Polyethylene furanoate (PEF) represents a promising renewable resource-based bioplastic as replacement for fossil-based polyethylene terephthalate (PET) with improved material properties. However, the synthesis of PEF through conventional polycondensation remains challenging, since the time-intensive reaction leads to degradation and undesired discolouration of the product. Here we show the successful rapid synthesis of bottle-grade PEF via ring-opening polymerisation (ROP) from cyclic PEF oligomers within minutes, thereby avoiding degradation and discolouration. The melting point of such mixture of cyclic oligomers lies around 370 °C, well above the degradation temperature of PEF (~329 °C). This challenge can be overcome, exploiting the self-plasticising effect of the forming polymer itself (which melts around 220 °C) by initiation in the presence of a high boiling, yet removable, and inert liquid plasticiser. This concept yields polymer grades required for bottle applications (Mn > 30 kg mol−1, conversion > 95%, colour-free products), and can be extended to other diffusion-limited polymer systems.

nature of polymer-based adhesives prevent their easy removal and stifle or complicate debonding, rebonding, (end-of-life) recycling, and repair. In this context, the development of debonding-on-demand (DoD) adhesive technologies is attracting rapidly growing interest. Indeed, DoD techniques have already entered commercial exploitation in applications such as easily removable wound dressings, [2,3] temporal fixation in semiconductor manufacturing, [4][5][6] and the repair, replacement, or recycling of components. [7][8][9] While many debonding technologies employ heat to reduce the adhesive strength by imparting physical property changes of the adhesive, [10][11][12][13][14] light-induced debonding technologies represent an emerging field and have been much less explored. Photoirradiation is an attractive alternative to thermal debonding as it allows an efficient, contactless, remote stimulation that can be temporally and spatially controlled. [15][16][17][18] Moreover, factors such as the irradiation wavelength, intensity, and time can easily be tuned and it is often possible to focus the energy entry to the adhesive and minimize or avoid exposure of (sensitive) substrates. Of course, the approach requires that at least one of the substrates to be bonded is sufficiently transparent.The design of a light-debondable adhesive system is strongly related to the adhesive type and the requirements imparted by the application(s) for which the adhesive is designed. For instance, pressure-sensitive adhesives (PSAs), such as used in adhesive tapes, need to efficiently adhere under ambient conditions with only a brief application of pressure, they should withstand the (comparably small) loads experienced while bonded, and they must also be easily removable, ideally without leaving any residues on the substrate. [19,20] PSAs are therefore normally based on lightly physically or chemically cross-linked rubbery polymers such as natural rubber, styrene butadiene block copolymers, and acrylics. These materials provide a balance between adhesive and cohesive performance, i.e., adequate stiffness and strength to resist deformation and cohesive failure, and appropriate elasticity in order to establish adequate contact with the substrate. [1] On the other hand, structural adhesives must be able to effectively transmit large loads across the bonded joint and the high strength and high rigidity required for this function are usually achieved by the formation of glassy networks. Examples of such materials include cross-linked epoxy resins, which may possess shear strengths of >35 MPa, cyanoacrylates (superglues), acrylics, and polyurethanes. [19] Adhesives that enable bonding and especially debonding on demand (DoD) have attracted rapidly growing interest in the last decade, as these capabilities greatly improve the functionality of adhesives, particularly in connection with temporal fixation, repair, and recycling. Indeed, DoD techniques have already entered commercial exploitation in applications such as easily removable wound dressin...

The stimuli responsiveness of supramolecular polymers has recently been exploited for the development of adhesives that can be (de)bonded on demand when heated or exposed to UV light. However, it remains difficult to combine competitive solid-state mechanical properties and very low melt viscosity in one material. Here we report a new supramolecular polymer adhesives platform based on soybean oil as a multifunctional low-molecular-weight monomer (∼1500 g/mol) and isophthalic acid (IPA) groups that show hydrogen bonding and promote the formation of a reversible network. The polarity difference between the triglyceride backbone and the IPA groups leads to microphase separation, and the crystalline IPA domains act as physical cross-links. Heating the polymer above the melting temperature of the IPA-rich domains results in a dramatic viscosity reduction to 8 Pa•s at 120 °C. Once cooled to room temperature, the material properties are fully recovered as a result of the reassembly of the supramolecular network. Single lap joint adhesive tests performed at room temperature using glass and stainless steel substrates reveal shear strength values of 1.2 and 1.7 MPa, respectively, and heat and UV light can be used as external stimuli to debond on command. In addition, composites were prepared by adding 5 or 10 wt % microcrystalline cellulose (MCC) to the polymer, and this led to an increase of strength and modulus below the glass transition by up to 80% and 170%, respectively. Because the introduction of MCC partially hinders the crystallization of the matrix, the stiffness and tensile strength are reduced above the glass transition, while the elongation at break is significantly increased.

