Morphology control of poly(3-hexylthiophene)-b-poly(ethylene oxide) block copolymer by solvent blending

Thermal Stability of π-Conjugated n-Ethylene-Glycol-Terminated Quaterthiophene Oligomers: A Computational and Experimental Study

This work represents a joint computational and experimental study on a series of n-ethylene glycol (PEOn)-terminated quaterthiophene (4T) oligomers for 1 < n < 10 to elucidate their self-assembly behavior into a smectic-like lamellar phase. This study builds on an earlier study for n = 4 that showed that our model predictions were consistent with experimental data on the melting behavior and structure of the lamellar phase, with the latter consisting of crystal-like 4T domains and liquid-like PEO4 domains. The present study aims to understand how the length of the terminal PEOn chains modulates the disordering temperature of the lamellar phase and hence the relative stability of the ordered structure. A simplified bilayer model, where the 4T domains are not explicitly described, is put forward to efficiently estimate the disordering effect of the PEO domains with increasing n; this method is first validated by correctly predicting that layers of alkyl (PE)-capped 4T oligomers (for 1 < n < 10) stay ordered at room temperature. Both 4T-domain implicit and explicit model simulations reveal that the order-disorder temperature decreases with the length of the PEO capping chains, as the associated increase in conformational entropy drives a tendency toward disorder that overtakes the cohesive energy, keeping the ordered packing of the 4T domains.

Exclusive Synthesis of Poly(3-hexylthiophene) with an Ethynyl Group at Only One End for Effective Block Copolymerization

Well-controlled synthesis of ethynyl-functionalized poly(3-hexylthiophene) (P3HT) is crucial for preparation of block copolymers containing the P3HT segment by means of click coupling reaction. A well-known chain end modification method, in which Kumada-Tamao catalyst-transfer polymerization is quenched with ethynylmagnesium chloride, under various conditions is re-examined, but in all cases not only P3HT with an ethynyl group at one end but also P3HT di-ethynylated at both ends is obtained. Accordingly, Sonogashira coupling reaction of P3HT having H/Br ends with trimethylsilylacetylene is tried, followed by removal of the trimethylsilyl group, and it is found that this protocol affords exclusively P3HT with an ethynyl group at one end. This post end-modification method is applied to the synthesis of an amphiphilic diblock copolymer of P3HT and poly(2-ethyl-2-oxazoline) (PEtOx) by means of click reaction between ethynylated P3HT and PEtOx with an azide group at one end, and the product is confirmed to be free from contamination with triblock copolymer. Micellization of this block copolymer is confirmed in tetrahydrofuran (THF)/water and THF/methanol mixtures.

Controlling the morphology and crystallization of a thiophene-based all-conjugated diblock copolymer by solvent blending

We report the crystallization and microphase separation behavior of an all-conjugated poly(3-hexylthiophene)-b-poly[3-(6-hydroxy)hexylthiophene] (P3HT-b-P3HHT) block copolymer in mixed solvents and demonstrate how the conformations of P3HT and P3HHT chains influence the photophysical properties of the copolymer. It is shown that the balance among π-π stacking of P3HT, P3HHT and microphase separation of the copolymer can be dynamically shifted by controlling the rod-rod interactions of the copolymer via changing the block ratio and solvent blending. A series of nanostructures such as well-ordered nanofibers, spheres and lamellar structures are formed and their formation mechanisms and kinetics are discussed in detail. The variations in P3HT-b-P3HHT conformations are concomitant with a hybrid photophysical property depending on the competition between intrachain and interchain excitonic coupling, resulting in the transformation between J- and H-aggregation. Overall, this work demonstrates how the P3HT-b-P3HHT conformations crystallize and phase-separate in the solution and solid state, and the correlation between their structures and photophysical properties, which improves our understanding of all-conjugated rod-rod block copolymer systems.