Investigations on the Phase Diagram and Interaction Parameter of

Mar 15, 2017 - Shared Materials Instrumentation Facility, Duke University, Durham, ... Department of Chemistry and Biochemistry, Florida State Univers...
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Investigations on the Phase Diagram and Interaction Parameter of Poly(styrene‑b‑1,3-cyclohexadiene) Copolymers Konstantinos Misichronis,†,∥,⊥ Jihua Chen,‡ Adam Imel,∥ Rajeev Kumar,‡,§ James Thostenson,# Kunlun Hong,‡ Mark Dadmun,∥ Bobby G. Sumpter,‡,§ Justin G. Kennemur,*,% Nikos Hadjichristidis,& Jimmy W. Mays,∥ and Apostolos Avgeropoulos*,⊥ †

Chemical Sciences Division, ‡Center for Nanophase Materials Sciences, and §Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States ∥ Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States ⊥ Department of Materials Science and Engineering, University of Ioannina, University Campus-Dourouti, 45110 Ioannina, Greece # Shared Materials Instrumentation Facility, Duke University, Durham, North Carolina 27708, United States % Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States & Physical Sciences and Engineering Division, KAUST Catalysis Center, Polymer Synthesis Laboratory, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955, Saudi Arabia S Supporting Information *

ABSTRACT: A series of linear diblock copolymers containing polystyrene (PS) and poly(1,3-cyclohexadiene) (PCHD) with high 1,4-microstructure (>87%) was synthesized by anionic polymerization and high vacuum techniques. Microphase separation in the bulk was examined by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) and compared to computational analysis of the predicted morphological phase diagram for this system. Because of the high conformational asymmetry between PS and PCHD, these materials self-assemble into typical morphologies expected for linear diblock copolymer systems and atypical structures. Rheological measurements were conducted and revealed order−disorder transition temperatures (TODT), for the first time for PS-b-PCHD copolymers, resulting in a working expression for the effective interaction parameter χeff = 32/T − 0.016. Furthermore, we performed computational studies that coincide with the experimental results. These copolymers exhibit well-ordered structures even at high temperatures (∼260 °C) therefore providing a better insight concerning their microphase separation at the nanoscale which is important for their potential use in nanotechnology and/or nanolithography applications.

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thermal and chemical stability7−20 when compared with the widely used poly(butadiene) and poly(isoprene). A firm understanding of the morphological behavior of diblock copolymers containing PCHD is still in the early stages, and previous reports11,12,21−26 have shown that microphase separation can occur in PS-b-PCHD and PI-b-PCHD diblocks as well as in ABA triblock copolymers and ABC triblock

INTRODUCTION

The self-assembly and resulting morphologies of block copolymers (BCPs) continue to garner interest1−3 due to the unique physical, chemical, and mechanical properties in addition to their numerous applications (i.e., nanopatterning, biomedical applications, nanocomposites, surfactants, nanoporous membranes, film coatings, etc.).4 There has been tremendous interest concerning the nanoscale self-assembly of BCPs, especially in thin-film applications.5,6 An intriguing and relatively new segment for BCPs is poly(1,3-cyclohexadiene) (PCHD) which is a glassy polydiene that exhibits better © XXXX American Chemical Society

Received: January 15, 2017 Revised: February 21, 2017

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Macromolecules terpolymers containing PCHD and either PS, PI, or PB as the other blocks. The high conformational asymmetry for these systems has led to a variety of unique morphologies but only when the PCHD segment contains high 1,4-microstructure.The rigid, cyclohexene-tehhered PCHD backbone microstructure in comparison with the most random coil of the other segments has led to these unique structures. PCHD segments with high 1,2-microstructure, in combination with PS, PI, or PB, do not self-assemble23 at similar degree of polymerization (N) values and compositions investigated, a phenomenon that warrants further investigation into the effective interaction parameter (χeff) between PCHD and other random coil blocks. In this report, we have synthesized a series of PS-b-PCHD copolymers, with high 1,4-PCHD microstructure and identified χeff as a function of temperature. We also explore morphological behavior through self-assembly of copolymers of varying composition in a kinetically trapped solvent-cast state and in a thermodynamically driven annealed state and compare our findings to a computational analysis of the phase diagram for these systems.

