Reverse iodine transfer polymerization of methyl acrylate and n-butyl acrylate

Solution polymerization of methyl acrylate initiated by 2,2'-azobis(isobutyronitrile) (AIBN) at 65 degrees C in the presence of molecular iodine 12 has been studied. The process, called reverse iodine transfer polymerization (RITP), efficiently controls the molecular weight (determined by size exclusion chromatography, SEC) and the structure of the polymer. For instance, poly(methyl acrylate) samples of M-n,M-SEC = 5700 g mol(-1) and M-w/M-n = 1.79 (M-n,M-theoretical = 5500 g mol(-1)), M-n,M-SEC = 10 900 g mol(-1) and M-w/M-n = 1.91 (M-n,M-theoretical = 10 500 g mol(-1)), and M-n,M-SEC = 21800 gmol(-1) and M-w/M-n = 1.98 (M-n,M-theoretical = 20 700 g mol-1) were successfully prepared. The polymerization was followed by on-line 1H NMR spectroscopy to investigate the evolution of several compounds in the reaction medium, especially the adduct between primary radicals and iodine (A-I, where A stands for the radical fragment from the initiator), the monoadduct A-M-1-I (where M stands for the monomer unit), and the monomer conversion. The iodine-end-capped structure of the polymers (A-M-n-I, where n is the mean number degree of polymerization) was further demonstrated by mass-assisted laser desorption ionization time-of-flight (MALDI-TOF). The inhibition period in RITP of n-butyl acrylate was shortened at higher temperature (about 30 min at 95 degrees C) without detrimental effect on the control of the molecular weight of the final polymer: M-n,M-SEC = 8600 g mol(-1) and M-w/M-n = 1.88 (M-n,M-theoretical = 9200 g mol(-1)). Furthermore, RITP of acrylates was successfully performed in a large variety of media (in bulk, toluene, alpha,alpha,alpha-trifluorotoluene, anisole, methyl ethyl ketone, butyl acetate, propylene carbonate, propionitrile, and dimethylformamide). Last, the living nature of the polymer was confirmed by the preparation of a poly(methyl acrylate)-b-polystyrene block copolymer.