Macromolecular Engineering in Polymer Systems

Research Interests

The efforts of our group lie broadly in the following areas

Conjugated Polymers
Foldamers
Hyperbranched Polymers
Polymerizable Surfactants
Novel Polyethers
All else....

Designer Macromoleules

Conjugated Polymers

Our efforts in this area are primarily directed toward PPV and its derivatives, specifically with the objective of controlling the molecular conjugation length and fluorescence quantum yield. A novel approach, wherein the sulfonium groups on the Wessling precursor polyelectrolyte precursor are competitively displaced by two different nucleophiles one that is readily eliminated while the other remains intact, yielded segmented dialkoxyPPV's with complete statistical control of the molecular conjugation length. Nucleophiles that have been used successfully are acetate, xanthate and more recently dithiocarbamate. Thus, the colour of emission from these was readily controlled over a 100 nm window. Utilizing soluble segmented MEHPPV's several interesting fundamental problems relating to the polymer conformation, intra-chain energy transfer and solvent-induced conformational collapse have been addressed. Our current focus is on developing novel routes to graft functional polymeric segments onto the PPV backbone for exploiting intra-chain energy transfer for colour control and also to develop approaches for preparing PPV-based gels.

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Synthetic polymers that mimic the structure and function of their biological cousins have interested polymer scientists for many decades because of the intrinsic desire to emulate the sheer elegance of such control exercised by nature, on the one hand, and the immense potential technological applications that could result from success in such an endeavor, on the other. Foldamers represent a class of synthetic polymers, which can be coerced to adopt one particular conformation of the often numerous options that they have the entropic penalty that has to be paid as a result will have to be met by inclusion of appropriate inter-segment interactions that provide the requisite enthalpic stabilization. We are presently designing macromolecules that possess equispaced segments that can interact with each other via weak interactions, such as p - stacking, charge transfer and solvophobic exclusion, often times in tandem. We are also engaged in designing special experimental tools to examine such folding in solution.

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Over the past decade our efforts have focussed on the development of new methodologies for synthesis of hyperbranched polymers, such as polyurethanes, polyesters, polyethers and more recently on polybenzyls. Apart from developing novel approaches, we have tried to address key issues, such as the effect of the nature and length of the spacer between branching points on the thermal properties of the resulting polymers, utilization of copolymerization of AB and AB2 type monomers for control of the branching density, use of monofunctional monomers to incorporate mesogens etc. More recently, by the use of PEG segments to link the branching junctions, we are preparing branched PEO equivalents that should be very sluggish to crystallize and could be potentially useful as candidates for solid polymer electrolyte applications. Other applications such as terminal group modification to generate unimer micelles and also use of hyperbranched polymers for generating amphiphilic and ionically conducting gels are the focus of our current attention.

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A large variety of polymerizable surfactants have been described during the past two decades. Most of these have polymerizable groups that form an integral part of the surfactants, while very few have them included as a counter-ion. Our focus during the last couple of years has been the design and utilization of polymerizable surfactants, wherein the polymerizable group functions as the counter-ion. Such systems have the added potential of being able to generate nanostructured polymeric materials in which the aggregated long hydrocarbon tails functions as supramolecular templates and can be removed after polymerization. Such polymeric materials may be considered as polymeric analogues of molecular sieves with the added advantage of being able to tailor the functionality by appropriate design of the surfactants. Studies to prepare surface-functionalized polymeric colloidal particles based on these surfactants are also currently being investigated.

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A novel melt condensation methodology for the synthesis of segmented polyethers, based on a transetherification reaction has been developed. This process was used for the preparation of segmented PEO's and hyperbranched polyethers. Approaches to design PEO-analogues that have very low propensity for crystallization are being currently examined as routes for the generation of materials suitable as solid polymer electrolyte applications. Extensive studies to understand the role of catalyst type and polymerization conditions has recently enabled the synthesis of polyethers with greatly improved molecular weights and polydispersity, thus permitting complete preclusion of the side reactions that plagued some of our early efforts.

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A few other topics that have engaged our interests in the past are discotic liquid crystals, molecular materials for NLO studies, moisture-induced crosslinkable polymers etc. In the area of discotic liquid crystals, we probed the effect of molecular asymmetry in Rufigallol-based discotics and also developed a novel approach for the inclusion of such discoidal units into main chain polymers. In NLO systems, we established the existence of odd-even oscillations in the SHG efficiency in twin NLO molecules, both in the micro-crystalline powders as well in poled doped polymeric films. Currently we are also engaged in designing novel functional group containing crosslinkers for molecular and metal-ion imprinting studies.