| As a kind of oilfield chemicals, hydrophobically modified polyacrylamide (HMPAM) is better than polyacrylamide about viscoelasticity and the shear degradation resistance, and is well applied to enhanced oil recovery. At present. HMPAM is mainly synthesized using thermal initiation polymerization method, but increasing the viscosity during the polymerization results in decreasing thermal conductivity of the polymerization system and the system temperature is difficult to control, so the polymer molecular weight is increased difficultly. To solve this problem, this article found photo-initiation polymerization employing the advantages of good reproducibility and easy control of the light intensity by comparing photo-initiation with thermal initiation. Therefore, in order to achieve the purpose of increasing the polymer molecular weight, a new polymerization technology was proposed via controling the process of polymerization in the background of photo-initiation.This article studied systematically the new polymerization technology, including the design of experimental instrument for controling ultraviolet radiant energy, the regulation and control strength of controllable factors, the main polymerization stage affected of polymer molecular weight, and the effective regulation and control way of polymerization process.Firstly, the decomposition kinetics of photoinitiator was investigated using 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure 2959) as photoinitiator in this paper, which was the control step of the free-radical polymerization chain reaction. The effects of light intensity, the slit width and the rotation speed on the rate of decomposition were investigated by periodically sampling method. The light intensity was identified to be the main factor of modulating photoinitiator decomposition rate. The representation method of the free-radical concentration was proposed with the rate of photoinitiator depletion. And the two kinds of ways to adjust the free-radical concentration were explored, which were decomposition rate constant (kd) and photoinitiator initial concentration ([I]0) respectively. The method of polymerization process-control based on the decomposition kinetics of photoinitiator was established, the specific contents were as follows:(1) Homopolymerization process of acrylamide (AM) was firstly investigated. The three-stage model of the polymerization process was established by the photoinitiator consumption based on studying the kinetics of the polymerization, and the polymerization process was divided into the pre-polymerization period, the polymerization period and the late polymerization period. The effects of kd on different stages of the polymerization process were studied, and the second stage was regulated with different [I]0 under using initial concentration of the photoinitiator to compensate the defect of adjustment range about kd. The results showed that the optimum concentration range of free-radicals during the polymerization process was 10.82～12.56×10-8mol·L’-1s-1.(2) Polyacrylamide was hydrophobically modified by mutual-solvent polymerization with AM and hydrophobic monomers (NaAMC14S) in aqueous solution. On basis of the above investigation, the second stage of the polymerization process was divided into three equal Ⅰ,ⅡI and Ⅲ with consumption amount of the photoinitiator. The regulation ways in the second stage of the polymerization process were studied through different combinations using kd in Ⅰ～Ⅲ, the intrinsic viscosities of different polymers were measured respectively under different synthesis conditions:kd is constant, decreasing, increasing and in steady-state rate of polymerization. The best polymerization process was obtained, namely, kd was 4.00×10-4 s11 ultraviolet radiation 23.7 min.1.90×10-4 s-1 ultraviolet radiation 23.5 min. 2.86×10-4 s-1 ultraviolet radiation 21.5 min,1.90×10-4 s-1 ultraviolet radiation 23.3 min.Under the new polymerization technology, the three hydrophobically modified polymers of different hydrophobe content, namely, HMPAM-1, HMPAM-2 and HMPAM-3, were synthesized by controling over the critical micelle concentration (CMC). The intrinsic viscosities of above polymers measured in formamide mixed solvent were about 1000 mL/g, which were increased by more than 50% compared with the polymer synthesized by low temperature redox initiator system. Then the structure of polymer was characterized by FTIR and 1HNMR. The method to indirectly determine polymer compositions was established by the UV absorbance method to determine AM residual content and the improved single-phase titration method to determine NaAMC14S residual content, which was Higher accuracy compared with the direct 1HNMR method. The kinetics of photo-initiation copolymerization was investigated based on this method, the phenomenon that the polymer components weren’t varied with the polymerization proces was found, which showed the new polymerization technology had a significant advantage compared with thermal initiation in copolymer component homogeneity. The particle size distribution was measured by dynamic light scattering (DLS) in the benign solvent contained formamide, the result shows the polymer molecular weight obtained through photo-initiation was narrow distribution in contrast to thermal initiation.In the aspect of polymer solution properties, this article qualitatively demonstrated the HMPAMs were associative polymers through the relationship between viscosity and concentration. In this paper, the slope A and intercept B of Sukpisan equation in study of specific viscosity were used to investigate the microscopic mechanism about the effects of the molecular structure on the polymer solution structure and the molecular conformation under different solvent conditions. The apparent viscosities were measured in different solvent to provide a macro argument for microscopic mechanism, and formamide was confirmed an anti-associative agent. The Fedors-equation was identified as the first choice compared with different fitting equations in the intrinsic viscosity measurement of HMPAMs in the benign solvent. The relationship between polymer molecular structure and rheological properties was explored through the testing of shear viscosity and deformation recovery at the same concentration, and increasing the hydrophobic group content had been found to improve the viscosity and elasticity of polymer. The rheological properties of the polymer solution obtained through photo-initiation were superior to that of thermal initiation at the same hydrophobic group content, through the process of hydrolysis and purification by alcohol precipitation, the rheological properties were consistent with the unhydrolyzed polymer compared the photo-initiation with the thermal initiation.The innovation of this article is that, a new polymerization technology about the quantitative regulation of photopolymerization process based on the decomposition kinetics of photoinitiator was developed, the polymerization process optimization had been simplified. The molecular weight of HMPAM synthesised was higher than the redox initiation system at low temperature.Copolymerization kinetics showed the composition of HMPAM synthesised was homogeneous, therefore, it was more persuasive in the researches of polymer solution properties than that synthesised by the thermal initiation. |
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