Structure of Partially HydrogenatedPolybutadienes

GUILLERMO CASSANO; ENRIQUE M. VALLÉS; LIDIA MARÍA QUINZANI

POLYMER

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 1998 vol. 39 p. 5573 - 5577

0032-3861

An analysis of the molecular structure ofpartially hydrogenated fractions of a monodisperse polybutadiene has beencarried out in order to study the nature of the heterogeneous hydrogenationprocess.  The polybutadiene wassynthesized by polymerization of butadiene with t-butyl lithium in a non polarmedium.  This reaction produces linearpolibutadiene chains with about 7 1,2 addition units every 100 structuralunits.  The catalytic hydrogenation ofthe polybutadiene fractions was done either in cyclohexane with Pd/CaCO3 catalystor in heptane with Pd/BaSO4 catalyst. The reaction time was varied in order to obtain materials with differentamount of unsaturations.  The resultingpolymers were characterized by gel permeation chromatography, differentialscanning calorimetry, and infrared spectroscopy.  Solvent extraction using n-hexane was alsoperformed over thin films of several samples of hydrogenatedpolybutadienes.  The resulting fractionsof the non-extracted material, and of some of the extracted ones, were  analyzed using infrared spectroscopy.  The results show that the hydrogenationreaction generates a bimodal distribution of polymer species for globalconversions lower than approximately 89%. The catalytic reaction takes place in such a way that, in eachadsorption step, approximately 89% of the unsaturated groups of each adsorptedmolecule are hydrogenated.  This processgenerates a mixture of polymers that are either highly hydrogenatedpoly(ethylene©¤1-butene©¤butadiene) copolymer or non-hydrogenatedpolybutadiene.  The resulting blends areimmiscible at all the studied global conversions (12-89%).