Star polymers and compositions thereof

A process for preparing an ATRP star-polymer having greater than five, up to 40 arms, comprising the steps of:

• (1) contacting:
• (i) a radically polymerisable monomer, wherein the radically polymerisable monomer consisting of an alkyl (meth)acrylate ester, wherein the alkyl (meth)acrylate ester is:
• (a) a mixture of an alkyl ester group containing 10 to 15 carbon atoms present in at least 50% to 100% of the alkyl groups;
• (b) an alkyl ester alkyl group containing 6 to 9 carbon atoms present at 0% to 20% of the alkyl groups;
• (c) an alkyl ester alkyl group containing 1 to 5 carbon atoms present at 0% to 30% of the alkyl groups;
• (d) an alkyl ester group containing 16 to 30 carbon atoms present at 0% of the alkyl groups;
• and
• (e) a nitrogen containing monomer present at 0 wt % to 10 wt %;
• (ii) a transition metal catalyst;
• (iii) a nitrogen or phosphorus containing ligand;
• (iv) a halogen initiator that contains one or more atoms or groups of atoms which may be transferred by a radical mechanism under the polymerisation conditions, wherein the halogen initiator is represented by formulae (III)-(X):
• R5R6R7C—X;
• (III)
• R5C(═O)—X;
• (IV)
• R5R6R7Si—X;
• (V)
• R5R6N—X;
• (VI)
• R5N—X2;
• (VII)
• (R5)nP(O)m—X3-n;
• (VIII)
• (R5O)nP(O)m—X3-n;
• and (IX)
• (R5)(R6O)P(O)m—X, (X)
• wherein
• n is 0, 1 or 2;
• m is 0 to 1;
• X is Cl, Br, I, OR4, SR8, SeR8, OC(—O)R8, OP(—O)R8, OP(—O)(OR8)2, OP(═O)OR8, O—N(R8)2, S—C(—S)N(R8)2;
• R4 is
• an alkyl group with 1 to 20 carbon atoms and containing at least one halogen, in which each hydrogen atom in said alkyl group independently may be replaced by a halide;
• an alkenyl group with 2 to 20 carbon atoms and containing at least one halogen, or
• an aralkyl(aryl-substituted alkyl and containing at least one halogen, in which the aryl group is phenyl or substituted phenyl and the alkyl group represents an alkyl with 1 to 6 carbon atoms;
• R8 is an aryl group or a straight-chain or branched alkyl group with 1 to 20 carbon atoms and containing at least one halogen, or R8 is a ring containing at least one halogen functional group;
• and
• R5, R6 and R7 are independently hydrogen, halogens or hydrocarbyl groups, or a cycloalkyl group with 3 to 8 carbon atoms;
• and
• (v) optionally a free radical mediator, to form a polymer chain;
• (2) contacting the polymer chain of step (1) with a polyvalent coupling agent to form a star-polymer, wherein the polyvalent coupling agent is a divalent (meth) acrylic monomer, oligomer or polymer thereof or a divalent divinyl non-acrylic monomer, oligomer or polymer thereof;
• and at least one of steps (3) to (4);
• (3) contacting the polymer prepared by step (1) or step (2) with a polymerisation inhibitor;
• (4) mixing the polymer prepared by step (2) or step (3) with an oil of lubricating viscosity to form a lubricating composition.