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Table 1. Characterization Results for PS-b-PCHD Samples sample

(M̅ n)1st blocka (g/mol)

(M̅ n)diblocka (g/mol)

Đb

ϕPSc

% 1,4PCHDe

Ndiblockf

S37C3 S30C6 S28C16 S11C7 S24C16 S24C17 C6S6d C10S6d

37 600 30 200 28 100 11 200 24 500 24 500 6 000 10 000

40 000 36 600 43 700 17 800 40 000 40 600 12 000 16 000

1.07 1.06 1.16 1.07 1.09 1.10 1.03 1.10

0.89 0.79 0.62 0.61 0.59 0.58 0.49 0.36

94 93 90 92 94 89 90 87

391 370 465 238 429 437 160 213

Determined using SEC-TALLS in THF at 25 °C. bPolydispersity indices determined by SEC analysis. cPolystyrene volume fraction ϕPS calculated from the equation ϕPS = f PSdPS/( f PSdPS + f PCHDdPCHD), using densities dPS = 1.05 g/mL and dPCHD = 1.07 g/mL15 and the weight fractions (f). dPCHD was the first block synthesized. ePCHD 1,4-microstructure determined by 1H NMR. fVolume corrected degree of polymerization N based on 118 Å3 reference volume (V0). a

molecular weight heterogeneity. A variety of polystyrene volume fractions (0.89 > ϕPS > 0.36) were chosen, providing a wide range of the phase diagram to investigate. Two samples, C6S6 and C10S6, are of PCHD majority, and in these cases the CHD was polymerized first. When CHD was polymerized as the second monomer, complete conversions were difficult due to side reactions, resulting in lower PCHD molecular weights and volume fractions than those initially targeted. By polymerizing CHD first, we were able to synthesize higher PCHD molecular weights and volume fractions while very low traces of side and/or termination reactions were observed.15 The polymerization system sec-BuLi/DABCO/benzene concluded to approximately 87−94% 1,4- and 6−13% 1,2microstructures for the PCHD block. In Table 2 the observed microphase for each sample in both the solvent-cast (“as-cast”) and thermally annealed films are summarized.

EXPERIMENTAL SECTION

Materials. Detailed description of the high-vacuum technique and the purification procedures for styrene, benzene (solvent), and secBuLi (initiator) required for anionic polymerization are described elsewhere.27,28 The purification procedure for 1,3-cyclohexadiene (1,3CHD, Aldrich, 97%) as well as for the polar additive 1,4diazabicyclo[2.2.2]octane (DABCO, Aldrich, 98%) are thoroughly described in previous literature.24−26 Synthesis. The PS-b-PCHD diblock copolymers were prepared in benzene by anionic polymerization29−31 through sequential monomer addition using a high-vacuum technique in an evacuated, n-BuLi washed, and benzene-rinsed glass vessel. The initiator used was secBuLi (Acros, 1.3 M) diluted in hexane to the desired concentration. DABCO (Aldrich, 98%) was used to promote PCHD with high 1,4microstructure. Details on the synthesis and the characterization techniques used for all samples are given in the Supporting Information. Molecular Characterization. Molar mass, dispersity, and composition of the BCPs were determined through a combination of two-angle laser light scattering size exclusion chromatography (TALLS-SEC) and 1H NMR spectroscopy. Details on the instruments and methods used are described in the Supporting Information. The backbone microstructure of PCHD (1,4 versus 1,2 content) for each sample was also determined by 1H NMR through a method reported by Quirk et al.32 Morphological Characterization. Bulk films of each BCP were slowly cast from toluene (a nonselective solvent) over a period of 5 days. A portion of these “as cast” films were then annealed for 6 days at 140 °C, which is above the glass transition temperature (Tg) of both segments. Visualization of morphologies was accomplished by transmission electron microscopy (TEM).33 Small-angle X-ray scattering (SAXS)34 data were obtained from two different instruments with one located at UTK and the other at Duke. Specific details on all these instruments in additional to sample preparation procedures can be found in the Supporting Information.

Table 2. Observed Morphologies for the Annealed and AsCast Films

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DATA AND RESULTS The molecular characteristics of all PS-b-PCHD samples synthesized are given in Table 1. Subscript numbers in the sample IDs represent the number-average molar mass (Mn) of the respective segments in kg/mol. For example, S30C6 means that the PS block has Mn = 30 kg/mol and the PCHD block has Mn = 6 kg/mol. All samples exhibit narrow and monomodal molecular weight distributions implying low degree of compositional and

sample

ϕPS

S37C3 S30C6

0.89 0.79

S28C16

0.62

S11C7

0.61

S24C16

0.59

S24C17 C6S6 C10S6

0.58 0.49 0.36

annealed BCC spheres hexagonally closepacked cylinders hexagonally closepacked cylinders well-ordered hexagonally closepacked cylinders well-ordered hexagonally closepacked cylinders alternating lamellae disordered alternating lamellae

as-cast

Ndiblock

spheres BCC spheres

391 370

core−shell cylinders

465

tetragonal stitch pattern

238

well-ordered hexagonally closepacked cylinders poor ordered cylinders alternating lamellae alternating lamellae

