Elasticity copolymers

The properties of ethylene-vinyl acetate copolymers vary widely with their ester content. At the lowest levels of vinyl acetate, they have physical properties that are similar to those of low density polyethylene. As the comonomer content increases, the material becomes less crystalline and more elastic. Copolymers made with the highest comonomer levels contain no measurable crystallinity. The resulting products are tough, flexible, and clear. The ester... 

In this work, the film properties made from mixtures of latex based on hard-chain and elastic copolymers, undergone by vibrowave treatment have been considered. Process of a film formation in this case is known to start with the evaporation of the dispersion media (water) and finishes with transformation of a dispersion into a coating. The period between the change of the film sizes during the coating formation and achievement of an equilibrium condition is governed by relaxation processes [7],... 

As discussed earlier, ethylene propylene rubber (EPR or EPM) has been blended with PP and PE to improve the impact strength and to render the materials softer. Recently, metallocene catalysts or postmetallocene catalysts provide new pathways to generate elastic copolymers that can replace EPR. These pathways possess cheaper manufacturing cost and generate new materials with better compatibility to PP or PE. Such new materials included ethylene-propylene random copolymers with dominant ethylene component (33-34) or propylene-dominant component (35 1), propylene-ethylene block copolymer (42), ethylene-octene copolymer (43), poly(propylene-co-ethylene) (44), ethylene-hexene copolymer (45), ethylene-butene copolymer (46), low isotactic PP (47), and stereoblock PP (48). These materials are generally compatible with PP or PE, thus can be used to tailor the toughness (or the softness) of... 

Copolymerizations of aldehydes take place by both anionic and cationic mechanisms. An elastic copolymer of formaldehyde and acetaldehyde forms with triisobutylaluminum. The rate of copolymerization is very rapid at-78 C. The reaction is complete within 30 minutes. The product, however, is crosslinked. Aldehydes also copolymerize with some vinyl monomers. An acetone... 

Butyl rubber n (1940). A synthetic elastomer produced by copolymerizing isobutylene with a small amount (ca 2%) of isoprene or butadiene. It has good resistance to hear, oxygen and ozone, and low gas permeability. Thus, it is widely used in inner tubes and to line tubeless tires. Butyl rubber is a vinyl polymer, and is very similar to polyethylene and polypropylene in structure, except that every other carbon is substituted with two methyl groups. It is made from the monomer isobutylene, by cationic vinyl polymerization. It can also go by the name of polyisobutylene. (1) Generic name for vulcanizable elastic copolymers of isobutylene and small amounts of diolefins. (2) Mixture of isobutylene, 98% and... 

Elastic copolymer from an acrylic ester and a small proportion of a vulcanizable monomer, e.g., 2-chlorovinyl ether (ANSI, ASTM)... 

Elastic copolymer from ethylene and propylene see also APR, E/P, EPM, and EPR (older German literature)... 

A number of friction studies have been carried out on organic polymers in recent years. Coefficients of friction are for the most part in the normal range, with values about as expected from Eq. XII-5. The detailed results show some serious complications, however. First, n is very dependent on load, as illustrated in Fig. XlI-5, for a copolymer of hexafluoroethylene and hexafluoropropylene [31], and evidently the area of contact is determined more by elastic than by plastic deformation. The difference between static and kinetic coefficients of friction was attributed to transfer of an oriented film of polymer to the steel rider during sliding and to low adhesion between this film and the polymer surface. Tetrafluoroethylene (Telfon) has a low coefficient of friction, around 0.1, and in a detailed study, this lower coefficient and other differences were attributed to the rather smooth molecular profile of the Teflon molecule [32]. 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestmctive method is the measurement of torsional modulus. A number of instmments are available (13—18). More details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

Content of Ot-Olefin. An increase in the a-olefin content of a copolymer results in a decrease of both crystallinity and density, accompanied by a significant reduction of the polymer mechanical modulus (stiffness). Eor example, the modulus values of ethylene—1-butene copolymers with a nonuniform compositional distribution decrease as shown in Table 2 (6). A similar dependence exists for ethylene—1-octene copolymers with uniform branching distribution (7), even though all such materials are, in general, much more elastic (see Table 2). An increase in the a-olefin content in the copolymers also results in a decrease of their tensile strength but a small increase in the elongation at break (8). These two dependencies, however, are not as pronounced as that for the resin modulus. 

Branchings Uniformity. Comparison of uniformly and nonuniformly branched ethylene—1-butene copolymers of the same density (Table 4) shows that uniformly branched resins are much more elastic, their tensile modulus is lower, and their strain recovery is neady complete. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Several other elastic materials may be made by copolymerising one of the above monomers with lesser amounts of one or more monomers. Notable amongst these are SBR, a copolymer of butadiene and styrene, and nitrile rubber (NBR), a copolymer of butadiene and acrylonitrile. The natural rubber molecule is structurally a c/i -1,4-polyisoprene so that it is convenient to consider natural rubber in this chapter. Some idea of the relative importance of these materials may be gauged from the data in Table 11.14. 

In 1978 Hiils (Mumcu et al ) described the properties of a block copolymer prepared by condensation of polytetramethylene ether glycol with laurin lactam and decane-1,10-dicarboxylic acid. The materials were introduced as XR3808 and X4006. The polyamide XR3808 is reported to have a specific gravity of 1.02, a yield stress of 24 MPa, a modulus of elasticity of 300 MPa and an elongation of break of 360%. The Swiss company Emser Werke also introduced similar... 

With most homopolymers and copolymers the apparent viscosity is less dependent on temperature and shear stress (up to 10 dyn/cm ) than that of the polyolefins, thus simplifying die design. On the other hand the melt has a low elasticity and strength and this requires that extruded sections be... 

Various elastic elements are added to disposable sanitary products. Strands of lycra, natural rubber, polyurethane foam, and other elastic laminates are applied to provide good fit and avoid leakage. These are attached with adhesives. While non-PSA formulas such as polybutene-based [64] and polyamide [65] adhesives have shown utility, as well as benefits in terms of resistance to baby oils and lotions, adhesives based on styrenic block copolymers still dominate. SBC-based... 

As it is known at present in all countries producing PAN fibres, AN copolymers containing 5—10% of a second monomer are used to increase the elasticity and, in most cases, a third monomer (1-25%) is added to improve the dyeability. 

As it can be seen from the above data, by introducing 4—15% of monomeric units of ISP into the macromolecules of the AN copolymer, the elastic properties of PAN fibres and, especially, their resistance to abrasion and double bends can considerably be improved. 

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