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

Abstract

We have introduced a facile synthetic route for well-defined [poly(3-dodecylthiophene)] 2 poly(methyl methacrylate) miktoarm star copolymer (P3DDT 2 PMMA) 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 P3DDT 2 PMMA 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 P3DDT 2 PMMA by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). P3DDT 2 PMMA 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, P3DDT 2 PMMA 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, P3DDT 2 PMMA 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. ■ INTRODUCTIONRegioregular poly(3-alkylthiophene) (P3AT) is one of the most attractive semicrystalline polymers due to its high charge carrier mobility and good solubility in organic solvents. 1−3 To achieve high performance organic electronic devices, one challenge is fabrication of P3AT nanostructures with nanometer length scale. 4,5 For this purpose, various block copolymers consisting of P3AT and coil blocks have been synthesized 6−15 because of their self-assembly ability to form periodic nanostructures. 16−18 However, most poly(3-hexylthiophene) (P3HT)-containing block copolymers usually exhibit only fibril morphology due to strong rod/rod interaction of P3HT. 18−22 In the rod−coil block copolymer system, the phase behavior is determined by the competition between rod/rod interaction (μ) of rod block and the segregation power (governed by the Flory's segmental interaction parameter χ) between rod and coil blocks. 23−25 These two factors are adjusted by varying the composition of each block or tuning the crystallinity of the rod moiety. Some research groups used P3AT with longer (or bulkier) alkyl side chain than P3HT to depress the crystallization of the rod block. Ho et al. 26 reported various na...

Rod–coil type miktoarm star copolymers consisting of polyfluorene and polylactide: precise synthesis and structure–morphology relationship

“…[19][20][21][22] However, a challenge still exists in the precise synthesis of miktoarm star polymers containing rod-like blocks mainly due to the difficulty in the preparation of the well-defined rod-like polymer segment. Although several pioneering studies concerning the miktoarm star polymers containing rod-like blocks, such as poly(L-glutamic acid), 23,24 poly(n-hexyl isocyanate), [25][26][27][28] and poly(3-alkylthiopehe)s, [29][30][31] have been reported, the effect of the miktoarm type architectures on the self-assembling behaviors remains largely unexplored.…”

Recent progress in block copolymer crystallization

“…There have been several studies concerning the morphological behavior of the most common BCP rod‐like polymer, poly(3‐hexylthiophene) (P3HT), because of its value as a conductor and light absorber. Because the alkyl chain on the 3‐position of polythiophenes helps to organize the structure and provide increased solvent processability, work has focused on other polythiophene block copolymers such as poly(3‐(2′‐ethyl)hexylthiophene) (P3EHT) and other poly(alkylthiophenes), such as poly(3‐butylthiophene) (P3BT) and poly(3‐dodecylthiophene) (P3DDT) . With longer substituent alkyl chains, poly(alkylthiophenes) exhibit depressed melting temperatures relative to P3HT which allows them to robustly form microphase‐separated domains that confine the other block in block copolymer mixtures …”

“…Several groups also studied the influence of architecture on the crystallizability of one block. For conjugated polymer crystallization, P3DDT was studied in a PMMA‐P3DDT 2 miktoarm star copolymer and compared to PMMA‐ b ‐P3DDT . For the linear BCP, larger PMMA fractions led to typical BCP microphase‐separated morphologies; however, with larger P3DDT, break‐out crystallization occurred giving a crystalline fibril structure morphology .…”

“…For the linear BCP, larger PMMA fractions led to typical BCP microphase‐separated morphologies; however, with larger P3DDT, break‐out crystallization occurred giving a crystalline fibril structure morphology . In an attempt to control the morphology of majority‐phase P3DDT, Park et al . chose to make miktoarm star PMMA‐P3DDT 2 copolymers, where the PMMA block can be thought of as tethered to the central portion of the P3DDT component.…”

Precise Synthesis of Block and Miktoarm Star‐Branched Polymers Containing Polythiophene Segments with Low Dispersity by Combination of Living Anionic Polymerization and Catalyst‐Transfer Polycondensation Systems

“…(P3HT) 2 ‐ star ‐PMMA has an M n value of 21.5 kDa and low Ð M value of 1.18. Based on a modified synthetic procedure, the same group succeeded in synthesizing an A 2 B‐type miktoarm star‐branched polymers where A and B were P3DDT and PMMA segments, respectively ((P3DDT) 2 ‐ star ‐PMMA, M n = 13.5–31.2 kDa, Ð M = 1.14–1.19) . Recently, the same group also synthesized an AB 2 ‐type miktoarm star‐branched polymers where A and B were P3HT and PMMA segments, respectively, (P3HT‐ star ‐(PMMA) 2 , M n = 6.40–20.5 kDa, Ð M = 1.17–1.21) based on the direct coupling reaction of living anionic PMMA with ω‐chain‐end‐functional P3HT with two bromometyl groups …”