Patent ID: 7592381

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 185° 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 while maintaining the temperature from 185° C. to 221° C. for a period of time from 4 hours to 30 hours thereby forming a cured polymer modified bituminous binder composition; wherein said block copolymer composition comprises (i) a diblock copolymer comprising one block of a monovinylaromatic hydrocarbon and one block of a conjugated diene having a peak molecular weight from 30,000 to 78,000 and a vinyl content from 35 to 80 mol percent based on the number of repeat monomer units in the conjugated diene block, and (ii) optionally one or more block copolymers comprising at least two blocks of monovinylaromatic hydrocarbon and at least one block of conjugated diene, the block copolymer selected from linear triblock copolymers having a peak molecular weight that is 1.5 to 3.0 times the peak molecular weight of the diblock copolymer, multiarm coupled block copolymers having a peak molecular weight that is 1.5 to 9.0 times the peak molecular weight of the diblock copolymer, and mixtures thereof, wherein each block copolymer has a vinyl content from 35 to 80 mol percent based on the number of repeat monomer units in the conjugated diene block, wherein when both (i) and (ii) are present in the block copolymer composition, the ratio of (i) to (ii) is greater than 1:1, and wherein the melt index for the block copolymer composition is from about 20 g/10 min to about 35 g/10 min as determined by ASTM D 1238, condition G (200° C., 5 kg load).