Soap-free emulsion polymerization of poly(ethylene glycol)--poly(-isopropylacrylamide); Elucidation of specific reaction fields for quasi-living polymerization by time-resolved SANS

Motokawa, Ryuhei   ; Koizumi, Satoshi*; Hashimoto, Takeji*; Annaka, Masahiko*; Nakahira, Takayuki*

Poly(ethylene glycol)--poly(-isopropylacrylamide) (PEG--PNIPAAm) was synthesized by radical polymerization of -isopropylacrylamide (NIPAAm) from the radically activated chain ends generated on PEG. The polymerization process was investigated by a conventional observation of molecular weight and its distribution as well as monomer conversion, (), as a function of the polymerization time and temperature , by means of time-resolved GPC. The reaction fields in which the polymerization takes place were explored by time-resolved small-angle neutron scattering (SANS). The results elucidated the following characteristics on the temperature-dependence of the solution structure and, hence, the reaction fields: (1) at 15 (C) 30, the solution is composed of swollen micelles in which PNIPAAmand PEG block chains form swollen cores and brushes emanating from the interface between them, respectively; and (2) at 34 (C) 60, the solution is composed of dehydrated PNIPAAm cores (hard cores) and swollen PEG brushes with well-defined interfaces between them. As for (1) and (2), the micelles were formed from a very early stage of the polymerization as being as small as 0.05, hence, yielding a "soap-free emulsion polymerization" field for NIPAAm. The results obtained in this work reveal that the hard-core micelle formation is the necessary and sufficient condition for the "quasi-living soap-free emulsion polymerization.