Silicone rubber Polymer

Ghosh, A.K., Rajeev, R.S., Bhattacharya, A.K., Bhowmick, A.K., and De, S.K., Recyebng of silicone rubber waste Effect of ground silicone rubber vulcanizate powder on the properties of silicone rubber, Polym. Eng. Sci., 43, 279, 2003. 

An alternative method of representing the movement of an individual molecule by computational techniques is shown in Figure 2.4 [9], This figure shows the movement of three different permeate molecules over a period of 200 ps in a silicone rubber polymer matrix. The smaller helium molecule moves more frequently and makes larger jumps than the larger methane molecule. Helium, with a molecular diameter of 2.55 A, has many more opportunities to move from one... 

Bessarabov s devices use composite membranes consisting of a thin silicone rubber polymer layer coated onto a microporous poly(vinylidene fluoride) support layer. These membranes have high fluxes and minimal selectivities for the hydrocarbon gases, but the dense silicone layer provides a more positive barrier to bleed-through of liquid than do capillary effects with simple micro-porous membranes. 

Silicone rubber polymers have been used as membrane materials because of their high permeability due to the high flexibility of the silicone rubber backbone [67-71]. However, PE is a rigid, crystalline polymer with relatively low permeability, bnt on addition of small amounts of VAc it becomes rubbery and permeable. Thus, the change of the polymer morphology by the comonomer ratios has an effect on the... 

Stevenson I, David L, Gauthier C, Arambourg L, Davenas J, Vigier G (2001) Influence of Si02 fillers on the radiation ageing of silicone rubbers. Polymer 42 9287-92... 

Silicone rubber polymers have the more stable Si atom compared with carhon. Silicone s property signature is its combined (1) high-temperature resistance [>500°F (260°C)], (2) good flexibility at <-100°F (-73°C), (3) good electrical properties, (4) good compression set, and (5) tear resistance and stability over a wide temperature range. When exposed to decomposition level temperature, the polymer forms Si02, which can continue to serve as an electrical insulator. ... 

Acrylonitrile-butadiene rubber (NBR) - Europrene N3960, acrylonitrile unit content 28 % produced by Lanxess, ethylene-propylene rubber (EPM) Dutral CO 054, propylene unit content 40 % produced by Montedison Ferrara, silicone rubber - Polymer MVQ 0,07 produced by Z. Chem. Silikony Polskie Sp. z o.o., Nowa Sarzyna, ENGAGE Polyolefin Elastomer ethylene-octene copolymer produced by DOW Chem. Comp. USA, polyoctenamer VESTENAMER 8012 -semicrystalline rubber produced by Degussa GmbH Germany. 

Data shown in Table 3 demonstrate that for polymers with the same substitution pattern it is ffexibility of the backbone that dominates the permeation properties. The Si—O backbone allows rapid chain-segment motion to occur in the silicone rubber (polymer C) and substitution of the Si—O linkage by Si—CH2 (polymer B) dramatically reduces the permeability to a value even less than that of butyl rubber (polymer A). Insertion of (CH2) sequences into a siloxane backbone (polymer D) also leads to a decrease in permeability. Similarly, the Si—O backbone substitution of methyl by more bulky substituents decreases the permeability (polymer E). 

Foamed polymers Foamed sheet Foamed silicone rubber Foam fractionation... 

Silicone Rubber. These polymers are based on chains of siUcon rather than carbon atoms, and owe thek temperature properties to thek unique stmcture. The most common types of siUcone mbbers are specifically and almost exclusively the polysdoxanes. The Si—O—Si bonds can rotate much more freely than the C—C bond, or even the C—O bond, so the siUcone chain is much more flexible and less affected by temperature (see Silicon COMPOUNDS, silicones). 

Polymer-Fluid Equilibria and the Glass Transition Most polymer systems fall in the Class HI or Class V phase diagrams, and the same system can often change from one class into the other as the polymer s molecular weight changes. Most polymers are insoluble in CO9 below 100°C, yet CO9 can be quite sohible in the polymer. For example, the sorption of CO9 into silicone rubber is highly dependent upon temperature and pressure, since these properties have a large influence on the density and activity of CO9. 

Whilst the Tg of poly(dimethylsiloxane) rubbers is reported to be as low as -123°C they do become stiff at about -60 to -80°C due to some crystallisation. Copolymerisation of the dimethyl intermediate with a small amount of a dichlorodiphenylsilane or, preferably, phenylmethyldichlorosilane, leads to an irregular structure and hence amorphous polymer which thus remains a rubber down to its Tg. Although this is higher than the Tg of the dimethylsiloxane it is lower than the so that the polymer remains rubbery down to a lower temperature (in some cases down to -100°C). The Tg does, however, increase steadily with the fraction of phenylsiloxane and eventually rises above that of the of the dimethylsilicone rubber. In practice the use of about 10% of phenyldichlorosilane is sufficient to inhibit crystallisation without causing an excess rise in the glass transition temperature. As with the polydimethylsilox-anes, most methylphenyl silicone rubbers also contain a small amount of vinyl groups. 

MQ Silicone rubbers having only methyl substituent groups on tbe polymer chain (polydimethyl siloxanes). 

VMQ Silicone rubbers having both methyl and vinyl substituent groups on the polymer chain. 

Substantial improvements in the heat-resisting capability of silicone rubbers were achieved with the appearance of the poly(carborane siloxanes). First described in 1966, they were introduced commercially by the Olin Corporation in 1971 as Dexsil. The polymers have the essential structure... 

Continuous porous polymer rods have been prepared by an in situ polymerization within the confines of a chromatographic column. The column is filled with glycidyl methacrylate and ethylene dimethacrylate monomer mixtures, cyclo-hexanol and dodecanol diluents, and AIBN initiator. They are then purged with nitrogen, stopped, and closed with a silicon rubber septum. The polymerization is allowed to proceed for 6 hr at 70°C with the column acting as a mold (47). 

The major applications of rubbery materials today include automotive tires, rubber bands, tubing of various kinds, electric wire insulation, elastomeric urethane fibers for undergarments, and silicone rubber. Such types of polymers are important materials in our 21st-century world. 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

Blending of polymers provides a convenient way of combining the different properties of individual polymers. Hydrophilization of the silicone mbber can be obtained by blending silicone rubber with hydrogels. These kinds of composites combine the good mechanical properties with the hydrophilicity. 

Hron P. Hydrophilisation of silicone rubber for medical applications. Polym Int, 2003, 52, 1531-1539. Tcholakian RK and Raad. Durability of anti-infective effect of long term silicone sheath catheters impregnated with antimicrobial agents. Antimicrob Agents Chemother, 2001, 45(7), 1990-1993. 

An analysis of partition coefficient data and drug solubilities in PCL and silicone rubber has been used to show how the relative permeabilities in PCL vary with the lipophilicity of the drug (58,59). The permeabilities of copolymers of e-caprolactone and dl-lactic acid have also been measured and found to be relatively invariant for compositions up to 50% lactic acid (67). The permeability then decreases rapidly to that of the homopolymer of dl-lactic acid, which is 10 times smaller than the value of PCL. These results have been discussed in terms of the polymer morphologies. 

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