Indene/coumarone resins

The products bear a strong formal resemblance to styrene and may be polymerised. For commercial purposes the monomers are not separated but are polymerised in situ in the crude naphtha, sulphuric acid acting as an ionic catalyst to give polymers with a degree of polymerisation of 20-25. 

In one process the naphtha fraction boiling between 160 and 180°C is washed with caustic soda to remove the acids and then with suilphuric acid to remove basic constituents such as pyridine and quinoline. The naphtha is then frozen to remove naphthalene, and agitated with sulphuric acid, then with caustic soda and finally with water. Concentrated sulphuric acid is then run into the purified naphtha at a temperature below 0°C. The reaction is stopped by addition of water after 5-10 minutes, any sediment is removed, and the solution is neutralised and then washed with water. Residual naphtha is distilled off under vacuum, leaving behind the resin, which is run into trays for cooling. 

By varying the coumarone/indene ratio and also the polymerisation conditions it is possible to obtain a range of products varying from hard and brittle to soft and sticky resins. 

Being either brittle or soft, these resins do not have the properties for moulding or extrusion compounds. These are, however, a number of properties which lead to these resins being used in large quantities. The resins are chemically inert and have good electrical insulation properties. They are compatible with a wide range of other plastics, rubbers, waxes, drying oils and bitumens and are soluble in hydrocarbons, ketones and esters. 

The resins tend to be dark in colour and it has been suggested that this is due to a fulvenation process involving the unsaturated end group of a polymer molecule. Hydrogenation of the polymer molecule, thus eliminating unsaturation, helps to reduce discolouration. 

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G-9 Aromatic Petroleum Resins. Feedstocks typically used for aromatic petroleum resin synthesis boil in the approximate range of 100—300°C at atmospheric pressure, with most boiling in the 130—200°C range. The C-9 designation actually includes styrene (C-8) through C-10 hydrocarbons (eg, methylindene). Many of the polymerizable monomers identified in Table 1 for coumarone—indene type cmdes from coal tar are also present in aromatic fractions from cracked petroleum distillates. Therefore, the technology developed for the polymerization of coal-tar cmdes is also appHcable to petroleum-derived aromatic feedstocks. In addition to availabiHty, aromatic petroleum resins offer several advantages over coumarone—indene resins. These include improved color and odor, as weU as uv and thermal stabiHty (46). 

Uses. Coumarone-indene resins have outlets in paints, as tackifiers in mbber compounding, and as adhesives in the manufacturing of flooring tiles (see Hydrocarbon resins). 

Natural rubber displays the phenomenon known as natural tack. When two clean surfaces of masticated rubber (rubber whose molecular weight has been reduced by mechanical shearing) are brought into contact the two surfaces become strongly attached to each other. This is a consequence of interpenetration of molecular ends followed by crystallisation. Amorphous rubbers such as SBR do not exhibit such tack and it is necessary to add tackifiers such as rosin derivatives and polyterpenes. Several other miscellaneous materials such as factice, pine tar, coumarone-indene resins (see Chapter 17) and bitumens (see Chapter 30) are also used as processing aids. 

To facilitate moulding a softener is incorporated. These may include soft industrial pitches or heavy tars, coumarone-indene resins or waxes. 

Butyl phenolic resin is a typical tackifier for solvent-borne polychloroprene adhesives. For these adhesives, rosin esters and coumarone-indene resins can also be used. For nitrile rubber adhesives, hydrogenated rosins and coumarone-indene resins can be used. For particular applications of both polychloroprene and nitrile rubber adhesives, chlorinated rubber can be added. Styrene-butadiene rubber adhesives use rosins, coumarone-indene, pinene-based resins and other aromatic resins. 

Fig. 10. Chemical structure of components in coumarone-indene resins.

According to the typical chemical composition of these resins, the coumarone content in the feedstock (and in the final resin) is very low compared to that for indene. Therefore, the use of the term polyindene resins would be more appropriate than coumarone-indene resins however, this is not a common practice. 

The raw material has to be washed to remove impurities. Diluted sodium hydroxide allows the removal of phenols and benzonitrile, and diluted sulphuric acid reacts with pyridine bases. The resulting material is distilled to concentrate the unsaturated compounds (raw feedstock for coumarone-indene resin production), and separate and recover interesting non-polymerizable compounds (naphthalene, benzene, toluene, xylenes). Once the unsaturated compounds are distilled, they are treated with small amounts of sulphuric acid to improve their colour activated carbons or clays can be also used. The resulting material is subjected to polymerization. It is important to avoid long storage time of the feedstock because oxidation processes can easily occur, affecting the polymerization reaction and the colour of the coumarone-indene resins. 

Coumarone-indene resins were produced by adding sulphuric acid to the stirred feedstock at 20-35°C, taking care to produce a good dispersion of the sulphuric acid to avoid scorching (dark-coloured resins are obtained), and to con-... 

Coumarone-indene resins ean be modified to mateh speeifie properties. Some of the most eommon modifieations in those resins are the following. 

Aromatic hydrocarbon resins. The polymerization procedure and variables in the reactions of the aromatic hydrocarbon resins are similar to those for the coumarone-indene resins. However, the Cg feedstreams used in the polymerization of the aromatic hydrocarbon resins do not contain significant amounts of phenols or pyridine bases, so they are submitted directly to fractional distillation. Distillation produced more byproducts than light coal-tar oils. The aromatic hydrocarbon resins obtained have softening points between liquid and 125°C and Gardner colour of 6 to 11. By changing distillation conditions, aromatic hydrocarbon resins with softening points between 65 and 170°C and Gardner colour of 5 to 10 can also be obtained. 

Production of these resins is similar to that for the coumarone-indene resins. As the raw material does not contain impurities, a small amount of the initiating system can be used. 

Hydrocarbon resins, rosin, rosin ester, coumarone indene resins, and terpene resins can be directly added to solvent-borne adhesives. For latex adhesives, resin emulsification must be produced before addition. 

Tackifiers. Phenolic resins are added to increase strength, oils resistance and resiliency of NBR adhesives. On the other hand, tack and adhesive properties can be improved by adding chlorinated alkyl carbonates. To impart tack, hydrogenated rosin resins and coumarone-indene resins can be added. 

Nitrile rubber is compatible with phenol-formaldehyde resins, resorcinol-formaldehyde resins, vinyl chloride resins, alkyd resins, coumarone-indene resins, chlorinated rubber, epoxies and other resins, forming compositions which can be cured providing excellent adhesives of high strength, high oil resistance and high resilience. On the other hand, NBR adhesives are compatible with polar adherends such as fibres, textiles, paper and wood. Specific formulations of NBR adhesives can be found in [12]. 

Johnston, W.D.J. Separation of magnetic catalysts from polymers such as hydrogenated coumarone-indene resins. US Patent (1941) 2,264,756. 

The highly aromatic resins are often used as coumarone/indene resin substitutes. A range of soft aromatic resins is available, produced from the alkylation of xylene and other aromatic hydrocarbons with dicyclopentadiene. These are excellent softeners for a wide range of rubbers. In common with other aromatic materials derived from petroleum sources, some of the resins used within the rubber industry are deemed to be carcinogenic. 

Uses. As an intermediate in the polymerization of coumarone-indene resins found in various corrosion-resistant coatings such as paints and varnishes in water-resistant coatings for paper products and fabrics in adhesives for use in food containers... 

Polyterpenes, coumarone-indene resins, and so-called petroleum resins are produced commercially using cationic polymerization. These are used as additives for rubber, coatings, floor coverings, and adhesives. 

Cumar Coumarone-indene resins Allied Chemical... 

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