| In emulsion polymerization, emulsifier plays an important role in providing space for polymerization and stabilizing colloidal particles, although the adding amount of emulsifier is tiny. The category and amount of emulsifier have a great impact on the particle size and distribution of latex. However, it is easier for non-polymerizable surfactant to migrate to the film surface in the process of film forming, which will inevitably weaken some specific properties including water resistance, gloss and adhesive. To solve the defect induced by surfactant migration, polymerizable surfactant was put forward. Compared with the conventional small molecular surfactant, polymerizable surfactant could anchor to the micelle via chemical bonding, which is beneficial to inhibit the surfactant migration, and thereby improve the film performance mentioned above. However, migration issue will still remain unless polymerizable surfactants were totally polymerized. The alternative solution is to employ the macrosurfactants of high molecular weight which can effectively prevent migration, and the macrosurfactants with well-designed block or graft structure are the most common surfactants. For the objective, polymers with controlled structure and molecule weight distribution(MWD) have been prepared through living radical polymerization, including radical addition-fragmentation chain transfer (RAFT), and atom transfer radical polymerization (ATRP). However, the flaws of those methods can’t be ignored, such as low conversion, metal ion contamination, and harsh reaction condition.Herein we utilized a synthetic route named catalytic chain transfer polymerization (CCTP) via Co(II)complex as catalyst. Macrosurfactants synthesized through CCTP method are functionalized with reactive vinyl groups and possess ordered block structure, and the molecular weight is more controllable and lower. The macrosurfactants with a terminal unsaturation can thereby anchor into the final colloidal particles and enhance the product properties. To our best knowledge, the macrosurfactants prepared through CCTP method have been utilized in the emulsion polymerization of polyacrylate. Few reports has been attempted to prepare poly (urethane-acrylate) emulsion with the assistance of macrosurfactants prepared through CCTP methods.The conclusions of this paper as follows:(1) Series of Anionic block copolymer surfactant (MSA-r and MSA-c) was prepared using Methacrylate (MAA) as hydrophilic monomer and Butyl methacrylate (BMA) as oleophilic monomer. MSA-r and MSA-c’s molecular weight (MW) and molecular weight distribution (MWD) was studied using gel permeation chromatography (GPC) measurement. Results showed that MSA-r and MSA-c’s MW ranged from 3×103～6×103, and their MWD was between 1.60 and 1.80, which represent lower and more regular MW compared to MSA-t synthesized via traditional radical polymerization and MSA-c0 synthesized without CoBF during hydrophobic chain’s polymerization.(2) FT-Raman and 1H NMR was used to characterize the copolymer’s structure, and the terminal unsaturated double bond was testified. Iodimetry was applied to study the content of unsaturated double bond along with MW of each sample, and result showed agreement with GPC test, and content of unsaturated double bond rise with hydrophobic monomer ratio or CoBF amount. Through Thermal gravimetric analysis(TGA) copolymer’s thermal stability has been discussed, compared to MSA-t and MSA-cO, MSA prepared by CCTP method showed an unique loss stage around 300℃ which was caused by double bond. Besides, the weight loss and loss rate was coincident with the result obtained from iodimetry.(3) Surface tension(ST) analysis indicated solution of MSA-r and MSA-c own the property of surface activity, and the minimum ST could be decreased to 42.72mN/m. According to the result from ST analysis and fluorescence excitation spectrum, critical micelle concentration (CMC) and other adsorptionn parameters of each sample were acquired, the Molecular limit area of MSA-r and MSA-c ranged from 150 to 250 A2 which was lower than MSA-t, indicating block copolymer via CCTP method could be arranged more tightly between air-water interface, so the ST could be reduced with more efficiency.(4) Viscosity and conductivity tests show that the phase transition point (PIP) could be affected significantly by MSA’ amount, hydrophobic monomer ratio and CoBF amout. And PIP has direct impact on the emulsion’s final solid content and stability. PU-A prepolymer solution with MSA-c6 needs least water to reach PIP, and solid content of WPUA/MSA-c6 was highest to 45%.(5) Stability of the emulsion and phase separation behavior of WPUA/MSA emulsion was analyzed through dynamic rheological time scanning and particle size along with its variation. WPUA emulsion prepared with MSA via CCTP method showed less practice size and better storage stability compared to MSA-t and MSA-c0. The particle size of WPUA/MSA-rl was 88.7nm, which was minimum in all sample, and the amplification was only 0.1% after 12 months.(6) The water resistance of WPUA/MSA latex film was studied using water absorption and contact angle test. WPUA emulsion prepared with MSA via CCTP method showed good water resistance, and the contact angle of WPUA/MSA-g1.3 was highest to 94.7°, and its water absorption was lowest to 3.72%. According to FT-Raman characterization, the group distribution of WPUA/MSA-r1.5 and WPUA/MSA-t at different interface was studied. The result indicated that the group distribution of WPUA/MSA-r1.5 was same on the whole, while group distribution of WPUA/MSA-t differed obviously. So the assumption that MSA as polymerizable emulsifier surfactant could prevent migration during the latex curing was verified. Besides, AFM observation also provide the evidence that the migration has been prevented by using MSA from CCTP, after washed by water, surface of WPUA/MSA-t film may be partially dissolved and swollen when immersing into water, resulting in the significant change in the surface morphology. However, subtle change is detected for the surface morphology of WPUA/MSA-r1.5 film, demonstrating better water resistance for WPUA/MSA-rl.5 film. |
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