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

ポリ(-イソプロピルアクリルアミド)とポリエチレングリコールにブロック共重合体のソープフリー乳化重合; 時間分割中性子小角散乱法による準リビング重合における特異的反応場の解明

元川 竜平   ; 小泉 智*; 橋本 竹治*; 安中 雅彦*; 中平 隆幸*

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.