Thermoreversible Cross-Linking of Furan-Containing Ethylene/Vinyl Acetate Rubber with Bismaleimide

Thermoreversible Cross-Linked Rubber Prepared via Melt Blending and Its Nanocomposites

A covalent adaptable network based on the thermoreversible cross-linking of an ethylene-propylene rubber through Diels-Alder (DA) reaction was prepared for the first time through melt blending as an environmental-friendly alternative to traditional synthesis in organic solvents. Functionalization of the rubber with furan groups was performed in a melt blender and subsequently mixed with different amounts of bismaleimide in a microextruder. Cross-linking was confirmed by FT-IR spectroscopy and insolubility at room temperature, while its thermoreversible character was confirmed by a solubility test at 110 °C and by remolding via hot-pressing. Mechanical and thermomechanical properties of the obtained rubbers showed potential to compete with conventionally cross-linked elastomers, with stiffness in the range 1-1.7 MPa and strain at break in the range 200-500%, while allowing recycling via a simple melt processing step. Nanocomposites based on the thermoreversible rubber were prepared with reduced graphene oxide (rGO), showing significantly increasing stiffness up to ca. 8 MPa, ∼2-fold increased strength, and thermal conductivity up to ∼0.5 W/(m K). Results in this paper may open for industrially viable and sustainable applications of thermoreversible elastomers.

Progress, challenges and future directions of heterocycles as building blocks in iterative methodologies towards sequence-defined oligomers and polymers

Heterocyclic building blocks for iterative methodologies leading to sequence-defined oligomers and polymers are reviewed. Solid- as well as solution-phase methods, challenges surrounding these systems and potential future directions are presented.

Recyclability of Photoinduced Cross-Linked EPM Rubber with Anthracene-Grafted Groups: Problems and Their Solutions

In this paper, we present the formation of reversible covalently cross-linked networks in ethylene propylene rubber with grafted anthracene groups (EPM-g-AN) based on the principles of photoinduced anthracene dimerization. First, an industrial-grade EPM rubber grafted with maleic anhydride functional groups (EPM-g-MA) was modified with 9-anthracenemethanol. By irradiating EPM-g-AN with UV light (365 nm), the anthracene moieties dimerize via [4 + 4]cycloaddition, forming a covalent network. The network cleavage proceeds at high temperatures (>170 °C), even if with considerable (chemical) degradation. Furthermore, one of the degradation routes has been identified by ¹H NMR to occur via the ester bond cleavage releasing 9-anthracenemethanol. Nevertheless, the reversibility of cross-linking has been achieved by performing the reverse reaction in decalin. The UV-vis spectroscopy clearly shows that the de-cross-linking process in these conditions is due to the anthracene dimer cleavage. Although the recovery in mechanical properties upon recycling is yet to be optimized, the disclosed results pave the way toward the use of anthracene chemistry in thermally reversible networks with possible industrial perspective applications.

Enhancement of Thermal and Mechanical Properties of Bismaleimide Using a Graphene Oxide Modified by Epoxy Silane

A thermosetting resin system, based on bismaleimide (BMI), has been developed via copolymerization of 4,4′-diaminodiphenylsulfone with a newly synthesized graphene oxide modified using epoxy silane (ES-GO). The effect of ES-GO on the thermomechanical and mechanical properties of cured modified resin was studied. To evaluate the efficiency of the modified BMI systems, the composite samples using glass fiber cloth were molded and tested. Thermogravimetric analysis indicates that the cured sample systems displays a high char yield at lower concentrations of ES-GO (≤0.5 wt.%), suggesting an improved thermal stability. Using dynamic mechanical analysis, a marked increase in glass transition temperature (Tg) with increasing ES-GO content was observed. Analysis of mechanical properties reveals a possible effect of ES-GO as a toughener. The results also showed that the addition of 0.3 wt.% ES-GO maximizes the toughness of the modified resin systems, which was further confirmed by the result of analysis of fracture surfaces. At the same time, a molded composite with ES-GO showed improved mechanical properties and retention rate at 150 °C as compared to that made with neat resin.

Coupling Dynamic Covalent Bonds and Ionic Crosslinking Network to Promote Shape Memory Properties of Ethylene-vinyl Acetate Copolymers

Dynamic crosslinking networks based on Diels–Alder (DA) chemistry and ionic interactions were introduced to maleic anhydride modified ethylene-vinyl acetate copolymer (mEVA) via in situ melt processing. The dual dynamic crosslinking networks were characterized by temperature-dependent FTIR, and the effects on the shape memory properties of mEVA were evaluated with dynamic mechanical thermal analysis and cyclic tensile testing. A crosslinking density was achieved at 2.36 × 10⁻⁴ mol·cm⁻³ for DA-crosslinked mEVA; as a result, the stress at 100% extension was increased from 3.8 to 5.6 MPa, and tensile strength and elongation at break were kept as high as 30.3 MPa and 486%, respectively. The further introduction of 10 wt % zinc methacrylate increased the dynamic crosslinking density to 3.74 × 10⁻⁴ mol·cm⁻³ and the stress at 100% extension to 9.0 MPa, while providing a tensile strength of 28.4 MPa and strain at break of 308%. The combination of reversible DA covalent crosslinking and ionic network in mEVA enabled a fixing ratio of 76.4% and recovery ratio of 99.4%, exhibiting an enhanced shape memory performance, especially at higher temperatures. The enhanced shape memory and mechanical performance of the dual crosslinked mEVA showed promising reprocessing and recycling abilities of the end-of-life products in comparison to traditional peroxide initiated covalent crosslinked counterparts.

Smart and Modern Thermoplastic Polymer Materials

Smart and modern thermoplastic polymer materials are defined as novel thermoplastic materials that are capable of responding to external stimuli through a macroscopic output in which the energy of the stimulus is transduced appropriately as a function of external interference. [...].

Aluminium-catalyzed terpolymerization of furfuryl glycidyl ether with epichlorohydrin and ethylene oxide: synthesis of thermoreversible polyepichlorohydrin elastomers with furan/maleimide covalent crosslinks

A novel family of well-designed thermoreversible polyepichlorohydrin elastomers with furan/maleimide covalent crosslinks possessed excellent mechanical, self-healing ability and recyclability.

Synthesis of switchable intelligent molecularly imprinted polymers with selective adsorption of ethyl carbamate and their application in electrochemical sensor analysis

A cyclodextrin aldehyde based molecularly imprinted polymer with thermally responsive Diels–Alder (DA) linkages of grafted furan-type dienes was polymerized. The synthesized DA-MIP has dienophile characteristics and the specific absorption of ethyl carbamate (EC) can be switched on or off simply by thermal adjustment to 130 °C and 60 °C, respectively. The imprinting factors (α) of the MIP and rDA-MIP to EC were 6.2 and 5.0, and the selection factors (β) were 5.2 and 4.0, respectively. The restoration of the molecular target ratio was 88%, as determined by absorption and desorption experiments. The thermal restoration ratio, determined by thermal cycling experiments, was 78%. A new electrochemical sensor was prepared using the DA-MIP and its responsiveness for detecting trace amounts of EC was investigated. The results indicate that the electrode response has good affinity and excellent specific recognition performance for template molecular chemicals.

A cyclodextrin aldehyde based molecularly imprinted polymer with thermally responsive Diels–Alder (DA) linkages of grafted furan-type dienes was polymerized. The synthesized DA-MIP has dienophile characteristics and the specific adsorption of ethyl carbamate (EC) can be switched on or off simply by thermal adjustment.

Effect of Rubber Polarity on Cluster Formation in Rubbers Cross-Linked with Diels-Alder Chemistry

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.