In most cases unmodified aliphatic resins are used for HMPSA systems. They are mid-block compatible and do not change the end-block properties of styrene isoprene styrene (SIS) block copolymer-based formulations. Oils, generally used in these systems, are partially compatible with the end-blocks and addition of such oils will decrease the "hardness" and adversely affect shear adhesion. Other resins such as rosin esters, styrene modified terpene resins, or aromatic modified aliphatic resins can be used for tackification. Generally these resins exhibit mid-block and some degree of end-block compatibility.

Table 1: Formulations Based on Three Different Tackifier Resins

The conclusion can be made that the aromatic modified hydrocarbon resins Piccotac™ 9095 (Formulation 3), and Piccotac™ 8095 (Formulation 4) gives a much lower viscosity at 175°C than an aliphatic resin, such as Piccotac™ 1095-N. This is not surprising for aromatic modified resins, since the aromatic components of the resin will decrease the formation of styrene polymer endblock domain structure at high temperatures and thus creates an adhesive with a lower viscosity.