Structure and properties of carboxylato-telechelic polyisoprene

• Published in: Polymer (Guilford) 1992, Vol.33 (7), p.1347-1358
• Main Authors: Tant, M.R, Venkateshwaran, L.N, Song, J.H, Subramanian, R, Wilkes, G.L, Charlier, P, Jérôme, R
• Format: Article
• Language: English
• Subjects: Applied sciences; carboxylato-telechelic ionomers; Exact sciences and technology; Mechanical properties; neutralization; Organic polymers; Physicochemistry of polymers; polyisoprene; Properties and characterization; small-angle X-ray scattering; structure
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/0032-3861(92)90105-6

The effects of molecular weight, type of neutralizing cation and excess neutralizing agent on the structure and properties of carboxylato-telechelic polyisoprene have been studied. In particular, the effects of cation valence and cation size were studied for group IA and IIA elements, for which the bonding to the carboxylate anion is primarily ionic. It was found that increasing cation valence and decreasing cation size have the general effect of increasing the electrostatic association of the ion pairs, resulting in a more elastic stress-strain response. Neutralization with zinc( ii) and nickel( ii), elements of the first transition series that form less ionic, more coordinative complexes with the carboxylate ion, resulted in materials with quite different mechanical 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) were observed to display a wide range of properties depending upon the amount of cation incorporated. It was determined that at least four times the stoichiometric amount of titanium ( iv) is necessary to crosslink the material effectively. Materials of higher number-average molecular weight (33 000 vs. 15 000) displayed higher stresses and higher ultimate elongations owing to the development of a more extensive entanglement network. Finally, small-angle X-ray scattering studies of the M ̄ n = 15 000 and 33 000 materials indicate that an ionic peak is observed for the M ̄ n = 15 000 materials but is generally not observed for the M ̄ n = 33 000 materials even with 100% excess neutralizing agent. The position of this peak is essentially unaffected by the type of neutralizing agent used. Analysis of the tail region of the scattering curves indicates that the interface between the ionic and non-ionic regions is sharp.