Polymerisation diene

In addition to the torque-rise behaviour the steepness of the curve may be expressed with the torque/time ratio, which is the stress/strain ratio, i.e., modulus. Between the two gum-rubbers in question, there is a significant difference in modulus. The gum rubber giving a steeper curve is stiffer than the other one. The peak may be interpreted as the failure point [4]. The stiffer rubber has a smaller strain to break and the softer rubber is more deformable. The former tends to fall in Region I of mill processability and the latter in Region II. The former may contain macrogel in a significant amount, if it is an emulsion-polymerised diene rubber. See Chapters 4 and 6 for additional information. 

Lipids (496-497) containing UV-polymerisable diene moieties and extremely useful for the construction of micelles and lipid bilayers, have been synthesised by the Chabrier reaction of from the cycUc phospholane... 

It is of interest to note that synthetic rubbers are produced by the polymerisation of dienes and are therefore examples of additive polymerisation. Thus ... 

Isoprene is highly reactive both as a diene and through its allyhc hydrogens, and its reactions are similar to those of butadiene (qv) (8). Apart from polymerisation, the most widely investigated isoprene reactions are the formation of six-membered rings by the Diels-Alder reaction ... 

T. J. PuUukat, M. Shida, and R. E. Hoff, ia R. P. Quirk, ed.. Transition Metal Catalysed Polymerisations Mlkenes and Dienes, Harwood Academic Pubhshers, New York, 1983, p. 697. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

In solution-based polymerisation, use of the initiating anionic species allows control over the trans /cis microstmcture of the diene portion of the copolymer. In solution SBR, the alkyUithium catalyst allows the 1,2 content to be changed with certain modifying agents such as ethers or amines. The use of anionic initiators to control the molecular weight, molecular weight distribution, and the microstmcture of the copolymer has been reviewed (15). 

Tetraneopentyltitanium [36945-13-8] Np Ti, forms from the reaction of TiCl and neopentyllithium ia hexane at —80° C ia modest yield only because of extensive reduction of Ti(IV). Tetranorbomyltitanium [36333-76-3] can be prepared similarly. When exposed to oxygen, (NpO)4Ti forms. If it is boiled ia ben2ene, it decomposes to neopentane. When dissolved ia monomers, eg, a-olefins or dienes, styrene, or methyl methacrylate, it initiates a slow polymerisation (211,212). Results from copolymerisation studies iadicate a radical mechanism (212). Ultraviolet light iacreases the rate of dissociation to... 

The reactivity of ethylene is high, whereas that of propylene is low and the various dienes have different polymerisation reactivities. The viscous mbber solution contains some unpolymerised ethylene, propylene, unpolymerised diene, and about 10% EPDM, all in homogeneous solution. This solution is passed continuously into a flash tank, where reduced pressure causes most of the unpolymerised monomers to escape as gases, which are collected and recycled. 

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. 

Tbe system may be used for homopolymers and for block copolymers. Some commercial SBS triblock thermoplastic rubbers and the closely related K-resins produced by Phillips are of this type. Anionic polymerisation methods are of current interest in the preparation of certain diene rubbers. 

Polymerisation of conjugated dienes can frequently lead to the formation of linear polymers containing main chain double bonds. Examples of such diene... 

The monomer, 2-chlorobuta-1,3-diene, better known as chloroprene, is polymerised by free-radical emulsion methods to give a polymer which is predominantly (-85%) fr<2 s-l, 4-polychloroprene but which also contains about 10% cii-1,4- 1.5%, 1,2- and 1% of 3,4-structures (Figure 11.17). The commercial polymers have a Tg of about -A3°C and a of about 45°C so that at usual ambient temperatures the rubber exhibits a measure of crystallinity. 

The styrene-diene triblocks, the main subject of this section, are made by sequential anionic polymerisation (see Chapter 2). In a typical system cc-butyl-lithium is used to initiate styrene polymerisation in a solvent such as cyclohexane. This is a specific reaction of the type... 

