Search

International audience; The cationic ring-opening polymerization of 2-methyl-2-oxazoline (MOx) using iodine initiating system was reported. Uncolored polyoxazolines were produced in spite of the use of iodine initiator, well-known dye molecule. Low molecular weight asymmetric telechelic polyoxazolines carrying an acetylimine head group and an oxazolinium end group were synthesized, with a good control over the molecular weight. NMR and MALDI-Tof experiments allowed the full determination of the chemical structures of the produced poly(2-methyl-2-oxazoline)s, notably with the acetylimine head group, explained by spontaneous α-HI elimination. Finally, to our knowledge, we reported the first detailed mechanism of cationic ring-opening polymerization of 2-methyl-2-oxazoline in acetonitrile according to UV experiments. An ionic-type mechanism was involved with the dissociation of molecular iodine to active initiating species.

International audience; The polymerization of methyl methacrylate (MMA) initiated by 2,2'-azobis(isobutyronitrile) (AIBN) as radical initiator in the presence of iodine (I2) was studied at different temperatures (T = 70 C and 80 C). This process, called reverse iodine transfer polymerization (RITP), is based on the direct reaction of radicals with molecular iodine. RITP efficiently controls the molecular weight (determined by size exclusion chromatography, SEC) and the structure of the polymer chains (confirmed by 1H and 13C NMR spectroscopy). For instance, PMMA samples of Mn,SEC = 2300 g mol-1 and polydispersity index PDI = Mw/Mn = 1.5 (Mn,theoretical = 2300 g mol-1), Mn,SEC = 4600 g mol-1 and PDI = 1.6 (Mn,theoretical = 4700 g mol-1), Mn,SEC = 9600 g mol-1 and PDI = 1.6 (Mn,theoretical = 10 000 g mol-1), and Mn,SEC = 19 200 g mol-1 and PDI = 1.5 (Mn,theoretical = 18400 g mol-1) were successfully prepared by RITP. The polymerization was followed by on-line 1H NMR spectroscopy, and the conversion of iodine was followed by titration with a thiol (thioglycolic acid). It was shown by SEC, titration of iodine, gas chromatography, and NMR analyses that RITP was split into two different periods: a first "inhibition" period during which iodine is consumed to form very short -iodotelomers, and a second period where the polymerization follows the kinetics of a conventional free radical polymerization governed by degenerative chain transfer. The degenerative chain transfer constant was estimated to be Cex 2.6 at T = 80 C. Last, the iodine-end-capped structure of the polymers was demonstrated by different analytical techniques, and the iodine functionality of the PMMA chains was up to 95%.