Studies Of Synthesis Of Water Soluble Polyamides And Their Applications In Metal Chelation And Antifreeze Activities

A variety of water soluble polymers with both hydrophilic and hydrophobic groups haveadjustable physicochemical properties. They are widely used in such industries as oil and gasdrilling, water-treatment, textiles, mineral processing, coatings, adhesives, and papermanufacturing. Low dosage hydrate inhibitors (LDHI) based on water soluble polymers haveplayed a vital role in off-shore natural gas drilling by inhibiting the formation of gas hydrates.Amphiphilic polymers also have excellent solubilization effect, and pronounced metalcomplexation and interfacial properties. In selective solvents, they can form nanoparticleswith hydrophobic cores and hydrophilic shells by a self-assembly process with potentialapplications in catalysis, material separation and drug delivery.In this thesis, novel water soluble polyamides were synthesized by polycondensationreactions using tributyl citrate (TBC) and ethylene diamine (EDA) as raw materials. Thepoly(ethylene citramide)s were modified in order to adjust their hydrophobicities and watersolubilities. Three different types of hydrophobic groups were introduced by different alkylisocyanates into the poly(ethylene citramide)s and their structures were characterized by FTIR,1H NMR,13C NMR, two dimensional1H-1H COSY,1H-13C HSQC and HMBC NMRspectroscopic techniques. Gel permeation chromatography (GPC) characterization found themodified poly(ethylene citramide)s have molecular weights ranging from3,000to10,000.The influence of hydrophobic modification on the thermodynamic properties of theaqueous solutions of the polycitramides was investigated. The modified poly(ethylenecitramide)s were shown to have excellent antifreeze activities (AF), with a significant amountof water in supercooled state, as revealed from differential scanning calorimetry (DSC)studies. Nonfreezable bound water (NFBW) values were measured by DSC analysis for theprepared polycitramides. The NFBW values of the hydrophobically modified polycitramidesare much higher than commercial LDHIs such as poly(N-vinyl caprolactam)(PVCap) andpoly(N-vinyl pyrrolidinone)(PVP). Measurement of specific heat capacities (Cp) indicatesthat the hydrophobically modified polycitramides have significantly higher Cp values than theunmodified polycitramide, and higher than pure water. The hydrophilic unmodifiedpoly(ethylene citramide) has Cp values lower than pure water. Studies of the inhibiting effect on natural gas hydrates found that the gas hydrate onset temperature (To) and fast formationtemperature (Ta) of the modified polycitramides decrease when going from the modificationby isopropyl, n-butyl, to cyclohexyl isocyanate. These experiments show that cyclohexylisocyanate modified polycitramide is a kind of good inhibitor for natural gas hydrate. There isa good correlation between Cp, NFBW, and To temperatures. The higher the Cp values, thehigher the NFBW values, and the lower the To temperatures. In addition, experiments werealso performed for the modified polycitramides on metal chelating ability. Compared withcommercial chelating resins, the polycitramides exhibit excellent calcium and lead ionchelating capacities.In the final part of the thesis, a polymerization reaction between citric acid andhexamethylene diisocyanate was carried out to yield poly(hexamethylene citramide imide)(PHMCI). PHMCI polymers were characterized by FT-IR, FT-Raman NMR spectroscopiesand GPC. In alkaline solutions, PHMCI was hydrolyzed through a ring opening reaction,resulting in a novel type of ionomers, poly(hexamethylene citramide)(PHMC) withcarboxylate side chains. The properties of PHMC were characterized by DSC, TEM anddynamic light scattering techniques. The results show that PHMC can form nanoparticles inwater through self-assembly, with hydrodynamic radii of20nm. It was also found that theparticle size varies with solution pH values. With the increase of pH from5.0to9.0, theparticle size increases at first, reaches a maximum of2300nm at pH=6.8, and then decreaseswith the further increase of solution pH values. Evidently, the synthesized nanoparticles ofPHMC exhibited a unique pH dependence of their hydrodynamic radii. DSC measurementshows the PHMC has AF values similar to the hydrophobically modified polycitramides.Calcium ion chelating capacities of the PHMC are nearly the same as those of thepoly(ethylene citramide)s while the lead ion chelating capacities of the former are about100mg/g lower than those of the latter.