429 437 160 213

Microphase separation of diblock copolymer films resulting from evaporation of a casting solvent has been known to kinetically trap the copolymer chains into morphologies that are nonequilibrium and possibly disorganized depending upon the selectivity of the solvent and the casting conditions.35 We decided to examine such films “as-cast” from toluene solution (a good solvent for both PS and PCHD) prior to thermal annealing to explore any similarities or alternations in B

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observed morphology for the S37C3 as-cast film since the SAXS plot did not show any peaks (Figure 1c, as-cast). The TEM image of Figure 1d corresponds to S30C6 annealed sample which exhibits a cylindrical morphology while S30C6 as-cast sample showed a spherical structure (Figure 1e). The microphase separation of S30C6 annealed sample is verified by the corresponding peaks of the SAXS plot (Figure 1f, annealed) while the SAXS plot of the as-cast sample, even though it is noisy, appears to have several peaks corresponding to BCC spherical structure (Figure 1f, as-cast). As the content of PCHD in the diblock copolymers increases, the self-assembly of the system is improved as can be seen from the TEM images of annealed samples S28C16 and S11C7 (Figures 2a and 2d), which exhibit similar volume fractions for the two blocks (ϕPS = 0.62 and ϕPS = 0.61 respectively) but different molecular weights. It is evident that the lower molecular weight sample (S11C7) exhibits better order than S28C16, which is not normally expected since S11C7 lays closer to the weak segregation limit but may be explained by the increased time that higher molar mass chains require to restate into an optimally ordered state. The TEM image of the S28C16 as-cast film shows a very wellordered structure of core−shell cylinders of PS core surrounded by PCHD cylinders in the matrix of PS. The observed reflections on the FFT image corresponding to Figure 2b verify the hexagonally packed cylindrical morphology. This result has been reported previously by Mays et al. for PS-b-PCHD copolymers different in total molecular weight but identical to sample S28C16 in PS volume fraction.21 They observed core−shell cylinders for both annealed and as-cast cases with the annealing procedure promoting long-range order of the core−shell cylindrical structure. In the case of the S28C16 sample, improvement of the morphology with annealing is not observed, but the reproduction of this structure in the as-cast sections provides an interesting insight concerning the selfassembly of the PS-b-PCHD BCPs. The as-cast S11C7 is not well-ordered even though a tetragonal “stitch-pattern” structure is observed which does not correlate with any of the theoretically and experimentally known morphologies from other well-studied diblock copolymer systems.36−44 The rather large folds evident in Figure 2e possibly imply that mechanical deformations occurred most likely during the trimming procedure. The SAXS plot for the as-cast S28C16 film (Figure 2c) confirms the cylindrical morphology observed. The SAXS plot of the S 11 C7 annealed film exhibits weak peaks corresponding to a cylindrical structure while S11C7 as-cast film did not show any significant peaks (Figure 2f). Significant differences are observed in the annealed S24C16 and S24C17 samples which exhibit well-ordered hexagonally close-packed cylinders and alternating lamellae, respectively (Figures 3a and 3d), even though their degree of polymerization and volume fractions of the two blocks are almost identical (ϕPS = 0.59 and N = 429 for S24C16 and ϕPS = 0.58 and N = 437 for S24C17). These two almost identical samples lay upon the phase boundaries of the cylindrical and lamellar phases, and with minor changes in the PCHD content, an order-to-order transition occurs. For the S24C16 as-cast film, a very well-ordered structure of hexagonally close-packed cylinders is observed while for the S24C17 as-cast film, a cylindrical morphology is observed with poor order (Figures 3b and 3e, respectively). The SAXS plots of the annealed and ascast S24C16 films confirm the observed well-ordered cylindrical structures (Figure 3c). The S24C17 as-cast film exhibits several

morphology as a function of molecular weight and composition of each block. An alternate batch of the same sample films was thermally annealed above the Tg of both blocks to induce a thermodynamically driven morphology for comparison. Figures 1−4 and Table 2 outline our TEM and SAXS observations for the as-cast and annealed films for each PS-b-PCHD sample as indicated in Table 2.

