Diels-Alder elastomers

To the extent that degradation of the material occurs, the introduction of self-healing properties may also be considered. These have as yet no commercial application, but self-healing properties have been experimentally demonstrated in the case of polydimethylsiloxanes and Diels-Alder elastomers [68]. From the point of view of resource cascading, it is important that the inclusion of substances conferring self-healing properties does not interfere with later stages in the resource cascade. 

Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

Uses Synthetic rubbers and elastomers (styrene-butadiene, polybutadiene, neoprene) organic synthesis (Diels-Alder reactions) latex paints resins chemical intermediate. 

Gheneim R, Perez-Beramen C, Gandini A. Diels-Alder reactions with novel polymeric dienes and dienophiles synthesis of reversibly cross-linked elastomers. Macromolecules 2002 35 7246-7253. 

Cyclopentene is readily available as a byproduct in the ethylene production. Norbornene 2-ethylhexyl carboxylate is obtained by the Diels-Alder reaction of 2-ethylhexyl acrylate with cyclopenta-diene (5). Norbornene isobornyl carboxylate, norbornene phen-oxyethyl carboxylate, and other related monomers are synthesized according to the same route. Polymers obtained from these esters exhibit excellent properties in terms of controlling the crosslinking density, the associated product modulus, and the glass transition temperature (Tg), thus allowing tailoring the properties of elastomers, plastics and composites. Other suitable monomers are summarized in Table 1.1 and sketched in Figure 1.2. 

The metathesis polymerisation of dicyclopentadiene, an inexpensive monomer (commercially available cyclopentadiene dimer produced by a Diels-Alder addition reaction containing ca 95 % endo and ca 5 % exo form), leads to a polymer that may be transformed into a technically useful elastomer [144-146, 179] and thermosetting resin [180,181]. The polymerisation has characteristics that make it readily adaptable to the reaction injection moulding ( rim ) process [182], The main feature of this process comes from the fact that the polymerisation is carried out directly in the mould of the desired final product. The active metathesis catalyst is formed when two separate reactants, a precatalyst (tungsten-based) component and an activator (aluminium-based) component, are combined. Monomer streams containing one respective component are mixed directly just before entering the mould, and the polymerisation into a partly crosslinked material takes place directly in this mould (Figure 6.5) [147,168,183-186],... 

A comonomer for the synthesis of ethylene/propene elastomers - 2-ethylidene-norbomene (7) - is synthesised via a Diels-Alder cycloaddition of cyclopenta-diene and butadiene followed by an isomerization with titanium-based catalysts of the intermediate 2-vinyl derivative 6 in excellent yield (98 %) (eq. (12)) [22]. 

The use of Diels-Alder and platinum-catalyzed polyaddition reactions of vinylferrocene derivatives to prepare ferrocene-containing polycarbosilanes has also been described. " These reactions were also used to prepare materials with additional functional groups that led to ferrocene and silicon-containing polyesters, polyamides, and polyurethanes. Molecular weights varied in the range of 3,800-6,000 and products were liquids or elastomers. 

Butadiene is a petroleum product obtained by catalytic cracking of naphtha or light oil or by dehydrogenation of butene or butane. It is used to produce butadiene-styrene elastomer (for tires), synthetic rubber, thermoplastic elastomers, food wrapping materials, and in the manufacture of adiponitrile. It is also used for the synthesis of organics by Diels-Alder condensation. 

Diels-Alder condensations of fumaric and maleic acid polyesters with various dienes can serve as another example. These reactions require 20 hours at room temperature. Diels-Alder condensations can also be carried out on polymers of 1,3,5-hexatriene, 1,3,5-heptatriene, and 2,4,6-octatriene. Sulfonate-substituted maleic anhydride adds to low-functionality hydrocarbon elastomers, like EPDM, presumably via an Alder-ene-type reaction ... 

Ninh, C. and Bettinger, C.J. (2013) Reconfigurable biodegradable shape-memory elastomers via Diels-Alder coupling. Biomacromolecules, 14 (7), 2162-2170. 

Polynorbornene, the first metathesis polymer produced in industrial scale, was marketed in 1976 by CdF Chimie under the trade name Norsorex . The monomer is produced by Diels Alder reaction of cyclopentadiene and ethylene and polymerized in n-butanol using an RuCls/HCl catalyst. Norsorex is a very high molecular weight (Mn > 2 x 10 g/mol), thermoplast (rg = 35°C) with approximately 90% trans-dovhXe bonds. The polymer is compatible with high loads of extending oils and plasticizers (up to 700%) and easily vulcanizable. By addition of suitable amounts of plasticizers the polymer is converted into an elastomer (Tg = —60 °C). 

One of the most interesting of the newer elastomers is the aromatic equivalent of a polyalkenamer, polynorbornene, which is used in its plasticized form. Its introduction followed about 10 years of study of the Diels-Alder reactions of olefins with cyclopentadiene undertaken by CdF Chimie in France. In 1976 this company put on stream a plant with a capacity of 5000 tonnes per annum to produce the polymer which they market as Norsorex. 

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