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| - Critical Analysis of Network Defects in Cross-Linked Isobutylene-BasedElastomers by NMR Imaging
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| - The analysis of chemical and physical network heterogeneities has been carried out forsynthetic isobutylene-based elastomers using 1H spin echo NMR imaging. Spatial homogeneity wascompared for isobutylene−p-methylstyrene−p-bromomethylstyrene (PIB−PMS/BrPMS) terpolymers curedwith inorganic versus organic curatives and unfilled materials versus those filled with carbon black.Surprising differences in the network structure were found for materials cured with an inorganic curative(ZnO) relative to those cured with an organic curative (1,6-hexamethylenediamine). Voids and voiddistributions were found to be an important performance variable on the basis of comparisons betweenthe NMR imaging data and mechanical testing. Systematic comparison of solvent images and polymerimages revealed the optimum experimental conditions for enhancing network density contrast or detectingmicrovoids. For the first time, direct 1H images of polymer spins in a fully compounded, commercialpolyisobutylene-based elastomer were acquired in the absence of any swelling solvent. Multislice imagingexperiments were investigated as a method to construct three-dimensional void densities in elastomercompounds. Chemical-shift selective polymer imaging was used to selectively obtain network densityinformation for either component of a two-phase blend containing the PIB−PMS/BrPMS terpolymer andpolybutadiene. The ability of NMR imaging to provide data over statistically relevant sampling areas(hundreds of mm3) for both neat polymers and fully compounded commercial materials (containing carbonblack) represents a unique advantage over microscopic imaging methods for material property analyses.
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