Thermo-Responsive Diblock Copolymers of Poly(N-isopropylacrylamide) and Poly(N-vinyl-2-pyrroridone) Synthesized via Organotellurium-Mediated Controlled Radical Polymerization (TERP)

Diblock copolymers of poly( N -isopropylacrylamide) (PNIPAM) and poly( N -vinyl-2-pyrrolidone) (PNVP) (PNIPAM m - b -PNVP n ) with well-defined block lengths were successfully synthesized by organotellurium-mediated controlled radical polymerization (TERP) based on the finding that the homopolymerization of N -vinyl-2-pyrrolidone was better-controlled by TERP than by macromolecular architecture designed by interchange of xanthates (MADIX), TERP resulting in a narrower molecular weight distribution of PNVP. Heat-induced association properties in water of three block copolymers with different block lengths, PNIPAM 110 - b -PNVP 53, PNIPAM 110 - b -PNVP 234, and PNIPAM 76 - b -PNVP 219, were characterized by 1 H NMR, turbidity, quasi-elastic light scattering (QELS), and static light scattering (SLS) techniques. All three block copolymers dissolve in water molecularly (as a unimer state) when the solution temperature is below an aggregation temperature ( T a ) that is near a lower critical solution temperature (LCST) for the PNIPAM block. Comparing T a between the two block copolymers of the same the PNIPAM block lengths (DP n = 110), the diblock copolymer with a shorter PNVP block length tend to associate at a lower temperature. On the other hand, the association occurred at a higher temperature for the diblock copolymers with shorter PNIPAM block lengths. When the temperature was raised above T a, PNIPAM 110 - b -PNVP 234 and PNIPAM 76 - b -PNVP 219 formed apparently spherical core−corona micelles with aggregation numbers ( N agg ) of 808 and 298, respectively at 60 °C. In contrast, PNIPAM 110 - b -PNVP 53 formed a much larger aggregate with N agg = 27 000. This aggregate was speculated to be a multi core aggregate formed by the association of individual core−corona micelles. The copolymers were found to be bound to gold nanoparticles in water through coordination interaction of the PNVP block with Au. The polymer coated gold nanoparticles indicated a temperature-dependent color change arising from a shift of the maximum wavelength of the plasomon band.