Block copolymer and polymer modified bituminous binder composition for use in base course asphalt paving application

A polymeric composition comprising:

• (a) a coupled block copolymer having a plurality of arms comprising at least two blocks of a monovinylaromatic hydrocarbon and at least one block of a conjugated diene;
• and
• (b) optionally one or more block copolymers comprising at least one block of monovinylaromatic hydrocarbon and at least one block of a conjugated diene, the block copolymer may be selected from linear copolymers, linear triblock copolymers, multiarm coupled block copolymers, and mixtures thereof.
• wherein the molecular weight of the polymeric composition is in the range from about 100 kg/mol to about 400 kg/mol and the coupling efficiency is equal to or less than 40%.

A polymer modified bituminous binder composition for use as a base course in an asphalt paving application, comprising:

• about 90 to about 98% by weight of a bitumen component;
• and
• about 2 to about 10% by weight of a coupled block copolymer composition comprising:
• (a) a coupled block copolymer having a plurality of arms comprising at least two blocks of a monovinylaromatic hydrocarbon located on at least two of the plurality of arms, and at least one block of a conjugated diene located on at least one of the plurality of arms, and
• (b) optionally one or more block copolymers comprising at least one block of monovinylaromatic hydrocarbon and at least one block of a conjugated diene, the block copolymer selected from linear triblock copolymers, multiarm coupled block copolymers, and mixtures thereof.
• wherein the molecular weight of the polymeric composition is in the range from about 100 kg/mol to about 400 kg/mol.

A process for preparing a coupled block copolymer composition, the process comprising the steps of:

• (a) providing a solvent at a temperature of about 40° C. to about 60° C.
• (b) adding polystyrene and sec-butyl lithium to the solvent;
• (c) allowing the reaction to proceed for about 45 minutes to about 2 hours;
• (d) adding polystyrene for obtaining a predetermined molecular weight;
• (e) adding sec-butyl lithium and butadiene;
• (f) allowing polymerization to proceed from about 15 minutes to about 1 hour;
• (e) adding a coupling agent;
• and
• terminating the reaction from about 5 minutes to about 30 minutes after the coupling agent was added by the addition of a terminating agent.