TY - JOUR
T1 - Sequence Effects on Block Copolymer Self-Assembly through Tuning Chain Conformation and Segregation Strength Utilizing Sequence-Defined Polypeptoids
AU - Patterson, Anastasia L.
AU - Danielsen, Scott P.O.
AU - Yu, Beihang
AU - Davidson, Emily C.
AU - Fredrickson, Glenn H.
AU - Segalman, Rachel A.
N1 - Funding Information:
The authors gratefully acknowledge funding from the National Science Foundation (NSF) Division of Materials Research (DMR) Polymers program (DMR-1608297) for synthesis and characterization of block copolymers and the NSF Condensed Matter and Materials Theory Program (DMR-1822215) for the SCFT simulations. A.L.P. gratefully acknowledges the NSF for a graduate research fellowship. Polypeptoid characterization and block copolymer purification were performed with guidance from Dr. Rachel Behrens and with support from the MRL Shared Experimental Facilities (supported by the MRSEC Program of the NSF, DMR-1720256; a member of the NSF-funded Materials Research Facilities Network). SCFT simulations utilized resources of the Center for Scientific Computing from the UCSB CNSI, MRL, and NSF MRSEC (DMR-1720256) and NSF CNS-1725797. X-ray scattering experiments utilized resources of the Advanced Light Source (a U.S. Department of Energy (DOE) Office of Science User Facility, DE-AC02-05CH11231; beamline 7.3.3), the Stanford Synchrotron Radiation Lightsource (supported by the U.S. DOE Office of Science, Office of Basic Energy Sciences, DE-AC02-76SF00515; beamline 1-5), the National Synchrotron Light Source II (a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory, DE-SC0012704; beamline 11-BM), and the Advanced Photon Source (a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory, DE-AC02-06CH11357; beam-line 12-ID-B). A.L.P. thanks Dr. Morgan Schulze (UCSB) for X-ray scattering resources and Andrew Turner (MIT) for input in programming the sequence selection. The authors also thank Dr. Ron Zuckermann at the Molecular Foundry of the Lawrence Berkeley National Lab for helpful discussions regarding polypeptoid synthesis.
Publisher Copyright:
© Copyright 2019 American Chemical Society.
PY - 2019/2/12
Y1 - 2019/2/12
N2 - Polymers with sequence control offer the possibility of tuning segregation strength with comonomer sequence instead of chemical identity. Here, we have synthesized polystyrene-b-polypeptoid diblock copolymers that differ only in the sequence of comonomers in the polypeptoid block, where nonpolar phenyl side chains are incorporated to tune compatibility with polystyrene. Using small-angle X-ray scattering, we see that these materials readily self-assemble into lamellae, with domain spacings and order-disorder transition temperatures varying with sequence, despite identical composition. The ordered state is likely governed by chain conformational effects that localize compatibilizing comonomers at the block-block interface. These altered chain conformations are supported by simulations with self-consistent field theory (SCFT) and lead to the observed changes in domain spacing. However, the trends seen in the order-disorder transition are not captured by SCFT simulations or effective χ parameters, measured in the disordered phase by approximating the copolypeptoid as a uniform block. The disagreement between measured thermodynamic properties and coarse-grained approaches like SCFT and effective χ points to the importance of molecular-scale effects in sequence-defined materials. Additionally, a reversal in relative disordering temperatures between forward and inverse taper sequences is observed compared to previous studies, likely due to a combination of sequence definition at the monomer length scale and the use of a "styrene-like" compatibilizing side chain rather than a true polystyrene repeat unit. These results demonstrate that comonomer sequence tunes chain conformation and segregation strength, suggesting that sequence design could be used to target desired properties and morphologies in block copolymer materials while retaining important chemical functionalities.
AB - Polymers with sequence control offer the possibility of tuning segregation strength with comonomer sequence instead of chemical identity. Here, we have synthesized polystyrene-b-polypeptoid diblock copolymers that differ only in the sequence of comonomers in the polypeptoid block, where nonpolar phenyl side chains are incorporated to tune compatibility with polystyrene. Using small-angle X-ray scattering, we see that these materials readily self-assemble into lamellae, with domain spacings and order-disorder transition temperatures varying with sequence, despite identical composition. The ordered state is likely governed by chain conformational effects that localize compatibilizing comonomers at the block-block interface. These altered chain conformations are supported by simulations with self-consistent field theory (SCFT) and lead to the observed changes in domain spacing. However, the trends seen in the order-disorder transition are not captured by SCFT simulations or effective χ parameters, measured in the disordered phase by approximating the copolypeptoid as a uniform block. The disagreement between measured thermodynamic properties and coarse-grained approaches like SCFT and effective χ points to the importance of molecular-scale effects in sequence-defined materials. Additionally, a reversal in relative disordering temperatures between forward and inverse taper sequences is observed compared to previous studies, likely due to a combination of sequence definition at the monomer length scale and the use of a "styrene-like" compatibilizing side chain rather than a true polystyrene repeat unit. These results demonstrate that comonomer sequence tunes chain conformation and segregation strength, suggesting that sequence design could be used to target desired properties and morphologies in block copolymer materials while retaining important chemical functionalities.
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U2 - 10.1021/acs.macromol.8b02298
DO - 10.1021/acs.macromol.8b02298
M3 - Article
AN - SCOPUS:85061656461
VL - 52
SP - 1277
EP - 1286
JO - Macromolecules
JF - Macromolecules
SN - 0024-9297
IS - 3
ER -