The Synthesis, Properties Study And Computer Simulation Of Polymers Based On N, N-diethylacrylamide

To get better knowledges of thermo-sensitivity polymer systems based on N, N-diethylacrylamide(DEA),the copolymers of DEA and acrylic acid(AA),DEA and methylacrylic acid(MAA)were synthesized and their phase behaviors,properties of aqueous solutions were studied.The computer simulations of aqueous solutions of Poly (N,N-diethylacrylamide)(PDEA)and copolymer of DEA and AA(P(DEA-co-AA))were conducted by molecular dynamics.The chain properties of PDEA were also investigated by calculation and viscosity measurements.The results are summarized as follows:1.PDEA,Poly(acrylic acid)(PAA)and a series random copolymers of (N,N-diethylacrylamide-co-acrylic acid)(DEA-AA)were synthesized by the method of radical polymerization.It showed that the phase behaviors of the brine solutions of the copolymers changed dramatically with the mole fraction(x)of DEA in these copolymers. Copolymers of cop6(x=0.06)and cop11(x=0.11)in which content of acrylic acid was higher presented the phase behaviors of Upper Critical Solution Temperature(UCST)similar to PAA.The copolymer cop27(x=0.27)presented the behavior of Lower Critical Solution Temperature(LCST)similar to PDEA.The copolymer cop18(x=0.18)in which acrylic acid content was moderate presented both UCST and LCST behaviors.The solution properties of the polymers were investigated by measurements of viscosity,fluorescence and pH.It was reasonable to suggest that the sharp change of the phase behavior might be attributed to the interaction between acrylamide group and carboxylic group in the(DEA-AA)copolymers.2.A series of pH and temperature-responsive poly(N,N-diethylacryamide-co-methylacrylic acid) copolymers were synthesized by radical copolymerization and characterized by elemental analysis and FT-IR.The effects of salt,pH and MAA content in the copolymer on the phase transition behaviors of copolymers were investigated by UV-visible spectrophotometry.The LCST of the copolymers decreased obviously as a function of NaCl concentration which may be ascribed to the "salt out effect".The LCST increased with pH of the solution within the pH range of 3.0-8.0,it was ascribed to the ionized degree of the copolymer and the hydrogen bonding between intra- and interchain.Changing MAA content of the copolymer also varied the LCST of copolymers.3.Molecular dynamics(MD)was used to simulate a aqueous solution of a 50-units oligomer model for the thermoresponsive polymer poly(N,N-diethylacrylamide)at 300 and 310 K,i.e., below and above its LCST in water,corresponding to the compacted and extended chain conformations,respectively Statistical analyses of the system trajectories showed that the polymer caused the formation of the first and second water shells around it and the water molecules arranged in more ordered structure and produced more hydrogen bonds in the shells.When the polymer chain exhibited a compact conformation,the number of water molecules surround the polymer reduced,accompanying with the decrease of the total hydrogen bond number in the solution.As a result,the enthalpy and entropy of the solution increased.Furthermore,the translational self-diffusion coefficient,the distribution of the solvent molecules and the lifetime of the water molecules and the hydrogen bond in the first shell were also discussed.4.Molecular dynamics(MD)was used to simulate the aqueous solution of a 60-units oligomer model for the copolymers of DEA and AA.Statistical analyses of the system trajectories showed that AA unit affected the surrounding water molecules in different way comparing with DEA unit.The stronger interaction between AA unit and water molecules,the formation of hydrogen bonds between AA unit and water molecules stabilized the solution.But the hydrogen bond number between waters molecules did not increase in the disolution process. The intrachain hydrogen bond of the copolymers solutions was investigated and was found to drive the chain of copolymers to be more compacted and the its hydrophobicity increased rapidly.Furthermore,the translational self-diffusion coefficient,the distribution of the solvent molecules and the lifetime of the first shell water molecules and hydrogen bonds were also discussed.5.Conformational energies of meso and racemic dyads of PDEA were computed as functions of keletal bond rotations and statistical weight matrices of order 3×3 were formulated.The mean square of end to end distance ,the radius of gyration ,and the characteristic ratios C_n of the polymer molecules were calculated by the rotational isomeric state(RIS) method.The values of C_n of isotactic PDEA and syndiotactic PDEA were 8.4 and 14.5 respectively.The intrinsic viscosity for THF solution of PDEA was measured.The value of characteristic ratio C_n for PDEA in the THF solution was determined to be 10.5 by using Kurata-Stockmayer equation,indicating that the flexibility of PDEA chain is close to that of polystyrene and Poly(N-isopropylacrylamide).The value of C_n was larger than that of isotactic PDEA and smaller than that of syndiotactic PDEA,which indicates that the PDEA synthesized by reversible addition-fragmentation chain transfer(RAFT)polymerization method was atactic chain.