GB640567A - Improvements in or relating to mineral oil compositions - Google Patents

Abstract

Alkylated polystyrenes suitable for use as V.I. improvers in mineral oils (see Group III) comprise a polystyrene of mean mol. wt. between 20,000 and 60,000 alkylated with 0.2 to 0.8 part by weight of propylene polymer. The propylene polymer may boil above 55 DEG C. and consist predominantly of the trimer. The alkylation may be carried out using a Friedel-Crafts catalyst such as AlCl3, HF or BF3. Depolymerization of the polystyrene when using AlCl3 may be prevented by the presence of a small proportion of an organic nitro compound such as nitromethane or nitrobenzene. When anhydrous HF is used as an alkylation catalyst it is added to a solution of the polystyrene in a solvent such as ethylene dichloride cooled to 0-+5 DEG C. The olefin is then added slowly with stirring, the reaction time being about 3 hours at 0-+5 DEG C. After the completion of the reaction the HF is removed with ice water or by heating, the organic layer thoroughly washed with water and the product precipitated by adding slowly to alcohol with agitation. The precipitate is filtered off and dried in vacuo at 60-70 DEG C. The proportions used in an example are solvent 300 g., polystyrene 30 g., olefine 20 g., HF 30 g. The solvents used may be ethylene dichloride, nitrobenzene, dichlorobenzene, carbon tetrachloride, dichloro-ethylether, monochlorbenzene, chloroform, carbon bisulphide or chloronitromethane. A very similar procedure is used when AlCl3 is used as the alkylation catalyst, but in this case the polystyrene solution may be saturated with dry HCl prior to the addition of the A1Cl3. The latter may be added in the form of a solution. Polystyrene of the required mol. wt. may be prepared either by polymerization of the monomer or by milling of a polystyrene of higher mol. wt. on hot rolls until degradation to the required mean mol. wt. has occurred. Alternatively, the degradation of the polymer may be carried out by stirring a solution of the polystyrene with A1Cl3 at room temperature or somewhat above until the mol. wt. of the polystyrene has been reduced to the required degree, after which the depolymerization action of the A1Cl3 may be arrested either by washing with dilute HCl or by the addition of a depolymerization inhibitor. In the latter case the propylene polymer may be added and the A1Cl3 may then be used as the alkylation catalyst. Suitable polymerization inhibitors are any organic nitro compounds, either aliphatic, aromatic or mixed, e.g. nitro alkanes, such as nitromethane, nitroethane or nitropropane, or any aromatic nitro compound such as nitrobenzene, nitrotoluene, nitroethylbenzene or nitronaphthalene. The organic nitro compound may be used in any desired proportion, but small proportions suffice. Where the organic nitro compound is a solvent for either the polystyrene or the A1Cl3 it may be employed both as an alkylation solvent and a depolymerization inhibitor. Specification 640,566 is referred to.ALSO:Hydrocarbon oils of improved V.I. for lubrication or operation of hydraulic mechanisms and transmissions, contain in solution a small proportion, e.g. 0.1 to 12 per cent by weight, of polystyrene having an average molecular weight between 20,000 and 60,000 and which has been alkylated by reaction with a propylene polymer in the proportion of from 0.2 to 0.8 part by weight of propylene polymer per part of polystyrene. The propylene polymer may be a fraction boiling above 55 DEG C. at atmospheric pressure and may be predominantly the trimer. Alkylations may be carried out using a Friedel-Crafts catalyst with or without an organic nitro compound as depolymerization inhibitor (see Group IV (a)). The preferred propylene polymer-polystyrene ratio is 0.2 to 0.5 when the alkylate is intended for naphthenic oils used largely for hydraulic purposes, and 0.4 to 0.8 for paraffinic oils.