No abstract

was found to give reasonably controlled/living nitroxide-mediated (NMP) precipitation polymerizations of styrene in supercritical carbon dioxide (scCO 2 ). In contrast under the same conditions, the analogous SG1 (N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide)-alkoxyamine gave higher rates of polymerization and inferior controlled/living character. The circumvention of the requirement for excess free [nitroxide] 0 allowed the study of nitroxide partitioning effects in scCO 2 for three newly synthesized fluorinated alkoxyamines. Two alkoxyamines dissociated into scCO 2 -philic fluorinated TIPNO-nitroxide derivatives, while another contains a similar sized fluorinated "foot". Despite the increase steric bulk about the N-O bond for the novel fluorinated alkoxyamines, all polymerizations proceeded at a similar rate and level of control to the TIPNO system in solution (toluene). PREDICI simulations for the styrene/TIPNO system are used to support extensive partitioning effects observed in scCO 2 for the fluorinated alkoxyamines. IntroductionSupercritical carbon dioxide (scCO 2 ) is a benign solvent used to circumvent the requirement for environmentally damaging volatile organic solvents. [1][2][3] Advantages include a readily accessible critical point (31 °C and 7.4 MPa), 4 variable solubility by subtle changes in pressure and temperature, 5 and the lack of chain transfer to solvent in radical polymerizations. 6,7 It is particularly well-suited for heterogeneous radical polymerizations, since reagents such as the monomer, initiator and controlling agent are generally soluble in scCO 2 , but the resultant polymer is insoluble and precipitates. 2,3 If the precipitation system is carried out in the presence of a colloidal stabilizer to prevent coagulation of particles, then dispersion polymerization results giving polymer of narrow particle size distributions and well-defined particles (d ≈ 100 nm to 15 μm). 1-3The monomer is not always soluble in the reaction medium, such as in the controlled/living nitroxide-mediated radical polymerization (NMP) of N-isopropylacrylamide (NIPAM) in scCO 2 , where an inverse suspension system is generated. 8,9 In recent years, there has been a proliferation in the numbers of reported controlled/living precipitation and dispersion polymerizations in scCO 2 with NMP, [9][10][11][12][13][14][15][16][17][18][19][20][21] atom transfer radical polymerization (ATRP), 22-29 reversible addition-fragmentation chain transfer (RAFT) 3, 30-39 and iodine transfer polymerization (ITP). 40,41 The slow build up in molecular weight (MW) in a controlled/living system by virtue of the equilibrium between active propagating radicals and dormant polymer chains allows measurement of the critical degree of polymerization (J crit ) before polymer chains precipitate from solution or the continuous phase (containing monomer and scCO 2 ). After J crit , the polymerization continues in the monomer-rich particle phase. For controlled/living precipitation/dispersion polymerizations, J crit can be ...

CO 2-responsive polyacrylamide copolymer vesicles with acid-sensitive morpholine moieties and large hydrophobic RAFT endgroup,