Cyclic polymers represent an exciting class of topologically distinctive polymers. The influence of “end-to-end” tethering and the unusual conformational properties associated with cyclic topologies have prompted studies of bulk properties such as viscosity, Tg, and crystallization. On the other hand, very few studies have investigated properties of ring polymers in confined films. High purity cyclic polystyrene (c-PS) was obtained via ATRP and “click” chemistry with high monodispersity and nearly quantitative conversion of the linear precursor. In the absence of chain ends, bulk c-PS samples exhibit very weak Tg- and fragility-MW dependences compared to linear PS. In stark contrast to the substantial Tg-confinement effects in linear PS supported on silica, low MW c-PS exhibits a nearly complete suppression of this confinement effect. Due to its very limited conformational mobility, the cyclic topology strongly restricts polymer-substrate interactions. Therefore, the near elimination of the Tg-confinement effect in c-PS originates mainly from a very weak perturbation to Tg near the free surface (in comparison to linear PS). Upon nanoscale confinement, linear PS films have been shown to have significantly reduced fragility compared to bulk. Despite having similar bulk fragility as high MW linear PS, low MW c-PS films show major suppression in fragility reduction with decreasing thickness. Due to a lack of chain ends, properties associated with the low MW ring structure are not prone to be perturbed by either MW reduction or confinement. This result indicates a strong correlation between the susceptibility of fragility perturbation and the susceptibility of Tg perturbation, caused by chain topology and/or by confinement. Lastly, c-PS thin films exhibit superior thermal stability against dewetting compared to their linear analogues, making novel cyclic polymer architectures attractive materials for practical usage. Taking advantage of different chain topologies and their specific attributes may be the next step in materials design and technology breakthrough.

Distinct thermophysical and interfacial properties associated with low molecular weight cyclic polystyrene in bulk and confined states: Tg, fragility, and thin film stability

253rd National Meeting (2017)

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