incompatible, which will strongly influence their properties. Of particular interest are triblocks with incompatible sequences, the middle block of which is rubbery, and the end blocks of which are glassy and form the minor phase. When such polymers phase-segregate, it is possible for the end blocks of a single molecule to be incorporated into separate domains. Thus, a number of rubbery mid-block chains connect the glassy phases to one another. These materials display rubber-like properties, with the glassy domains acting as physical crosslinks. Examples of such materials are polystyrene/isoprene/polystyrene and polystyrene/polybutadiene/polystyrene triblock copolymers. 

Here we describe the strain history with the Finger strain tensor C 1(t t ) as proposed by Lodge [55] in his rubber-like liquid theory. This equation was found to describe the stress in deforming polymer melts as long as the strains are small (second strain invariant below about 3 [56] ). The permanent contribution GcC 1 (r t0) has to be added for a linear viscoelastic solid only. C 1(t t0) is the strain between the stress free state t0 and the instantaneous state t. Other strain measures or a combination of strain tensors, as discussed in detail by Larson [57], might also be appropriate and will be considered in future studies. A combination of Finger C 1(t t ) and Cauchy C(t /. ) strain tensors is known to express the finite second normal stress difference in shear, for instance. 

J.E. Mark and B. Erman, Molecular aspects of rubber-like elasticity. In R.F.T. Stepto (Ed.), Polymer Networks, Blackie Academic, Chapman Hall, Glasgow, 1998. 

JThe effect of the substituent on the properties of the polyphosphazenes is not fully understood. For instance, [NP(OCH ) ]n and [NP C CH. homopolymers are elastomers (8,29). Synthesis using lithium, in contrast to sodium, salts is claimed to produce rubber-like fluoroalkoxyphosphazene polymers (30). The presence of unreacted chlorine or low molecular weight oligomers can affect the bulk properties (31,32). Studies with phosphazene copolymers both in solution and in the bulk state (29,33-38) indicate a rather complex structure, which points out the need for additional work on the chain structure and morphology of these polymers. 

Also termed glass temperature or Tg. The temperature at which the stiffness of an elastomer subjected to low temperatures changes most rapidly. If the glass temperature is close to the operational temperature the material will be leathery in its behaviour rather than rubber-like. Approximate glass transition temperatures for different polymers are NR -70 °C SBR -52 °C HR -75 °C PCP -40 °C and silicone rubber -85 °C. 

Polymerised isobutylene, a non-vulcanisable, rubber-like polymer. See Butyl Rubber. Polyisoprene... 

Rubber-like materials now superseding the traditional mastics and putties used in the building industry. Such sealants (also termed mastics) are based on butyl rubber, liquid polysulphides, silicone rubbers, polybutylene, nitrile rubbers and plasticised vinyl polymers. SEBS... 

That particular combination of properties possessed by high polymers, characterising the rubber-like state. Depending on the temperature and the time of stressing, a high polymer may show viscous flow or high elasticity. See Elasticity, Glass Transition, Thixotropy and Viscosity. 

Mo2(0R)6 compounds in hydrocarbon solvents rapidly polymerize acetylene to a black metallic-looking form of polyacetylene. Propyne is polymerized to a yellow powder, while but-2-yne yields a gelatinous rubber-like material (45). The detailed nature of these polymers is not yet known and the only molybdenum containing compounds recovered from these polymerization reactions were the Mo2(0R)6 compounds. When the reactions were carried out in the presence of pyridine/hexane solvent mixtures, simple adducts Mo2(0R)6(py)2(ac) were isolated for R = i-Pr and CH2-t-Bu, and ac = HCCH, MeCCH and MeCCMe (45,46). 

Polymers having average Molecular weight of 15000 are sticky viscous liquids but those with Molecular weight 1,00,000 to 2,00,000 are rubber like. It is soluble in hydrocarbon and halogenated hydrocarbon solvents at room temperature. It is largely used as adhesive, for fibre and paper coating, etc. 

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