Oxidative Polymerization Of 2,6-dimethylphenol In Water With Cu(Ⅱ)-PAMAM Complexes

Solution polymerization has been widely used to produce poly(2,6-dimethyl-l,4-phenylene oxide) (PPO), an important enginnering plastic. However, both a solvent-recovery process and an anti-explosive reactor are required since the polymerization usually proceeds in an organic solvent under oxygen atmosphere. From the view of green chemistry, the use of water as the solvent is the desired approach. Therefore, the study of oxidative polymerization of 2,6-dimethylphenol (DMP) to form PPO in water has both important theoretical and practical values.We report the first catalytic Cu(II)-polyamidoamines (PAMAMs, EDA core with NH₂ terminal groups) dendrimer complexes that catalyze aerobic oxidative polymerization of DMP in water, resulting in a good yield of PPO and an extremely low content of byproduct, 3,3,5,5-tertramethyl-4,4-diphenoquinone (DPQ). The catalytic activity of Cu(II)-PAMAM complexes enhances greatly compared with the conventional catalyst. The major factors that influence the catalytic activity of Cu(II)-PAMAM dendrimer complexes in DMP polymerization are the generations of PAMAM dendrimer and the molar ratio of copper ions to the ligands. When copper concentration reduces from 200μmol/L to 25μmol/L, the PPO yields drop significantly with Cu(II)-PAMAMGl complex, while the yields of PPO decrease gently by Cu(II)-PAMAMG3 complex and Cu(II)-PAMAMG5 complex. The yields of PPO by Cu(II)-PAMAMG5 complex are somewhat higher than those with Cu(II)-PAMAMG3 complex under the same condition. Another important factor on catalytic activity of Cu(II)-PAMAM dendrimer complex is the molar ratio of copper ions to the ligands. Each polymerization was carried out at the same concentration of copper ions (25μmol L^-1) and the PPO yield increases with the increase of the [Cu(II)]/[PAMAMG3] molar ratio from 1 to 11.We have designed and prepared a novel magnetic nanoparticle supported Cu(II)-PAMAM dendrimer catalyst. TEM, FTIR, EA and TGA have been employed to analyze the prepared Cu(II)-PAMAM complex catalyst supported on magnetic nanoparticles. It was found that the PAMAM dendrimers from generation 1-3 have been successfully immobilized on the magnetic nanoparticles. Furthermore, the novel catalysts have been used in the oxidative polymerization of DMP in water. The catalysts exhibit excellent C-O/C-C coupling selectivity to form PPO. After polymerization the catalysts could be recovered from the two types of solid particles (PPO particles and immobilized catalysts) by an external magnetic field and used repeatedly for the polymerization.