Self-complementary multiple hydrogen bonding interactions increase the glass transition temperatures to supramolecular poly(methyl methacrylate) copolymers

P(MMA-co-MAA)/cellulose nanofibers composites: Effect of hydrogen bonds on molecular mobility

Cellulose nanofibers (CNFs) nanocomposites were prepared using poly(methylmethacrylate-co-methacrylic acid) (PMMA-co-MAA) to investigate the macromolecular mobility within the composite, with particular focus on the effect of H-bonding. Dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS) were used to fully characterize the molecular mobility for which the effect of the introduction of H-bond forming moieties and the addition of CNFs (5 and 15 wt%) were assessed. Despite similar Tg values (determined by Differential Scanning Calorimetry), a deeper analysis of the relaxation times associated with the α-relaxation evidenced a significant effect induced by CNFs, which is in fact slowing down the macromolecular relaxation processes. The activation energy of the β-relaxation remained unchanged despite the introduction of MAA units in the main chain and the successive addition of CNFs. However, the latter led to the appearance at low frequencies of a new β'-relaxation correlated with the interactions between the CNF surface -OH groups and the -COOH groups of the matrix. The γ-relaxation showed a 45 % increase in activation energy from PMMA to PMMA-co-MAA + CNF nanocomposites regardless of the CNF content, due to the possibility of CNFs to interact and hinder the motion of the main chain methyl groups in α position.

Supramolecular Association of a Block Copolymer via Strong Hydrogen Bonding to Form Self-Healable Ionogels

The drive to enhance the operational durability and reliability of stretchable and wearable electronic and electrochemical devices has led to the exploration of self-healing materials that can recover from both physical and functional failures. In the present study, we fabricated a self-healable solid polymer electrolyte, referred to as an ionogel, using reversible hydrogen bonding between the ureidopyrimidone units of a block copolymer (BCP) network swollen in an ionic liquid (IL). The BCP consisted of poly(styrene-b-(methyl acrylate-r-ureidopyrimidone methacrylate)) [poly(S-b-(MA-r-UPyMA)], with the IL-phobic polystyrene forming micellar cores that were interconnected via intercorona hydrogen bonding between the ureidopyrimidone units. By precisely regulating the molecular weight and the composition of the hydrogen-bondable motifs, the mechanical, electrical, and self-healing characteristics of the ionogel were systematically evaluated. The resulting ionogel samples exhibited suitable stretchability, ionic conductivity, and room-temperature self-healability due to reversible hydrogen bonding. To highlight the applicability of the self-healing ionogel as a high-capacitance gate insulator, an electrolyte-gated transistor (EGT) was fabricated using a poly(3-hexylthiophene-2,5-diyl) semiconductor, and the performance of the EGT was fully recovered from a complete cut without any external stimuli.

Thermally healable polyurethane with tailored mechanical performance using dynamic crosslinking motifs

A tunable dynamic cross-linked polyurethane that makes a tradeoff between superior mechanical performance and excellent self-healing ability.

Towards Dynamic but Supertough Healable Polymers through Biomimetic Hierarchical Hydrogen-Bonding Interactions

A biomimetic (titin protein molecular structure) strategy is reported for preparing transparent and healable elastomers featuring supertoughness (345 MJ m^-3 ) and high tensile strength (44 MPa) after self-healing enabled by hierarchical (single, double, and quadruple) hydrogen-bonding moieties in the polymer backbone. The rigid domain containing hierarchical H-bonds formed with urethane, urea, and 2-ureido-4[1H]-pyrimidinone groups leads to a durable network structure that has enhanced mechanical properties and is also dynamic for rapid self-healing. Healable polymers with hierarchical hydrogen-bonding interactions show excellent recoverability and high energy dissipation owing to the durable interaction between polymer chains. This biomimetic strategy of using hierarchical hydrogen bonds as building blocks is an alternative approach for obtaining dynamic, strong, yet smart self-healing polymers for heavy-duty protection materials and wearable electronics.

Supramolecular Cross-Links in Poly(alkyl methacrylate) Copolymers and Their Impact on the Mechanical and Reversible Adhesive Properties

Hydrogen-bonded, side-chain-functionalized supramolecular poly(alkyl methacrylate)s were investigated as light- and temperature-responsive reversible adhesives that are useful for bonding and debonding on demand applications. Here, 2-hydroxyethyl methacrylate (HEMA) was functionalized with 2-ureido-4[1H]pyrimidinone (UPy) via a hexamethylenediisocyanate (HMDI) linker, to create a monomer (UPy-HMDI-HEMA) that serves to form supramolecular cross-links by way of forming quadruple hydrogen bonded dimers. UPy-HMDI-HEMA was copolymerized with either hexyl methacrylate or butyl methacrylate to create copolymers comprising 2.5, 5, or 10 mol % of the cross-linker. The mechanical properties of all (co)polymers were investigated with stress-strain experiments and dynamic mechanical analysis. Furthermore, the adhesive properties were studied at temperatures between 20 and 60 °C by testing single lap joints formed with stainless steel substrates. It was found that increasing the concentration of the UPy-HMDI-HEMA cross-linker leads to improved mechanical and adhesive properties at elevated temperatures. Concurrently, the reversibility of the bond formation remained unaffected, where rebonded samples displayed the same adhesive strength as regularly bonded samples. Debonding on demand abilities were also tested exemplarily for one copolymer, which for light-induced debonding experiments was blended with a UV-absorber that served as light-heat converter. Single lap joints were subjected to a constant force and heated or irradiated with UV light until debonding occurred. The necessary debonding temperature was comparable for direct heating and UV irradiation and varied between 28 and 82 °C, depending on the applied force. The latter also influenced the debonding time, which under the chosen conditions ranged from 30 s to 12 min.