Whilst the ASA materials are of European origin, the AES polymers have been developed in Japan and the US. The rubber used is an ethylene-propylene terpolymer rubber of the EPDM type (see Chapter 11) which has a small amount of a diene monomer in the polymerisation recipe. The residual double bonds that exist in the polymer are important in enabling grafting with styrene and acrylonitrile. The blends are claimed to exhibit very good weathering resistance but to be otherwise similar to ABS. 

The described experimental rig for the anionic polymerisation of dienes has been shown to behave as an ideal CSTR. The mathematical model developed allows the prediction of the MWD at future points in the reactor history, once suitable kinetic parameters have been estimated. 

Emulsion polymerisation is used in the commercial production of synthetic diene elastomers and also to produce commercial latexes of the type used in paints these paints are known incorrectly as emulsion paints and... 

Aspects of mechanism of coordination polymerisation of conjugated dienes... 

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

Ichikawa and Nakao 89) have investigated the additive effect of 2,3-dimethyl-butane on the polymerisation of 2,3-dimethylbuta-1,3-diene in thiourea canals. Although yields were reduced sharply, polymerisation was found still to occur in the presence of surprisingly high percentages of alkane. Molecular weights were reduced in this procedure for example the maximum yields of dimers were obtained with an 80 % alkane content. 

Aromatic character is thus lost, and the cation behaves like a conjugated diene in undergoing very ready polymerisation. 

See Other DIENES, HALOALKENES, PEROXIDISABLE COMPOUNDS, POLYMERISATION INCIDENTS... 

The hydrocarbon-phenol reaction, catalysed by the etherate, was being run in petroleum ether solution in a sealed pressure bottle. The bottle burst, possibly owing to exothermic polymerisation of the diene. 

Dimerisation is highly exothermic, the rate increasing rapidly with temperature, and may cause rupture of a closed uncooled container. The monomer may largely be prevented from dimerising by storage at — 80°C or below [1]. The polymerisation of the undiluted diene may become explosive within the range 0-40°C and at pressures above 2300 bar. The effect of diluents was also studied [2], A polymerisation was... 

It explodes on heating or in contact with concentrated acids (the latter possibly involving Beckmann rearrangement and/or polymerisation of the oxime form, which is effectively a 1,3-diene). 

Attempted high-vacuum fractional distillation of an isomeric mixture (10% cis-) led to explosive decomposition. The diene polymerises if stored at 20°C. 

Use of a symmetrical acyclic alkene limits the possible metathesis products to the desired diene (for example 45) and products formed from polymerisation of the cyclic substrate. Competing ROMP was suppressed in these reactions by using dilute conditions and a tenfold excess of hex-3-ene. By adding the cyclic substrate slowly to a solution of the catalyst and ris-hex-3-ene (which was significantly more reactive than the trans isomer), less than two equivalents of the acyclic alkene were used without causing a significant drop in the cross-metathesis yield. 

Polymerisation reaction, particularly of olefins and dienes catalysed by organometallic compounds fall under the category of coordination polymerisation, or Ziegler-Natta polymerisation. 

The "Alfin" catalyst (Morton 1964 Reich 1966) is made up to a suspension, in an inert solvent like pentane, of a mixture of an alkylenyl sodium compound (such as allyl sodium), an alkoxide of a secondary alcohol (such as sodium isopropoxide), and an alkali halide (such as sodium chloride). The catalyst is highly specific for the polymerisation of dienes into the 1, 4-forms. 

Another application of an isomerisation reaction can be found in the production of the third monomer that is used in the production of EPDM rubber, an elastomeric polymerisation product of Ethene, Propene and a Diene using vanadium chloride catalysts. The starting diene is made from vinylnorbomene via an isomerisation reaction using a titanium catalyst. The titanium catalyst is made from tetravalent salts and main group hydride reagents, according to patent literature. 

Industrially this diene is made the same way as ethylidenenorbomene from butadiene and ethene, but now isomerisation to 2,4-hexadiene should be prevented as the polymerisation should concern the terminal alkene only. In both systems nickel or titanium hydride species react with the more reactive diene first, then undergo ethene insertion followed by (3-hydride elimination. Both diene products are useful as the diene component in EPDM rubbers (ethene, propene, diene). The nickel hydride chemistry with butadiene represents one of the early examples of organometallic reactions studied in great detail [22] (Figure 9.14). 

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