Abstract
We present a structural and dynamic study on the simplest supramolecular hetero-association, recently investigated by the authors to prepare architectural homogeneous structures in the melt state, based on the bio-inspired hydrogen-bonding of thymine/diaminotriazine (thy–DAT) base-pairs. In the combination with an amorphous low Tg poly(butylene oxide) (PBO), no micellar structures are formed, which is expected for nonpolar polymers because of noncompatibility with the highly polar supramolecular groups. Instead, a clear polymer-like transient architecture is retrieved. This makes the heterocomplementary thy–DAT association an ideal candidate for further exploitation of the hydrogen-bonding ability in the bulk for self-healing purposes, damage management in rubbers or even the development of easily processable branched polymers with built-in plasticizer. In the present work, we investigate the temperature range from Tg + 20 °C to Tg + 150 °C of an oligomeric PBO using small-angle X-ray scattering (SAXS) and linear rheology on the pure thy and pure DAT monofunctionals and on an equimolar mixture of thy/DAT oligomers. The linear rheology performed at low temperature is found to correspond to fully closed-state dimeric configurations. At intermediate temperatures, SAXS probes the equilibrium between open and closed states of the thy–DAT mixtures. The temperature-dependent association constant in the full range between open and closed H-bonds and an enhancement of the monomeric friction coefficient due to the groups is obtained. The thy–DAT association in the melt is more stable than the DAT–DAT, whereas the thy–thy association seems to involve additional long-lived interactions.
Highlights
Biological, ‘living’ materials have shown to be the most advanced functional systems, and their efficiency in complexity cannot be imitated artificially
Based on the experimental miscibility of thy/DAT and poly(butylene oxide) (PBO) deduced from the former studies [40,41,42], we propose in the following an N-star-diblock copolymer approach, which should be general to capture any signature of supramolecular star-like aggregates with a H-bonding core and with N arms attached to it
The former structural small-angle X-ray scattering (SAXS) study of the thy–DAT association already indicated from extrapolation that the degree of H-bonding would be virtually complete at the reference temperature T0 of −25 ◦ C, at which all former work on PBO was more or less accidently mastered to [40,41,42]
Summary
Biological, ‘living’ materials have shown to be the most advanced functional systems, and their efficiency in complexity cannot be imitated artificially. The polarity of the H-bonding groups causes a natural energetic incompatibility between the groups and the polymer to which they are bound [14,17,18] They would tend to microphase separation or micellarization in the melt and introduce new time dependencies in their properties that are linked to the morphology and structure of hydrogen-bonding nanodomains, rather than to the H-bond itself. The association of thy and DAT groups in functionalized polymers like moderately polar PPO [22,23,35] and strongly apolar polyisobutylene (PIB) [8,36,37] has been extensively studied For both systems, a microphase separation was reported. The work attempts to provide a firm base for future work under mechanical or oscillatory deformation with medium-to-large amplitude as in real operation cases, thereby leading to a control of dissipation mechanisms
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