Thermosensitive copolymer with cobalt phthalocyanine and catalytic behavior based on adjustable LCST

Thermosensitive polymers with metallophthalocyanine were prepared by immobilizing cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine (Co-TDTAPc) on poly(N-isopropylacrylamide) (PNIPA) and copolymers of N-isopropylacrylamide (NIPA) with acrylamide (AM) (P(NIPA-co-AM)) to obtain Co-TDTAPc-PNIPA and Co-TDTAPc-P(NIPA-co-AM). Examination of the thermosensitive behavior of these polymers showed that the proportion of AM in Co-TDTAPc-P(NIPA-co-AM) had a significant effect on the low critical solution temperature (LCST) in aqueous solution. The LCST of Co-TDTAPc-P(NIPA-co-AM) was adjustable from 34.5 °C to 90.0 °C by changing the AM molar fraction from 0% to 40%. The copolymers showed a high level of catalytic activity on the oxidation of 2-mercaptoethanol in the homogeneous phase when the reaction temperature was below the LCST, and the copolymers could be precipitated and recovered by heterogeneous separation when the temperature was above the LCST. Compared to Co-TDTAPc-PNIPA, the catalytic system with Co-TDTAPc-P(NIPA-co-AM) is able to maintain homogeneity at a higher temperature due to the higher LCST of the copolymers. In addition, strong salting-out salts, such as NaCl and Na2SO4, can decrease the LCST of the copolymers dramatically and obviate the need for more heat to drive the catalytic reaction system to achieve heterogeneous separation. Co-TDTAPc-P(NIPA-co-AM) was stable and remained efficient during repetitive test cycles with no obvious decrease of catalytic activity.