Self-healing Polyurethane Elastomer Based on Molecular Design: Combination of Reversible Hydrogen Bonds and High Segment Mobility

Nanoimprinting of Crosslinked Polyurethane / Polycaprolactone Blends: Scratch Recovery of Surface Topographies

Scratch recovery of micro-nano-patterned polymer surfaces extends the service life of products that require tunable surface properties and contributes to more sustainable development. Scratch recovery has been widely studied in bulk and 4D-printed polymers via intrinsic self-healing mechanisms. Existing studies on self-healing of micro/nano-scale polymeric surfaces are limited to the recovery of controlled tensile or compressive strain. Scratch recovery requires material transport to close the gap created by a scratch. Here, for the first time, scratch recovery of thermally nanoimprinted polymer surfaces in a heterogeneous polymer is reported. A blend of Polyurethane (TPU) and poly(caprolactone) (PCL) with selectively crosslinked TPU imparts shape-memory properties, and the uncrosslinked PCL retains chain mobility for molecular diffusion during scratch recovery. Scratch recovery of nanoimprinted micro-pillars has been achieved spontaneously and completely by heat and without any pressure input. The healing temperature is determined to be the melting point of PCL at 60 °C. Rapid recovery is also achieved at 60 s with complete closure of scratch width of 5 µm and topography recovery of the nanoimprinted micro-pillars.

Influence of the Molecular Weight of the Polycarbonate Polyol on the Intrinsic Self-Healing at 20 °C of Polyurethanes

Different polyurethanes (PUs) were synthesized with polycarbonate polyols of molecular weights of 500, 1000, and 2000 Da. Their self-healing abilities at 20 °C were tested, and their structural, thermal, and mechanical properties were analyzed. The PUs made with polycarbonates of molecular weights 500 (YC500) and 1000 Da (YC1000) exhibited self-healing at 20 °C, and the self-healing time of YC1000 was the shortest. The absence of crystallinity and the low degree of micro-phase separation favored self-healing at 20 °C in YC500. However, the presence of tack and the existence of allophanate species and urethane-carbonate and urea-carbonate hydrogen bonds disfavored self-healing. Consequently, the self-healing time at 20 °C of YC500 was longer than expected. On the other hand, YC1000 exhibited an "equilibrium" between urethane-carbonate and urea-carbonate hydrogen bonds and carbonate-carbonate interactions among the soft segments, so a particular structural order was produced that was associated with its fastest self-healing at 20 °C. The PU made with the polycarbonate of molecular weight 2000 Da did not exhibit self-healing at 20 °C because of its significant micro-phase separation, the presence of semi-crystalline soft domains, and the lower density of hydrogen bonds.

Combing experimental methods and molecular simulations to study self-healing behaviors of polyurethane elastomers containing multiple hydrogen bond networks and flexible blocks

The preparation of polymers with high self-healing ability is conducive to environmental protection and resource conservation. In the present work, two kinds of polyurethane (PU) elastomers were prepared: the one containing flexible end blocks (polypropylene glycol) and the other containing flexible end blocks and 2-ureido-4[1H]-pyrimidinone (UPy) groups that can form reversible quadruple hydrogen bonds. Both of the two PU elastomers have self-healing ability. At low temperatures the PU without UPy groups exhibits stronger self-healing ability, while at high temperatures the PU with UPy groups has better self-healing function. The difference can be attributed to the combined effect of segmental mobility and reversible network strength. Based on molecular simulations, we further observed that the self-healing behaviors are affected by four factors: healing temperature, reversible interaction strength, reversible interaction site density and segment diffusion ability.

Room-Temperature Self-Healable Blends of Waterborne Polyurethanes with 2-Hydroxyethyl Methacrylate-Based Polymers

The design of self-healing agents is a topic of important scientific interest for the development of high-performance materials for coating applications. Herein, two series of copolymers of 2-hydroxyethyl methacrylate (HEMA) with either the hydrophilic N,N-dimethylacrylamide (DMAM) or the epoxy group-bearing hydrophobic glycidyl methacrylate were synthesized and studied as potential self-healing agents of waterborne polyurethanes (WPU). The molar percentage of DMAM or GMA units in the P(HEMA-co-DMAMy) and P(HEMA-co-GMAy) copolymers varies from 0% up to 80%. WPU/polymer composites with a 10% w/w or 20% w/w copolymer content were prepared with the facile method of solution mixing. Thanks to the presence of P(HEMA-co-DMAMy) copolymers, WPU/P(HEMA-co-DMAMy) composite films exhibited surface hydrophilicity (water contact angle studies), and tendency for water uptake (water sorption kinetics studies). In contrast, the surfaces of the WPU/P(HEMA-co-GMAy) composites were less hydrophilic compared with the WPU/P(HEMA-co-DMAMy) ones. The room-temperature, water-mediated self-healing ability of these composites was investigated through addition of water drops on the damaged area. Both copolymer series exhibited healing abilities, with the hydrophilic P(HEMA-co-DMAMy) copolymers being more promising. This green healing procedure, in combination with the simple film fabrication process and simple healing triggering, makes these materials attractive for practical applications.

