Synthesis and Characterization of [Poly(3-dodecylthiophene)]₂Poly(methyl methacrylate) Miktoarm Star Copolymer

We have introduced a facile synthetic route for well-defined [poly(3-dodecylthiophene)]₂ poly(methyl methacrylate) miktoarm star copolymer (P3DDT₂PMMA) by using a click reaction. For this purpose, PMMA with two ethynyl groups (PMMA-(≡)₂) and ω-azidopropyl-P3DDT were synthesized. We found that the use of alkyl linker (here, propyl group) between P3DDT and azido group is very essential to minimize the steric hindrance arising from bulky side group in P3DDT during the click reaction. When we employed a slightly excess amount of the ω-azidopropyl-P3DDT, we obtained a well-defined P3DDT₂PMMA with a narrow molecular weight distribution (polydispersity index <1.20) after selective removal of the unreacted ω-azidopropyl-P3DDT in a crude product by using column chromatography. We also investigated self-assembled structure of P3DDT₂PMMA by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). P3DDT₂PMMA with weight fraction of P3DDT block (w_P3DDT) of 0.33 had lamellar microdomains, while a linear diblock copolymer (P3DDT-b-PMMA) with w_P3DDT = 0.37 showed cylindrical microdomains. Also, P3DDT₂PMMA with w_P3DDT = 0.59 showed the HEX cylindrical microdomains of PMMA in the P3DDT matrix, whereas P3DDT-b-PMMA with w_P3DDT = 0.56 exhibited lamellar microdomains. More interestingly, P3DDT₂PMMA with w_P3DDT of 0.76 showed hexagonally packed PMMA cylinders in the P3DDT matrix at molten state, and this morphology was maintained even after crystallization of the P3DDT block. This behavior is quite different from linear P3DDT-b-PMMA diblock with the same weight fraction of P3DDT because the latter shows fibril structures after P3DDT crystallization. These results imply that controlling the molecular architecture is an effective way to tune the morphology of P3AT-containing block copolymers.