ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Melt rheology of elastomeric triarm sulfonated polyisobutylene model ionomers has been studied. The molecular weights (Mn) of the polymers have been varied from 8300 to 34,000. The sulfonated materials were neutralized with potassium hydroxide either to the exact stoichiometric equivalence point or to twice this amount, i.e., 100% excess neutralizing agent was added. For comparison one nonsulfonated precursor of Mn = 8300 was also studied. It was observed that the introduction of one sulfonate group at each chain end of the triarm poly-isobutylene molecule changes the state of matter at room temperature. Specifically, the unsulfonated materials are viscous liquids while the sulfonated ionomers are solid elastomers at room temperature. The zero-shear melt viscosity of the unsulfonated precursor is 900 poise (90 Pa·s), at room temperature while for those materials neutralized with potassium hydroxide to the exact stoichiometric point it is above 9 × 103 poise (900 Pa·s) at 180°C. As expected, the zero shear viscosity increases with an increase in the molecular weight. Significant ionic interactions still persist at 180°C as evident by the high viscosity of the ionomers. However, at higher frequencies (∼600 rad/s), the melt viscosity decreases to about 5 × 103 poise for the different molecular weight materials. The melt viscosity of ionomers containing 100% excess neutralizing agent shows a dramatic increase. The excess KOH is speculated to be incorporated into the ionic domains rather than uniformly distributed throughout the matrix. This results in an increased strength of the ionic aggregates, thereby increasing the melt viscosities. Thus, due to the very pronounced effect on rheological properties it is important to know not only the extent of neutralization (up to full neutralization) but also the amount of excess neutralizing agent, if any, which is present in the sample.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1984.070291011
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