Self-Healable, Strong, and Tough Polyurethane Elastomer Enabled by Carbamate-Containing Chain Extenders Derived from Ethyl Carbonate

Commercial diol chain extenders generally could only form two urethane bonds, while abundant hydrogen bonds were required to construct self-healing thermoplastic polyurethane elastomers (TPU). Herein, two diol chain extenders bis(2-hydroxyethyl) (1,3-pheny-lene-bis-(methylene)) dicarbamate (BDM) and bis(2-hydroxyethyl) (methylenebis(cyclohexane-4,1-diy-l)) dicarbamate (BDH), containing two carbamate groups were successfully synthesized through the ring-opening reaction of ethylene carbonate (EC) with 1,3-benzenedimetha-namine (MX-DA) and 4, 4'-diaminodicyclohexylmethane (HMDA). The two chain extenders were applied to successfully achieve both high strength and high self-healing ability. The BDM-1.7 and BDH-1.7 elastomers had high comprehensive self-healing efficiency (100%, 95%) after heated treatment at 60 °C, and exhibited exceptional comprehensive mechanical performances in tensile strength (20.6 ± 1.3 MPa, 37.1 ± 1.7 MPa), toughness (83.5 ± 2.0 MJ/m3, 118.8 ± 5.1 MJ/m3), puncture resistance (196.0 mJ, 626.0 mJ), and adhesion (4.6 MPa, 4.8 MPa). The peculiar mechanical and self-healing properties of TPUs originated from the coexisting short and long hard segments, strain-induced crystallization (SIC). The two elastomers with excellent properties could be applied to engineering-grade fields such as commercial sealants, adhesives, and so on.

Systematic Evaluation of a Novel Self-Healing Poly(acrylamide-co-vinyl acetate)/Alginate Polymer Gel for Fluid Flow Control in High Temperature and High Salinity Reservoirs

Preferential fluid flow often occurs when water and CO₂ is injected into mature oilfields, significantly reducing their injection efficiency. Particle gels have been evaluated and applied to control the short circulation problems. This study systematically investigated a novel poly(acrylamide-co-vinyl acetate)/alginate-based interpenetrated gel system (Alg-IPNG) which is designed to control the preferential fluid flow problems in high-temperature reservoirs. Chromium acetate was incorporated into the gel system to provide the delayed crosslinking feature of the particle gels. The alginate polymer system can also take advantage of the Ca²⁺ ions in the formation water, which exist in most reservoirs, to reinforce its strength by capturing the Ca²⁺ to form Ca–alginate bonds. In this paper, various characterizations for the Alg-IPNGs before and after the self-healing process were introduced: (1) the elastic modulus is set at up to 1890 Pa, and (2) the water uptake ratio is set at up to 20. In addition, we also discuss their possible self-healing and reinforcement mechanisms. In particular, the self-healing starting time of the Alg-IPNG particles are modified between 38 to 60 h, which is related to the water uptake ratio, Ca²⁺ concentration, and temperature. The reinforced Alg-IPNG gel has an enhanced thermal stability (180 days) at the temperature up to 110 °C.

Synthesis and properties of responsive self-healing polyurethane containing dynamic disulfide bonds

The polymers with pH responsiveness and temperature sensitivity exhibit important applications in many fields. To endow the responsive polymers with self-healing is meaningful work, which contributes to increase their service life and reduce waste of resources significantly. In this research, a series of pH-responsive polyurethanes containing dynamic disulfide bonds and carboxylic acid functional groups were prepared by mixing polycaprolactone diol (PCL), hexamethylene diisocyanate (HDI), 2,2-dimethylolbutyric acid, and bis(2-hydroxyethyl) disulfide. The structure of the polymer was confirmed by some characterization methods such as infrared absorption spectroscopy, Raman scattering spectroscopy, X-ray diffraction, and differential scanning calorimetry. Many performances of the polymer such as the contact angle, thermal stability, mechanics, and self-healing properties can be adjusted by changing the functional units of polyurethanes. The dynamic disulfide bonds in the main chain were observed no harm to the pH response performance, instead which were beneficial to the promotion of heat resistance, tensile properties, and self-healing performance of polyurethane. The elongation at break and the tensile strength are increased by 85.3% and 54.9%, respectively. All the polyurethane exhibited considerable self-healing effects at 110°C, with the highest healing efficiency reaching 93.7%, as a result of the dissociation of hydrogen bonds and the exchange reaction of disulfide bonds.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.