Polymer elastic

Polyacetaldehyde, a mbbery polymer with an acetal stmcture, was first discovered in 1936 (49,50). More recentiy, it has been shown that a white, nontacky, and highly elastic polymer can be formed by cationic polymerization using BF in Hquid ethylene (51). At temperatures below —75° C using anionic initiators, such as metal alkyls in a hydrocarbon solvent, a crystalline, isotactic polymer is obtained (52). This polymer also has an acetal [poly(oxymethylene)] stmcture. Molecular weights in the range of 800,000—3,000,000 have been reported. Polyacetaldehyde is unstable and depolymerizes in a few days to acetaldehyde. The methods used for stabilizing polyformaldehyde have not been successful with poly acetaldehyde and the polymer has no practical significance (see Acetalresins). 

Langley, N.R. and Polmanteer, K.E., Role of chain entanglements in rubber elasticity. Polym. Prep. Am. Chem. Soc. Div. Polym. Chem., 13(1), 235-240 (1972). 

Emulsion polymerization is the most important process for production of elastic polymers based on butadiene. Copolymers of butadiene with styrene and acrylonitrile have attained particular significance. Polymerized 2-chlorobutadiene is known as chloroprene rubber. Emulsion polymerization provides the advantage of running a low viscosity during the entire time of polymerization. Hence the temperature can easily be controlled. The polymerizate is formed as a latex similar to natural rubber latex. In this way the production of mixed lattices is relieved. The temperature of polymerization is usually 50°C. Low-temperature polymerization is carried out by the help of redox systems at a temperature of 5°C. This kind of polymerization leads to a higher amount of desired trans-1,4 structures instead of cis-1,4 structures. Chloroprene rubber from poly-2-chlorbutadiene is equally formed by emulsion polymerization. Chloroprene polymerizes considerably more rapidly than butadiene and isoprene. Especially in low-temperature polymerization emulsifiers must show good solubility and... 

When an elastic polymer network is stretched, the polymer chains are deformed. The verification of the theory has been largely based on measurements of the elastic restoring forces... 

ABA-type triblock copolymerization of MMA/BuA/MMA should give rubberlike elastic polymers. The resulting copolymers should have two vitreous outer blocks, where the poly(MMA) moiety (hard segment) associates with the nodules, and the central soft poly(BuA) elastomeric block provides rubber elasticity. Ihara et al. [35] were the first to synthesize an AB-type block copolymer, with MMA (190 equivalents of initiator) first polymerized by... 

There is also a growing interest in the association of elastic polymers, which assume sealing or damping functionalities, with rigid plastics or composites that have the structural role. One of the materials can be overmoulded on the other or the two materials can be co-moulded. 

Figure 5.58 The stress-strain behavior of brittle polymer (curve A), ductile polymer (curve B), and highly elastic polymer (curve C). Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 475. Copyright 2000 by John Wiley Sons, Inc.

Eiser et al. (2009) have recently reported on the pH-induced transformation of a hard-boiled egg from a white, brittle particulate gel to a transparent, elastic polymer gel (see Figure 6.20). Eggs were incubated in their hard protective shells for up to 26 days in a strong alkaline solution (0.9 M NaOH + 0.5 M NaCl, pH 12) at room temperature. These harsh experimental conditions are apparently rather similar to those used in a traditional Chinese method developed over two thousand years ago as a way of preserving eggs so that they would remain safely edible for many months. 

The present status of the theory of rubber elasticity. Polymer 7,373 (1966). 

Short time after pressure release in the plant an elastic polymer seal is often internally pressurised by dissolved gas and contains stored energy which leads to an explosionlike expansion and damage of the seal. 

Representative Synthetic Thermoplastic and Elastic Polymers and Their Uses3... 

Crosslinked LC elastomers (Figure 19d) are very promising for piezoelectric and ferroelectric applications, and also as non-linear optic materials. The first synthetic step to such materials is the preparation of usual side chain or combined LC copolymers doped with a small part of side chains containing a polymerizable >C=C< double bond at the end (Figure 23 shows a particular example of a crosslinkable LC polymer64). The copolymer can be further photocrosslinked, giving an elastic polymer film which reveals... 

