High Monomer Conversion Polymerization

A copper-based ATRP catalyst that is sufficiently stable and active can be used at very low concentrations. However, it is very important to mention that a copper(I) complex is constantly being converted to the corresponding copper(II) complex as a result of unavoidable and often diffusion-controlled radical termination reactions (k=l.0-4.0 x 109 M 1 s 1). Therefore, the deactivator (copper(II) complex) will accumulate as the reaction proceeds resulting in slowing down of the polymerization rate and limiting high monomer conversions. 

The reason why the experimental values of particle number are somewhat lower than the theoretical values seems to be that the time where the number of polymer particles was measured is not at infinite but at only 1 hour after the start of polymerization. Figure 9 shows that the number of polymer particles increases with reaction time. The solid lines represent the theoretical values predicted by the Nomura and Harada model. However, since Nt= 0 when Mq= 0, there would be an optimum value of MQ where the number of polymer particles formed becomes maximum. Unfortunately, it is difficult at present to predict the optimum value of MQ theoretically because any reaction model cannot yet explain perfectly the kinetic behavior at high monomer-conversion range. Therefore, one cannot help determining, at present, the optimum value of MQ experimentally. Figures 7 and 8 also show that Eq.(40) roughly satisfies the experimental results. 

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

In spite of the presence of Nd-clusters, partial alkylation and micro heterogeneities the number of active Nd-species seems to be fairly constant during the course of a polymerization. Otherwise neither consistent polymerization kinetics (particularly lst-order monomer consumption up to high monomer conversion) nor linear increases of molar mass during the whole course of the polymerization would be observed in so many studies. It therefore can be concluded that the fraction of active Nd as well as the number of active catalyst species are fixed either at an early stage of the polymerization or even prior to initiation of the polymerization. It can be speculated whether the fixation of the number of active species occurs during catalyst prefor-mation/activation or even during the preparation of the Nd compound. In contrast to this consideration Jun et al. report on the decay of active cen-... 

HIGH MONOMER CONVERSION POLYMERIZATION 2.5.1 Free Radical... 

At high monomer conversion, the viscosity inside the polymer particles increases sharply and further polymerization becomes diffusion controlled. The particles are referred to as a glassy polymer and the kinetics for a zero-one system is no longer valid. To account for these changes, the propagation rate coefficient can be expressed as follows... 

The emulsion polymerization process has various advantages as compared to bulk or solution polymerization as the reaction proceeds at low viscosity. The low viscosity during the process allows adequate removal of heat of polymerization and the production of higher solid latexes in combination with high monomer conversion and short cycle time. This process is... 

Heat-resistant hyperbranched copolymers of VBC and CMI have also been synthesized by ATRP. Under identical polymerization conditions and after the same reaction time, high monomer conversions occurred near the equimolar feed composition, indicating the formation of charge transfer complexes between VBC (electron-donor) and maleimide (electron-acceptor). As expected, the Tg of the copolymer increased with an increasing content of maleimide in the feed [266]. 

Kp is constant during most of the polymerization, but it may diminish toward the end of interval III, at high monomer conversions, due to diffusion limitations. 

High monomer conversions were intentional in order to minimize the waste of expensive monomers, although this led to a steep viscosity increase of the reaction mixture and even solidification. To examine if this change in viscosity and the reaction conditions supported a living chain growth, samples were drawn from the reaction solution of PFS23 at different stages of the polymerization and analyzed by means... 

Nanogel synthesis by direct RAFT polymerization is a promising route to industrial setup because of high monomer conversion and high solids content of such processes. The control of nanogel architectures can be realized through the rational selection of polymerization systans such... 

For the ring-opening metathesis polymerization (ROMP) in heterophase [81], a water-soluble ruthenium alkylidene was employed for the emulsion polymerization of norbornene, and an oil-soluble catalyst for the miniemulsion polymerization of norbornene and 1,5-cyclooctadiene. Similar to the polymerization of ethylene in heterophase, an organic solution of the catalyst was first miniemulsified in water, after which the monomer was added to the miniemulsion. This resulted in a high monomer conversion for norbornene ( up to 97%), and a particle size of 250nm. 

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