We present a quasielastic neutron scattering (QENS) study of the effect of tacticity on the local dynamics of polypropylene (PP). QENS measurements were carried out on different spectrometers. On IN10 (ILL, France) we have measured the decrease of the elastic intensity as a function of temperature for atactic (a-PP), isotactic (i-PP), and syndiotactic (s-PP) PP. The results show that the polyproylene sub-Tg dynamics is independent of tacticity. Measurements of the dynamic incoherent structure factor were carried out on the spectrometers IRIS and OSIRIS (ISIS, UK) and, after Fourier transform, the intermediate scattering functions were computed and analyzed. For all samples investigated, the intermediate scattering functions I(Q,t) show good overlap using shift factors that are close to those reported in the literature. Detailed analysis of the incoherent dynamic structure factor in terms of fast and slow decay processes indicates that in the subpicoseconds regime molecular motion is independent of tacticity. The slower segmental process depends on the sample stereoregularity and, consistently with C13 NMR measurements and molecular dynamics simulations, isotactic PP relaxes faster than the other polymers, while s-PP is the slowest. Correlation times display a non-Arrhenius temperature dependence that is described by a Vogel–Fulcher–Tamman relationship, with parameters that depend on tacticity. Thus the ratio between the correlation times is temperature dependent, and while the dynamic behavior of the samples is very similar at 460 K, considerable differences are observed at lower temperature.

The polymerization of styrene mediated by copper/N-n-alkyl-2-pyridylmethanimine is reported. Two different types of initiator were employed, viz., 1-phenylethyl bromide, chosen for its similar structure to the final end group of the polymer, and alkyl-2-bromisobutyrates, as models for the synthesis of diblock copolymers via macroinitiators. The copper catalyst structure was varied by changing the alkyl group on the N-n-alkyl-2-pyridylmethanimine ligand where alkyl = propyl (3), pentyl (4), and octyl (5) and used over a temperature range of 90−130 °C. At 90 °C, polymerization reactions were relatively slow with polymerization taking approximately 7 days to reach 100% conversion, 12 h to reach 36% conversion at 110 °C, and 7 h to reach 90% conversion at 130 °C. The PDI of the polymer broadens on increasing the temperature, reaching 1.15, 1.17, and 1.32 at 90, 110, and 130 °C, respectively, when the reaction was stopped. Thus, 110 °C is the optimal temperature for the polymerization of styrene with this type of ligand. The catalyst prepared with N-n-propyl-2-pyridylmethanimine is not completely soluble over all temperatures, and the catalyst solubility affects both the rate and the control of the polymerization. As the length of the alkyl chain increases, the solubility in nonpolar solvent also increases. Hence, N-n-pentyl-2-pyridylmethanimine is the best ligand for copper bromide to ensure homogeneity of the reaction and achieve good control over the polymerization. The effect of the solvent polarity was also investigated to elaborate the optimal polymerization conditions using xylene, anisole, and ethylene glycol diethyl ether. Based on these results, the synthesis of di- and triblock copolymers was undertaken using respectively poly(ethylene glycol) methyl ether and poly(propylene glycol) derived initiators. The latter led to an amphiphilic block copolymer with a low PDI = 1.27 and a molecular weight close to the theoretical value (M n SEC = 10 900 mol g-1). A large batch (40 g) of block copolymer was synthesized with a block of PS = 5000 g mol-1 by stopping the reaction at 50% conversion, which had [St]/[I] = 100.

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