Atactic polypropylene at high pressure. I. Deuteron-NMR determination of the glass-transition temperature

Abstract The effect of pressure on the glass-transition temperature T g in atactic poly(propylene) (aPP) has been investigated in the pressure range up to 5000 bar. The decay rate of the deuteron-NMR quadrupole echo is used to monitor the glass transition. The increase of T g and the decrease of d T g /d p with pressure are similar to their behavior in other hydrocarbon polymers. It appears that in aPP along the glass-transition line, the dependence of T g ( p ) on the density ρ g ( p ) can be represented by a power law T g ( p )/ T g (0)=[ ρ g ( p )/ ρ g (0)] m with m =2.0. This behavior is compared with the one in other polymers and in orthoterphenyl. The decrease of d T g /d p is compared with the results of the lattice model by DiMarzio et al.