Adhesion
The results show that the hot melt adhesive two resin mix had peel resistance and loop tack performance dominated by the Regalite S1100, the fully hydrogenated hydrocarbon resin, which had the best mid-block compatibility.

There was little effect from the partially hydrogenated hydrocarbon resin, Regalite S5100, which had poor isoprene mid-block compatibility. Since Regalite R7100 is a partially hydrogenated hydrocarbon resin, it only had partial compatibility with the mid-block and therefore the adhesion was less.

Viscosity Curves
At temperatures >160°C, the resin made a major contribution to the adhesive viscosity and at temperatures up to 180°C all resins tested produced similar viscosities. At these mixing temperatures most resins have a good compatibility; that is, the adhesive is a homogeneous blend. As temperature decreases, a change in the slope of the viscosity curve is observed because the end-blocks of the polymer begin to associate and the viscosity begins to increase more rapidly as temperature falls.

The temperature of this transition depends on the styrene content of the polymer and the compatibility of the resin with the end-block. Regalite S1100, the fully hydrogenated hydrocarbon resin, produced the highest adhesive viscosity; that is, it provided the most significant viscosity increase upon cooling due to its low association with the end-blocks. Regalite S5100 partially hydrogenated hydrocarbon resin offered a significantly lower viscosity since it was much more compatible with styrene. The synergy of the two resins was very clearly seen at 120°C. There was a significant effect from Regalite S5100 which had good compatibility with the end-block producing an overall viscosity lower than either of the one resin systems.

Comments on Cohesion and Creep Resistance
The hot melt adhesvies made with a mixture of fully and partially hydrogenated tackifiers had higher cohesion than those made with either resin by itself. These differences were more apparent as the test temperature increased. At 25°C the styrenic end-block domains had completely formed and the shear results did not distinguish between the test formulas.

At 40° and 70°C the differences in cohesion became clear. The fully hydrogenated Regalite S1100 produced a tackier, but softer adhesive with low cohesive strength due mainly to the dilution of the mid-blocks. The partially hydrogenated Regalite S5100 did not produce as much tack due to incompatibility with the mid-blocks, but decreased cohesion due to end-block softening. The mixed tackifier systems and Regalite R7100 produced higher cohesion due to the partial compatibility with both the mid-and end-blocks. The advantage of Regalite R7100 is that it achieves an effect comparable to the mixture of Regalite S1100 and Regalite S5100 with the formulating simplicity of using only a single tackifier.

Comments on Cohesion at Higher Temperature
The improved cohesion performance parameters at 40°C and 70°C confirmed the superior higher temperature cohesion performance for fully hydrogenated resins (containing no aromaticity). At higher temperatures partially hydrogenated hydrocarbon resins provided lower cohesion due to their good compatibility with the end-block.

This resulted in a weakening of the end-block domains. The effect increased with lower hydrogenation levels due to increasing aromaticity of the resin. Again, the synergistic effects of the two resins could be seen; at 40°C Regalite S5100 provided a significant cohesive strength contribution. At 70°C, however, both resins combined for total synergy producing a shear resistance value greater than each resin alone. The higher SAFT results confirm these observations.