Study On The Homopolymerization Of Epoxides And Their Copolymerization With Carbon Disulfide By Double Metal Cyanide Complex Catalyst

The ring-opening polymerization of epoxide catalyzed by highly effective Double Metal Cyanide Complex (DMCC) catalyst based on Zn₃[Co(CN)₆]₂ (ZHCC) was investigated.The copolymerization of epoxide with carbon disulfide (CS₂) was successfully achieved using DMCC catalyst. Poly(thiocarbonate), a sulfur-containing polymer with a complex structure sequence was synthesized by a convenient one-pot copolymerization of propylene oxide (PO) with CS₂.¹³C NMR proved that there are five kinds of carbonate and thiocarbonate linkages in the structure of the obtained polymer, -O(O)CO-, -S(O)CO-, -S(O)CS-, -S(S)CO- and -S(S)CS-. The number average molecular weight (Mn) of the obtained polymer ranged in 1.2-5.4 kg/mol, which larger than the reported one (560 g/mol), and the molecular weight distribution (MWD) of the polymer ranged in 1.24-3.50. Seven cyclic compounds propylene (thio) carbonate were also obtained as byproducts with an amount less than 15%. The effect of different conditions such as temperature, the molar ratio of PO/CS₂ as well as the amount of catalyst employed on the copolymerization were also studied systematically. The results showed that the optimal conditions for the copolymerization were found to be a temperature of 100℃with a CS₂/PO molar ratio of 1.5-2.0 and a DMCC loading of 3.2×10^-4 g catalyst/g reactants.The DMCC catalyst was also employed successfully in the copolymerization of cyclohexene oxide (CHO) with CS₂ and a poly (thiocarbonate) with alicyclic structure was obtained. There were also five kinds of carbonate and thiocarbonate linkages in the main chain structure of the polymer. The Mn of the polymer was 700-800 g/mol and the MWD was 1.6. Four cyclic compounds propylene (thio) carbonate were also obtained as well as small amount of polyether and polythioether, and the amount of those compounds was more than 50% of the obtained products. And also, the effect of different conditions such as reaction time, temperature, the molar ratio of CHO/CS₂ as well as the amount of catalyst employed on the copolymerization were studied systematically.The homopolymerization of PO catalyzed by DMCC catalyst in the present of different co-catalysts was also studied. The effect of Lewis acid (such as phenolic compounds and iodine) and Lewis base (such as quarternary ammonium salt) on the homopolymerizaiton of PO was carefully investigated. It was found that Lewis acid co-catalysts had a positive effect on the polymerization of PO. The efficiency of the polymerization increased when stronger Lewis acid was used as co-catalyst. On the other hand, the Lewis base had a negative effect on the polymerization of PO. The efficiency of the polymerization decreased when stronger Lewis base was used as co-catalyst. For example, the efficiency decreased by 69% when tertbutyl ammonium bromide (TBAB) was used as co-catalyst. The polymerization of PO can not achieve when dimethylaminopyridine (DMAP), a Lewis base with strong coordination ability to the DMCC catalyst, was used as co-catalyst. The structure of the co-catalyst would also have effect on the efficiency of the polymerization.The effect of different conditions such as the amount of catalyst added, the molar ratio of catalyst to co-catalyst, temperature, reaction time, the amount of initiator agent as well as solvent on the polymerization of PO were thoroughly studied using nitrophenol as co-catalyst. The results showed that when the amount of catalyst was 2.5 mg, the polymerization had a highest efficiency (89%). Increasing the amount of nitrophenol will increase the efficiency, while further increase would bring negative effect to the polymerization. A relatively high molar ratio of co-catalyst to catalyst (3:1) resulted in a product with high Mn (18915 g/mol). The polymerization of PO can be successfully achieved at 40℃when 5.0 mg DMCC catalyst was added. When decreasing the amount of DMCC catalyst to 1.5mg, the initiate temperature of the reaction increased to 60℃. Increasing the reaction time led to higher polymerization efficiency. The amount of initiator agent had little influence on the efficiency of polymerization. However, large amount of initiator agent would decrease the Mn of the obtained polymer. The use of solvent can increase the efficiency of the polymerization up to 94%. DMCC catalysts were synthesized by a new method called acidic impregnation. By using this method, Cl^- and proton can be introduced quantitatively to the DMCC catalyst. Therefore, the effect of the concentration of Cl^- and proton on the efficiency of the polymerization of PO by DMCC catalyst was then carefully investigated. The results demonstrated that when the acid ratio increased to 10.418 mol/mol Zn(OH)₂, the amount of Cl in the DMCC catalyst increased to 24.3 %w/w, while the amount of proton decreased to 1.135 %w/w, and the catalytic efficiency of the DMCC catalyst increased to 95%. Further increase of the acid ratio to 18.250 mol/mol Zn(OH)₂ would further increase the amount of Cl to 30.8 %w/w, the amount of proton would also increase to 1.457 %w/w and the obtained catalyst had no catalytic activity.Other acids without Cl such as HNO₃ and H₂SO₄ were also used in preparing DMCC catalysts by acid impregnation. The results indicated that all the obtained DMCC catalysts impregnated by different acid were effective when ZnCl₂ was used as precursor. On the other hand, when other Zinc salts were used as precursor, the obtained DMCC catalyst would be effective only when Zn(NO₃)₂ precursor impregnated by HNO₃ and ZnSO₄ precursor impregnated by HCl, and both of the two catalysts had high efficiency(nearly 90%).The possible chemical structure of the active site of the DMCC catalyst was proposed. The possible mechanisms of the homopolymerization of PO and copolymerization of PO/CS₂ were also suggested. The proposed active site was an ion pair where Cl^- and other anion such as NO₃^- and SO₄^2- serve as counter ion. Those ions can be easily dissociated and the remained Zinc structure would become a center of positive charge where the nucleophilic attack of epoxide would occur and the polymerization will be initiated. Moreover, a new type of polymerization mechanism called atom-exchange coordination polymerization (AECP) was proposed to explain the copolymerization of PO/CS₂. The O/S atom exchange reaction was proposed and proved. The AECP mechanism can explain all the experimental facts observed.