Rubber-like properties

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

Synthesis of hydrolytically stable siloxane-urethanes by the melt reaction of organo-hydroxy terminated siloxane oligomers with various diisocyanates have been reported i97,i98) -yhg polymers obtained by this route are reported to be soluble in cresol and displayed rubber-like properties. However the molecular weights obtained were not very high. A later report56) described the use of hydroxybutyl terminated disiloxanes in the synthesis of poly(urethane-siloxanes). No data on the characterization of the copolymers have been given. However, from our independent kinetic and synthetic studies on the same system 199), unfortunately, it is clear that these types of materials do not result in well defined multiphase copolymers. The use of low molecular weight hydroxypropyl-terminated siloxanes in the synthesis of siloxane-urethane type structures has also been reported 198). 

Triblock copolymers, as shown in Fig. 5.8 d), comprise a central homopolymer block of one type, the ends of which are attached to homopolymer chains of another type. As with other block copolymers, the components of triblocks may be compatible or incompatible, which will strongly influence their properties. Of particular interest are triblocks with incompatible sequences, the middle block of which is rubbery, and the end blocks of which are glassy and form the minor phase. When such polymers phase-segregate, it is possible for the end blocks of a single molecule to be incorporated into separate domains. Thus, a number of rubbery mid-block chains connect the glassy phases to one another. These materials display rubber-like properties, with the glassy domains acting as physical crosslinks. Examples of such materials are polystyrene/isoprene/polystyrene and polystyrene/polybutadiene/polystyrene triblock copolymers. 

One of the first applications envisioned of ROMP was the preparation of polyenes with rubber-like properties by ROMP of cyclopentene. Although this polymer did not have the optimum product profile, the polymer obtained by ROMP of cyclooctene can indeed be used in blends with other rubbers, conferring on the final product improved mechanical properties and simplifying its processing. This polymer, called Vestenamer 8012, is being produced by Chemische Werke Hiils, Marl, Germany, and the annual capacity in 1990 reached 12000t. 

CHo—COt=--CH—CH2—)n it led to suggestions on the molecular basis of rubber-like properties and to stereochemical explanations of the differences between the physical properties of the substances mentioned and finally it led to a general consideration of the stereochemistry of... 

Function and location of elastin Cause of Marfan syn drome Elastin is a connective tissue protein with rubber-like properties. Elastic fibers composed of elastin and glycoprotein microfibrils, such as fibrillin, are found in the lungs, the walls of large arteries, and elastic ligaments. [Note Mutations in the fibrillin gene are responsible for Marfan syndrome]... 

Perfluoroalkyl-l,3,5-triazines are very stable to oxidation and heat. They have potential as lubricating fluids for use in aerospace work (B-74MI22003). Their polymeric products are stable elastomers with excellent rubber-like properties for use as electrical wire insulation and seals for hydraulic, lubricating and fuel systems of aircraft (B-80MI22001). Perfluoro-2,4,6-tri-n-heptyl-l,3,5-triazine is a valuable reference standard for precise mass... 

Metallocene Catalysts. Higher a-olefins can be polymerized with catalyst systems containing metallocene complexes. The first catalysts of this type (Kaminsky catalysts) include metallocene complexes of zirconium such as biscyclopentadienylzirconium dichloride, activated by methylaluminoxane. These catalysts polymerize a-olefins with the formation of amorphous atactic polymers. Polymers with high molecular weights are produced at decreased temperatures and have rubber-like properties. 

The low vinyl acetate ethylene—vinyl acetate copolymers, ie, those containing 10—40 wt % vinyl acetate, are made by processes similar to those used to make low density polyethylene for which pressures are usually > 103 MPa (15,000 psi). A medium, ie, 45 wt % vinyl acetate copolymer with rubber-like properties is made by solution polymerization in /-butyl alcohol at 34.5 MPa (5000 psi). The 70—95 wt % vinyl acetate emulsion copolymers are made in emulsion processes under ethylene pressures of 2.07—10.4 MPa (300—1500 psi). 

A natural polymer isolated from the latex that exudes from cuts in the bark of the South American mbber tree. Alternatively, synthetic polymers with rubber-like properties are called synthetic rubber, (p. 1230)... 

Dr. Judit Puskas holds Canada s first Industrial Research Chair in Elastomer Technology at the University of Western Ontario in London, Ontario. She thinks that an elastomer called polyisobutylene, along with some of its derivatives, looks promising. In the future, it may be used to make better artificial arteries. It may also be useful for other implants, since it can imitate the rubber-like properties of elastin. 

