Covalent Cross-Linking of Polymers through Ionene Formation and Their Thermal De-Cross-Linking

Abstract

Quaternization and dequaternization of tertiary amines were employed to generate thermally reversible covalent ionene networks. Chlorine or tertiary amine containing polymers were cross-linked with ditertiary amines and dihalide compounds, respectively, to generate ionene networks. The crosslinking reactivity of the dihalide decreased with decreasing carbonium ion character of its alkyl, and the reactivity of the ditertiary amine was dependent on the steric effect of its alkyl groups and the flexibility of the alkyl connecting the two nitrogen atoms of its molecule. IR and NMR tests, reactive solubility experiments and conductivity, differential scanning calorimetry, and flowability (at 215 °C) determinations have been carried out to investigate the thermal reversibility of cross-linked polymers. The thermal decross-linking/re-cross-linking was markedly affected by the nature of the tertiary amine and halide that took part in quaternization. Poor reversibility was found when the Cl-containing polymer was crosslinked with a diamine whose nitrogen atoms belonged to a saturated ring, such as dipiperidinomethane and 1,4-dimethylpiperazine. The de-cross-linking and re-cross-linking were rapid when either one or both bridging alkyls of the nitrogen atoms possessed a higher carbonium ion character than the two nonbridging alkyls. The (co)polymers obtained through the (co)polymerization of chloromethylstyrene, 2-(dimethylamino)ethyl acrylate, or vinylpyridine could be effectively quaternized with selected cross-linkers under moderate conditions to generate networks that exhibited thermal reversibility.

Poly(propylene glycol)‐based ammonium ionenes as segmented ion‐containing block copolymers

“…The faster degradation was attributed to the higher concentrations of HS with lower SS molecular weights. The actual mechanism for thermal degradation is complex; however, Ruckenstein and Chen42 and Jerome and coworkers43 proposed the dequaternization of nitrogens according to the Hoffman elimination pathway.…”

Synthesis of 12,12‐Ammonium Ionenes with Functionality for Chain Extension and Cross‐Linking via UV Irradiation

“…Ammonium ionenes are known to degrade at elevated temperatures in order to form many degradation products that result from various reactions, including reverse Menshutkin reactions and Hoffman eliminations. [24][25][26][27][28][29][30][31] The dimethylamino-terminated 12,12-ammonium ionene formed a brittle film, and the dynamic mechanical behavior was evaluated. However, the film was too brittle to evaluate via tensile testing.…”

Emulsion procedures for thermally reversible covalent crosslinking of polymers

“…5 The NMR spectra provided additional support for this mechanism. The high intensity of the N ϩ CH 3 peak in the spectra [Figs.…”

“…However, this equilibrium could be displaced toward dequaternization by the addition of a monofunctional halide compound, such as benzyl bromide. 5 Tables II-V show that all crosslinked polymers became completely or almost completely soluble after they were heated at 200°C in chloronitrobenzene containing benzyl bromide. The dissociation (dequaternization) of the ionene bridges occurred when the crosslinked polymer was heated at about 215°C.…”

“…Then, the polymer could flow under stress (thermocompression). 5 The thermocompression of some representative crosslinked polymers was carried out to investigate their flowability and thermal reversibility. A crosslinked polymer was regarded as thermally flowable when (1) a continuous, transparent thin film about 0.2 mm thick could be obtained through thermocompression and (2) the film did not dissolve or crack into small gel pieces when, after compression, it was submerged in THF.…”