Effects of Asymmetric Molecular Architecture on Chain Stretching and Dynamics in Miktoarm Star Copolymers

Abstract

We use broad-band dielectric spectroscopy (BDS) and small-angle X-ray scattering (SAXS) to investigate the impact of architectural asymmetry in the miktoarm star copolymer on the dielectric polymer relaxations. The miktoarm copolymers studied contain one or two polystyrene (PS) chains of constant molecular weight and two identical poly(cis-1,4-isoprene) (PI) chains with varied molecular weights. Using the chains in the PI block as dielectric probes, we find that the architecturally asymmetric miktoarm star copolymer systems (PSPI 2 ) feature distributions in chain relaxation times and dielectric relaxation strengths that are not dependent on molecular weight or morphology, in stark contrast to the effects of morphological confinement observed for symmetric diblock systems (PS-b-PI or PS 2 PI 2 ). Along with evidence from the SAXS measurements regarding phase separation, these results are attributed to influences from chain stretching within the framework of the Gaussian chain model for block copolymer systems. As such, the molecular architecture in block copolymers happens to be a versatile handle to control polymer chain dynamics and, ultimately, the macroscopic physicochemical properties in architecturally complex polymers.

Non-equilibrium Effects of Polymer Dynamics under Nanometer Confinement: Effects of Architecture and Molar Mass

“…Other estimates of density based on negative pressure effects under confinement provide a larger density change during equilibration (∼1%). , Nevertheless, the increase in the dielectric strength is beyond any estimates of the effect of densification. Alternatively, the increasing dielectric strength during annealing can reflect enhanced orientation correlations of PI subchains. , This is not unlike the subchains next to the adsorbed layer which can have non-Gaussian configurations and their relaxation toward the equilibrium can involve orientationally correlated subchains. Because ratio Δε NM /Δε α remains constant during annealing, we can conclude that the same g K appears in both.…”

“…Alternatively, the increasing dielectric strength during annealing can reflect enhanced orientation correlations of PI subchains. 51,52 This is not unlike the subchains next to the adsorbed layer which can have non-Gaussian configurations and their relaxation toward the equilibrium can involve orientationally correlated subchains. Because ratio Δε NM /Δε α remains constant during annealing, we can conclude that the same g K appears in both.…”

Ultrafast Self-Assembly of Bottlebrush Statistical Copolymers: Well-Ordered Nanostructures from One-Pot Polymerizations

“…Over the past several decades, block copolymers have garnered significant interest in academia and industry due to their ability to microphase separate into well-defined nanoscale structures. − Directed self-assembly, in particular, has been widely explored as an alternative patterning approach for electronic devices and data storage. − However, the self-assembly of linear block copolymers (LBCP) is rather constrained when forming well-ordered, defect-free structures, particularly with large lattice spacings, due to the kinetic frustrations in entangled systems of high-molecular-weight polymers. − In the pursuit of alleviating the constraints in LBCPs and expanding upon the achievable range of nanostructures, recent studies have explored the self-assembly of alternate architectures of copolymers, such as multiblock, mitko star, − comb block copolymers, and bottlebrush block copolymers (BBCP). − BBCPs are densely grafted macromolecules with polymeric side chains tethered to a linear backbone in separate block segments . Combining short side chains with high grafting density leads to a reduction in the overall chain entanglements in the system, increasing molecular mobility and overcoming many barriers of assembly present in entangled LBCPs .…”

Small-Angle Neutron Scattering Study of the Structural Relaxation of Elongationally Oriented, Moderately Stretched Three-Arm Star Polymers

“…Architecturally complex polymers attract increased attention due to the remarkable properties. Star polymers, for example, have been the subject of several studies [1][2][3][4][5][6][7][8][9][10][11][12][13].…”