Tapered triblock copolymers

A process for making a tapered triblock copolymer, comprising:

• adding a solvent, a polar modifier and conjugated diene and monovinyl aromatic monomers to a reactor to form an initial reaction mixture, wherein the amount of the polar modifier in the initial reaction mixture is less than 10 wt %;
• adding an organolithium initiator compound to the reactor and anionically polymerizing the monomers to form a first and block, wherein the conjugated diene monomer in the first block ranges between 70 and 90 wt %;
• adding additional conjugated diene monomer and/or additional monovinyl aromatic monomer to the reactor and polymerizing to form a second block, wherein the conjugated diene monomer in the second block ranges between 45 and 66 wt %;
• and
• forming a third block, which is another end block, thereby forming the tapered triblock copolymer, wherein the third block is a homopolymer of the monovinyl aromatic monomer, wherein the second block is bound directly to the first and third blocks, wherein the first block comprises 34 to 51 wt % of the tapered triblock copolymer, wherein the second block comprises 24 to 46 wt % of the tapered triblock copolymer, wherein the third block comprises 17 to 31 wt % of the tapered triblock copolymer,
• wherein the amount of monovinyl aromatic monomer in the tapered triblock copolymer is no more than about 53 wt %,
• wherein the solvent, the polar modifier, the conjugated diene monomer and the monovinyl aromatic monomers comprise a total reaction mixture, wherein the polar modifier is less than 5 wt % of the total reaction mixture,
• wherein the peak average molecular weight of the tapered triblock copolymer is between 75,000 and 250,000,
• wherein the peak average molecular weight of the first block is between 40,000 and 80,000, and
• wherein the number average molecular weight of the third block is between 5,000 and 40,000.

A tapered triblock copolymer composition, comprising:

• first and second end blocks and a middle block between and bound directly to the first and second end blocks;
• the first end block and the middle block comprising a copolymer of conjugated diene and monovinyl aromatic monomers and the second and block comprising a monovinyl aromatic polymer;
• the first end block comprising 30 to 60 wt % of the tapered triblock copolymer, wherein the first end block contains an amount of conjugated diene monomer of from about 70 to about 90 wt %;
• the middle block comprising 20 to 50 wt % of the tapered triblock copolymer, wherein the middle block contains an amount of conjugated diene monomer of from about 45 to about 66 wt %;
• the second end block comprising 10 to 40 wt % of the tapered triblock copolymer;
• and
• the tapered triblock copolymer having a peak average molecular weight between about 118,000 and about 250,000,
• wherein the amount of monovinyl aromatic monomer in the tapered triblock copolymer is from about 33 to about 53 wt %.

A tapered triblock copolymer composition, comprising:

• first and second end blocks and a middle block between and bound directly to the first and second end blocks, wherein:
• the first end block and the middle block are each a copolymer of a conjugated diene and styrene,
• the conjugated diene is butadiene and/or isoprene,
• the second end block is a styrene polymer,
• the first end block is within the range of 34 to 51 wt % of the triblock copolymer,
• the first end block is 70 to 90 wt % conjugated diene and 10 to 30 wt % styrene,
• the first end block has a 1,2-addition-vinyl content of 20 to 41 wt % of the amount of the conjugated diene in the first block,
• the middle block is within the range of 25 to 45 wt % of the triblock copolymer,
• the middle block is 46 to % conjugated diene and 34 to 54 wt % styrene,
• the second end block is within the range of 17 to 31 wt % of the triblock copolymer,
• the styrene content of the triblock copolymer is within the range of 33 to 53 wt %, and wherein the content of the conjugated diene in the triblock copolymer is within the range of 45 to 67 wt %.