SYNOPSISThree samples of styrene-isoprene-styrene ( S-I-S ) block copolymers were chosen; copolymer A had 25% styrene, and copolymers B and C had 14% styrene. Copolymers A and B contained 20% diblock polymer and copolymer C contained 40% diblock polymer. All copolymers were mixed with a terpene type tackifier to make 56% and 48% weight tackifier concentration. These represent our model samples of pressure sensitive adhesives. The determination of tack, room-temperature peel-strength, and failure temperature under static shear were performed. The above results have been interpreted with the basic rheological data. The dynamic viscoelastic measurements and tensile stress-strain measurements were used. The effects of tackifier on the rubbery plateau moduli were treated with the GuthGold-type equation. The implications of the deviation from the equation are discussed in terms of the connectivity between polystyrene domains and the stability of the hard domains affected by inclusion of rubber segments.

For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.