Title

Investigation of the structure and properties of polyisobutylene-based telechelic ionomers of narrow molecular weight distribution .2. Mechanical

Document Type

Article

Publication Date

1-24-1997

Department

Polymers and High Performance Materials

Abstract

Sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) have been recently developed, providing additional control over the structure and properties of these novel polymers. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, and a secondary peak, were recently observed in the narrow MWD sulfonated PIB telechelics for the first time. SAXS evidence, given earlier as part I of this two-part series, suggests that compression-molded sulfonated PIB telechelic ionomers with a narrow MWD (<(M)over bar (w)>/<(M)over bar (n)>approximate to 1.15) may have a local secondary structure of ionic lamellae or cylinders, and no such structure is found in similar broad MWD (<(M)over bar (w)>/<(M)over bar (n)>approximate to 1.8) telechelics. It is shown that narrowing the MWD, which acts to promote locally continuous structure in the tri-arms, alters the character of the network, in that the modulus of the tri-arm telechelic systems increases and the elongation at break is lowered by narrowing the MWD or decreasing the <(M)over bar (n)>. The tri-arms of the highest <(M)over bar (n)> (49.5 kg/mol) exhibit strain hardening and the lowest modulus, highest-breaking stress, and highest elongation at break in the ionomers studied. The presence of local ionic structure is also indicated by stress relaxation experiments in which the long-term or near-equilibrium stress is seen to decrease when the MWD is broadened or <(M)over (n)>, increases. It is believed that the difunctional materials do not form extensive ionic networks at all, but principally chain-extend, as has also been found before. It is observed that the properties of a solution 'blend'' of narrow MWD ionomers that has the same counterion, <(M)over bar (n)>, and polydispersity as a broad MWD system exhibits lower elongation to break, lower breaking stress, and modulus of narrow MWD systems relative to the broader MWD material. Dynamic mechanical data indicate that narrowing the MWD or decreasing <(M)over bar (n)>,increases the flow transition temperature and rubbery plateau modulus. The ''blend'' exhibits dynamic mechanical properties between the narrow and broad, having a higher flow transition temperature than the broad MWD, but lower than the narrow MWD, and a rubbery plateau modulus between the other two. (C) 1997 John Wiley & Sons, Inc.

Publication Title

JOURNAL OF APPLIED POLYMER SCIENCE

Volume

63

Issue

4

First Page

507

Last Page

519