Study On The Coordination Crosslinking Of AR,NBR And AR/NBR Blend And The Reversibility Of The Coordination-bonded Networks

The development of methodologies for material recycling, especially chemical recycling of crosslinked polymers, such as thermosetting resins and rubbers, is one of the most important issues in polymer and material science. Because of the difficulty in developing suitable recycling methodologies owing to the network structure of polymers, a new recycling concept has long been sought after. Reversible crosslinking-decrosslinking may constitute an efficacious recycling protocol.Coordination bond is the strongest non-covalent bond and reversible. In this study coordination bond was employed to build rubber network structures; vulcanization technology based on coordination-bonded crosslink was developed;novel reversible crosslinked rubber/metallic salt composites were prepared.Infrared spectra (FT-IR) and electron spin resonance (ESR) were applied to characterize the coordination bonds formed between metal ions and polymeric ligends.The formation of coordination-bonded networks was analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and a swell equilibrium method.The morphology of metallic salt particles dispersed in polymer matrix and the interface between polymer and particles were observed by scanning electron microscope (SEM).Compatibility is one of the most important factors affecting the performance of polymer-metal salt composites. On this issue efforts were made in three aspects:first, NBR/ Cu(NH3)4SO4·H2O composites with strong interface interactions were prepared, in that Cu(NH3)4SO4·H2O was active to form coordination bond with nitrile groups when ammonia released on heating; second, owing to the good compatibility between organic polymer and transitional metallic streates, well-dispersed coordination-crosslinked NBR/zinc streate, NBR/copper streate, NBR/ferric streate and NBR/ manganese streate composites were obtained;third, a homogeneous NBR/ZnCl2 composite were prepared when the content of ZnCl2 was no more than 10 phr, as a result of great deliquescence of ZnCl2.Acrylic rubber (AR) is a saturated rubber with ester carbonyl groups as potential ligends. It is of significance to vulcanize AR via coordination bonds.Both of the two oxygen atoms of ester carbonyl group coordinated with copper ion in AR/CuSO4 composites. The coordination reaction between AR and CuSO4 can carry out at room temperature.The coordination bonded networks formed fast at 180℃, and CuSO4 particles were encapsulated by a 500 nm thick interface layer.Copper sulfate was incorporated into AR/NBR alloy to co-vulcanize the two components through simultaneous formation of -COOR→Cu2+ and -CN→Cu2+ coordination bonds. The nearer the ratio of AR/NBR approached 1, the harder the coordination reactions took place and the looser crosslinking networks formed in AR/NBR/CuSO4 compounds. Moreover, shapes and sizes of copper sulfate particles changed with the ratio of AR/NBR. AR/NBR/CuSO4(10/90/10) composite had the optimum mechanical properties (932.23%, 43.73MPa) and good thermal stability (decompose temperature 411℃,22.63% residue at 700℃).Finally, the reversibility of networks of coordination-bonded NBR-based composites was investigated in this study. The coordination-bonded cross linking networks of NBR/CuSO4 and NBR/ZnCl2 composites could dissolve in DMF at 95℃. A reversible crosslinking-decrosslinking- crosslinking was achieved in NBR/ZnCl2 composites.