Synthesis of fluorinated alkoxyamines and alkoxyamine-initiated nitroxide-mediated precipitation polymerizations of styrene in supercritical carbon dioxide

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 ...

Cobalt-Mediated Radical Polymerization of Vinyl Acetate and Acrylonitrile in Supercritical Carbon Dioxide

“…[ 30 ] Polymers were also produced in precipitation, suspension or by dispersion NMP using appropriate CO 2 -soluble nitroxides or alkoxyamines. [ 31 ] RAFT polymerization was also implemented to the dispersion polymerization of vinyl monomers in scCO 2 . [ 32 ] Recent advances in CRP in dispersed media have been recently reviewed in an excellent article by Zetterlund et al [ 33 ] In this communication, we report on the fi rst implementation of CMRP of VAc and AN in scCO 2 .…”

“…Briefly, ATRP was implemented for the homogeneous polymerization of perfluorinated (meth)acrylates or for the dispersion polymerization of methyl methacrylate or styrene by using specifically designed CO 2 ‐soluble copper complexes . Polymers were also produced in precipitation, suspension or by dispersion NMP using appropriate CO 2 ‐soluble nitroxides or alkoxyamines . RAFT polymerization was also implemented to the dispersion polymerization of vinyl monomers in scCO 2 .…”

Polymerization-induced self-assembly based on ATRP in supercritical carbon dioxide

“…S3). Poor controlled/living character for nitroxide-mediated radical polymerization (NMP) conducted as precipitation polymerization in scCO2 in previous work has been attributed to the high heterogenity of the system [49][50][51][52]. It can be speculated that similar factors are at play in the present ATRP system, with low monomer loadings causing partitioning of reagents (catalyst and ligand) away from the locus of polymerization.…”

RAFT polymerization in supercritical carbon dioxide based on an induced precipitation approach: Synthesis of 2-ethoxyethyl methacrylate/acrylamide block copolymers

“…Over the past decade, heterogeneous controlled/living radical polymerizations in benign supercritical carbon dioxide (scCO 2 ) have become commonplace, and have been the subject of recent reviews . Nitroxide‐mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer (RAFT), and iodine transfer polymerization (ITP) have all been reported in scCO 2 . Most of these systems are classified as precipitation or dispersion polymerizations, where the monomer is initially soluble in the reaction medium, but the resultant polymer precipitates at a critical degree of polymerization ( J crit ) .…”