Grosberg, A. Yu. (1979) Certain possible conformational states of a uniform elastic polymer chain. Biopysics., 24, 30-36. 

The molecular weight of the prepolymer is too low to form an elastic polymer. The overall molecular weight must be increased by joining prepolymer chains using either diols or diamines. 

The aliphatic poly(ether lactonejs are a group of synthetic polymers with high elasticity and high tissue absorptivity [293]. The ether function in the polymer backbone adds flexibility to the ester chain. Ring-opening polymerization of l,4-dioxan-2-one yields an elastic polymer, polydioxanone, with a tensile strength similar to that of human tissue [294]. Polydioxanone has been successfully used to prepare monofilament sutures, with a flexibility superior to that of PGA sutures [294]. Recently, the lipase-catalyzed polymerization of polydioxanone was demonstrated [295]. 

The introduction of difunctional elements (dimethylsiloxy, diethylsiloxy or methylphenylsiloxy elements) into the main chain of the polymer forms relatively elastic polymers, mainly cyclolinear ... 

Two atomistic approaches have been presented briefly above molecular dynamics and the transition-state approach. They are still not ideal tools for the prediction of diffusion constants because (i) in order to obtain a reliable chain packing with a MD simulation one still needs the experimental density of the polymer and (ii) though TSA does not require classical dynamics it involves a number of simplifying assumptions, i.e. duration of jump mechanism, elastic polymer matrix, size of smearing factor, that impair to a certain degree the ab initio character of the method. However MD and TSA are valuable achievements, they are complementary in several... 

Another common method of flexibilizing epoxy adhesives is by blending the primary epoxy resin with other, more elastic polymers. Epoxy-nylon, epoxy-polysulfide, and to a certain extent epoxy-urethane hybrids use such a mechanism to provide flexibility. These flexibilizers are important additives for epoxy adhesives even though they may reduce certain... 

There are over 30 broad groups of chemical types of elastic polymers. These are arranged by ASTM D 1418 into categories of materials having similar chemical chain structures. There are several problems with joining elastomer materials. 

So far the micro-mechanical origin of the Mullins effect is not totally understood [26, 36, 61]. Beside the action of the entropy elastic polymer network that is quite well understood on a molecular-statistical basis [24, 62], the impact of filler particles on stress-strain properties is of high importance. On the one hand the addition of hard filler particles leads to a stiffening of the rubber matrix that can be described by a hydrodynamic strain amplification factor [22, 63-65]. On the other, the constraints introduced into the system by filler-polymer bonds result in a decreased network entropy. Accordingly, the free energy that equals the negative entropy times the temperature increases linear with the effective number of network junctions [64-67]. A further effect is obtained from the formation of filler clusters or a... 

Plastics and polymers take much of the production of the petrochemical industiy in the form of monomers such as styrene, acrylates, and vinyl chloride. The products of this enormous industry are everything made of plastic including solid plastics for household goods and furniture, fibres for clothes (24 million tonnes per annum), elastic polymers for car tyres, light bubble-filled polymers for packing, and so on. Companies such as BASE, Dupont, Amoco, Monsanto, Laporte, floechst, and ICT are leaders here, Worldwide polymer production approaches 100 million tonnes per annum and PVC manufacture alone employs over 50 000 people to make over 20 million tonnes per annum. 

These exceptional characteristics have been used later in several interesting applications. An elastic polymer film containing the same MV2 + salts as part of the main chain was found to be photochromic and results indicate that data can be written optically X > 365 nm) and erased thermally [212]. The photo-chromism was also observed in monolayer assemblies (Langmuir-Bloodgett films) made of mixtures of N,N hexadecyl-4,4 -bipyridinium salts of TFPB-and arachidic acid [213, 214, 215]. 

According to Thomas elastic polymers often produce open-cell foamed plastics, whereas rigid polymers generally form closed-cell materials. However, there are many exceptions to this rule, owing to the variety of blowing techniques. Closed-cell structures are more likely to be produced from polyurethanes, epoxy resins, silicones, poly(vinyl chloride), polystyrene, etc., whereas open-cell materials mainly result from phenolic and carbamide foamed plastics. 

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