How to Determine the Role of an Additive on the Length of Supramolecular Polymers?

Abstract

In polymer chemistry, modulation of sequence and control over chain length are routinely applied to alter and fine-tune the properties of covalent (co)polymers. For supramolecular polymers, the same principles underlying this control have not been fully elucidated up to this date. Particularly, rational control over molecular weight in dynamic supramolecular polymers is not trivial, especially when a cooperative mechanism is operative. We start this review by summarizing how molecular-weight control has been achieved in seminal examples in the field of supramolecular polymerizations. Following this, we propose to classify the avenues taken to control molecular weights in supramolecular polymerizations. We focus on dynamic cooperative supramolecular polymerization as this is the most challenging in terms of molecular weight control. We use a mass-balance equilibrium model to predict how the nature of the interaction of an additive B with the monomers and supramolecular polymers of component A affects the degree of aggregation and the degree of polymerization. We put forward a classification system that distinguishes between B acting as a chain capper, a sequestrator, a comonomer, or an intercalator. We also highlight the experimental methods applied to probe supramolecular polymerization processes, the type of information they provide in relation to molecular weight and degree of aggregation, and how this can be used to classify the role of B. The guidelines and classification delineated in this review to assess and control molecular weights in supramolecular polymers can serve to reevaluate exciting systems present in current literature and contribute to broaden the understanding of multicomponent systems.

Controlling the Length of Cooperative Supramolecular Polymers with Chain Cappers

“…This suggests that the thermal stability of the a‐BTA polymers is not affected by the presence of S ‐nMe‐BTA . These results point to either an absence of interactions between a‐BTA polymers and S ‐nMe‐BTA (self‐sorting) or to a chain‐capper role of S ‐nMe‐BTA for a‐BTA stacks . This is in contrast to two other scenarios: 1) an increase in T e is expected if S ‐nMe‐BTA intercalates into a‐BTA stacks because the total concentration of BTAs present in supramolecular polymers increases, or 2) a decrease of T e is expected when S ‐nMe‐BTA interacts with a‐BTA monomers by forming short stable side species in a competitive pathway, which effectively decreases the concentration of BTAs present in the supramolecular polymers .…”

“…The development of kinetically controlled supramolecular polymerization techniques, such as living supramolecular polymerization, has allowed significant progress in that direction . For systems under thermodynamic equilibrium, we recently reported on the various mechanisms directing the chain length in supramolecular (co)polymerizations . Next to the addition of good solvent, supramolecular additives can reduce the chain length by chain‐capping the polymers or by stabilizing the monomers.…”

Long-Lived Charge-Transfer State from B–N Frustrated Lewis Pairs Enchained in Supramolecular Copolymers

“…We introduced O -bridged triphenylborane and triarylamine cores and demonstrated their potential as appealing units for supramolecular optoelectronics by forming controlled chiral 1D supramolecular polymers. Studies on the copolymerization mechanism and microstructure indicate that B and N monomers act as true comonomers, 59 excluding the hypothesis of other interaction modes such as chain cappers or intercalator. 59 Supramolecular copolymers based on this pair display intriguing photoluminescence properties as a result of cofacial B–N contacts embedded in the chiral copolymers’ structure.…”

“…Studies on the copolymerization mechanism and microstructure indicate that B and N monomers act as true comonomers, 59 excluding the hypothesis of other interaction modes such as chain cappers or intercalator. 59 Supramolecular copolymers based on this pair display intriguing photoluminescence properties as a result of cofacial B–N contacts embedded in the chiral copolymers’ structure. Upon excitation, this molecular arrangement facilitates the formation of an excited-state complex at the B–N interfaces, followed by circularly polarized emission.…”

Supramolecular double-stranded Archimedean spirals and concentric toroids

“…Recently, mass-balance models have proven to be powerful tools for elucidating supramolecular polymerization mechanisms 35 – 38 . To quantify the thermodynamic parameters of the formation of the Archimedean spiral, a mass-balance model incorporating competition between the isodesmic J-aggregation and the nucleated H-aggregation (see Supplementary Information for full details) was fitted to the temperature-dependent changes in absorbance 35 .…”