The use of architecturally complex copolymer additives provides a versatile approach to decoupling surface and bulk chemistries, enabling the introduction of new surface properties or functionalities. As examples, the preferential segregation of a component to an air surface or substrate can be leveraged for antifouling properties, orienting block copolymer films, and tailoring the properties of organic electronic devices. In this presentation, we show that bottlebrush polymers provide a convenient platform for the design of surface-active polymer additives. Bottlebrush polymers have polymeric side chains densely grafted to a linear polymer, and this molecular architecture enables tuning entropic and enthalpic interactions with other polymers and with surfaces. The strength of the entropic attraction towards surfaces can be tuned in blends of bottlebrush and linear polymers by varying the number of bottlebrush side chains, the length of the bottlebrush side chains, and the length of the linear polymer host, and enthalpic interactions can be controlled by incorporating different side chain and side chain end-group chemistries. We present studies of bottlebrush polymers blended with linear polymers to understand the role of enthalpic and entropic effects that can drive segregation to film interfaces. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) is used to quantify the distribution of bottlebrushes through the film thickness as a function of homopolymer type, homopolymer molecular weight, and processing conditions. Modeling using the self-consistent field theory (SCFT) highlighted effects of conformational entropy and enthalpic interactions in driving segregation of the bottlebrush additives toward interfaces. Furthermore, enthalpic interactions were predicted to cause lateral phase segregation in cases where the homopolymer is preferred over the bottlebrush copolymer at the substrate, an effect that was also observed in experiments. This study demonstrates that bottlebrush copolymer additives can be designed to spontaneously segregate to surfaces in thermal blends, providing a possible route to decouple surface properties from bulk properties.

Development of bottlebrush copolymers as surface-active additives

ACS Spring Meeting 2021

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