Patent ID: 7622519

Claim:
A process for preparing a polymer modified bituminous binder composition in the substantial absence of crosslinking agents, said process comprising the steps of: (a) heating a bitumen component in a stirred tank to a temperature from 160° C. to 221° C.; (b) adding a block copolymer composition to the bitumen component while the bitumen component is being stirred to form a homogeneous mixture of the bitumen component and the block copolymer composition; and (c) continuing to stir the homogeneous mixture at a temperature from 180° C. to 221° C. for a total period of time from 2 hours to 30 hours thereby forming a cured polymer modified bituminous binder composition; wherein said block copolymer composition comprises (i) a block copolymer of the formula S-B1-B2 wherein S is a monovinylaromatic hydrocarbon block having a peak molecular weight from 10,000 to 25,000, B1 is a polybutadiene block having a vinyl content of less than 15 mol percent, B2 is a polybutadiene block having a vinyl content of greater than 25 mol percent, wherein the weight ratio of B1 to B2 is greater than or equal to 1:1, and wherein the S-B1-B2 block copolymer has a peak molecular weight from 40,000 to 200,000; and (ii) optionally one or more block copolymers of the formula (S-B1-B2) n X wherein each S is a monovinylaromatic hydrocarbon block having a peak molecular weight from 10,000 to 25,000, each B1 is a polybutadiene block having a vinyl content of less than 15 mol percent, each B2 is a polybutadiene block having a vinyl content of greater than 25 mol percent, n is an integer from 2 to 6, and X is the residue of a coupling agent, wherein the weight ratio of 1 to B2 is greater than or equal to 1:1, and wherein the (S-B1-B2) n X block copolymer has a peak molecular weight that is from 1.5 to 6.0 times the peak molecular weight of the S-B1-B2 block copolymer; with the proviso that when the temperature in step c is greater than 199° C., the total time for stirring the homogeneous mixture in step (c) will range from 2 to 15 hours; and with the further proviso that when both S-1-B2 and (S-1-B2) n X are present in the block copolymer composition, the ratio of S-B1-B2 to (S-B1-B2) n X is greater than 1:1.