AbstractIt is demonstrated that the improved tack and green strength accompanying the IAD modification of polybutadiene arise strictly from the introduction of bulky, polar groups. The fact that addition of 1,4‐PB occurs in a blocked arrangement is not a factor in the development of high green strength, as can be seen by the large increase in strength of modified 1,2‐PB, wherein the IAD groups are randomly attached. The tack is also elevated through random IAD addition; however, the relevance of blocked vs. random structure in this regard cannot be completely judged since it depends as well on the absolute IAD level and the polymer'sTg, as well as the test temperature. At high levels of IAD (about 38 mol ), the modified PB becomes a phase‐separated material, exhibiting high stiffness and brittleness. This heterogeneous system is quite unlike the PB modified with only 15 mol IAD. These latter elastomeric materials are homogenous, and remain so during deformation. The attainment of high tack and green strength relies upon maximal addition of the IAD groups, provided the molecules retain their flexibility. In blending the modified PB with other rubbers, optimum behavior in the blends appears to be achieved when the IAD–PB is present as a continuou
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