Re-usable thermally reversible crosslinked adhesives from robust polyester and poly(ester urethane) Diels–Alder networks

The sustainable design of polymers for applications requires careful consideration of how they can be re-used or recycled at the end of service life. There has been considerable interest in covalent adaptable networks (CANs) which offer the potential of the properties of crosslinked polymers but where the materials can be reprocessed like thermoplastics. Although there have been advances in CAN chemistry, materials tend to creep and industrial applications are limited. Here we show thermally reversible crosslinked adhesives from dissociative Diels–Alder networks which can be re-used repeatedly with versatile adhesion and creep resistance. Monomer and isocyanate-free polyester and poly(ester urethane) prepolymers were successfully synthesized by facile techniques with high atom efficiency and the resulting CANs are easy to apply in bulk from the melt. Mechanical properties can be tuned depending on the prepolymer design with the networks providing versatile adhesion to different substrates and creep resistance to 70–80 °C, above both the Tg and Tm of the networks. The adhesives are thermally stable during application and can be re-used repeatedly by simple heating/cooling cycles in bulk, without solvents or additional process steps, providing the same level of performance. Our results demonstrate that these Diels–Alder networks are robust in mechanical performance up to the temperature where significant dissociation begins to occur. This opens the possibility for the considered design of prepolymer architecture and reversible chemistry to meet the performance requirements of different applications in a truly sustainable fashion via scalable, efficient, industrially facile methodologies – where materials are free of solvents or monomers in their synthesis, processing, application and re-use

Many happy returns: combining insights from the environmental and behavioural sciences to understand what is required to make reusable packaging mainstream

The introduction of reusable packaging systems (both refill and return) has the potential to significantly reduce waste from single-use plastic packaging. However, for these schemes to be successful, both the environmental impact and the willingness of consumers to engage with such systems need to be carefully considered. This paper combines and discusses two complementary studies: (i) a life cycle assessment comparing the environmental impacts of single-use, refillable, and returnable containers for a takeaway meal, and (ii) a large online survey of UK adults exploring what types of product and packaging consumers are willing to reuse, how, and why. The findings of the life cycle assessment indicate that reusable containers outperform single-use plastic containers on most measures of environmental impact. The survey found that given the choice of disposal, reuse or recycling, that recycling is the preferred method of dealing with packaging once empty in the UK, and that people's decisions with regards to what types of packaging they are willing to reuse are largely driven by the aspects of the packaging itself (e.g., material and type) rather than the nature of the product inside of the packaging (e.g., state of matter of the contents). The survey also showed that people were more willing to engage in reuse systems with which they were already familiar. Additionally the language used to describe these schemes and the term ‘reuse’ needs to be considered. Combined, these factors can be used to determine the best packaging reuse system for a given product and situation

Graft copolymer stabilizers for non-aqueous polymer dispersions

SIGLEAvailable from British Library Document Supply Centre- DSC:DX184535 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Branched methacrylate copolymers from multifunctional comonomers: the effect of multifunctional monomer functionality on polymer architecture and properties

Soluble. branched (meth)acrylic copolymers have been synthesised via facile, one-step, batch solution polymerisations taken to high conversion. Methyl methacrylate has been copolymerised with a number of multifunctional comonomers using a chain transfer agent to prevent gelation. A variety of soluble, branched copolymer architectures have been synthesised using multifunctional monomers containing between two and six acrylate functional groups. Independent of polymer composition, all copolymers were proven to be branched with broader molecular weight distributions compared to linear analogues. The molecular weights, Mark-Houwink constants and T-g's all varied systematically depending on the functionality and concentration of the multifunctional monomer copolymerised. Although the polymer architectures are complex, this methodology is pragmatic, highly practical and very convenient. The need for high control of polymer architecture via controlled radical polymerisation for satisfying applications is questioned. It is proposed that precise control may not be necessary for many applications, whereas new, heterogeneous structures via pragmatic routes may be sufficient and more easily exploited

Branched methacrylate copolymers from multifunctional monomers: chemical composition and physical architecture distributions

Soluble, branched (meth)acrylic copolymers have been made via facile, one-step, batch solution polymerisations taken to high conversion. Methyl methacrylate has been copolymerised with a bifunctional monomer using a chain transfer agent to inhibit gelation. Conventional chain transfer using a mercaptan has been compared to catalytic chain transfer (CCT) using a cobalt porphyrin. The polymerisations have been monitored as a function of monomer conversion and the polymer prepared at high conversion has been fractionated across the molecular weight distribution. The polymerisations remain isotropic, with both the chemical composition and physical architecture distribution varying systematically as a function of monomer conversion and copolymer molecular weight. A mechanism for the polymerisation is proposed based on the experimental data

Facile bisurethane supramolecular polymers containing flexible alicyclic receptor units

This paper details the synthesis, characterisation and physical analyses of a series of hydrogen bonded urethane supramolecular polymer systems that are created by a facile one-step synthesis from inexpensive and commercially available starting materials. We report the synthesis and characterisation of a series of low molecular weight bisurethanes (<650 a.m.u.) that exhibit physical properties in the bulk that are characteristic of polyurethane materials possessing far higher molecular weight. The physical characteristics of these low molecular weight bisurethanes were investigated by using temperature-dependent rheological analysis and viscometry and the nature in which these compounds assembled was assessed using IR and NMR spectroscopies. These studies reveal that these simple bisurethanes self-assemble via hydrogen bonding interactions

Electrospun supramolecular polymer fibres

The electrospinning of urethane based low molecular weight polymers differing only in the nature of the hydrogen bonding end-groups has been investigated. For the end-groups with the lowest binding constants at maximum solubility only droplets, are produced at the electrode; in contrast, increasing the binding constant of the end-group results in electrospun fibres being produced. The properties of the fibres produced are subject to changes in solvent, concentration and temperature. Typical diameters for these fibres were found to be some 10 s of µm, rather than the sub-micron dimensions often produced in electrospinning systems. Such diameters are related to the high initial concentrations required; this also may influence the rate of solvent removal and preferential surface solidification which feature in these examples. A simple theoretical model is used to relate the association constant to the molecular weight required for fibre formation; significantly lower levels of association are required for higher molecular weight macromonomers compared to smaller molecular systems