Polydiene rubbers polymers

This PSH technique was later utilized as an effective method of reductive modification for the unsaturated polymers such as polydiene rubbers and polypentenamer by Mango (2) and Samui et al ( ) ... 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

In the case of polymers containing double bonds in the main chain, such as polydiene rubber, certain workers [38, 160, 161] assume that these bonds may add oxygen ... 

Unsaturated carbon-chain polymers e.g. the polydiene rubbers discussed above) are very susceptible to peroxidation and hence biodegradation. Some of these have been studied as photodegradable polymers in their own right. For example 1,2-poly (butadiene) is a plastic with properties similar to the polyolefins. In unstabilised form it photo-oxidises and thermooxidises rather too rapidly to be very useful commercially. 

The 1,4- polydiene rubbers may have a variety of cis-ltrans- ratios ranging from the 100% cis- structure of natural rubber to polybutadienes with a trans- content in excess of 99%. In the late 1950s it was found that these polymers could be chemically treated in such a way that the cis-ltrans- ratio of an already formed polymer was altered. This process is known as cis-ltrans- isomerization and in the case of natural rubber leads to products with interesting properties. 

Treatment of polydienes with osmium tetroxide (OSO4) was introduced by Andrews (1964) and Andrews and Stubbs (1964). A later development by Kato (1965 1966 1967) showed that OSO4 was able to stain the rubber component in polymer blends. Osmium tetroxide adds to the double bonds and the density of rubber phase is increased. Since it crosslinks the rubber polymer by reacting with two double bonds located in two different polymer chains (Fig. 11.10), the rubber is fixed and sectioning can be carried out without smearing. Osmium tetroxide... 

The polydiene rubber-carbon black compoimd is one of the simplest in terms of component interaction. The major components are polymers, carbon black, and oil. The elastomer compounds are miscible or nearly so. The hydrocarbon oils dissolve roughly equally in the amorphous rubbery polydienes. The various polydiene elastomers and oils are almost as one phase. It appears they dissolve in each other at elevated temperatures and form a cross-Hnked structure together while miscible [7,8]. One problem is that the oils can distribute themselves differently among the various elastomers (Section 6.4). 

However, for construction purposes, solid ebonites were chosen. As is known from rubber chemistry, solid ebonite, commonly known as hard rubber, is a polymer material with sulfur content used for vulcanization. Ebonite, like elastomeric or flexible rubber, is made from a combination of sulfur with polydienes (unsaturated rubbers containing double bonds). The sulfur and polydienes are combined with some auxiliary additives and heated to produce vulcanization. Typical mass ratios of sulfur to rubber are 2 100 for elastomeric rubber and 40 100 for hard rubber. Due to the large degree of sulfide cross linking formed in the vulcanization process, solid ebonite is a hard, non-flexible, plastic-like material possessed of... 

Polyisoprene on hydrogenation gives a rubber directly—an alternating ethylene-propylene polymer. Polybutadiene can give polyethylene on hydrogenation if it is all 1,4 in structure or a variety of flexible-to-rubbery ethylene-butene copolymers as the 1,2 content of the polybutadiene is increased. These polydiene structures can be incorporated as segments in anionic styrene copolymers. 

Besides the addition of halogens and hydrohalogens across the double bond just covered, there are many other reagents that will react similarly with unsaturated polymers by free radical, ionic, or radical-ion mechanisms. Of prime importance is the addition of ethylene derivatives to polydienes. One of the earliest reactions of natural rubber to be studied in detail was the combination with maleic anhydride (Cunneen and Porter, 1965). Depending on the reaction conditions and the presence or absence of free radical initiators, one or more of four basic reactions may take place, with the products shown (the arrows indicate where the addition has taken place and the new bonds formed). 

Rubbers, often based on poly diene rubbers or else copolymers of dienes like 1,3-butadiene, were the first successful toughening additives, and they are effective partly because they have a low modulus, 100 to 500 times lower than that of most thermoplastic polymers. Unfortunately polydienes introduce chemical double bonds which are susceptible to UV, thermal and oxidative degradation. Hydrogenation removes some of them. Acrylic compounds and ethylene copolymers are also popular impact modifiers, and they do not necessarily introduce double bonds. 

Block-Copolymer Rubbers. Block copolymer rubbers are thermoplastic elastomers that are the most widely used class of PSAs (see Elastomers, Thermoplastic). The most commonly used are ABA block copolymers, where A is polystyrene and B is a polydiene. Polyisoprene (R = CH3) and polybutadiene (R = H) are the most common B poljnners, giving SIS and SBS copolsnners, respectively (see Butadiene Polymers Isoprene Polymers). 

Polydienes are amongst the largest worldwide produced and manufactured classes of polymers. This is because of their elastomeric properties, which make them suitable for many applications as synthetic rubbers. ... 

Cross-linking can be done by various techniques depending on the chemical composition of the polymer. Thus, if the polymer contains C=C unsaturation, e.g. in polydienes, natural rubber, polyisobutylenes (from copolymerized isoprene), then reaction with sulphur forms —S—S— links. With polysiloxanes or EP rubbers (no C=C) then peroxides are used. With fluorocarbon elastomers, e.g. Viton (a copolymer of vinylidene difluoride and hexafluoropropylene), diamines are used which form H-bonded cross-links. With polyurethanes (formed from diols and di-isocyanates) a controlled number (low) of cross-links are formed during the polymerization by the addition of triols. 

The interest in the reaction of ozone with polydienes is due mainly to the problems of ozone degradation of rubber materials [1-4] and the application of this reaction to the elucidation of the structures of elastomers [5-8], It is also associated with the possibilities of preparing bifunctional oligomers by partial ozonolysis of some unsaturated polymers [9-12], Usually the interpretation of experimental results are based on a simplified scheme of Criegee s mechanism of C=C-double bond ozonolysis, explaining only the formation of the basic product - ozonides [13, 14],... 

Polydienes constitute an extremely important group of polymers. This group comprises natural rubber (and related natural materials) and its derivatives together with the products of polymerization and copolymerization of conjugated dienes. These various materials make up the contents of this chapter. The importance of the polydienes lies in the fact that they encompass the bulk of the commercial elastomers currently in use. 

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