Effect of side chain and backbone length on lamellar spacing in polystyrene‐block‐poly(dimethyl siloxane) brush block copolymers

Abstract

We report the synthesis of polystyrene‐block‐poly(dimethyl siloxane) (PS‐b‐PDMS) brush block copolymers (BBCPs) through sequential ROMP of norbornene‐modified macromonomers (‐NB) and explore the effect of side chain length (Nsc) and total backbone degree of polymerization (Nbb) on the self‐assembly of lamellar morphologies. Group I (PS‐NB Mn = 2.9 kg/mol, PDMS‐NB Mn = 4.8 kg/mol) exhibits asymmetric side chains, while Group II (PS‐NB Mn = 4.7 kg/mol, PDMS‐NB Mn = 4.8 kg/mol) possess a more symmetric arrangement. Both families rapidly self‐assemble into well‐ordered lamellar morphologies with domain spacings (d0) ranging from d0 = 54 to 140 nm. The scaling relationship between d0 and Nbb (d0 ~Nbbα) was determined as the measure of backbone flexibility. Exponents of α = 0.71 and α = 0.81 are observed for Groups I and II, respectively, indicating the BBCPs adopt an extended backbone conformation. The presence of a low Tg side chain such as PDMS increases apparent flexibility of the backbone. The interplay between contrasting characteristics of the side chains is discussed and reveals the importance of understanding the physical consequences of block architecture on controlling BBCP assembly. These findings provide necessary information for future investigations of complex phases and well‐defined nanostructures fabricated using the brush architecture. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 691–699

Confinement and Processing Can Alter the Morphology and Periodicity of Bottlebrush Block Copolymers in Thin Films

“…Investigations into bulk materials shown that symmetry between the side chain lengths stabilizes the lamellar phase. 41 PGMEA is a nearly equally good solvent for both blocks resulting in equivalent degree of stretching for both side chains relative to the melt. This will increase the native asymmetry between the two phases.…”

“…Because of the difference in chain length between the PLA and PS side chains, this results in nearly equivalent radii for both portions of the chain. Investigations into bulk materials have shown that symmetry between the side chain lengths stabilizes the lamellar phase . PGMEA is a nearly equally good solvent for both blocks resulting in equivalent degree of stretching for both side chains relative to the melt.…”

“…The enhanced rigidity of the backbone results in significantly larger scaling exponents for L 0 than observed in linear BCPs. In a BBCP L 0 ≈ N BB α , where α ranges from ≈0.7 to 0.9 and is influenced by factors such as side chain composition, length, asymmetry, and by the grafting density. ,− These scaling exponents exceed the values for linear BCPs in the strongly stretched regime (α = 0.66), suggesting that the backbones are more extended compared to linear systems. In spite of this enhanced rigidity the BBCPs should not be thought of as rigid rods, as the polymers maintain significant flexibility over longer length scales and appear to pack in the same arrangement as linear BCPs .…”

Impact of bottlebrush chain architecture on Tg‐confinement and fragility‐confinement effects enabled by thermo‐cleavable bottlebrush polymers synthesized by radical coupling and atom transfer radical polymerization

“…To the best of our knowledge, there has been no previous report in the refereed literature on the T g ‐confinement behavior of bottlebrush polymer in nanoscale thick films. With advancements in synthetic techniques over the past two decades, a wide range of bottlebrush polymers have been synthesized [ 53–87 ] and various potential applications have been advanced based on bottlebrush structures and properties, [ 82–88 ] for example, polymer photonics, [ 82 ] supersoft/superelastic materials, [ 83–85 ] self‐assembly for nanopatterning, [ 86 ] and artificial tissues that are both firm and soft. [ 87 ] Thus, investigating bottlebrush behavior under conditions of nanoscale confinement may be important not only for advancing the scientific understanding of polymer topology‐property effects, including confinement effects, but also for advancing the applications of bottlebrushes.…”

Complete Photonic Band Gaps with Nonfrustrated ABC Bottlebrush Block Polymers

“…Bottlebrush polymers are an exceptionally versatile polymer architecture for self-assembly and possess an expansive set of molecular parameters that can be tuned. In addition to molecular parameters present in linear architectures like block fractions and Flory–Huggins χ parameters, bottlebrush polymers can be designed with different grafting densities, − side-chain lengths, − shapes, − and composition gradients. , Multiblock architectures, such as ABC triblock bottlebrushes, have also begun to be explored. ,, This vast range of parameters permits nearly endless variation in the design of bottlebrush polymers and should permit the self-assembly of a wide range of different phases. Though the phase behavior of bottlebrush polymers across this vast parameter space is still being explored, all classical phases, including lamellar, − ,,,− cylindrical, ,,,, spherical, , and gyroid morphologies have been observed in bottlebrush block polymers, albeit with varying degrees of order.…”