Figure 1. TEM images of S37C3 (a) annealed, (b) as-cast and S30C6 (d) annealed, and (e) as-cast. Dark areas correspond to the OsO4 stained PCHD blocks. SAXS 1-D plot overlays (log I vs q) of (c) S37C3 annealed and as-cast and of (f) S30C6 annealed and as-cast. Black triangles on the S37C3 annealed and S30C6 as-cast are in secondary reflection positions expected for BCC spheres (q/q* = √2, √3, √4, √5, √6, √7, √8, and √9) with respect to the principal scattering peak (q*) while triangles on the S30C6 annealed are secondary reflections expected for hexagonally packed cylinders (q/q* = √3, √4, √7, √9, and √12). The designations “Duke” and “UTK” represent the instrument upon which the data were taken (see Experimental Section).

The TEM image in Figure 1a shows a poor-ordered spherical morphology for the annealed S37C3 sample while Figure 1b shows a much better ordered spherical morphology for the S37C3 as-cast film. The SAXS plot of the S37C3 annealed case shows several weak peaks that correspond to secondary BCC spherical reflections while it was not possible to verify the C

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Figure 3. TEM images of S24C16 (a) annealed, (b) as-cast and S24C17 (d) annealed, and (e) as-cast. Dark areas correspond to the OsO4 stained PCHD blocks. SAXS 1-D plot overlays (log I vs q) of (c) S24C16 annealed and as-cast and of (f) S24C17 annealed and as-cast. Black triangles on the S24C16 annealed and as-cast and on the S24C17 as-cast are in secondary reflection positions expected for hexagonally packed cylindrical morphology (q/q*= √3, √4, √7, √9, and √12). The q* value for S24C17 annealed film is undetermined due to instrument limitations. The designations “Duke” and “UTK” represent the instrument upon which the data were taken (see Experimental Section).

Figure 2. TEM images of S28C16 (a) annealed, (b) as-cast and S11C7 (d) annealed, and (e) as-cast. Dark areas correspond to the OsO4 stained PCHD blocks. SAXS 1-D plot overlays (log I vs q) of (c) S28C16 annealed and as-cast and of (f) S11C7 annealed and as-cast. Black triangles on the S28C16 as-cast and on the S11C7 annealed are in secondary reflection positions expected for hexagonal cylindrical morphology (q/q* = √3, √4, √7, √9, and √12). The q* value for S28C16 is undetermined due to instrument limitations while there are no reflections for S11C7 as-cast film. The designations “Duke” and “UTK” represent the instrument upon which the data were taken (see Experimental Section).

film is verified from the relative peak ratio in the SAXS plot (Figure 4f, as-cast). The SAXS plot of the annealed C6S6 (Figure 4c, annealed) exhibits no other peak than the one corresponding to the beamstop (q*) verifying the disordered structure observed in the TEM. The SAXS plot of the as-cast C6S6 (Figure 4c, as-cast) confirms the lamellar morphology observed in the TEM images. From the above results it can be concluded that the phase boundaries between lamellae and cylinders are significantly shifted in these type of diblock copolymers if compared with the usual and most studied case of PS-b-PI. The most significant factor is that the PCHD block introduces high conformational asymmetry as well unexpected morphologies to the system for particular volume fraction and molecular weight combinations. The lamellar morphology is present even at ϕPS = 0.36 where the cylindrical morphology is normally expected

reflections peaks corresponding to the poorly ordered cylinders observed in the TEM image. Sample C6S6 (1,3-CHD was polymerized first in this case in order to achieve higher conversion and volume fraction for the PCHD block and the same procedure was followed for sample C10S6) has the lowest total M̅ n among all samples of this study. The sample appears disordered after annealing (Figure 4a), whereas alternating lamellar morphology is observed (Figure 4b) in the as-cast case. For sample C10S6 both annealed and as-cast films exhibit the alternating lamellae morphology as shown from the TEM images (Figures 4d and 4e, respectively), but the absence of peaks in the SAXS plot of the C10S6 annealed film indicates the coexistence of ordered and disordered areas (Figure 4f, annealed) while the lamellar morphology of the C10S6 as-cast D

