The linear expansions of two materials have been measured, a double-base propellant and a carboxyl-terminated polybutadiene. The glass transition temperature,Tg and expansion coefficients below and aboveTg have been calculated. The influence of the heating and cooling rates and sample thickness has been investigated. The results show that the value ofTg is dependent on the rates of heating and cooling but not on the sample thickness. Extrapolating to zero rate gives the sameTg for both heating and cooling. The expansion coefficients are not influenced by the rates of heating and cooling or by the sample thickness.