Accelerated discovery and mapping of block copolymer phase diagrams

Block copolymers are widely used in many applications due to their spontaneous self-assembly into a variety of nanoscale morphologies. However, a grand challenge in navigating this diverse and ever-growing array of possible structures is the accelerated discovery, design, and implementation of materials. Here, we report a versatile and efficient strategy to accelerate materials discovery by rapidly building expansive, high-quality, and detailed block copolymer libraries through a combination of controlled polymerization and chromatographic separation. To illustrate the potential of this approach, a family of 16 parent diblock copolymers was synthesized and separated, leading to over 300 distinct and well-defined samples at the multigram scale. The resulting materials span a wide range of compositions with exceptional resolution in volume fraction and domain spacing that allows for the impact of monomer design on polymer self-assembly to be elucidated. Phase behavior that can be gleaned from these libraries includes the precise location of order-order boundaries and the identification of morphologies with extremely narrow windows of stability. This user-friendly, scalable, and automated approach to discovery significantly increases the availability of well-defined block copolymers with tailored molecular weights, molar-mass dispersities, compositions, and segregation strengths, accelerating the study of structure-property relationships in advanced soft materials.

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Figure 1

Automated chromatographic fractionation of an as-synthesized parent diblock copolymer leads to a well-defined library of samples enabling the accelerated development of detailed phase diagrams.

Figure 2

${}^1\mathrm{H}$ nuclear magnetic resonance (NMR) spectra of D-1F, D-5F, D-9F, and D-12F diblock copolymers. The initiator fragment, poly(dodecyl acrylate) block, and fluorinated blocks all exhibit unique resonances.

Figure 3

Size-exclusion chromatograms (normalized differential refractive index signal, dRI) of representative D-1F, D-5F, D-9F, and D-12F diblock copolymers prepared by sequential photomediated atom transfer radical polymerization (ATRP). Dodecyl acrylate was polymerized first (dashed blue lines) followed by growth of the fluorinated block (solid black lines). Note that the dodecyl acrylate homopolymer and D-1F diblock have positive $\mathrm{d}n/\mathrm{d}c$ values in chloroform whereas D-5F, D-9F, and D-12F have negative $\mathrm{d}n/\mathrm{d}c$ values.

Figure 4

Chromatographic separation of parent diblock copolymers affords large libraries of fractionated samples. The F-block volume fraction systematically increases in all cases, regardless of starting parent chemistry and composition. Representative fractionations of D-1F, D-5F, D-9F, and D-12F diblock copolymers under similar separation conditions. Fraction represents the polymer recovered in numbered test tubes collected in 22 mL increments. Dashed lines represent the average composition $\langle f\rangle$ of the starting parent diblock copolymer before fractionation.

Figure 5

A library of >320 well-ordered diblock copolymers derived from the synthesis and separation of only 16 samples enabled the preparation of four comprehensive phase diagrams with a high degree of compositional resolution. As-synthesized parent materials are depicted with an open symbol. Fractionated diblock copolymers are depicted with the same shape as their respective parent material but filled. Color indicates the morphology as determined by small-angle x-ray scattering.

Figure 6

Automated chromatographic fractionation of block copolymers allows for a high degree of precision in fractionated samples. (a) Domain spacing of hexagonally packed cylinders systematically increases with $f_{\mathrm{F}}$ after fractionation. Note the as-synthesized parent material has a domain spacing 9.4 Å larger than the analogous fraction. As-synthesized parent material is depicted with an open symbol. Fractionated diblock copolymers are depicted with filled symbols. (b) Selected small-angle x-ray scattering (SAXS) profiles of a parent diblock copolymer D-12F-31% and fractions derived therefrom. All SAXS experiments were conducted at room temperature. Vertical lines represent theoretical reflections of the given crystal system as calculated based on the experimental $q^{*}$. The position of $q^{*}$ progressively shifts toward lower $q$ and larger domain spacings with increasing $f_{\mathrm{F}}$.

Figure 7

(a) The domain spacing of fractionated diblock copolymers that form lamellae systematically increases with $f_{\mathrm{F}}$. As-synthesized parent material has a domain spacing 24 Å larger than the corresponding fractionated material with $f_{\mathrm{F}}=0.67$. As-synthesized parent material is depicted with an open symbol. Fractionated diblock copolymers are depicted with filled symbols. (b) Selected small-angle x-ray scattering (SAXS) profiles of a parent diblock copolymer D-5F-67% and fractions derived therefrom. All SAXS experiments were conducted at room temperature. Vertical lines represent theoretical reflections of the given crystal system as calculated based on the experimental $q^{*}$. The position of $q^{*}$ progressively shifts toward lower $q$ and larger domain spacings with increasing $f_{\mathrm{F}}$.

Figure 8

Synthesis of D-1F, D-5F, D-9F, and D-12F diblock copolymers through sequential photoinitiated atom-transfer radical polymerization.