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morphology is reached. Moreover, there are several cases (C6S6, S37C3, S30C6, and S28C16) where annealing above Tg did not improve microphase separation or altered the observed morphology (C6S6, S24C17, S30C6, and S28C16) while we were able to reproduce a core−shell cylindrical morphology (as-cast case) reported previously for an identical sample (S28C16). Rheological Characterization. Rheology measurements were performed for comparison to the morphological characterization results and to probe any changes in viscoelastic behavior of these samples over a wider range of temperature. Such changes can be correlated to alternations of the morphology45 (order−order transitions). Additionally, order−disorder transitions, reached at a critical temperature (TODT), can provide information on the effective interaction parameter χeff46−48 between PS and PCHD segments for the first time.49,50 Prior to the analysis and in order to reduce thermal cross-linking of the PCHD blocks at higher temperatures, each sample was dissolved in methylene chloride and precipitated in methanol containing ∼5% (w/w) BHT as a stabilization dopant. The samples were fully dried in a vacuum oven prior to testing. Samples were loaded into the rheometer at a gap setting of 1− 1.5 mm, and all experiments were performed in the linear, parallel viscoelastic regime as determined by periodic low frequency (ω = 1 rad/s) strain sweeps at the respective temperatures of analysis. The gap was maintained autonomously by the instrument during temperature ramps to account for thermal expansion of the plates. Time−temperature superposition (TTS) master curves of the dynamic elastic (G′) and loss (G″) moduli for sample C6S6 are shown in Figure 5. TTS was performed using shift factors (aT) based on a reference temperature, Tref = 130 °C, and a critical frequency, ωc, above which the moduli superpose.

Figure 4. TEM images of C6S6 (a) annealed, (b) as-cast and C10S6 (d) annealed, and (e) as cast. Dark areas correspond to the OsO4 stained PCHD blocks. SAXS 1-D plot overlays (log I vs q) of (c) C6S6 annealed and as-cast and of (f) C10S6 annealed and as-cast. Black triangles on the C6S6 as-cast and on the C10S6 annealed and as-cast are in secondary reflection positions expected for lamellar morphology (q/ q* = 2, 3, and 4). For the C6S6 annealed film, no secondary reflections were detected. The designations “Duke” and “UTK” represent the instrument upon which the data were taken (see Experimental Section).

for two random coil blocks. When the diblock copolymers are in thermodynamic equilibrium (annealed above their Tg), there are some interesting observations we can report. In the case of S28C16 (ϕPS = 0.62 and N = 465) and S11C7 (ϕPS = 0.61 and N = 238) annealed films, reducing the total molecular weight of the diblock copolymer but keeping the volume fraction of the two components almost identical improves microphase separation instead of impairing it. Furthermore, for samples S24C16 and S24C17, by keeping the total molecular weight of the two diblock copolymers almost the same and by slightly changing the volume fraction of PCHD block, an order-to-order transition occurs from wellordered cylinders to lamellae, suggesting these volume fractions lie near the phase boundary. Additionally, for samples C6S6 and C10S6, by increasing the PCHD content and overall N, while keeping PS segment molar mass the same, the critical boundary of N from a disordered state to the ordered alternating lamellar

Figure 5. Time−temperature superposition (TTS) master curves displaying the dynamic elastic (G′) and loss (G″) moduli response to frequency sweeps taken at various temperatures using appropriate shift factors aT and a reference temperature Tref = 130 °C for sample C6S6.

The Rouse-like behavior (G′ ∼ ω2) throughout all temperatures (130−180 °C) is indicative of a disordered system. However, a notable increase in low-frequency viscoelastic response at 130 °C may be indicative of the onset of composition fluctuations which have been shown to present a gradual increase in G′ upon cooling within 40 °C above the TODT even in untangled systems.51−58 The disorder of this sample at 140 °C agrees with our TEM and SAXS results where the annealed sample at 140 °C is also disordered (Figures 4a and 4c, annealed, respectively). Interestingly, a lamellar morphology (Figures 4b and 4c, as-cast, respectively) E

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TODT observed on first heating which we believe is due to thermal decomposition of the polymer through extended periods at these high temperatures. Sample C10S6 also showed a TODT upon first heating (ω = 0.5 rad/s) at an onset of 216 ± 3 °C (Figure 7a). A second

