Adhesive for bonding to low surface energy surfaces

A pressure sensitive adhesive having a rubber phase, said adhesive comprising:

• (a) 100 parts by weight of a polymodal asymmetric elastomeric block copolymer;
• (b) at least one tackifier in an amount sufficient to raise the calculated Fox Tg of the rubber phase of said adhesive to at least 245° K.;
• (c) 0 to about 50 parts by weight of a crosslinking agent;
• and
• (d) 0 to about 300 parts by weight of a plasticizer;
• wherein said polymodal asymmetric elastomeric block copolymer has the formula Qn Y and comprises from about 4 to about 40 percent by weight of a polymerized monovinyl aromatic compound and from about 96 to about 60 percent by weight of polymerized conjugated diene, wherein:
• Q represents an individual arm of said block copolymer and has the formula S—B;
• n represents the number of arms Q in said block copolymer and is a whole number of at least 3;
• and
• Y is the residue of a multifunctional coupling agent;
• and further wherein:
• (a) S is a nonelastomeric polymer segment endblock of a polymerized monovinyl aromatic homopolymer, there being at least two different molecular weight endblocks in said copolymer, a higher molecular weight endblock and a lower molecular weight endblock, wherein:
• (i) the number average molecular weight of said higher molecular weight endblock (Mn)H is in the range of from about 5,000 to about 50,000;
• (ii) the number average molecular weight of said lower molecular weight endblock (Mn)L is in the range of from about 1,000 to about 10,000;
• and
• (iii) the ratio (Mn)H/(Mn)L is at least 1.25;
• and
• (b) B is an elastomeric polymer segment midblock which connects each arm to the residue of a multifunctional coupling agent (Y) and comprises a polymerized conjugated diene or combination of conjugated dienes, and
• wherein said adhesive has a rubber phase exhibiting a calculated Fox Tg of at least 245° K and said adhesive forms a high strength bond to low surface energy surfaces.