Viscoelastic properties of supramolecular soft materials with transient polymer network

Unravelling the Mechanism of Viscoelasticity in Polymers with Phase-Separated Dynamic Bonds

Incorporation of dynamic (reversible) bonds within polymer structure enables properties such as self-healing, shape transformation, and recyclability. These dynamic bonds, sometimes refer as stickers, can form clusters by phase-segregation from the polymer matrix. These systems can exhibit interesting viscoelastic properties with an unusually high and extremely long rubbery plateau. Understanding how viscoelastic properties of these materials are controlled by the hierarchical structure is crucial for engineering of recyclable materials for various future applications. Here we studied such systems made from short telechelic polydimethylsiloxane chains by employing a broad range of experimental techniques. We demonstrate that formation of a percolated network of interfacial layers surrounding clusters enhances mechanical modulus in these phase-separated systems, whereas single chain hopping between the clusters results in macroscopic flow. On the basis of the results, we formulated a general scenario describing viscoelastic properties of phase-separated dynamic polymers, which will foster development of recyclable materials with tunable rheological properties.

A Critical Approach to Polymer Dynamics in Supramolecular Polymers

Over the past few years, the concurrent (1) development of polymer synthesis and (2) introduction of new mathematical models for polymer dynamics have evolved the classical framework for polymer dynamics once established by Doi-Edwards/de Gennes. Although the analysis of supramolecular polymer dynamics based on linear rheology has improved a lot recently, there are a large number of insecurities behind the conclusions, which originate from the complexity of these novel systems. The interdependent effect of supramolecular entities (stickers) and chain dynamics can be overwhelming depending on the type and location of stickers as well as the architecture and chemistry of polymers. This Perspective illustrates these parameters and strives to determine what is still missing and has to be improved in the future works.

Synthesis of amorphous low Tg polyesters with multiple COOH side groups and their utilization for elastomeric vitrimers based on post-polymerization cross-linking

Elastomeric vitrimer materials with tunable cross-link densities are prepared using cross-linking precursor polyesters with multiple COOH side groups in the presence of diepoxy cross-linkers and trans-esterification catalysts.

Thermoset elastomers covalently crosslinked by hard nanodomains of triblock copolymers derived from carvomenthide and lactide: tunable strength and hydrolytic degradability

Sustainable, mechanically reinforced, and hydrolytically degradable thermoset elastomers were synthesized by one-pot, three-step synthesis & crosslinking.

Thermal stability enhancement of hydrogen bonded semicrystalline thermoplastics achieved by combination of aramide chemistry and supramolecular chemistry

Supramolecular polymers based on an amorphous fatty acid central block and crystallizable H-bonding end-groups of increasing size show low melt viscosity and tunable thermo-stability.

Control over the assembly and rheology of supramolecular networks via multi-responsive double hydrophilic copolymers

An orthogonal control over network formation and dynamics is achieved in metallo-supramolecular micellar gels via multi-responsive double hydrophilic copolymers.

Unveiling the molecular mechanism of self-healing in a telechelic, supramolecular polymer network

Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing.

Highly Extensible Supramolecular Elastomers with Large Stress Generation Capability Originating from Multiple Hydrogen Bonds on the Long Soft Network Strands

Highly extensible supramolecular elastomers are prepared from ABA triblock-type copolymers bearing glassy end blocks and a long soft middle block with multiple hydrogen bonds. The copolymer used is polystyrene-b-[poly(butyl acrylate)-co-polyacrylamide]-b-polystyrene (S-Ba-S), which is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Tensile tests reveal that the breaking elongation (εb ) increases with an increase in the middle block molecular weight (Mmiddle ). Especially, the largest S-Ba-S with Mmiddle of 3140k, which is synthesized via high-pressure RAFT polymerization, achieves εb of over 2000% with a maximum tensile stress of 3.6 MPa, while the control sample without any middle block hydrogen bonds, polystyrene-b-poly(butyl acrylate)-b-polystyrene with Mmiddle of 2780k, is merely a viscous material due to the large volume fraction of soft block. Thus, incorporation of hydrogen bonds into the large molecular weight soft middle block is found to be beneficial to prepare supramolecular elastomers attaining high extensibility and sufficiently large stress generation ability simultaneously. This outcome is probably due to concerted combination of entropic changes and internal potential energy changes originating from the dissociation of multiple hydrogen bonds by elongation.

Adhesive Materials Utilizing a Thymine-Adenine Interaction and Thymine Photodimerization

A cross-linking reagent having two adenine units was mixed with polymers bearing thymine units to form adhesive materials utilizing both intermolecular hydrogen bonding and in situ formation of covalent bonds. In the case of 58 mol % of adenine units relative to thymine units, formation of intermolecular hydrogen bonds because of a thymine-adenine interaction was observed at room temperature using FT-IR. The peel strength became weak with heating above 60 °C, indicating breakup of intermolecular bonds between thymine and adenine units. On the other hand, UV-vis spectral measurements showed that heating at 80 °C with 254 nm light irradiation facilitated the photodimerization reaction between thymine units even in the presence of adenine cross-linking reagents. This result was consistent with a large value for the peel strength (6.5 N/10 mm) after the dual treatment, heating at 80 °C with 400 mJ/cm² of UV irradiation.

A novel supramolecular polymer fabricated via stronger hydrogen-bonding interactions between substituted amide groups: design, synthesis, properties and mechanism

By modulating the electron densities of substitutes of both a proton donor (N–H) and proton acceptor (CO), the molecules of DPCHP-DODE assemble into a supramolecular polymer during the cooling process of the melt DPCHP-DODE.