Patent ID: 8513172

Claim:
A process for preparing a polymer and a lubricating composition thereof, comprising the steps of: (1) contacting: (i) a free radical initiator; (ii) a chain transfer agent containing a thiocarbonyl thio group and a free radical leaving group; and (iii) a radically polymerisable monomer, to form a polymer chain; wherein the process of step (1) is a controlled radical polymerisation process with living characteristics; and at least about 50% of the polymer chains from step (1) contain a reactive end group capable of reacting with a polyvalent coupling agent; (2) contacting the polymer prepared by step (1) with a polyvalent coupling agent to form a star-polymer, wherein the star-polymer is a block-arm star polymer or a hetero-arm star polymer; and wherein the star polymer is derived from at least two monomers comprising: (a) at least 50 wt % of a mixture of C12 to C15 alkyl substituted (meth)acrylate monomers; and (b) less than 50 wt % of an alkyl (meth)acrylate monomer containing 1 to 30 carbon atoms in the alkyl group, other than the C12 to C15 alkyl substituted (meth)acrylate monomer; (c) optionally containing less than 20 wt % styrene; and (d) optionally containing less than 10 wt % alkyl (meth)acrylamide, and wherein the star-polymer has about 2 to about 50 arms present on the star polymer; (3) optionally contacting the polymer prepared by step (1) or step (2) with a polymerisation inhibitor; and (4) mixing the polymer prepared by step (2) or step (3) with an oil of lubricating viscosity to form a lubricating composition.