Rubber, conjugated diene

Cellulose butyrate (also carbon black reinforcing pigment) Chlorinated butadiene rubber Conjugated diene butyl elastomer Cellulose plastics in general... 

The conjugated diene 1 3 butadiene is used m the manufacture of synthetic rubber and IS prepared on an industrial scale m vast quantities Production m the United States is currently 4 X 10 Ib/year One industrial process is similar to that used for the prepara tion of ethylene In the presence of a suitable catalyst butane undergoes thermal dehy drogenation to yield 1 3 butadiene... 

The discovery by Ziegler that ethylene and propylene can be polymerized with transition-metal salts reduced with trialkyl aluminum gave impetus to investigations of the polymerization of conjugated dienes (7—9). In 1955, synthetic polyisoprene (90—97% tij -l,4) was prepared using two new catalysts. A transition-metal catalyst was developed at B. E. Goodrich (10) and an alkaU metal catalyst was developed at the Ekestone Tke Rubber Co. (11). Both catalysts were used to prepare tij -l,4-polyisoprene on a commercial scale (9—19). 

One other variant in double-bond polymerisations may be mentioned here. Many conjugated dienes may be polymerised in such a way as to generate long chain molecules with residual double bonds in the chain. Well-known examples of such dienes are buta-1,3-diene and isoprene, which yield 1,4-polybutadiene and 1,4-polyisoprene respectively (Figure 2.4). Natural rubber has a formula corresponding to the 1,4-polyisoprene. 

Figure 11.15. Typical chemical groupings in a sulphur-vulcanised natural rubber network, (a) Monosulphide cross-link (b) disulphide cross-link (c) polysulphide cross-link (j = 3-6) (d) parallel vicinal cross-link (n = 1-6) attached to adjacent main-chain atoms and which have the same influence as a single cross-link (e) cross-links attached to common or adjacent carbon atom (f) intra-chain cyclic monosulphide (g) intra-chain cyclic disulphide (h) pendent sulphide group terminated by moiety X derived from accelerator (i) conjugated diene (j) conjugated triene (k) extra-network material (1) carbon-carbon cross-links (probably absent)...

Functionalized rubbers. Butyl rubber (isobutylene with about 2% iso-prene) has been functionalized through the residual double bonds via the bro-mobutyl intermediate to produce a material with 2% conjugated diene (see Fig. 19). This resin shows high reactivity towards e-beam or UV (free radical or cationic [53]). The bromo butyl intermediate has also been used to attach acrylate or photoinitiator groups to the butyl backbone [54]. 

Conjugated dienes (diolefms) are used in the manufacture of synthetic rubbers, and as starting materials in the synthesis of insecticides and flame proofing paints. 

Isoprene is the second important conjugated diene for synthetic rubber production. The main source for isoprene is the dehydrogenation of C5 olefins (tertiary amylenes) obtained by the extraction of a C5 fraction from catalytic cracking units. It can also be produced through several synthetic routes using reactive chemicals such as isobutene, formaldehyde, and propene (Chapter 3). 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

On 7-irradiation, a decay of unsaturation is observed in the microstmcture of EPDM mbber containing 2-4 mol% of 5-ethyhdene-2-norbomene [368]. The formation of trani -vinylenes and conjugated dienes has been noted in ethylene-rich EPR rubbers [369]. Gas production in EPR under the influence of 7-radiation has also been reported [370]. 

Conjugated dienes such as 1,3-butadiene very readily polymerize free radically. The important thing to remember here is that there are double bonds still present in the polymer. This is especially important in the case of elastomers (synthetic rubbers) because some cross-linking with disulfide bridges (vulcanization) can occur in the finished polymer at the allylic sites still present to provide elastic properties to the overall polymers. Vulcanization will be discussed in detail in Chapter 18, Section 3. The mechanism shown in Fig. 14.3 demonstrates only the 1,4-addition of butadiene for simplicity. 1,2-Addition also occurs, and the double bonds may be cis or trans in their stereochemistry. Only with the metal complex... 

These copolymers were made by anionically polymerizing 1,3-butadiene with n-Buli followed by the addition of isoprene to the live cement. The molecular weight was varied in the 1,H poly(bd) block to produce the maximum physical properties. The content of the Bd/isoprene in the copolymer was varied 30/70. Similarly, (Table VI) the molecular weight of the diblock was kept constant at 60 AO Bd isoprene ratio, while the molecular weight of the individual block was varied. In Tables V and VI the physical properties of the di block of the conjugated diene rubber showed elastomeric properties typical of that of the uncrossed elastomer. 

Title Modified Conjugated Diene Polymer, Polymerization Intitiator, Method of Producing the Same, and Rubber Composition... 

Many of the polymers formed from conjugated dienes are elastic and are used to manufacture synthetic rubbers. The raw polymers usually are tacky and of little direct use, except as adhesives and cements. They are transformed into materials with greater elasticity and strength by vulcanization, in which the polymer is heated with sulfur and various other substances called accelerators, with the result that the polymer chains become cross-linked to one another by carbon-sulfur and carbon-carbon bonds. Some of the cross-linking appears to occur by addition to the double bonds, but the amount of sulfur added generally is insufficient to saturate the polymer. With large proportions of sulfur, hard rubberis formed such as is used in storage-battery cases. 

Polybutadiene rubber, via conjugated diene polymerization, 4, 1084-1085 Polybutadienes... 

However, no method of polymerisation known before 1954 allowed one to obtain polymers with a high regularity of structure from the most common conjugated dienes. A true breakthrough in the development of conjugated diene rubbers took place after the discovery of stereospecific polymerisation with transition metal-based coordination catalysts. From the late 1950s, a rapid development of industrial production of solution types of polybutadiene by means of polymerisation with Ziegler-Natta catalysts was observed. 

These are the most important. The two double bonds mutually activate each other conjugation is essentially not destroyed by addition to the growing chain end. Therefore the conjugated dienes are difunctional monomers. They are polymerized by a relatively simple mechanism. Of all the polymers generated in living tissues, we have so far been able to imitate most closely natural rubber, poIy-cis-l,4-isoprene. Butadiene, isoprene and chloroprene are the dienes most often employed in macro-molecular chemistry. 

The introduction of conjugated diene functions in polyisobutene chains has been recently acconq>lished throu an indirect approach which utilizes the dehydro-haiogenation of chlorinated butyl rubber, i. e. randomly chlorinated poly(isobutene-co-isoprene), by means of basic agents ... 

Natural rubber has a structure that strongly resembles these synthetic poly-dienes. We could consider it to be a polymer of the conjugated diene 2-methyl-], 3-butadiene, isoprene. 

Copolymerization of styrene and conjugated dienes is another attractive subject which provides the most commonly used styrene-butadiene rubbers (SBRs). Boisson reported that by using neodymium amide Nd N(SrMe3)2 3 and TIBA and DEAC, SBRs with 10-15 mol% of styrene were produced [189], although drops in both activity and molecular weight were observed as compared with those of... 

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