ABSTRACT:The results are presented for a detailed investigation involving the free-radical photopolymerization of n-butyl acrylate in the form of thin static films. The aim of this work is to benchmark the performance of a novel thin film spinning disk reactor that may be used for the continuous production of linear polymers using photoinitiation. Industrially relevant film thicknesses (200 m to 1 mm) are studied as opposed to earlier work that looked into extremely thin films (5-25 m). Such extreme film thicknesses will be difficult to sustain in a thin film reactor without adversely affecting the wettability of the reaction surface and the uniformity of the film. The effects of four main variables (film thickness, UV intensity, initiator concentration, and exposure time) are studied under static film conditions. A 366-nm wavelength is utilized for the UV radiation with 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651) as the photoinitiator dissolved in n-butyl acrylate. The molecular weights, polydispersities, and monomer conversions are measured by gel permeation chromatography. In a 400 m thick film, conversions of Ͼ90% can be achieved with an exposure time of 40 s at a radiation intensity of 175 mW/cm 2 . The results using the same polymerization system in the spinning disk reactor are presented and compared with the static film results in Part II of this series.

It has been observed that when a prepolymer mix of styrene, poly(styrene), toluene, and benzoyl peroxide is transferred from a conventional stirred tank reactor (STR) to a spinning disc reactor (SDR), the rate of polymerization is substantially increased. Furthermore, the molecular weight and the molecular weight distribution of the polymer formed at conversions up to about 80% in the SDR is virtually unchanged from that of the polymer formed at 60% conversion in the STR. These results seem to indicate that the increase in polymerization rate is not the result of the well-known Trommsdorff-Norrish effect, which would be expected to lead to an increase in polydispersity. We believe that shear and centrifugal forces experienced by the film provide intense mixing and extension flow effects, which are responsible for the above-described observations. In this report an explanation has been put forward to describe the observed effects.

ABSTRACT:The carbo-cationic polymerization of styrene has been studied in a Spinning Disc Reactor (SDR) and the results were compared to those observed in a conventional Stirred Tank Reactor (STR). Addition of styrene to a slurry of silica-supported boron trifluoride (BF 3 /SiO 2 ) in 1,2-dichloroethane led to uncontrollable reactions in the STR at monomer concentrations Ͼ 25%w/w and initial temperatures of 20 -25°C. By comparison, monomer concentrations of 75% w/w were safely and controllably polymerized in the SDR at 40°C to yield polymers with molecular weights comparable to those reported in the literature for polymer prepared at Ϫ60°C. Exceptional heat transfer rates achieved in the SDR are sufficient to deal with the heat evolved when styrene is polymerized at concentrations as high as 75% w/w, the reaction proceeding under essentially isothermal conditions. In the present study, the effects of monomer/solvent feed rates, monomer concentrations, disc size, and disc speed on monomer conversions, polymer molecular weights, and polydispersities achieved in the SDR are investigated. Speculative explanations of the observed results are presented in terms of enhanced mixing effects on the polymerization mechanisms in the SDR.

A homogeneous liquid phase reaction between barium chloride (BaCl(2)) and sodium sulphate (Na(2)SO(4)) was conducted in a narrow channel reactor to produce barium sulphate (BaSO(4)) precipitate. The effects of channel dimensions and channel residence times on crystal size, crystal size distribution, nucleation rates, crystal morphology and conversion of reactants were investigated at different levels of reactant supersaturation ratio. Our results indicate that the smallest particle sizes are favoured when supersaturation ratios and channel velocities are high. The minimum average particle diameter observed was approximately 0.2 microm in a channel of hydraulic diameter 0.5 mm and length 20 cm at an initial supersaturation ratio of 4483 (0.1 M), which correspond to conditions giving rise to the highest nucleation rates. It has also been observed that particle size depends on the conversion to product, the smallest particles being formed when conversion lies within the range of 30 to 40%. Conversions in excess of 60% have been reached but there is a detectable limiting effect with increased supersaturation and reduced residence times. Experiments conducted at similar levels of supersaturation under stirred tank conditions showed that particle size was consistently larger and particle size distribution was much broader than that achieved in the narrow channel reactor. Scanning electron microscopy (SEM) images of the crystals formed in the narrow channels show that spherical particles dominate in the smallest channels at high velocities whilst coarse, tabular crystals are obtained in the larger channels. Greater tendency to agglomerate is also observed at high supersaturation ratios, after one minute of reaction.

Spinning disk reactor (SDR) technology has been demonstrated to achieve significant enhancements in free radical polymerization rates. The effect on the rate may be attributed to the unique hydrodynamic environment experienced by the reacting polymer films. The rotating surface of a SDR promotes extension of the polymer chains, which may prevent the propagating chains from terminating through bimolecular reactions. In this article, a numerical simulation is performed to investigate how reduced rates of termination would affect time conversion behavior of free radical initiated styrene polymerization. Comparisons have been made between model predictions and SDR experimental results. The closeness between predicted and experimental results yields strong evidence that the hydrodynamic regime created on the surface of a SDR can lead to reduced rates of bimolecular termination.

Spinning disc reactor technology has been demonstrated to achieve significant enhancements in the rates of free radical polymerization. It is believed that these enhancements are related to the centrifugal and shear conditions that exist on the disk and it is the objective of this study to elucidate the role of shear in thin films in a plug flow regime. Polymerizing systems have been subjected to shear fields in the range of 0.4 to 2,173 s Ϫ1 and comparisons between conversion profiles and polymer product properties have been made. It has been found that shear fields have little or no effect on these systems while the reaction is in the kinetically controlled regime and it is concluded that the observed rate enhancements of free radical polymerization on a spinning disk are not largely attributable to the high rates of shear experienced by the thin film as it traverses the disk. Our studies therefore continue to assess the role of flow divergence and centrifugal extension in the kinetics of polymerization.