A hot melt adhesive comprises at least one polymer selected from the group consisting of polystyrene, polybutene, polyisobutene, linear low density polyethylene, polypropylene random copolymer, polypropylene, olefin block copolymer, polyolefins, styrene block copolymers, and ethyl vinyl acetate polymers; a tackifying resin; and at least one precisely end-capped polystyrene (PECPS). The use of the styrene-based oligomers and polymers with the precisely controlled end-groups in hot melt adhesive formulations to improve compatibility with polymers and block copolymers frequently used in such adhesives.