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Bottlebrush polymers contain polymericside-chains attached to a linear polymer backbone, and they are currentlyof interest for a variety of potential applications that include drugdelivery, tailored surface wettability, and self-assembled photonics.These polymers are challenging to synthesize in large quantities,so for practical applications, it is of interest to study their propertiesas additives for low-cost linear polymers. In this work, we examinethe phase behavior of bottlebrush polystyrene (PS) and linear deuteratedpolystyrene (dPS) in thin films. These nearly athermal systems exhibitwetting and dewetting transitions that drive bottlebrush dispersionor aggregation, respectively, and these effects depend on the relativedegrees of polymerization of matrix chains Nmto those of bottlebrush side-chains Nsc. When Nm/Nscis low (≤1.6), the bottlebrushes are dispersed throughoutthe film thickness with a slight excess at the free surface and substrateinterfaces. When Nm/Nscis high (≥8), the bottlebrushes are depletedfrom the interior of the film and strongly segregated at the interfaces.The interfacial excess is driven by an entropic depletion attractioneffect: larger branched molecules are adsorbed (attracted) to theinterfaces, and the linear chains are displaced to the film’sinterior where they gain conformational entropy. The bottlebrushesprefer to accumulate at the silicon substrate over the air interface,and this may be driven by the more restrictive condition of a hardboundary or weak van der Waals interactions with the underlying silicon.These studies demonstrate that low concentrations of certain bottlebrushpolymer architectures can generate brushlike surfaces and interfacesin any thermoplastic material through a spontaneous, entropy-drivensegregation process. [ABSTRACT FROM AUTHOR]

Bottlebrush polymers are highly branchedmacromolecules with potentialapplications in antifouling coatings, rheological modifiers, and drugdelivery systems. However, the solution conformation of bottlebrushpolymers has been studied in only a limited set of materials madeprimarily by grafting-from polymerization. Here we present small-angleneutron scattering (SANS) measurements on a series of polystyrenebottlebrush polymers with varying side-chain and backbone lengthsin d8-toluene to analyze their size, shape,and conformation. Bottlebrush polymers with 2–7 kg mol–1polystyrene side chains (degree of polymerizationDP = 14–54) and poly(oxanorbornene) backbones (DP = 10–264)were synthesized using reversible addition–fragmentation chaintransfer (RAFT) followed by a ring-opening metathesis polymerization(ROMP) grafting-through synthesis scheme. Analysis by Guinier–Porod,rigid cylinder, and flexible cylinder models provided estimates ofthe bottlebrush polymer length, radius, and stiffness. The bottlebrushpolymer cross-sectional area depends primarily on side-chain DP, andthe radius of gyration Rgexhibits a power-lawdependence with side-chain DP. We also observe a sphere-to-cylindertransition with increasing backbone DP, with the transition occurringat a backbone DP of approximately 120 for the polystyrene bottlebrushpolymers studied. The maximum molecular dimension for the series studiedvaries from 25 to 350 nm. [ABSTRACT FROM AUTHOR]

Bottlebrush polymer thin films may be attractive forthe preparationof antifouling and/or stimuli-responsive surface coatings due to thehigh grafting density and conformational flexibility of polymericside chains, but bottlebrush polymer thin films have not been previouslyreported and their surface properties are unknown. Herein, we reporta study of the surface properties of mixed bottlebrush polymer (MBBPs)films. MBBPs with hydrophobic polystyrene (PS) and hydrophilic poly(ethyleneglycol) (PEG) side chains are synthesized using a “grafting-through”ring-opening metathesis polymerization (ROMP) approach. Stimuli-responsiveMBBPs films are prepared by spin-casting a solution of MBBPs ontoa solid surface, and the resulting film morphology and surface propertiesare characterized using atomic force microscopy (AFM), grazing-incidencesmall-angle X-ray scattering (GISAXS), water contact angle measurements,and X-ray photoelectron spectroscopy (XPS). The water contact anglesof MBBPs films decrease or increase upon exposure of the MBBPs filmsto selective solvents methanol or cyclohexane, respectively. Thiscontact angle change is dependent on the length of the PEG side chain;longer PEG side chains result in greater contact angle changes withsolvent exposure. Consistent with water-contact angle measurements,XPS indicates enrichment of PEG or PS chains at the film surface afterexposure of the MBBPs film to methanol or cyclohexane solvent vapors,respectively. Finally, it is demonstrated that bottlebrush polymerfilms can be stabilized by the addition of a radical cross-linkerand irradiation with UV light. This work demonstrates that bottlebrushpolymers enable the preparation of stimuli-responsive, “brush-like”polymeric coatings using simple solution processing methods. [ABSTRACT FROM AUTHOR]