STRUCTURE AND PROPERTIES OF CARBOXYLATO-TELECHELIC POLYISOPRENE

The effects of molecular weight, type of neutralizing cation and exces s neutralizing agent on the structure and properties of carboxylato-te lechelic polyisoprene have been studied. In particular, the effects of cation valence and cation size were studied for group IA and IIA elem ents, for which the bonding to the carboxylate anion is primarily ioni c. It was found that increasing cation valence and decreasing cation s ize have the general effect of increasing the electrostatic associatio n of the ion pairs, resulting in a more elastic stress-strain response . Neutralization with zinc(II) and nickel(II), elements of the first t ransition series that form less ionic, more coordinative complexes wit h the carboxylate ion, resulted in materials with quite different mech anical properties. The zinc-neutralized material displayed rather poor mechanical properties, while the nickel-neutralized material was much stronger. Materials neutralized with aluminium(III) or titanium(IV) w ere observed to display a wide range of properties depending upon the amount of cation incorporated. It was determined that at least four ti mes the stoichiometric amount of titanium(IV) is necessary to crosslin k the material effectively. Materials of higher number-average molecul ar weight (33 000 vs. 15 000) displayed higher stresses and higher ult imate elongations owing to the development of a more extensive entangl ement network. Finally, small-angle X-ray scattering studies of the M( n)BAR = 15 000 and 33 000 materials indicate that an ionic peak is obs erved for the M(n)BAR = 15 000 materials but is generally not observed for the M(n)BAR = 33 000 materials even with 100% excess neutralizing agent. The position of this peak is essentially unaffected by the typ e of neutralizing agent used. Analysis of the tail region of the scatt ering curves indicates that the interface between the ionic and non-io nic regions is sharp.