Study On Construction And Performance Of Bridged Cyclodextrin And Acrylamide Polymer

The chemical agent flooding, polyacrylamide is the main method of enhanced oil recoveries (EOR) in the tertiary oil recovery, and the acrylamide polymer with good performance has a very important significance for EOR. In this paper, the functional acrylamide polymer is synthesized by introducing the temperature-resistance, salt-tolerance and hydrophobic groups, and the copolymer is used to build the host-guest inclusion complex by being combined with the bis-cyclodextrin which has the properties of hydrophobic recognition and self-assembly, then the solution performances of the system are evaluated preliminarily.In the present work, the host, bis-cycoldextrin CD-(PEG)4oo-CD, and the guest, functional acrylamide polymer P(AM/VPPS/C18DMAAC) are synthesized. Then, they are used to prepare the host-guest inclusion complex Polymer/Bis-CD by the molecular recognition and self-assembly. Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H NMR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and simultaneous integrated thermal analysis (TG-DSC) characterizations are used to investigate the microstructures and stable performances of CD-(PEG)400-CD, P(AM/VPPS/C18DMAAC) and Polymer/Bis-CD. In addition, the recognition mechanism, self-assembling mechanism and the thermodynamic behavior of the inclusion process between the cyclodextrin cavity and the hydrophobic chain are analyzed by the UV-visible spectrophotometry. Ultimately, the solution properties of P(AM/VPPS/C1gDMAAC) and Polymer/Bis-CD such as viscosification property, viscoelasticity characteristic, temperature resistance, salt tolerance, shear resistance and the interaction with surfactant are preliminarily evaluated, which provide the theoretical foundation for a further application of this system in the tertiary oil recovery. The details are as follows:(1) Preparation of CD-(PEG)400-CD, P(AM/VPPS/C18DMAAC) and Polymer/Bis-CD. The preparation of CD-(PEG)400-CD is divided into two steps:the dichloro-substituted reaction of polyethylene glycol by thionyl chloride and the modification of β-cyclodextrin by the dichloro-substitute. The sulfonate monomer,4-vinyl-1,3-sulfopropyl pyridinium (VPPS) is synthesized by the sulfonation reaction of1,3-propane sultone using4-vinyl pyridine. The P(AM/VPPS/C18DMAAC) is obtained by the copolymerization of VPPS, stearyl dimethyl ammonium chloride C18DMAAC and acrylamide AM under the optimal reaction conditions:45℃of reaction temperature,5h of reaction time,0.15wt%of initiator dosage,25wt%of total monomer concentration,2mol%of VPPS content and1.2mol%of C18DMAAC content. On the basis of single factor experiment, the optimum conditions of the coplymerization process are tested by the response surface methodology, which are24.79wt%of total monomer concentration,44.94℃of reaction temperature and0.1516wt%of initiator dosage. Intrinsic viscosity of P(AM/VPPS/C18DMAAC) is590mL/g, which is measured by the dilution method. Polymer/Bis-CD is obtained by aqueous solution method under the ultrasound effect.(2) Characterization of CD-(PEG)4oo-CD, P(AM/VPPS/C18DMAAC) and Polymer/Bis-CD. FT-IR and XRD indicate the host-guest inclusion complex is a new kind of substance.1H NMR finds that the inclusion behavior is based on the inclusion effect between cyclodextrin cavity and hydrophobic chain of C18DMAAC. SEM proves that there exist significant differences in microscopic network structure of P(AM/VPPS/C18DMAAC) and Polymer/Bis-CD. TG and DSC analyses demonstrate that the mass loses of CD-(PEG)400-CD and P(AM/VPPS/C18DMAAC) show three stages, while that of Polymer/Bis-CD has four stages. Moreover, Polymer/Bis-CD shows better thermal stability than CD-(PEG)400-CD and P(AM/VPPS/C18DMAAC).(3) Process analysis of CD-(PEG)400-CD assembling P(AM/VPPS/C18DMAAC). The formation mechanism of Polymer/Bis-CD is that CD-(PEG)4oo-CD recognizes the hydrophobic long alkyl chain of C18DMAAC by hydrophobic interactions of cyclodextrin cavity, then the self-assembly is driven by hydrophobic interaction, and the structure of the assembly unit acts as a physical crosslinking point, connecting the copolymer molecular chain to induce the formation of macromolecular network structure. The inclusion ratio of cyclodextrin and C18DMAAC is1:1, and the inclusion constant K is1.0761×104L/mol. Thus, the inclusion ratio of CD-(PEG)4oo-CD and P(AM/VPPS/C18DMAAC) is1:2. The enthalpy change ΔH(?) and entropy change ΔS(?) are-19.227kJ/mol and12.65J/(mol·K), respectively. The Gibbs free energy change ΔG is below0, which indicates that the inclusion process is a spontaneous exothermic process.(4) Solution properties of P(AM/VPPS/C18DMAAC) and Polymer/Bis-CD. The critical association concentration of P(AM/VPPS/C18DMAAC) is1775mg/L, while the conformational transition concentration of Polymer/Bis-CD is2100mg/L. With the varitation of the frequency, the viscoelasticity of P(AM/VPPS/C18DMAAC) solution takes on a conversion from viscosity to elasticity, while that of Polymer/Bis-CD solution always presents an elasticity. The viscosity of P(AM/VPPS/C18DMAAC) increases first and then decreases with the increase of the temperature, and reaches a maximum value at40℃, while the viscosity of Polymer/Bis-CD shows an interesting variation, namely, first decreasing then rising followed by a decrease, reaching the maximum value at50℃. The viscosity of P(AM/VPPS/C18DMAAC) salt solution is larger than that of P(AM/VPPS/C18DMAAC) aqueous solution, and the viscosity of salt solution increases with the increasing salinity, presenting a significant anti polyelectrolyte behavior, but the viscosity reduces with the further increase of salinity. While the viscosity of Polymer/Bis-CD increases with the increasing salinity. In the low shear rate, the viscosity of P(AM/VPPS/C18DMAAC) increases with the ehancing shear rate, exhibiting a shear thickening. As the shear rate continues to increase, the viscosity decreases, showing a shear thinning. When it carries out the reply shearing, the viscosity of P(AM/VPPS/C18DMAAC) recovers to the original value, even exhibits a higher value at low shear rates, reaching the maximum. The viscosity of Polymer/Bis-CD decreases with increasing shear rate, and it is a little lower than the original one in the reply shearing process. With the increasing concentration of cetyltrimethylammonium chloride (CTAC), the viscosity of P(AM/VPPS/C18DMAAC) first increases gradually to a maximum and then reduces drastically until reaching a stable value, whle that of Polymer/Bis-CD takes an interesting variation, namely, first decreasing rapidly and then increasing gradually followed by an apparently reducing until achieving at a stablility.