Published: July 28, 2011 r2011 American Chemical Society 6581 dx.doi.org/10.1021/ma201255q | Macromolecules 2011, 44, 6581–6587 ARTICLE pubs.acs.org/Macromolecules Cooperative Two-Component Self-Assembly of Mono- and Ditopic Monomers Maarten M. J. Smulders,* ,† Marko M. L. Nieuwenhuizen, Madeleine Grossman, Ivo A. W. Filot, Cameron C. Lee, Tom F. A. de Greef, Albertus P. H. J. Schenning, Anja R. A. Palmans, and E. W. Meijer* Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands b S Supporting Information ’ INTRODUCTION The concept of self-assembly, whereby relatively small and simple molecular building blocks arrange themselves via non- covalent interactions into larger aggregates, has become an attractive approach for the preparation of functional nano- structures. 1À7 Moreover, the necessity for a comprehensive understanding of the supramolecular polymerization mechan- isms in order to allow the rational design of self-assembled functional nanostructures is acknowledged by more and more researchers. 8À12 Nowadays, for single-component self-assem- bly of monomers into one-dimensional aggregates, the corre- sponding mathematical models have been fully developed to describe—and predict—the properties of these aggregates. 13 A next step toward more complex, functional assemblies involves the introduction of a second component, as this opens up the route to new phenomena such as chiral amplification, 14 end-capping, 15,16 energy transfer, 17,18 or the preparation of supramolecular block copolymers. 19 Depending on how the components interact, control over one or more properties of the assemblies becomes possible, e.g., the helicity of the aggre- gates or the averaged length of the assemblies. However, predicting the behavior of such a binary supramolecular system is not trivial as it can include nonlinear behavior, as for example in the case of chiral amplification. Moreover, in the particular case of a cooperative supramolecular polymerization there is a bimodal distribution of monomeric and polymeric species, and the interaction between the added component and the monomeric or polymeric species is not necessarily equal. 20 One approach to characterize a supramolecular polymer and to control the degree of polymerization (DP) entails the introduction of a monotopic chain stopper as a second com- ponent to a supramolecular polymer. 15,16,21À24 For example, Bouteiller and co-workers have studied the effect of adding a monotopic monomer to their bis-urea supramolecular polymers, which self-assemble via a cooperative mechanism. 15 The authors showed that introduction of a chain stopper eliminated the concentration dependence of the molar mass of the bis-urea supramolecular polymer and allowed them derive the molecular weight and dimensions of the end-capped polymer chains. In a later publication these studies were extended to include rheo- metry and dynamic light scattering. 25 To describe the coopera- tive supramolecular polymerization in the presence of a monotopic chain stopper, the authors considered condi- tions in which the number of monomers is relatively small, which allowed them to only consider the interactions between Received: June 3, 2011 Revised: July 20, 2011 ABSTRACT: A N-methylated benzene-1,3,5-tricarboxamide (BTA) was synthesized, characterized, and introduced as a monotopic BTA monomer capable of interacting with the supramolecular polymer formed via the cooperative self-assem- bly of the analogous ditopic BTA monomers. Using optical spectroscopy and viscometry, in combination with mathema- tical modeling and DFT calculations, we were able to under- stand in detail the consequence of introducing a second monotopic component in the self-assembly of BTA monomers into long supramolecular polymers, taking explicitly the coop- erative nature of the self-assembly process into account. To this end, a binary self-assembly model that includes both the monotopic and ditopic BTA monomer and that addresses the presence of both monomers and polymers (characteristic of a cooperative supramolecular polymer) was developed and successfully applied to model the viscometry data. The binary self-assembly model presented herein can be more generally applied to other cooperative supramolecular polymers to which a second component is added that can interact with the monomers and/or polymers and thus can contribute to a better understanding of more complex self-assembling systems.