Rubbers structure

Both side groups and carbon-carbon double bonds can be incorporated into the polymer structure to produce highly resilient rubbers. Two typical examples are polyisoprene and polychloroprene rubbers. On the other hand, the incorporation of polar side groups into the rubber structure imparts a dipolar nature which provides oil resistance to these rubbers. Oil resistance is not found in rubber containing only carbon and hydrogen atoms (e.g. natural rubber). Increasing the number of polar substituents in the rubber usually increases density, reduces gas permeability, increases oil resistance and gives poorer low-temperature properties. 

This sulfur radical can attack another chain to give a cross-link or bite back to give a link within the same chain. Many different sulfur links are formed and the next diagram summarizes a part of the vulcanized rubber structure. There is some license here in reality the links would not be as dense as this, and more than two chains would be involved. 

Acid bottles, rubber Air-supported rubber structures Aprons, vulcanized rubber and rubberized fabric—mitse Bags, rubber or rubberized fabric... 

Gutta-percha. The name, derived from Malayan ge-tah pertcha=latex of the percha tree, for a natural rubber (structure, see there) from the gutta-percha trees Palaquium gutta and P. oblongifolia, Sapotaceae) with properties similar to those of balata. In Sumatra, Java, and south east India, the rapidly coagulating latex of incised trees is collected, rapidly kneaded, and marketed as raw G. Pure G. is the all-trans-isorntr of polyisoprene, related to balata molecular mass ca. 100000. In contrast to the cis-isomeric natural rubber, G. is hard and less elastic but not brittle, it softens at 25-30°C, becomes plastic at 60 °C, and melts at >100°C with decomposition and formation of a sticky mass. For uses, see literature. 

Oxygenated Functions. Oxygenated functions on carbon black surface were observed in the early 1950s [70] and completely characterized by H. P. Boehm in the 1960s [71]. At this time, interaction between carbon black and natural rubber was considered the consequence of chemical reactions between the carbon black surface s acidic groups and basic moieties present in the natural rubber structure [71a]. 

There are two possible structures for poly-l,4,polyisoprene. Natural rubber structure is of the cis form. The tram forms (the structure of guta perch or balata gum) have higher melting point and higher glass transition temperatures (see below). 

Chemicals derived from silica used in molding as a release agent and general lubricant. A silicon-based thermoset plastic material. Polyorganosiloxanes of different composition (e.g., polydimethylsiloxane, silicone rubber), structures (linear or network), and molecular weight, used as high-temperature oil, resin, or elastomer. 

Dr. N.R. Legge, 1987 Charles Goodyear medalist and, at that time, director of the synthetic polyisoprene program at Shell Development Company, recalled that it was in attempting to provide a solution to this problem of poor "green strength in alkyl lithium polymerized polyisoprene that the styrenic block copolymers were first synthesized. The functional use of the first block copolymers was not as an identifiable monolithic rubber structure but provided a vital function to another identifiable material and lost its identity in this process. 

Furthermore, the C=C bonds in the natural rubber structure might induce poor thermal and oxidative resistance in the natural rubber blends. Thus, Thawornwisit and coworkersproposed the preparation of hydrogenated natural rubber, which is one of the chemical modifications available to improve the oxidation and thermal resistance of diene-based natural rubber before blending with poly(methyl methacrylate-co-styrene). The poly(methyl methacrylate-co-styrene) was resistant to the outdoor environment and had excellent optical properties with a high refractive index, but it was extremely brittle and had low impact strength. Hydrogenated natural rubber could, however, be used as an impact modifier, as well as to improve its thermal and oxidative resistance for these acrylic plastics. 

---