The observation of chain conformation and mobility in polyethylene by solid‐state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon‐carbon bonds in the intermediate phase adopt, on the average, an all‐trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 107 Hz). Comparisons of crystallinities by differential scanning calorimetry, wide‐angle x‐ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from 13C spin‐lattice relaxation and 1H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.

A new polyimide was synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-l,3-(4-aminophenoxy)propane (DMDA), and abbreviated to be BTDA-DMDA. This polymer possesses three relaxation processes which have been observed through dynamic mechanical and dielectric analyses above -150°C. The a relaxation process has been assigned to be the glass transition and occurs at about 250 "C with an apparent activation energy of 420 kJ/mol. Two subglass relaxation processes are aprelaxation process at around 100-170 "C in a frequency range from 0,l Hz to 100 kHz with an activation energy of 182 kJ/mol and a y relaxation process occurs at around -80 "C with an activation energy of 44 kJ/mol. Carbon-13 solid state nuclear magnetic resonance experiments were carried out for the study of molecular dynamics at different temperatures. The results indicate that the y relaxation is responsible for an oscillation and R flipping motion of the two phenoxy rings in the DMDA portion. Theprelaxation was shown to pertain to the kHz-motion of the aromatic imide rings in the BTDA portion. The molecular motion of the DMDA and BTDA portions are largely decoupled from each other in the frequency region studied.

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