A New Method For Polymer Modification In Near Critical Water

Hydrolysis of polymers, As an important method to obtain water-soluble polymer, can make polymer molecular chain produce polar groups. The traditional methods use strong acid/base to accelerate the hydrolysis of polymers, which always causes gross pollution.Near-critical water(near-critical water, NCW) refers to the compressed liquid water at the temperature between 170℃and 350℃. The outstanding performance of NCW comparing to the water at normal temperature and pressure is the large ionization constant. And thus, it possesses the property of acid/base catalytic fuction which will enable some of the acid-base catalytic reactions to occur without the addition of any acid/base catalysts. NCW also has a small enough dielectric constant, and can dissolve the organic and inorganic compounds. At the same time, near-critical water also has an excellent mass transfer and green, environmental protection properties, etc. At present the critical water is regarded as promising technology for organic reactions, inorganic materials synthesis, coal liquefaction and biomass resources. However, domestic and international researches on polymer hydrolysis modification in near-critical water were relatively few and lack of systematical exploration and summary, In this dissertation, To explore the new applications of near-critial water (NCW), the modifications for polymers were conducted in NCW by the research on the conversion of (cyano-CN, amide-CONH2, acyl-OCOR, ester-COOR, ether-OR) to carboxyl (-COOH) or hydroxyl (-OH). The research work was summarized as below:Polyacrylonitrile fibre (PAN) and polyacrylamide (PAM) were selected as the model polymers with cyano and amide groups. The kinetics studies on the non-catatalyzed hydrolysis of which were systematically carried out in NCW at different initial concentrations and temperatures. The results revealed that the non-catatalyzed hydrolysis of PAN and PAM in NCW is feasible and can beultimately translated into acrylamide / acrylic acid copolymer which have many important applications in industry. Which hydrolysis exhibited typical first-order consecutive kinetics. And the polyacrylic acid from hydrolysis products showed an obvious selfcatalysis in the reaction The rate constants at different temperature were obtained by the assumption kinetics equation. And the hydrolysis apparent activation energies evaluated by Arrhenius plot.Polyethylene vinyl acetate (EVA,VA content of 18%,33%,42%) and polyvinyl acetate (PVAC) were selected as the model polymers with acyl group. The kinetics studies on non-catatalyzed hydrolysis of which were systematically carried out in NCW at different initial concentrations and temperatures. The results revealed that the non-catatalyzed hydrolysis of EVA and PVAC in NCW is feasible and can be ultimately translated into the corresponding alcohols polymer. Binary or ternary copolymers with different contents of functional groups can be obtained by altering the reaction conditions. The reaction temperature, material ratio and acetic acid concentration play an important role in hydrolysis rate of EVA and PVAC in NCW.The hydrolysis of all acyl polymer exhibited typical first-order an autocatalytic kinetics. The rate constants at different temperature were obtained by the assumption kinetics equation. And the hydrolysis apparent activation energies evaluated by Arrhenius plot were 58.8kJ-mol-1 for EVA and 51.93 kJ-mol-1 for PVAC.Polymethyl methacrylate (PMMA) was selected as the model polymer with ester group and its hydrolysis kinetics in near-critical water was investigated. After examining the repeatability of experiment data and studying the effect of the ratio of PMMA to water on hydrolysis reaction, the hydrolysis kinetics of PMMA was systematically studied under the conditions of non-catalyzed hydrolysis in NCW in the temperature range from 210℃ to 290℃ and hydrolysis products were characterized by IR, GPC and TG.The results revealed that non-catalyzed hydrolysis of PMMA in near-critical water is feasible. Binary or ternary copolymers with different contents of functional groups can be obtained by altering the reaction conditions. Both temperature and the material ratio play an important role in hydrolysis rate of PMMA. By the assumption of autocatalytic kinetics equation for hydrolysis of PMMA in NCW, the activation energy for non-catatalyzed reaction evaluated are 47.3kJ.mol"1. Moreover, the exploration on HAC-enrihed NCW reaction system were initialed. The effects of different acetic acid loading on PMMA hydrolysis were investigated. The hydrolysis rate of PMMA in HAC-enrihed NCW was higher than the rate in NWC. The rate constants at different temperature were obtained by the assumption kinetics equation in HAC-enrihed NCW. And the hydrolysis apparent activation energies evaluated in lmol·L-1 HAC-enrihed NCW by Arrhenius plot was 34.2 kJ-mol-1,which is slower than the rate in NCW.Polyethylene methyl ether (PVME) was selected as the model polymer with ether groups. The kinetics studies on the non-catatalyzed hydrolysis of which were systematically carried out in NCW at different initial concentrations and temperatures. The results revealed that the non-catatalyzed hydrolysis of PVME in NCW is feasible The rate constants at different temperature were obtained by the assumption kinetics equation. and the hydrolysis apparent activation energies and pre-exponential factors evaluated by Arrhenius plot were 183.25 kJ-mol"1 and 41.0.Finally, the hydrolysis data of the polymers with different side chains in NCW were summarized, and this paper also discusses polymer hydrolysis regularity and conducts a comprehensive comparsion study on the rate constants and apparent activation energies of the polymers for the end group respectively with cyano, amide, acyl, ester and ether. Moreover, the factors affecting on the hydrolysis of polymers were systematically summarized, in addition to reaction pressure, including reaction temperature, reaction time and initial concentrations.