2016-10-04
11:00 at HCI J 498

From Chain Folding to 2-D Polymers

S. Ramakrishnan

Indian Institute of Science, Bangalore, India

Control of chain conformation in solution has several interesting ramifications – from mimicking the exquisite conformational control seen in biological macromolecules to understanding factors that govern the lamellar crystallite sizes in semi-crystalline polymers. During the past decade we have examined several aspects dealing with control of chain conformation in solution; and we have also attempted to translate this control towards regulating the morphological characteristics of the bulk polymer. The lamellar morphology that is often realized in these attempts leads to the layering of different types of immiscible domains; a closer examination of these layered structures prompted us to begin exploring the similarity between these systems and 2D polymers. 2D polymers have begun to attract the attention of several groups world-wide; although many early efforts have examined polymerization at air-water interfaces and also within vesicles, these do not typically constitute robust structures that would withstand exfoliation. One of the prime drivers of this field is graphene, which could be viewed as the archetypical 2D polymer – a robust and reasonably stiff system that can be readily exfoliated to generate single atom-thick carbon sheets. The remarkable properties of graphene amply justify the incredible attention that this class of materials has received during the past decade. As a polymer chemist one can ask – what are the possible design strategies to prepare 2-dimensional polymers? Evidently, folding of polymer chains does constitute one way to generate 2-D polymeric nanoobjects; the thickness of these sheets would be the height of a folded chain – something we have recently demonstrated. However, these are not robust structures that can be prepared in bulk and exfoliated. It is with this challenge that we have just begun to examine alternate approaches to prepare 2D polymers; broadly, our strategy is to pre-organize multi-segmented monomers bearing at least two polymerizable units at the segment junctions. The pre-organization is designed to be driven by segment immiscibility and strengthened by the strong interactions, such as crystallization, within the domains; polymerization of the double bonds in the solid or semi-molten state it was expected would lead to the formation of a cross-linked and reasonably stiff sheet that would represent a 2D polymer. By suitable choice of the outer segments, it was felt that exfoliation could be made feasible. In the talk, I shall describe our efforts beginning with chain folding and I shall end with our recent foray into 2D polymers.