Morphological Consequences of Catalytic Hydrogenation of Polymers in the Bulk
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MORPHOLOGICAL CONSEQUENCES OF CATALYTIC HYDROGENATION OF POLYMERS IN THE BULK LAURA R. GILLIOM, DALE W. SCHAEFER AND JAMES E. MARK* Sandia National Laboratories, Albuquerque, NM 87185
ABSTRACT When suitable catalysts are molecularly dispersed in polymers, the polymers can be modified without added solvent. This paper describes studies on the morphology of samples of trans-l,4-polybutadiene and sMn1,2-polybutadiene which have been partially deuterated in the bulk. The development of a peak in the SANS data for the 1,2-polybutadiene suggests the formation of small domains upon deuteration. Possible explanations for this observation, including chemical and physical heterogeneity, are evaluated. Results of SAXS and thermal measurements are also considered.
INTRODUCTION We have previously shown that olefinic polymers can be hydrogenated in the bulk with transition metal catalysts [1]. The absence of added solvent is in contrast to more conventional solvent-based methods for polymer modification [2]. Both the molecularly dispersed (dissolved) catalyst and the flexible polymer chain provide the mobility required for high conversions to hydrogenated polymer. The reaction exotherm must be completely adsorbed by the polymer. Given the unique reaction conditions, it is appropriate to investigate the morphology of the product polymer at intermediate levels of hydrogenation. Small-angle x-ray (SAXS) and small-angle neutron (SANS) scattering provide structural information on the 5-500A length scale. Differential scanning calorimetry (DSC) probes physical transitions in materials. We have used these techniques to assess physical state and chemical heterogeneities resulting from the bulk modification. Typically, polymers were only partially deuterated. Since the huge difference in coherent scattering lengths of H and D enhances contrast between deuterated and undeuterated polymer regions, SANS is sensitive to chemical heterogeneity produced by localized deuteration. SAXS, on the other hand, is relatively insensitive to deuteration because of the small difference in x-ray scattering length of H and D. SAXS is, however, sensitive to density variations (e.g., crystallinity) on the 5-50OX length scale. This paper describes our studies using these techniques on trans-l,4-polybutadiene and syn-1,2-polybutadiene.
EXPERIMENTAL Sample Preparation: Materials: Sy=-l,2-polybutadiene (1,2-PB) was purchased from Polysciences. NMR analysis suggests approximately 10% 1,4-addition and 90% 1,2-addition. Purchased material was described as 28% crystalline. Trans-l,4-polybutadiene (1,4-PB), a gift of Gencorp, was 88% trans. Both polymers were purified by precipitation from toluene solution prior to use. Crabtree catalyst [Ir(COD)(py)(tcyp)]PF6 (COD-1,5-cyclooctadiene; py-pyridine; tcyp=tricyclohexylphosphine) was prepared according to literature procedures [3]. Sample Preparation: To polymer (l.5g) dissolved in 25 mL benzene was added 15 mg catalyst. The Mat. Res. Soc. Symp. Proc. Vol. 171. ©1990 Materials Research Society
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