Conjugated polymer nanoparticles (CP NPs) attract attention as nanoscale materials used for a variety of applications. In relation to this, the internal structure of CP NPs is an important factor for their properties, and numerous investigations have been carried out to control their nanomorphology. Here, we report the formation of CP NPs from defect-free cyclic poly(3-hexylthiophene) (c-P3HT) using a microfluidic device, and the effect of polymer topology on their structural and solvatochromic properties was investigated. CP NPs from c-P3HT exhibited reduced particle sizes and hypsochromic shifts in the absorption spectrum when compared to CP NPs obtained from corresponding linear P3HT (l-P3HT). Furthermore, steady responses in the solvatochromism of CP NPs from c-P3HT were observed, while those from l-P3HT displayed molecular weight dependency. These topology effects were caused by the change in the conjugation length, solubility, and crystallinity upon cyclization. Grazing incidence X-ray scattering (GIXS) studies of spin-coated P3HT films further showed a reduced interchain order and a larger proportion of face-on molecular orientation on a substrate for c-P3HTs. The various distinct structures observed for c-P3HT indicate the use of polymer topology as a means of nanostructure regulation.

Dispersion stabilization of nanoparticles for catalytic reactions is an important issue. However, dispersing agents should be carefully selected not to hinder catalytic performance. In the present study, physisorption of cyclic poly(ethylene glycol) (c-PEG) onto platinum nanoparticles (PtNPs) was investigated in comparison with unmodified PtNPs (PtNPs/No PEG), PtNPs mixed with linear PEG (PtNPs/HO-PEG-OH), and PtNPs chemisorbed with HS-PEG-OMe (PtNPs/HS-PEG-OMe). DLS showed a significant increase in the particle size for PtNPs/c-PEG and PtNPs/HS-PEG-OMe compared to PtNPs/No PEG and PtNPs/HO-PEG-OH. ζ-potential measurements revealed values around −30 mV for PtNPs/No PEG and PtNPs/HO-PEG-OH, whereas PtNPs/c-PEG and PtNPs/HS-PEG-OMe approached 0 mV, which indicated that c-PEG and HS-PEG-OMe adsorb onto PtNPs to form a shielding layer. Moreover, PtNPs/c-PEG and PtNPs/HS-PEG-OMe were stable in a phosphate-buffered saline (PBS) solution, but PtNPs/No PEG and PtNPs/HO-PEG-OH immediately aggregated. This suggests that high dispersion stability by c-PEG is comparable to ordinary surface modification using HS-PEG-OMe. Furthermore, the catalytic ability of PtNPs/c-PEG and PtNPs/HS-PEG-OMe was compared in various reactions. As a result, physisorbed PtNPs/c-PEG showed suitable catalytic activities, whereas chemisorbed PtNPs/HS-PEG-OMe was significantly hampered by the blocking of the catalytic sites with thiol in some reactions. Thus, physisorption of c-PEG endows PtNPs with dispersion stability and maintains the catalytic ability, leading to an alternative way of modifying metal nanoparticles.