Long chain branched isotactic polypropylene (LCB-PP) was synthesized using metallocene catalyst (rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride activated by methylaluminoxane). The branching was in situ generated in a diluted polymerization condition using hexane or toluene as diluent. The polymers have a significant population of branched molecules as evidenced by multiangle laser light scattering analysis. More importantly, such a branching structure in isotactic polypropylene has been, for the first time, identified by 13C NMR spectroscopy. The 13C NMR resonance assignments of the branching structure are based on the model polymer characterization, stereo environment analysis, and chemical shift calculation. The unique stereo environment of the branching structure provides insight into the mechanism of LCB formation in such isotactic polypropylenes. The branching levels determined by 13C NMR are directionally consistent with that estimated from laser light scattering analysis.

High‐resolution proton‐decoupled carbon‐13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of completely amorphous polymers, semicrystalline polymers, and a series of ethylene–vinyl acetate copolymers. With these samples the nature of the glass temperature, other postulated amorphous transitions, and the β transition were investigated. For the completely amorphous polymers, the average correlation times depend on temperature according to the Williams–Landel–Ferry relation. Spectral collapse occurs at temperatures whose ratio to Tg is in the range 1.2–1.4 and corresponds to a correlation time of about 10−7s. The loss of resolvable spectra is demonstrated to be a consequence of experimental methods and is not due to the occurrence of another amorphous transition. Both the methylene and methine carbons can be resolved for the ethylenevinyl acetate copolymers. Although the correlation time for the methylene carbon is continuous and resolvable through the β transition region, the methine branch‐point resonance is lost. The implication of these results to the molecular nature of the β transition is discussed.

Carbon‐13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of branched polyethylenes whose β transition temperatures were determined independently. Resolvable spectra could be obtained at temperatures either corresponding to or very close to the temperature of the β transition. Together with results for other systems, these observations preclude the indentification of the β transition with the glass temperature. From the measured spin relaxation times and nuclear Overhauser enhancements average correlation times were calculated as a function of temperature. The average correlation times were calculated as a function of temperature. The average correlation time is on the order of 10−8−10−9 s at the β transition. These results argue strongly against it being assigned to the glass temperature.