Rubbery materials molecular properties

Physical properties of rubbery materials are discussed in Chapters 5, 7, 8, 10, 12, 13,14 and 15, which cover the following topics phase structure and composition, molecular mobility, strain induced phenomena, phase separation and interfaces in rubbery materials. 

The above features of rubbery materials have long been known. The quantitative measurements of mechanical and thermodynamic properties of natural and other elastomers go back to 1805 and some of the studies were conducted by luminaries like Joule and Maxwell. The first molecular theory in polymer science dealt with the rubber elasticity (9-12). 

Cast material is stated to have a number average molecular weight of about 10. Whilst the Tg is about 104°C the molecular entanglements are so extensive that the material is incapable of flow below its decomposition temperature (approx. 170°C). There is thus a reasonably wide rubbery range and it is in this phase that such material is normally shaped. For injection moulding and extrusion much lower molecular weight materials are employed. Such polymers have a reasonable melt viscosity but marginally lower heat distortion temperatures and mechanical properties. 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

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