A proof of principle for the use of Diels–Alder chemistry as a thermoreversible cross-linking tool for rubber products is demonstrated. A commercial ethylene-propylene rubber grafted with maleic anhydride has been thermoreversibly cross-linked in two steps. The pending anhydride rings were first modified with furfurylamine to graft furan groups onto the rubber backbone. These pending furans were cross-linked with a bismaleimide via a Diels–Alder coupling reaction. The newly formed Diels–Alder cross-links break at elevated temperatures (>150 °C) and can be re-formed by thermal annealing (50–70 °C). Reversibility of the rubber network was proven with infrared spectroscopy and on the basis of the mechanical properties. Furthermore, reversibility was also shown in a practical way, i.e., by cutting the used material into pieces and pressing them into new samples displaying comparable mechanical properties (impossible for conventionally cross-linked rubbers). The physical properties of the resulting products are comparable to those of conventionally cross-linked EPDM rubber and superior compared to those of their non-cross-linked precursors.

The controlled synthesis of high molecular weight branched polyacrylamide (PAM) has been accomplished by using atomic transfer radical polymerization (ATRP) of acrylamide (AM) in water at room temperature. Halogen-functionalized aliphatic polyketones acted as macroinitiators in the polymerization. The obtained branched polymers were used in water solutions to study the effect of the molecular architecture on the rheological properties. For comparison purposes, linear PAM was synthesized by using the same procedure. The intrinsic viscosities and light scattering data suggest that the 13-and 17-arm PAMs are more extended in solution compared to the linear, 4-arm, and 8-arm analogues, at equal total molecular weight. The comparison of linear and 4-, 8-, 12-, 13-, and 17-arm PAM in semidilute solutions demonstrated that the 13-and 17-arm PAM have the highest solution viscosity at equal molecular weight. Depending on the PAM molecular weight and concentration, a significant (as much as 5-fold) increase in solution viscosity (at a shear rate of 10 s −1 ) is observed. The elastic response of aqueous solutions containing the polymers critically depended on the molecular architecture. Both the 4-and 8-arm polymers displayed a larger phase angle value compared to the linear analogue. The 13-and 17-arm PAMs displayed a lower phase angle than the linear one. Ultimately, the rheological properties are dependent on the number of arms present. The combination of a higher hydrodynamic volume and higher entanglement density leads to an improved thickening efficiency (for N ≥ 13, N being the average number of arms). The improved thickening efficiency of the branched (N ≥ 13) PAMs makes these polymers highly interesting for application in Enhanced Oil Recovery and drag reduction.

Diels–Alder chemistry has been used for the thermoreversible cross-linking of furan-functionalized ethylene/propylene (EPM) and ethylene/vinyl acetate (EVM) rubbers. Both furan-functionalized elastomers were successfully cross-linked with bismaleimide to yield products with a similar cross-link density. NMR relaxometry and SAXS measurements both show that the apolar EPM-g-furan precursor contains phase-separated polar clusters and that cross-linking with polar bismaleimide occurs in these clusters. The heterogeneously cross-linked network of EPM-g-furan contrasts with the homogeneous network in the polar EVM-g-furan. The heterogeneous character of the cross-links in EPM-g-furan results in a relatively high Young’s modulus, whereas the more uniform cross-linking in EVM-g-furan results in a higher tensile strength and elongation at break.

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