The microstructure of epoxy thermosets can be complex, and both molecular and physical microstructures are presumed. Unfortunately, the intractable nature of these materials makes direct structural characterization extremely difficult. The most accessible technique for direct structural characterization is evaluation of epoxy rubber-like properties above Tg. Sometimes, indirect characterization of epoxy structure is possible due to the fact that the chemistry of several epoxy systems is well behaved (e.g., epoxy-amine chemistry). This permits epoxy network structure to be modeled accurately as a function of the extent of the crosslinking reaction(s). This approach has been developed extensively by Du ek and coworkers for amine-linked epoxies ... 

Polymerization reactions involve the union of a number of similar molecules to form a single complex molecule. A polymer is any compound, each molecule of which is formed out of a number of molecules which are all alike, and which are called monomers. In many cases polsonerization can be reversed and the poisoner be resolved to the monomer. Many polymerization reactions which are of industrial importance involve in the initial stages condensations, that is, reactions in which elimination of water or other simple molecules takes place. Compounds which polymerize have some type of unsaturation in the molecule. Olefins, unsaturated halides, esters, aldehydes, dicarboxylic acids, anhydrides, amino acids and amides are among the important groups of compounds which are used in industrial polymerization reactions. The commercial products produced by polymerization reactions may be conveniently classified into (a) resinotds, or synthetic resins (b) elastomers, which possess rubber-like properties and (c) fibroids, used as textile fibers. Two types of resinoids are illustrated in this experiment Bakelite, formed from phenol and formaldehyde, and methacrylate resin formed from an unsaturated ester. 

Similar to the case of the polymers with saturated carbon chain backbone, different substitutions are possible to the backbone of the unsaturated macromolecules. One common substitution is with halogens. Chloroprene (also known as neoprene) is formed from the polymerization of 2-chloro-1,3-butadiene and probably is the most widely used polymer from this class. It has rubber-like properties and is known for its better oil... 

The yellow orthorhombic modification of sulfur is the thermodynamically most stable one. The crown-like structure of a-cyclo-Sg was discovered in 1935. fi-Cyclo-Sf, is monoclinic and is formed slowly above 95 °C, the transition temperature of orthorhombic sulfur. The third crystalline modification is y-cyc/o-Sg, which melts at 106.8 C on rapid heating and can be prepared as discussed above. There is a large number of well-studied cyclic oligomers of sulfur here we refer the reader to a standard textbook. When sulfur heated to about 400°C is subjected to quenching the product is polycatenasulfur, which exhibits rubber-like properties. 

Equation 11.21 shows another example, where 1-methylcyclobutene polymerizes to form polyisoprene primarily with cis stereochemistry about the C=C. The properties of this polymer are quite similar to those of natural rubber, which is also ct s-polyisoprene.52 In this case, Katz used a discrete metal-carbene complex to catalyze the polymerization. One reason why there has been general interest in ROMP is because cycloalkenes often polymerize to give materials with elastomeric (rubber-like) properties. 

Natural rubber Wide-meshed crosslinked polymer with rubber-like properties made of plant milk (rubber tree). 

Restraints on motion may be relaxed in respect of some coordinates and not of others and considerable degrees of order may persist even when rigidity of the structure has disappeared. Very varied relations of mobility and order are, in fact, met with in liquid crystals, in liquids, in substances with rubber-like properties, and in condensed helium. 

In summary, the requirements for a material to exhibit rubber-like properties are ... 

During the middle sixties a series of butadiene-styrene and isoprene-styrene block copolymer elastomers were developed. These materials possess typical rubber-like properties at ambient temperatures, but act like thermoplastic resins at elevated temperatures. The copolymers vary from diblock structures of styrene and butadiene ... 

The elastomers from the high molecular weight silicone polymers must be crosslinked to obtain rubber-like properties. One way to accomplish this is through hydrogen abstraction by free radicals that are generated by decomposition of added peroxides. 2,4-Dichlorobenzoyl peroxide is often used for this purpose. It is decomposed between 110-150 C. The reaction can be shown as follows ... 

A protein that is similar to collagen is elastin, which is present in elastic tissues, such as tendons and arteries. Hydrolyses of elastin, which has rubber-like properties, however, do not yield gelatin. Mildly hydrolyzed elastin can be fractionated into two proteins. ... 

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