Method of providing high coefficients of friction across oil-lubricating friction clutches

A method of increasing the friction in an oil-lubricated friction clutch having a cellulose-based friction lining, or in a power-transmission device utilising said clutch, the method comprising:

• (i) preparing or otherwise obtaining a lubricant composition comprising
• (i.a) a major amount of oil of lubricating viscosity, and
• (i.b) one or more copolymers of ethylenically unsaturated esters present in an amount effective to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device;
• and
• (ii) lubricating said clutch or device with the lubricant composition resulting from step (i);
• wherein at least one copolymer (i.b) is a statistical copolymer derived essentially from the following co-monomers (a) and (b):
• (a) at least one ethylenically unsaturated ester compound of the formula (I):
• in which R is hydrogen or methyl, R1 is a linear or branched chain alkyl group having from 6 to 36 carbon atoms, and R2 and R3 are each independently hydrogen or a group of the formula —COOR′ in which R′ is hydrogen or a linear or branched chain alkyl group having from 6 to 36 carbon atoms;
• and
• (b) at least one ethylenically unsaturated ester compound of the formula (II):
• in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NRa— in which Ra is an alkyl radical having from 1 to 40 carbon atoms, R4 is a radical comprising from 2 to 100 carbon atoms and contains at least 2 oxygen, sulfur or nitrogen atoms, R5 and R6 are each independently hydrogen or a group of the formula —COX′R7 in which X′ is oxygen or an amino group of the formula —NH— or —NRa′— in which Ra′ is an alkyl radical having from 1 to 40 carbon atoms, and R7 is a radical comprising from 1 to 100 carbon atoms;
• wherein the co-monomer units originating from co-monomer (b) constitute from 0.1 to 30 weight percent of the total weight of said statistical copolymer.