Molecular Approach to Supramolecular Polymer Assembly by Small Angle Neutron Scattering Ana R. Bra ́ s, †, * Claas H. Hö velmann, † Wiebke Antonius, † Jose ́ Teixeira, ‡ Aurel Radulescu, § Jü rgen Allgaier, † Wim Pyckhout-Hintzen, †, * Andreas Wischnewski, † and Dieter Richter † † JCNS-1/ICS-1, Forschungszentrum Jü lich, D-52425 Jü lich, Germany ‡ CEA Saclay, Lab Leon Brillouin, CEA CNRS, F-91191 Gif Sur Yvette, France § Outstation FRM 2, JCNS-1, Forschungszentrum Jü lich, D-85747 Garching, Germany * S Supporting Information ABSTRACT: We present a small angle neutron scattering (SANS) study of the association of heterocomplementary telechelic poly- propylene glycol (PPG) polymers, bearing either diaminotriazine (DAT) or thymine (Thy) stickers as end-groups, both in the melt and in dilute solution. The SANS data are critically examined for the architecture and morphology as well as relative extent of linear assembly in the apolar solvent toluene. A random phase approximation (RPA) approach, adapted for a supramolecularly assembled multiblock copolymer is presented, which allows to extract the interaction parameters between the constituents and the medium. From the proposed approach, which describes very well heterocomplementary hydrogen-bonding telechelic polymers in both diluted toluene solution and in the melt, we conclude that linear association prevails. ■ INTRODUCTION Supramolecular polymers have become an increasingly important class of polymers, which in contrast to covalently linked polymers, are able to assemble spontaneously by reversible noncovalent interactions such as metal ligand complexation or hydrogen bonding. 1-10 The noncovalent interaction implicates a dynamic equilibrium between bonded and free building blocks. As a consequence of this equilibrium, the average length of the supramolecular polymer chain depends on the monomer concentration and also on the choice of the solvent. Therefore, supramolecular polymers are known to give rise to a rich variety of self-organizing structures on the mesoscale with a multiplicity of macroscopic proper- ties. 11-17 These can be realized by changing the relevant parameters to adjust the chain length in situ. The transient nature of the supramolecular association makes these polymers ideal candidates for the development of new materials with, e.g., intrinsic self-healing properties, which has recently gained increased interest from both commercial and academic side. 18,19 One of the simplest examples of associating supramolecular systems are telechelic polymers. 20 Typical building blocks are oligomers (spacers) having self-complementary binding stickers with hydrogen bonding motifs. 21,22 Self-complementary denotes the association of two identical end-groups, whereas in the heterocomplementary case, two different end-groups are binding together (Figure 1). It is also well-known that in many of these systems, microphase segregation between the spacer and the stickers, may occur, due to the different chemical composition, e.g polar stickers connected to an apolar spacer oligomer. 23-44 The compatibility between both is typically very low but can be enhanced by the ability of the stickers to form hydrogen bonds. It is controlled by the Flory-Huggins χ parameter. This microphase segregation phenomenon can manifest itself either as a disordered clustering of the stickers 24,26-34 or as an ordered microphase separation as observed for block copolymers. 45-47 Here scattering techniques, in particular small angle neutron scattering (SANS), are most ideally suited since they explore both, phase morphology as well as chain structure by using the appropriate blending and contrast matching. 48-50 Consequently, for the design of new nanostructured materials based on telechelic supramolecular polymers, it is of utmost importance to gain a well founded and rigorous understanding of the underlying interactions, quantified by χ. Indeed, directed hydrogen bonds have been shown to be particularly effective in facilitating a tuning of binding constants. Also the selective, recognition controlled, association between molecular monomers bearing heterocomplementary stickers with specific hydrogen-bond matching pairs are important for novel material properties. 19,25,51-53 Received: August 15, 2013 Revised: October 30, 2013 Published: November 22, 2013 Article pubs.acs.org/Macromolecules © 2013 American Chemical Society 9446 dx.doi.org/10.1021/ma401714r | Macromolecules 2013, 46, 9446-9454