Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes

Abstract

Abstract. We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a π-conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, ω, while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, χN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly of rod-coil block copolymers in a weakly segregated regime. The two rod-coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b-styrene), whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b4vinylpyridine), for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion theories.PACS. 61.46.-w Nanoscale materials -61.30.Vx Polymer liquid crystals -64.60.Cn Order-disorder transformations; statistical mechanics of model systems

Block Copolymers for Organic Optoelectronics

“…Alternatively, weakly segregated rod-coil block copolymers of alkoxy-substituted derivatives of poly(phenylenevinylene) have attracted much interest. [26][27][28][29][30][31][32] In this class of materials, the conjugated rod is appropriate for photovoltaic and OLED applications, but the coil block is chosen simply for its ability to provide fundamental information about thermodynamics and self-assembly. Poly-(2,5-di(2 0 -ethylhexyloxy)-1,4-phenylenevinylene)-b-polyisoprene (PPV-PI) was the first polymeric weakly segregated system with accessible phase transitions, enabling the construction of the first phase diagram for conjugated rod-coil block copolymer selfassembly, as illustrated in Figures 2 and 3.…”

Poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene): Synthesis, microphase separation, thin film transistors, and photovoltaic applications

“…We note that the proton resonance at 3.05 and 2.82 ppm are characteristic of a-methylene protons in head-to-tail linkage of 3-alkylthiophene units whereas the proton resonance at 2.59 ppm is characteristic of a-methylene protons in head-to-head or tail-to-tail linkage shown in Figure S1. Poly(3-cyclohexylthiophene) (P3cHT) Butylmagnesium chloride (2 M solution in THF, 4.8 mL, 9.6 mmol) was added into a solution of 2,5-dibromo-3-cyclohexylthiophene (3.16 g, 9.8 mmol) in anhydrous THF (40 mL) at [10][11][12][13][14][15] C, and purged with N 2 . The solution was degassed and purged upon stirring for 30 min at 10-15 C, then heated at mild reflux for 1 h. Reflux is stopped before the addition of Ni(dppe)Cl 2 (36.2 mg, 0.068 mmol) and then the mixture was refluxed for at least 24 h. The mixture was cooled to room temperature and poured into methanol to form a precipitate.…”

“…INTRODUCTION Multicomponent-conjugated polymer systems, especially polymer blends [1][2][3][4][5][6][7] and block copolymers, [8][9][10][11][12][13][14][15][16][17][18][19][20] offer the opportunity to tailor their electronic and optical properties to levels well beyond those possible in homopolymers and random/alternating copolymers. Most polythiophene-based multicomponent conjugated polymer systems investigated so far have been based on poly(3-hexylthiophene) (P3HT), 1,27,28 which is known to be a high mobility p-type polymer semiconductor 29,30 and a good donor component in fullerene-based bulk heterojunction (BHJ) solar cells.…”

Synthesis and Self-Assembly of Poly(diethylhexyloxy-p-phenylenevinylene)-b-poly(methyl methacrylate) Rod−Coil Block Copolymers

“…60,61 Recent work has universalized these phase diagrams in terms of rod-rod interaction (μ) and rod-coil interaction ( χ) in a weakly segregated system (DEH-PPV-b-polyisoprene), 14 though recent work in a more highly segregated system (DEH-PPV-b-poly(4-vinylpyridine)) has demonstrated when the rod-coil repulsion is stronger, competition between the rod alignment and rod-coil separation results in intriguing phases not observed in the weak segregation limit. 60,61 Here, we use an intermediate system that retains phase transitions in an accessible temperature range, but in which the competition between rod alignment and rod-coil separation is stronger (competition term G = μ/χ). Similar to Sary et al, we find a stronger presence of the nonlamellar phases but are now able to place these on a complete phase diagram indicating both microphase and liquid crystalline order-order and orderdisorder transitions.…”