Transport phenomena aspects of the free-radical retrograde-precipitation polymerization (FRRPP) process

We have been studying free-radical polymerization that is accompanied by phase separation above the lower critical solution temperature. In the past, we have experimentally shown evidence of hot regions in the reactive system. We have also shown in the past that eventually the system exerts control over the rate of propagation as well as termination. In this work, we invoke a concept in polymer physics (the coil-to-globule transition) to help explain the mechanism of thermal trapping within the polymerization zones. The diffusivities of polymer chains at different stages in the reaction are calculated using appropriate methods. From the diffusivities, the propagation and termination rate coefficients are calculated using the Achilias-Kiparissides gel effect model. With experimental kinetic data, we then estimate rates of monomer consumption within polymer-rich particles. Using a pseudo-steadystate heat transfer model, we are able to show that interior temperatures of polymer-rich particle domains greater than about 1 mm can reach spinodal temperature values at the early stage of polymerization. Polymer-rich particle sizes are obtained from the same reactor system whereby a small amount of crosslinker is added to preserve particle morphology. This experiment indicates that even under turbulent flow conditions, relatively large particles can exist in the reactor fluid. This agrees with the physical implications of the coil-to-globule transition. However, since these particles were obtained during the period of slow conversion rate, our heat transfer calculations indicate that interior particle temperatures would be almost the same as surface temperatures. This points to an unknown radical-trapping mechanism at this stage of the polymerization process

Free-radical retrograde-precipitation polymerization: A mathematical modeling study of polymerization of styrene in diethyl ether

Polymerizing a monomer above the lower critical solution temperature (LCST) of its polymer-monomer-(non)solvent mixture has demonstrated better control characteristics than conventional free-radical polymerization kinetics. Reaction kinetics of polymerization in a poor solvent are strongly influenced by heat and mass transfer properties, as understood from modeling the transport phenomena in our earlier work. The study has now been extended to model the reaction kinetics in a styrene-diethyl ether system. The model was based on the CCS model for free radical polymerization, with the modification proposed by Achilias-Kiparissides. Computer simulation results agree well with those obtained from experiments carried under similar conditions, with the onset of phase separation as the only adjustable parameter. Drawbacks of the model are lack of analysis for the effect of monomer concentration and the absence of an appropriate radical trapping mechanism. © Taylor and Francis Inc

Modeling copolymerization of styrene and acrylic acid via the free-radical retrograde-precipitation polymerization (FRRPP) process

The free-radical retrograde-precipitation polymerization (or FRRPP) process is a free-radical-based chain polymerization process that occurs above a lower critical solution temperature (LCST). The unique features of FRRPP have been exploited for the synthesis of novel amphiphilic materials under industrially practicable conditions. In the work described here, the copolymerization of styrene and acrylic acid via FRRPP is modeled and simulated to derive greater understanding behind the polymerization mechanism. The penultimate model is used to calculate the reactivity ratios. These reactivity ratios are used to calculate conversion, composition, and molecular weight distributions using the mole balance equations for the different species in the system and the Achilias Kiparissides model for the calculation of reaction rate coefficients. The results suggest that precipitation and the resulting phase separation and change in diffusivities have a strong impact on the polymerization kinetics. The penultimate model provides a better representation of the reactivities, in comparison to other approaches. © 2008 American Chemical Society

Food texture design and optimization/ Edit.: Yadunandan Lal Dar

xi, 452 hal.: ill.; tab.:25 cm

Polymerization Control Through the Free-Radical Retrograde-Precipitation Polymerization Process

In this article, we present results of our work in a novel polymerization process [called the free-radical retrograde-precipitation polymerization (or FRRPP) process] that occurs at temperatures above the lower critical solution temperature. In this process, conversion-time plots for styrene polymerization in ether show autoacceleration at the beginning, followed by a relatively long period of reduced conversion rate starting at conversions as low as 30% and at operating temperatures way below the glass transition of the reacting system. Molecular weight and polydispersity index data also indicate early autoacceleration (in the form of overshoots in these values), whereas the latter period of slow conversion rate is accompanied by stable levels of molecular weight and polydispersity index. Polymer radical concentration measurements show an initial sharp rise, followed by an asymptotic value, even after almost all the initiator molecules have already decomposed into radicals. With end-group analyses of product polystyrene and polymer radical data, we calculate a proportion of live polymeric radicals to asymptote at levels of 80-84% of all polymeric species, even after almost all initiator molecules have already decomposed into radicals. All the data presented herein verify the postulate of a controlled polymerization mechanism for the FRRPP process. Our results have become the basis for an anti-gel effect phenomenon that is derived from prior theoretical and experimental observations, in which phenomenological diffusivities vanish at the spinodal curve of the phase envelope. The universality of this behavior in FRRPP systems is manifested from similar observations in styrene polymerization in acetone and methacrylic acid polymerization in water

Food texture design and optimization/ Edit.: Yadunandan Lal Dar

xi, 452 hal.: ill.; tab.:25 cm

Amphiphilic styrene-acrylic acid copolymers from the free-radical retrograde-precipitation polymerization (FRRPP) process

The free-radical retrograde-precipitation polymerization (or FRRPP) process, a free-radical polymerization that occurs above the lower critical solution temperature (LCST), was extended to copolymer formation. Control over the rate of polymerization and entrapment of polymer radicals in the FRRPP process was used to generate tapered styrene-acrylic acid block copolymers. To show the effectiveness of the FRRPP process, the same procedure was used with solvents that are not LCST-based precipitants for the polymer. Kinetic data show substantial chain termination in non-FRRPP copolymerization systems. Molecular weight information also shows propagation control in the FRRPP system. Solubilization and emulsification studies also indicate the capability of the FRRPP system in generating a much higher proportion of amphiphilic tapered block copolymers in the solid product

Nanoparticles from a controlled polymerization process

Free-radical retrograde precipitation polymerization process in the past has shown excellent control characteristics over reaction rate, molecular weight, and in the entrapment of live radicals for the generation of block copolymers. The same principle has now been extended to study the reaction confinement to a nanoscale region. Nanosized polymer particles have been reported to form from block copolymers, conventional precipitation polymerization methods, or through emulsion polymerization approaches. In this work, we present a new method of generating nanosized polymer particles by polymerizing the monomer in an environment that precipitates the polymer above the lower critical solution temperature. The nanoparticles have been characterized by both tapping-mode atomic force microscopy observations and in situ synchrotron time-resolved small-angle X-ray scattering analysis. The results from both the techniques showed the formation of nanoparticles in the size range of 15-30 nm, directly from the polymerization process