is seen for C6S6 as-cast: this indicates the TODT my be just below the point of vitrification ( 1. More particularly, for the annealed samples (yellow rhombs), where the system is in thermodynamic equilibrium, theoretical calculations are in very good agreement with our experimental results as the conformational asymmetry parameter ε takes higher values. The lamellar phase is dominant when ϕPCHD > 0.5, verifying our results for C10S6 and S6C6 samples. The cylindrical phase covers a wide range of the diagram when ϕPCHD < 0.5, verifying our results for S24C16, S24C17, S11C7, and S28C16. By carefully selecting the degree of polymerization N and combining it with the interaction parameter χ (12 < χNPS−PCHD < 16), it is possible to synthesize symmetric PS-b-PCHD diblock copolymers (ϕPS = ϕPCHD = 0.5) exhibiting cylindrical morphology which is something that was observed in our previous work26 where a PS-b-PCHD diblock copolymer with ϕPCHD = 0.55 showed core−shell cylinders of the majority component (PCHD) in the matrix of the minority block (PS). Only two BCPs, those exhibiting lower ϕPCHD (S30C6 and S37C3) show different morphological behavior in comparison with the theoretical calculations, a behavior which is not possible to explain with already existing theories. As the conformational asymmetry parameter ε becomes greater than 5, the phase boundaries do not shift significantly and the system becomes “saturated”.

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CONCLUSIONS This work investigated in detail the morphological and rheological behavior of a series of diblock copolymers of PS and PCHD. By using anionic polymerization and high vacuum techniques, eight well-defined diblock copolymers with narrow PDIs were synthesized, with varying molecular weights (12 000−43 700 g/mol) and volume fractions (0.89 < ϕPS < 0.36). The main goal was to understand the possible structures that these diblock copolymers can adopt by observing various samples and verify whether these morphologies are resulting from kinetically trapped (solvent cast) and/or thermodynamically driven (thermally annealed) cases. Ordered and disordered morphologies from these films provided a starting point for rheology measurements hoping to observe order− disorder transitions that would help us calculate the interaction parameter χeff. Three of the well-known morphologies for diblock copolymers (hexagonally close-packed cylinders, alternating lamellae and spherical body-centered cubic structure) were observed as well as the existence of the core−shell cylinder morphology which had been reported previously for a different PS-b-PCHD sample21 and is normally anticipated for triblock copolymers. Our TEM and SAXS results were consistent and rheological experiments showed that two samples S11C7 and C10S6 have an observable TODT of 258 ± 3 and 216 ± 3 °C,

Figure 8. Morphology diagram constructed using RPA theory and experimental results for conformational asymmetry parameter (a) 1, (b) 5, and (c) 10. Here, D, B, C, T, and L correspond to disordered, body-centered cubic spheres, hexagonally packed cylinders, tetragonally packed cylinders, and lamellar, respectively. G

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Macromolecules respectively, while C6S6 remains disordered above 130 °C and can order into lamellae when solvent-cast at room temperature. We were able to calculate the enthalpic and entropic factors (a and β, respectively) and produce an expression for the interaction parameter χeff = 32/TODT − 0.016 and extrapolate them to the rest of the BCPs, and their predicted TODT were consistent with the results obtained from TEM and SAXS. The high conformational asymmetry of the system shifts the boundaries of the phases to a great extent. The lamellar morphology is observed for φPS = 0.36, and the phase diagram is shifted toward the more rigid PCHD block. BCPs containing PCHD with a high content of 1,4-microstructure could be potential candidates for high-temperature lithographic applications due to the enhanced mechanical and thermal properties provided by the PCHD segment,60−64 the unique morphologies possible, and the relocation of phase boundaries caused by the high conformational asymmetry.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b00104. Description of materials synthesis, instrumentation details, preparation (casting, annealing, microtoming) for TEM and SAXS measurements and supplementary DMS plots (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.G.K.). *E-mail: [email protected] (A.A.). ORCID

Konstantinos Misichronis: 0000-0002-2620-1738 Rajeev Kumar: 0000-0001-9494-3488 Kunlun Hong: 0000-0002-2852-5111 Mark Dadmun: 0000-0003-4304-6087 Bobby G. Sumpter: 0000-0001-6341-0355 Nikos Hadjichristidis: 0000-0003-1442-1714 Apostolos Avgeropoulos: 0000-0002-6203-9942 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Materials Science and Engineering Division, U.S. Department of Energy (DoE), Office of Basic Energy Sciences (BES), LLC, at Oak Ridge National Laboratory (ORNL). Part of the research was done at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. A.A. also thanks the Nuclear Magnetic Resonance Spectroscopy Facility and the Electron Microscopy Unit of the University of Ioannina. J.G.K. thanks the FSU Materials and Energy Hiring Initiative and the Donors of the American Chemical Society Petroleum Research Fund (55378-DNI7) for partial support during the preparation of this manuscript. N.H. acknowledges the support of King Abdullah University of Science and Technology (KAUST).

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