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 new 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.

Methods
Nuclear Magnetic Resonance Spectroscopy: Solution state 1H nuclear magnetic resonance (NMR) spectra were recorded on a Varian 600 MHz spectrometer. Chemical shifts (δ) are reported in ppm relative to residual protio-solvent in CDCl3 (7.26 ppm).

Size Exclusion Chromatography: Size-exclusion chromatography (SEC) was conducted on a Waters Alliance HPLC System, 2690 Separation Module using chloroform with 0.25% triethylamine as the eluent with a flow rate of 0.35 mL/min. Refractive index traces from a Waters 2410 Differential Refractometer detector were used for estimates of the molar mass and dispersity relative to linear polystyrene standards with a chloroform mobile phase.

Small Angle X-Ray Scattering: SAXS measurements of bulk samples were conducted using a custom-built high brilliance laboratory beamline for small and wide angle X-ray scattering (SAXS/WAXS) at the BioPACIFIC Materials Innovation Platform at UCSB. The instrument is constructed using a high brightness liquid metal jet X-ray source (D2+ 70 kV from Excillum), a low background scatterless slit beam collimation system developed in house, and a 4-megapixel hybrid photon counting area detector (Eiger2 R 4M from Dectris) housed inside a 3 meter-long vacuum vessel. 

Differential Scanning Calorimetry: Differential scanning calorimetry (DSC) was performed using a TA Instruments DSC Q2000 from –90 to 55 °C at a heating/cooling rate of 10 °C/min using 3–5 mg of sample in a sealed Tzero aluminum pan.