Preparation of poly(N‐ethyl methacrylamide) particles via an emulsion/precipitation process: The role of the crosslinker

Monodisperse, thermosensitive poly(N‐ethyl methacrylamide) microgel particles were prepared by the batch precipitation/emulsion polymerization of water‐soluble N‐ethyl methacrylamide and the hydrophobic crosslinker ethylene glycol dimethacrylate initiated by potassium persulfate. Particular attention was paid to the effect of the crosslinker agent on the polymerization process (kinetics, conversion, and water‐soluble oligomer content). Particles were characterized in terms of their size distribution and swelling capacity. A polymerization mechanism for the water‐soluble monomer and non‐water‐soluble crosslinker is proposed and discussed on the basis of a combination of both emulsion and precipitation polymerization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1808–1817, 2002     

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide)

Samples of Poly(N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N,N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression-strain measurements to afford values of swelling ratio, polymer-solvent interaction parameters, elastic moduli and effective crosslinking density ν_e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν_e relative to the theoretical crosslinking density ν_t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν_e at ν_t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer-water interaction parameter. At a fixed content of BIS the values of ν_e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν_e and elastic moduli cf the value in water, has not been resolved satisfactorily.     

原油乳状液破乳的动态法研究

The stability of different crude oil emulsions from ASP flooding production well is studied by the method of a stirred tank. The demulsifying of crude-oil emulsion by different demulsifying agents is discussed. The breakage of the crude oil emulsions from the well PO11 by the different types and concentrations of the emulsifying agents is also discussed. The breaking mechanism of the demulsifying agent is described microscopically.     

MAA存在下VAc/BA核壳乳液聚合过程中的胶粒形态研究

用ＴＥＭ和电位滴定法对不同配方和工艺条件得到的胶粒形态结构和羧基分别进行了表征。结果表明：加入甲基丙烯酸有利于胶粒的稳定和形成规则的核壳胶粒。半连续加料不会形成完全反转的核壳结构,但是,核层在反应过程中由于聚合物簇的迁移会造成形变。由于胶粒中聚合物浓度高,粘度大,因而胶粒形态变化受动力学影响甚大,羧基分布主要是由动力学确定的。     

KPS—CuSO4—Na2SO3参与的无皂液聚合

研究了MMA-St在氧化还原引发剂KPS-CuSO_4-Na_2SO_3存在下的快速无皂乳液聚合.当[MMA]=0.51mol/L、[St]=0.49 mol/L、70℃对,在[KPS]=2.77×10~(-3)mol/L、[CuSO_4]=1.50×10~(-5)mol/L、[Na_2SO_3]=2.77×10~(-3) mol/L条件下反应100min,转化率大于90％;讨论了胶乳的分子量及其分布;求出了聚合反应活化能E_a=81.6 kJ/mol和聚合反应速率常数k_p=321.9 L/mol·s.     

无机纳米粒子/丁苯胶乳复合技术的研究

研究了无机纳米粒子／丁苯胶乳的复合材料，用脂肪酸对纳米粒子进行了表面改性，使之均匀分散在丁苯胶乳中，用红外、吸油性，润湿试验等方法对改性纳米微粒进行了表征，纸张涂布和老化试验证明，纳米碳酸钙和纳米氧化锌具有优良的隔热效果，纳米氧化锌还有很好的防紫外老化功能，对以纳米TiO2为核，包覆苯丙共聚物的乳液矣合也作了初步研究。     

Thermal Emulsion Polymerization without any Conventional Initiators and Emulsifiers

Stable poly(styrene-co-sodium styrene sulfonate) (P(St-NaSS) nanoparticles with broader size distribution were synthesized by thermal emulsion polymerization without any conventional initiators and emulsifiers. The obtained polymer nanoparticles have higher ξ potential, and the particle sizes have broad distribution. The stability of polymer particles originated from the addition of small amounts of ionic comonomer, NaSS, which can act as an emulsifier in somewhat. The monomer conversion could reach up to about 28 wt% in 48 h, and did not increase by further polymerization when higher polymerization temperature (120 ℃) was employed. This polymerization system may be give some further understand for mechanism of emulsion polymerization.     

Microporous, fast response cellulose ether hydrogel prepared by freeze-drying

A simple and effective method of preparing fast-response gels is developed. The freeze-drying and subsequent rehydration of thermosensitive gels alters the microstructural properties of the gels in a way that leads to rapid shrinking rates. Microporous hydroxypropyl cellulose (HPC) gels were created by this method to investigate the influence of the process on the swelling and shrinking kinetics of the gels in response to temperature changes. Micropores of different size ranges were produced by freezing gels with different amounts of water at −20 °C. Water content was the key factor to control the microporosity and the shrinking rates of gels. After the freezing treatment, an effective diffusion coefficient for shrinking could be determined by fitting Fick's law to the data (5.2 × 10⁻⁴ cm²/s). This was an increase of two orders of magnitude over that of the untreated, non-porous gel (6.0 × 10⁻⁶ cm²/s). The magnitude of the shrinking coefficient indicates that the shrinking rate of the microporous gel is probably limited by the convective flow, as unsteady flow through porous media follows the same differential equation as Fick's law, but with much greater transport coefficients, as observed here. Physically, the shrinking rate may be determined by the level of interconnected-cells in a microporous structure present at the beginning of shrinking process because the convection through the interconnected-cells is estimated to be much slower than the polymer network diffusion rate of the struts of micropores (0.1–3.0 μm) as well as heat transfer.     

A New Kind of Void Soap-free P（MMA-EA-MAA） Latex Particles

Soap-flee P(MMA-EA-MAA) particles with narrow size distribution were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and methacrylic acid (MAA), and large voids inside the particles were generated by alkali posttreatment in the presence of 2-butanone. Results indicated that the size of void and theparticle volume were related with the amount of 2-butanone. The generation mechanism of voids was proposed.     

Fluorinated monomer–styrene copolymer latex particles: I. kinetic studies in a soap-free aqueous medium

Soap-free emulsion copolymerization of 2, 2, 2-trifluoroethyl acrylate (3FEA) with styrene was carried out by using potassium persulfate as an initiator, and the effects of the weight fraction of 3FEA in the monomer feed on the kinetics and the particle size were investigated. Monomer conversions were followed by a gravimetric method, revealing that the overall polymerization rate increased exponentially with an increase in the weight fraction of 3FEA. According to dynamic light scattering measurement, the final particle size was found to decrease with an increase in the weight fraction of 3FEA. The number of particles for 3FEA homopolymerization was roughly twice as large as that at the fraction of 0.9, although both fractions had the almost same polymerization rates. These results indicate that soap-free emulsion homopolymerization of 3FEA would proceed not only inside the polymer particles but also in the aqueous phase throughout the polymerization.