Dynamic Contributions to the Bulk Mechanical Properties of Self‐Assembled Polymer Networks with Reconfigurable Bonds

Abstract

Catechol motifs are of particular interest owing to their ability to form many types of reversible bonds. [15][16][17][18][19] Polymer networks with catechol-cation coordination bonds have relaxation times that are governed by the affinity of the cation with the catechol group. [20][21][22] Grindy et al. [23] measured the viscoelastic modulus for networks with kinetically distinct metal coordinate crosslinks and demonstrated that reversible coordination junctions dominate the viscoelasticity of bulk materials. Catechol motifs with two hydroxy groups can also form hydrogen bonds among themselves. [24] Comparatively, there have been few reports on the role of hydrogen bonds between catechols in crosslinked networks. [25] Furthermore, the role of catechol concentration on bulk mechanics of polymer networks has yet to be elucidated in networks composed of model polymers. Here, we describe the role of hydrogen-bonded catechols on the bulk mechanical properties of the resulting networks.We recently synthesized catecholbearing ABA triblock copolymers that can self-assemble into mechanically robust networks wherein physical crosslinks are stabilized by inter-chain hydrogen bonding. [26] The copoly mer is synthesized through three steps and is processed into a network as shown in Scheme 1. Poly(ethylene glycol)-bromide (PEG-Br) macroinitiators are first prepared and then extended with an active esterified methacrylic acid (N-hydroxysuccinimide ester; NHSMA) by atom transfer radical polymerization. A blocks are then conjugated with dopamine to produce poly(NHSMA) 60 -b-PEG 227 -b-poly(NHSMA) 60 -Cat (ABA-Cat) polymers with a targeted conjugation ratio (r cat ) defined as the fraction of NHSMA monomers functionalized with a pendant catechol. Solutions of ABA-Cat polymer in N,Ndimethylformamide (DMF) self-assemble into networks through solvent exchange with water. We posit the network contains physical crosslinks composed of catechol-rich A blocks bridged together by PEG-based B blocks for following reasons. First, A and B blocks are immiscible in water and will be phase separated. Our previous study on structure showed solvent exchange disrupts crystalized PEG block by differential scanning calorimetry [26] and hydrogen-bonded Soft materials that contain dynamic and reversible bonds exhibit unique properties including unusual extensibility, reversible elasticity, and self-healing capabilities, for example. Catechol motifs are of particular interest owing to their ability to form many kinds of reversible bonds; however, there are few reports on the role of hydrogen bonds between catechols. Here, physically crosslinked self-assembled networks composed of catechol-functionalized ABA triblock co-polymers are synthesized and characterized to elucidate the role of intermolecular bonding between catechol motifs on bulk mechanical properties. The Young's moduli of equilibrated networks range from 16 to 43 MPa. Furthermore, the concentration of intermolecular interaction is controlled indirectly by synthesizing polymers with prescri...

Development of histamine reinforced poly(vinyl alcohol)/chitosan blended films for potential biomedical applications

“…By using the maximum viscosity values obtained for PVA/CS/H4 at 15 s −1 , the calculated E a value is of 34.015 kJ/mol, suggesting that, when supramolecular structures are formed at increased histamine content during flow, higher shear forces are required to induce the flow. Taking into account the complex dynamics of the formation and destruction of intermolecular interactions, some distinctive properties can be induced, such as reversible high elasticity or self‐healing ability 65 …”

Tuning the viscoelastic response of hydrogel scaffolds with covalent and dynamic bonds

“…A similar assumption was recently introduced and verified by Chen et al (2021). This approach is approximate because (i) the rates of rearrangement can be affected by interactions between chains bridged by different types of bonds (Han et al, 2017;Tang et al, 2020), and (ii) these rates are mutually dependent when the bonds are formed due to multivalent interactions (Badjic et al, 2005;von Krbek et al, 2017;Weng and Wang, 2020). To examine the accuracy of our assumption, we apply Eq.…”

Recent Progress in Materials Chemistry to Advance Flexible Bioelectronics in Medicine

“…Block copolymer (BCP)based elastomers are polymer net works with physical crosslinks that have been used in medical devices, such as catheters, drug delivery systems, and mate rials for regenerative medicine. [279][280][281][282][283][284] Polystyrenebased ABA triblock polymers are a prominent example of this molecular architecture, in which polystyrene A blocks flank a central B block with variable composition. [285] Typically, the middle block chain is composed of an aliphatic monomer, resulting in two rigid hydrophobic polystyrene blocks linked by a flexi ble polymer chain.…”