Willie Lau

Emulsion polymerization of hydrophobia monomers

Emulsion polymerization is the most important industrial polymerization process for manufacturing water based polymers. The heterogeneous nature of the process requires the diffusion of monomers from the emulsified droplets, through the aqueous medium, into the polymer particles where the polymerization takes place. Adequate solubility of the monomer is necessary for the diffusion process to occur effectively. Consequently, very hydrophobic monomers cannot be readily incorporated by emulsion polymerization. The use of a catalytic level of cyclodextrin allows the use of very hydrophobic monomers in emulsion polymerization.[1] The mechanism of the process is believed to involve a catalytic cycle in which cyclodextrin acts as a “Phase Transport Catalyst”, continuously complexing and solubilizing the hydrophobic monomers and releasing them to the polymer particles. The kinetics and thermodynamics are favorable for the reaction to proceed.

High-performance capillary gel electrochromatography with replaceable media.

Capillary gel electrochromatography is evaluated with an entangled polymer solution which is pumped into the capillary and run under fritless conditions. The polymer used has an acid backbone with grafted hydrophobic segments, the polyacid giving the electroosmotic flow and the hydrophobe segments providing the retentive component. Experimental evaluation of this type of system reveals performance similar to capillary electrophoresis and other forms of electrochromatography. The analysis of plate height data demonstrates that zone broadening is primarily due to diffusion with little contribution from nonequilibrium zone broadening. Hence, operation at high velocities (high voltages) is most desirable as opposed to most chromatographic methods. Some of the advantages of this type of experiment include being able to replace the retentive media in a few minutes, fast and reproducible high-performance separation, and having a retention mechanism similar to reversed-phase liquid chromatography. Disadvantages include a low retentive phase concentration and hence low sample loadability and limited solvent compatibility of the polymer. A number of different separations are demonstrated including separation of alkyl benzoates, alkylphenones, alkylbenzenes, oxidation inhibitors, and PAHs.

Tracking polymer diffusion in a wet latex film with fluorescence resonance energy transfer.

We describe an instrument to measure the polymer interdiffusion between donor-labeled and acceptor-labeled latex polymers in a partially wet latex film with fluorescence resonance energy transfer (FRET). It is possible to temporarily arrest the drying process of a wet latex film by sealing the film in an airtight chamber. In our approach, we measure donor fluorescence decays from 0.5 mm diameter spots at various positions across an arrested latex film with time-correlated single photon counting. We interpret the resulting decays with a Monte Carlo simulation of the FRET process and extract information about the extent of polymer diffusion as a function of position on the film. These results enable us to determine the extent of polymer interdiffusion as a function of distance from the wet-dry edge in the latex film. To highlight this devices ability to capture the rapid early stages of latex interdiffusion, we report results from an acrylate copolymer latex.

Influence of ethylene glycol and propylene glycol on polymer diffusion in poly(butyl acrylate-co-methyl methacrylate) latex films.

We describe fluorescence resonance energy transfer (FRET) experiments carried out to examine the effect of ethylene glycol and propylene glycol on the early stages of polymer diffusion in poly(butyl acrylate-co-methyl methacrylate) latex films. In our approach, we temporarily arrest the drying process of a wet latex film by sealing the film in a previously cooled airtight sample chamber. This arrests propagation of the drying front and suppresses polymer diffusion during the measurements. We then measure donor fluorescence decays from 0.5 mm diameter spots at various locations on the film. From our analysis, we obtain information about the earliest stages of polymer diffusion as the film is still drying. We also investigate the effect of these glycols on polymer diffusion at longer aging times on predried latex films. Ethylene glycol and propylene glycol retard polymer diffusion at early times immediately after the passing of the drying front but enhance the rate of polymer diffusion at later aging times. This behavior is described quantitatively in terms of free-volume theory and the partitioning of the glycols between the aqueous and polymer phases in the film.

Diffusion of oligomers in latex systems — A route to low volatile organic compound (VOC) coatings

We synthesize specially designed latex polymer systems by an in situ emulsion polymerization process that yields latex particles with both a high molecular weight polymer phase and a low molecular ...

BULK POLYMERIZATION OF STYRENE WITH DIETHYL 2,3-DICYANO-2,3-DI(p-TOLYL)-SUCCINATE AS A THERMAL INIFERTER

The bulk polymerization of styrene (St) was investigated using diethyl 2,3-dicyano-2,3-di(p-tolyl)succinate (DCDTS), a hexa-substituted ethane compound, as an initiator. The polymerization data show that DCDTS behaves as a thermal iniferter, and the polymerization proceeds by a “living” radical polymerization mechanism with a reversible deactivation. The polymerization can be carried out at quite low temperatures (such as 65–85°C) and the final conversions are high. The PSt possessed high molecular weights and molecular weight distributions (M w M n in the range of 1.4 to 1.6). End-group analysis by 1H NMR spectroscopy reveals that the resultant PSt contains the fragments of DCDTS at its chain ends. This polymer with an ω-penta-substituted C─C bond end group could be used as a macroinitiator to carry out chain-extension reaction with St and could also block copolymerization with methyl methacrylate.