Aqueous dispersions of polymer particles

A RAFT agent of general formula (5a)

• where R1 is —CH(CH3)COOH, —CH(CO2H)CH2CO2H, or —CH(CH3)CONRaRb, where Ra and Rb are the same or different and independently selected from H, C1-C6 alkyl, C1-C6 alkoxy, C6-C12 aryl, C7-C18 alkylaryl or C6-C12 heteroaryl, each of which is substituted with one or more hydrophilic groups selected from —CO2H, —CO2R′, —SO3H, —OSO3H, —SOR′, —SO2R′, —OP(OH)2, —P(OH)2, —PO(OH)2, —OH, —OR′, —(OCH2—CHR)<OH, —CONH2, CONHR′, CONR′R″, —NR′R″, —N+R′R″R′″, where R is selected from C1-C6 alkyl, w is 1 to 10, R′, R″ and R′″ are independently selected from C1-C6 alkyl and C6-C12 aryl which are optionally substituted with one or more hydrophilic substituents selected from —CO2H, —SO3H, —OSO3H, —OH, —(COCH2CHR), OH, —CONH2, —SOR and SO2R, and salts thereof;
• and
• Z is selected from optionally substituted alkyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted alkylthio, optionally substituted arylthio, optionally substituted arylalkylthio, and optionally substituted acylamino.

A method of preparing RAFT agents by conjugate addition of a dithiocarbonyl compound to an α,β-unsaturated carbonyl or thiocarbonyl compound.