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International audienceThis paper is devoted to the study of fiber breakage during compounding with a polyamide matrix in a Buss kneader. Results showed a drastic decrease of glass fiber length during compounding, typically from 3500 to 350 mu m. Fiber breakage depended on processing conditions: it increased with screw speed, but the effect of feed rate was less clear. Fiber breakage increased also with the severity of the screw profile. Characterizations of fiber length evolution along the screw profile have also been performed after dead-stop experiments. Generally speaking, fiber length evolution can be described using a modified Shon-Liu-White model, in which either the number of turns or the specific energy is considered

The radical polymerization of 1,3‐butadiene initiated by hydrogen peroxide and controlled by TEMPO is presented. Various parameters (e.g., the temperature and the [TEMPO]o/[H2O2]o initial molar ratio, γo), were studied to optimize the reaction. It was observed that the higher the temperature, the higher the yield, with optimal yields noted for γo = 0.10 with high molecular weights and broad polydispersity indexes. In addition, the kinetics of radical polymerization showed a decrease (by one order of magnitude) of the macroradical concentration all along the reaction. The ln [butadiene]/[butadiene]o increased relative to time and behaved linearly after 90 min. Further, the concentration of free TEMPO was ≈1000 times lower than the initial concentration, in good agreement with the decoloring of the medium. Thus a quasi‐living behavior of butadiene was noted from this system. Finally, the hydrolysis of these oligomers, either in the presence of zinc or thermally by means of a thin‐layer evaporator under vacuum allowed the production of telechelic hydroxy polybutadienes, the second technique enabling the obtaining of higher molecular weights by coupling and the recovery of TEMPO. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3293–3302, 2000

SUMMARY:The controlled radical polymerization of butadiene initiated with 2,29-azoisobutyronitrile (AIBN) and in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) is presented. The produced oligomers which have number average degrees of polymerization ranging between 3 and 12 were characterized by NMR. This led to the determination of both the end-groups and the functionality. The hydrolysis of these oligomers yields a -hydroxy-x-cyano-polybutadiene. 13 C and 1 H NMR spectra of these products exhibit two characteristic signals of hydroxymethyl groups. The mechanism of the polymerization allows the assignments to cis-and trans-CH 2 CH2CH1CH 2 OH groups. In fact, this method also shows that geraniol endgroups are negligible in commercially available products obtained by the polymerization initiated with hydrogen peroxide.