Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PEG-b-PNIPAAm) was synthesized by radical polymerization of N-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, CM(t), as a function of the polymerization time t and temperature Tp, 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: (i) at 15 ≤ T p (°C) ≤ 30, the solution is composed of swollen micelles in which PNIPAAm and PEG block chains form swollen cores and brushes emanating from the interface between them, respectively; and (ii) at 34 ≤ Tp (°C) ≤ 60, the solution is composed of dehydrated PNIPAAm cores (hard cores) and swollen PEG brushes with well-defined interfaces between them. As for (i) and (ii), the micelles were formed from a very early stage of the polymerization as CM 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".
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry