INFLUENCE OF MOLECULAR-WEIGHT ON THE THERMAL-DECOMPOSITION OF HYDROXYL TERMINATED POLYBUTADIENE

Thermogravimetric analysis of hydroxyl terminated polybutadiene (HTPB) and its fractions of different molecular weights separated by prepara tive GPC shows two major stages of weight loss of different nature in a nitrogen atmosphere. The first stage is primarily depolymerisation, cyclisation and crosslinking of molecules and the second stage is main ly the decomposition of the residue from the first stage. The kinetic parameters, viz. activation energy E and pre-exponential factor A usin g four different non-isothermal integral equations show a systematic i ncrease with increase in molecular weight for the first stage, whereas for the second stage, the effect of molecular weight on E and A value s is not prominent. The increase in E and A values for the first stage is attributed to the formation of greater number of cyclised and cros slinked products from molecules of higher dimensions. Quantitative cor relations between the kinetic constants and the molecular weight param eters were derived for the first stage as a quadratic curve following the equation: E or lnA = K-1 - K-2/M (where K-1 and K-2 are empirical constants whose values are different for the different molecular weigh t averages, viz. M-n, M-w and M-z and for the different equations). (C ) 1997 Elsevier Science B.V.