新型钴酞菁接枝温敏聚合物的制备及性能

PREPARATION AND PROPERTIES OF A NOVEL THERMOSENSITIVE POLYMER CONTAINING COBALT PHTHALOCYANINE

采用2,4,6-三氯-1,3,5-三嗪对四氨基钴酞菁进行改性,并以共价键接枝到聚N-异丙基丙烯酰胺上制得一种新型温敏性高分子催化剂——钴酞菁接枝温敏聚合物,并采用UV-Vis、TG等对其进行表征.对钴酞菁接枝温敏聚合物、温敏聚合物和小分子金属酞菁进行溶解性测试,结果表明与四氨基钴酞菁相比,所合成的钴酞菁接枝温敏聚合物能溶解于水和大多数有机溶剂,且该聚合物水溶液具有良好的温敏性,其最低临界溶解温度(LCST)为34.5℃.采用浊度法考察了不同比例的混合溶剂(乙醇/水、DMF/水)对LCST的影响,结果表明随着有机溶剂含量的增加,LCST先下降后升高,而当有机溶剂增加到一定程度时温敏性消失.本文还考察了钴酞菁接枝温敏聚合物对2-巯基乙醇的催化活性,结果表明随着温度升高,催化活性也不断提高,而当温度超过LCST时催化活性急剧下降,聚合物从溶液中析出.基于这些特性,该温敏聚合物负载酞菁作为一种新型的催化剂可实现均相催化、异相分离.

Metallophthalocyanine has attracted considerable attention as oxidation catalyst because its structure similar to the active center of cytochrome P-450,and it can promote many reactions through oxidase-like,catalase-like,as well as peroxidase-like mechanism,whereas it has the following problems：low solubility,high aggregation tendency,difficulty in catalyst recovery and recycling,which restrict its further application as catalyst.Poly（N-isopropylacrylamide） （PNIPAAm） is a typical thermosensitive polymer,and it can be homogeneous below its lower critical solution temperature （LCST） and completely precipitated above LCST,which makes it become an attractive polymer support for catalyst.A novel reactive and aqueous soluble metallophthalocyanine derivative,cobalt tetra（2,4-dichloro-1,3,5-triazine）aminophthalocyanine （Co-TDTAPc）,was synthesized by the modification of cobalt aminophthalocyanine with 2,4,6-trichloro-1,3,5-triazine and immobilized on PNIPAAm by covalent bond to obtain a thermosensitive polymer catalyst,PNIPAAm-g-Co-TDTAPc.The polymer catalyst was characterized by UV-Vis spectrometer in ethanol and THF,and the results showed that PNIPAAm-g-Co-TDTAPc had characteristic absorption peaks of cobalt phthalocyanine （B band： 280～330 nm;Q band： 620～700 nm） in both ethanol and THF,while PNIPAAm had no absorption in these area,which proved that the Co-TDTAPc had been successfully grafted on PNIPAAm.The thermal stability of the polymers were also tested by heating from room temperature to 600℃ at a rate of 20 K/min in a nitrogen environment with flow rate of 100 mL/min.The results indicated that the beginning decomposition temperature of PNIPAAm-g-Co-TDTAPc was 407℃,which confirmed that the polymer catalyst had high thermal stability.The solubility of small molecular cobalt phthalocyanine,PNIPAAm and PNIPAAm-g-Co-TDTAPc was investigated in different solvents.The results showed that PNIPAAm-g-Co-TDTAPc could dissolve in water and most organic solvents,while the small molecule cobalt phthaloyanine only dissolve in DMSO and DMF,which proved that the solubility of cobalt phthalocyanine was improved significantly after immobilization on PNIPAAm.The thermosensitive property of PNIPAAm-g-Co-TDTAPc was investigated by cloud point measurements,and the results showed that PNIPAAm-g-Co-TDTAPc exhibited excellent thermosensitive property in aqueous solutions, and its LCST was 34.5℃.The LCST of PNIPAAm-g-Co-TDTAPc in the mixture of water and organic solvents （ethanol and DMF） was also studied,and the experimental results showed that the LCST of PNIPAAm-g-Co-TDTAPc first decreased when the volume fraction of ethanol in mixed solvents increased below 27.5% and then sharply increased above 59.5% until the thermosensitivity of PNIPAAm-g-Co-TDTAPc disappeared.The experimental results in DMF/water mixed solvents were similar to those in water/ethanol.Furthermore,the catalytic activity of PNIPAAm-g-Co-TDTAPc on 2-mercaptoethanol was investigated by the consumption of oxygen at different temperature and pH 11.The results indicated that PNIPAAm-g-Co-TDTAPc had a high catalytic oxidation activity on 2-mercaptoethanol,and the reaction rate was first increased with the temperature increasing and then rapidly decreased when temperature was over LCST due to the precipitation of this catalyst from the solution.In conclusion,a novel high efficient polymer catalyst was prepared,which has both good solubility and excellent thermosensitive properties.Based on the above properties,it can be served as a homogeneous catalyst and separated just by heating,having potential applications in the fields of organic synthesis and degradation of organic pollutants.