Indene Resins

The tar fraction boiling between 150 and 200°C contains 20-30% cumarone (benzofuran), significant amounts of indene, as well as the main component, naphtha, which is a cyclic-paraffin-rich fraction  

Benzofuran and indene have very similar boiling points (174 and 182°C, respectively), and thus are not separated, but are polymerized as a mixture to resins of molecular weight 1000-3000 with H2SO4 or AICI3 as catalyst. The polymerization proceeds predominantly via the double bond of the five-membered ring. The naphtha is evaporated after the polymerization. Discoloration of the resin by air and light is retarded by hydrogenation. 

A series of low-molecular-weight resins from natural products or industrial side products is known as cumarone-indene-like resins, since these resins have similar physical properties to the actual cumarone-indene resins. For example, cyclopentadiene from the petroleum process dimerizes easily to what is known as dicyclopentadiene (lUPAC 4,7-methylene-4,7,8,9-tetrahydroindene). Dicyclopentadiene cationically polymerizes to polymers with different monomeric units. The commercially available polymers soften at 100-120°C and become insoluble as surface films on further heating. 

On the other hand, /S-pinene probably polymerizes to (V) without undergoing a preceding isomerization  

After an aldol-type condensation, or after a condensation with elimination of water, cyclohexanone yields polymers with the monomeric unit 

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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-... 

After deactivation and removal of the initiating system, the eoumarone-indene resin is separated from solvent and low moleeular weight materials by vacuum distillation. The removal of the low moleeular weight materials is important beeause they produce strong odour, they aet as softeners and they eause an undesirable deerease in softening point. Therefore, at this stage the softening point of the eoumarone-indene resins is adjusted. Finally, stabilizers are added to the liquid resin while it is still hot to inhibit further oxidation (whieh eauses diseolouration and odour). 

The struetural element of a eoumarone-indene resin is relatively similar to that for aromatie hydroearbon resins, as they differ only in the proportion of indene-type struetures which are present in higher eoneentration in the eoumarone-indene resins. The main monomers in the aromatie resins are styrene and indene. Styrene produces the atactic conformation of the resins, whereas indene introduees rigidity into the polymer chain. A typical structural element of an aromatie resin is given in Fig. 11. 

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]. 

Carbon black may serve as a low-cost additive for controlling the gas migration in cement slurries [303]. It is intended as a suitable substitute for polymer latex and silica fume and has been tested in field applications [304,1256]. The concentration of carbon black varies from 2 to 20 parts, based on the weight of the dry cement [1220]. The particle size varies from 10 to 200 nm. A surfactant is necessary for dispersion, for example, formaldehyde-condensed naphthalene sulfonate or sulfonated cumarone or indene resins. 

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. 

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