A Nuclear Magnetic Resonance Investigation of Polypropylene

Measurements of second moments have been made on polypropylene, poly(2d propylene) and poly(3d 3 propylene) over a wide range of temperatures. Calculations of the theoretical rigid-lattice second moment using a computer programme have been made for these polymers and these agree approximately with the experimental values at the lowest temperatures. The range of temperatures over which methyl-group rotation affects the second moment has been established using the poly(3d 3 propylene) material. Linewidth measurements coupled with dynamic mechanical measurements on a vibrating-reed apparatus have shown that there is a close correspondence between the temperature of appearance of a narrow nuclear magnetic resonance line and that of the peak in the dynamic mechanical loss curves. Measurements of spin-lattice relaxation times have shown that the predominant process by which nuclei lose energy to the lattice at low temperatures is through the methyl-group rotation mechanism and calculations have been made of the activation energy of this process.