A modular approach for the design of two-component supramolecular polymer (SMP) networks is reported. A series of materials was prepared by blending two (macro)­monomers based on trifunctional poly­(propylene oxide) (PPO) cores that were end-functionalized with hydrogen-bonding 2-ureido-4­[1H]­pyrimidinone (UPy) groups. One monomer was based on a PPO core with a number-average molecular weight (M n) of 440 g mol–1. The SMP formed by this building block is a glassy, brittle material with a glass transition temperature (T g) of about 86 °C. The second monomer featured a PPO core with an M n of 3000 g mol–1. The SMP formed by this building block adopts a microphase-segregated morphology that features a rubbery phase with a T g of −58 °C and crystalline domains formed by the UPy assemblies, which act as physical cross-links and melt around 90–130 °C. Combining the two components allows access to microphase-segregated blends comprised of a rubbery phase constituted by the high-M n cores, a glassy phase formed by the low-M n component, and a crystalline phase formed by UPy groups. This allowed tailoring of the mechanical properties and afforded materials with storage moduli of 37–609 MPa, tensile strengths of 2.0–5.4 MPa, and melt viscosities of as low as 11 Pa s at 140 °C. The materials can be used as reversible adhesives.

Due to their low melt viscosity, competitive adhesive properties, and the stimuli‐responsive nature of supramolecular interactions, various supramolecular polymers have recently been investigated as adhesives with on‐demand (de)bonding capability. The adhesive properties of a series of hydrogen‐bonded supramolecular polymer networks based on a telechelic poly(ethylene‐co‐butylene) (PEB) terminated with isophthalic acid (IPA) groups and a series of bifunctional pyridines (Py) are reported herein. These supramolecular polymers microphase segregate into an IPA‐Py rich hard phase and an amorphous low‐glass‐transition PEB phase, and their properties depend on the nature of the pyridine‐carrying monomer. Rheological measurements show that the polymers disassemble into low‐viscosity melts when heated above the melting or glass transition temperature of the hard phase. Lap joints bonded with the polymers display a shear strength of up to 1.3 MPa, and debonding is possible in less than 10 s upon heating or exposure to UV–light; to enable rapid light‐induced (de)bonding, a light–heat converter is introduced. Cyclic bonding/debonding experiments reveal that the shear strength remains unchanged over five cycles and demonstrate that the process is very robust.

A systematic investigation of the influence of the binding motif and the processing history on the formation, crystallization, and mechanical properties of supramolecular polymers (SMPs) with a crystallizable core is reported. Telechelic, low-molecular-weight poly­(butylene adipate) (PBA, 2700 g mol–1) was end-functionalized with either quadruple hydrogen-bonding 2-ureido-4­[1H]­pyrimidinone (UPy) motifs or 2,6-bis­(1′-methyl­benzimidazolyl)­pyridine (Mebip) ligands. The UPy-based macromonomer spontaneously self-assembles into an SMP, whereas the Mebip-terminated building block was chain-extended by complex formation with a stoichiometric amount of Zn­(NTf2)2. We show that the morphology and the properties of the SMPs are strongly affected by the nature of the supramolecular binding motif and also the processing parameters. In the case of the UPy-functionalized SMP, all processing conditions led to microphase segregation of the supramolecular binding motifs and the PBA cores. When this material was solution-cast or compression-molded, the crystallization of dimerized UPy stacks occurred first and stifled the PBA crystallization. This afforded flexible materials with storage moduli E′ of 72–92 MPa and a tensile strength (σmax) of 3.6 MPa (all at 25 °C). When UPy-functionalized PBA was rapidly quenched from the melt, both microphases crystallized readily, and this led to much stiffer materials, with E′ = 673 MPa and σmax = 5 MPa. No phase segregation was observed for the metallosupramolecular polymer. In this case, all processes investigated afforded materials with a crystalline PBA phase, but crystallization from the melt was, at least at ambient temperature, very slow. This material displays an E′ of 645–913 MPa and a σmax of 6.0–7.6 MPa, which represents a significant improvement over a low-molecular-weight PBA reference.

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