Published January 1978
The petroleum resins considered in this report are synthetic hydrocarbon resins made by polymerizing mixtures of unsaturated monomers (olefins, diolefins, and aromatic vinyl compounds) that are obtained as by-products from the cracking of natural gas liquids, gas oil, or petroleum naphthas. The resins are relatively low in molecular weight and they range from liquids to brittle solids in physical form. Most of the common plastics and resins such as polyethylene, polypropylene, polystyrene, etc., are also derived from petroleum but they differ from the petroleum resins being considered here in that they are made from pure monomers, they are of known, definite composition, and they are polymerized to much higher molecular weights.
The petroleum resins described above are sometimes referred to as petroleum hydrocarbon resins, or simply as hydrocarbon resins. However, the term hydrocarbon resins, as used in the industry, includes not only petroleum resins but also coal tar (coumarone-indene) resins, natural resins (rosin and polyterpenes), and certain condensation products of aromatic hydrocarbons and formaldehyde. Each kind of resin has properties that make it preferred for certain applications, though some interchange- ability is possible.
The main source of raw materials for petroleum resins are by-product refinery streams that result from the steam cracking of various petroleum fractions for ethylene production. These fractions are cracked in the presence of 50-90 mol% of steam at temperatures in the range of 1000 - 1600�F. Although the major products are ethylene and propylene, condensates containing a wide range of higher molecular weight products are also produced. These are usually fractionated into various cuts, for example, into
- A C5 fraction containing linear and alicyclic olefins and diolefins;
- A C6-C8 aromatic solvents fraction containing benzene, toluene, and xylene;
- A C9+ heavy solvents cut containing dicyclopentadiene, styrene, indene, vinyltoluene, etc. This cut can be further fractionated to separate the cyclopentadiene and the aromatic olefinic compounds.
Petroleum resins are frequently classified or identified according to their origins:
- Aliphatic or aliphatic/alicyclic resins are generally made from C5 monomers.
- Aromatic resins are made from C9 monomers.
- Reactive or cyclopentadiene resins are made from the cyclopentadiene fraction or from mixtures of cyclopentadiene withother monomers. These resins contain conjugated double bonds that can react with drying oils.
Within each classification, resin properties can vary widely depending on the source of the cracking feedstock and on the composition of the resin feedstock. Resin properties may be further modified by hydrogenation, which is used as a means of improving color and stability.
An additional class of resins results from the polymerization of one or more pure monomers to low molecular weight resins designed for specific end uses. Examples of such monomers are styrene, alpha-methylstyrene, vinyltoluene, and isobutylene.
Petroleum resins are produced by catalytic or thermal polymerization. Friedel-Crafts catalysts such as aluminum chloride or boron trifluoride are usually used.