Physically Cross-Linked Polybutadiene by Quadruple Hydrogen Bonding through Side-Chain Incorporation of Ureidopyrimidinone with Branched Alkyl Side Chains

Abstract

The synthesis of a supramolecular polymer network based on ureidopyrimidinone (UPy) is demonstrated starting from a low-molecular weight polybutadiene (PB) polymer, which was modified with UPy quadruple hydrogen-bonding motifs through UV-initiated thiol–ene chemistry under ambient conditions. Here, the UPy units contain a branched alkyl side chain rather than a methyl group, as is the case in most literature examples. The sterically demanding aliphatic 2-ethylpentyl side chain was introduced to prevent stacking of the UPy dimers and to enhance the compatibility of the UPy unit with the apolar PB polymer matrix. The UPy units were grafted onto PB with different functionalization degrees yielding materials with a relatively broad range of glass transition temperatures (T g) and material properties, as evaluated by thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamic mechanical thermoanalysis. Importantly, only the system with 13 mol % UPy functionalization showed some macroscopic phase separation as indicated by its partial opaque appearance, even though this was not detected by DSC. Previous reports on PB end functionalized with methyl-functional UPy revealed phase separation through DSC, indicating that the branched side chains indeed suppress the phase separation. The network dynamics were assessed by rheological measurements at different temperatures, which were subsequently fitted to the sticky Rouse model and creep experiments. We found that the sticky Rouse model satisfactorily fits the linear response of the systems in the terminal regime. However, significant discrepancy from theory still persists in the rubbery plateau regime. This deviation is attributed to the presence of structural defects in the systems. Altogether, this work demonstrates the importance of designing the supramolecular physical cross-linker unit with a branched aliphatic side chain to enhance the compatibility with the polymer matrix for the formation of supramolecular polymer networks.

Backbone Polarity Tunes Sticker Clustering in Hydrogen-Bonded Supramolecular Polymer Networks

“…A better overview of the relaxation process can be obtained by constructing dynamic moduli master curves according to the time–temperature superposition (tTS). However, supramolecular copolymers are prone to violate tTS, specifically if polymeric dynamics and supramolecular associations have significantly different activation energies. ,, In such cases, dynamic moduli are governed by distinct relaxation mechanisms at different frequencies and therefore need to be shifted horizontally by distinct shift factors at various frequency domains. ,,− To examine the applicability of tTS to the current samples we first use the van Gurp–Palmen (vGP) plot of phase angle versus complex modulus, which contains no frequency-dependent parameter and shift factor complexities. The constructed vGP curves demonstrate a good overlap between complex moduli obtained at different temperatures between 0 and 100 °C, as shown in Figure .…”

A Generalized Mechano-statistical Transient Network Model for Unravelling the Network Topology and Elasticity of Hydrophobically Associating Multiblock Copolymers in Aqueous Solutions

“…In this regard, the sticky Rouse , and sticky reptation , models for unentangled and entangled multisticker associative polymer solutions were developed based on a single-chain approach with pairwise interactions between sticky groups. Despite the extensive theoretical background of these “sticky” models, experimental rheological data often show limited agreement with the model predictions. − Moreover, most associative polymer solutions obeying similar scaling relations as predicted by the “sticky” frameworks almost never fulfill the assumption of simple pairwise association. − Alternatively, transient networks with cross-linking nodes formed by large-scale aggregates of sticky (end)­groups were treated by Semenov et al according to a collective approach, in which the dynamics of the overall aggregate assembly dominate over single chain relaxations. , However, recent NMR experiments by Mordvinkin et al on telechelically associating polymers have shown that also for networks formed by large, micellar cross-linking nodes, the relaxation is governed by single chain relaxation principles rather than micellar reorganization. , In summary, the lack of quantitative agreement between theoretical frameworks and experimental data, as well as the lack of a qualitative agreement between different model approaches, indicates that a thorough understanding of the rheological behavior of networks formed by nontelechelic associative polymer solutions remains an open question.…”

Preparation of functionalized diene-elastomers upon top-down pyrolysis of their vulcanizates via dynamic covalent polymerization

“…To address this issue, great efforts have been made to decorate the rubber matrix with various functional handles, mainly via the copolymerization of olefins with functional monomers 1 or post-modification of the rubber skeleton, 2 for the purpose of achieving the intrinsic functionalization of rubbers. Hitherto, various kinds of functional handle, including carboxyl, 3 hydroxyl, 4 epoxy, 5 amino, 6 ester, 7 cyano, 8 amide, 9 alkoxy, 10 and ureidopyrimidinone, 11 have been successfully introduced into the main/side chains of the rubber skeleton, leading to a series of novel applications of the obtained functionalized rubbers with respect to self-reinforcing, 12 self-healing 13 and shape memory materials, 14 dielectric elastomers, 15 and coupling agents. 16 In our previous studies, several functional handles, including maleic anhydride and triazolinedione, were also grafted onto commercial rubber skeletons, for the purpose of delivering multiple hydrogen-bonded linkages and hence self-healing and shape memory functions to the system.…”