Rubberlike properties

Polyester thermoplastic elastomers, which are obtained by replacing a part of the R2 diol by dihydroxy polyether macromonomer, present biphasic morphology and rubberlike properties. 

Rubberlike Properties. Figure 2 depicts the changes in the 13.7-micron infrared crystallinity band with increasing ethyl acrylate content. At 25-30% acrylate content in the copolymer, this band disappears, indicating that this polymer is essentially amorphous. This fact, plus the absence of carbon-carbon unsaturation, good filler compatibility, and... 

Polymerization of propene by the Ziegler process gives a very useful plastic material. It can be made into durable fibers or molded into a variety of shapes. Copolymers (polymers with more than one kind of monomer unit in the polymer chains) of ethene and propene made by the Ziegler process have highly desirable rubberlike properties and are potentially the cheapest useful elastomers... 

A number of different mechanisms have been proposed to account for the rubberlike properties of materials. In classical rubber theory these properties are attributed to a decrease in conformational entropy on deforming a network of kinetically free random polymer molecules. Stress orders the polymer chains and decreases their entropy by limiting their conformational freedom, thus providing the restoring force to the relaxed state. Such a theory was developed for elastin by Hoeve and Flory... 

Shrinkablefilm and tubing Cross linked semicrystalline thermoplastics display rubberlike properties at temperatures above their melting points. On deformation followed by fast cooling the polymer maintains its deformed shape. The polymer returns to its original shape when reheated. This memory effect is applied in the production of heat shrinkable films and tubing. Radiation doses of the order of 40 — 1(X) kGy are used in the production of heat shrinkable products. 

Lithium metal-catalyzed polyisoprene and polybutadiene have unusual microstructures compared to the analogous polymers made with the other alkali metals. The lithium metal-catalyzed polyisoprene, named Coral rubber, has a microstructure almost identical to that of Hevea rubber. The unusual microstructure of the lithium metal-catalyzed polybutadiene, or butadiene-styrene copolymer, probably accounts for its superior rubberlike properties at low temperatures. 

The carbon-carbon double bonds of this polymer are partly in the cis and partly in the trans position. The polymer itself has a melting temperature of 170-190 C and is a thermoplast with a glass transition temperature of 34-37 C. But it can absorb up to four times its own weight of mineral oil when it then has rubberlike properties and glass transition temperatures of —45 to -60 C. It can be conventionally vulcanized with sulfur. 

The elastomers from high molecular weight silicone polymers must be cross-linked to obtain rubberlike properties. One way this is accomplished is through hydrogen abstraction by ffee-radicals that are generated by decomposition of added peroxides. 2,4-Dichlorobenzoyl peroxide is often used for this purpose. It is decomposed between 110 and 150°C. The reaction can be shown as follows ... 

Thermoplastic vulcanizates (TPVs) are composed of a vulcanized rabber component, such as EPDM, nitrile rubber, and butyl rubber in a thermoplastic olelinic matrix. TPVs have a continuous thermoplastic phase and a discontinuous vulcanized rubber phase. The most common TPV polymer systan is PP/EPDM rubber however, a number of other polymer systems have been commercially developed. These include PP/NBR, PP/butyl and PP/halobutyl, PP/NR, and PP/EVA/EPDM. Producers include Advanced Elastomers Systems (Santoprene, Geolast, and Trefsin). The highly rubberlike properties of TPV have enabled than to perform as engineered thermoplastic rubbers. In numerous application areas they have directly replaced premium-performance thermoset rubber compounds. Prominent among these are dananding automotive applications, electrical insulation and connectors, compression seals, appliance parts, medical devices, and food and beverage contact applications. 

SBCs were developed in the US in the mid sixties. They are the largest volume thermoplastic elastomers, being polymers with rubberlike properties but able to be processed as thermoplastics. As a result of these properties, they present two advantages over conventional types vulcanisation is unnecessary and the scrap can be reprocessed. SBCs account for about 5 % of the total synthetic rubber production (see Table 8.1). The consumption within the EU is approximately 280000 tonnes/year. 

An elastomer may be defined as a natural or synthetic material that exhibits the rubberlike properties of high extensibility and flexibility. Although the term rubber originally meant the TS elastomeric material obtained from the para rubber tree (Hevea braziliensis) it now identifies any thermoset elastomer (TSE) or thermoplastic elastomeric (TPE) material. Such synthetics as neoprene, nitrile, styrene butadiene, and butadiene are now grouped with natural rubber. 

The time then came for Kurt H. Meyer of Geneva to shine in his own light. He presented a paper on Inorganic Substances with Rubberlike Properties. When crystalline sulfur is melted, its viscosity increases dramatically over time and eventually reaches an equilibrium state of very high viscosity. The viscosity changes with temperamre, but is quite stable under anaerobic conditions. The thermodynamic heat of polymerization is positive for Sg, so that it is the entropy of the chain molecule that drives the reaction. This means that the chains have a very large number of conformations in the melt. 

An elastomer is a natural or synthetic polymer with rubberlike properties. These materials exhibit high extensibility and quick, forceful recovery. Examples of elastomers used in adhesive applications are ... 

Elastomers are polymers with rubberlike properties. The word elastic refers to the ability of a material to return to its original dimensions when unloaded, and the term mer refers to the polymeric molecular make up in the word elastomer. Vulcanized rubber materials typically have more than 200% elongation in a tensile test and are capable of returning rapidly and forcibly to their original dimensions when load is removed. This elastic response is due to the three-dimensional cross-linked network molecular structure they have. An elastomer, on the other hand, typically has elongation rates of 100% or more and a significant amount of resilience. Resilience is represented by the area under the elastic portion of the stress-strain curve, and therefore, refers to a material s ability to undergo elastic deformations. 

Tack and building tack Retention of rubberlike properties at low temperatures over long periods of time... 

---