1,721,105 research outputs found
Evaluation of the chain, length distribution in free-radical polymerization, 1 - Bulk polymerization
No full textA method for the direct computation of the, chain length distribution in a bulk. polymerization is developed, based on the discretization, procedure introduced by Kumar and Ramkrishna (Chem. Eng. SA 1996,51, 1311) in the context of particle size. distribution. The overall distribution of chain,lengths is partitioned into a finite number of classes which are supposed to be concentrated at some appropriate pivotal chain, lengths. Several, of the involved reactions lead to the., formation, of chain whose length differs from the pivotal values. Rules have, been introduced in order to share chains between two contiguous classes, which have been designed so as to preserve two well-defined properties of the distribution, such as, for example, two of. its moments. The, method has been applied to a polymerization system, including propagation, bimolecular terminations and two different chain branching mechanisms: chain transfer to polymer and crosslinking. In addition, complex system such a one with chain rigth-dependent kinetic constants or a.two-dimensional distribution of chain length and number of branches have been considered
Miniemulsion living free radical polymerization by RAFT
No full textVarious living mechanisms have been used in bulk polymerization to produce via free radical polymerization both controlled polymers, i.e., with low polydispersity, and block copolymers. The common drawback of all these processes is the very low polymerization rate which derives from the decreased concentration of propagating radicals. This problem can be overcome in principle by operating in emulsion polymerization, so as to take advantage of radical segregation to decrease terminations without significantly reducing the polymerization rate with respect to the corresponding nonliving processes. In this work, it has been shown that this result can be achieved only using the RAFT (or degenerative transfer) living mechanism and operating in miniemulsion polymerization. Several experiments are presented where, using different monomers, living conditions are achieved without significant loss in productivity. The obtained results are supported by modeling arguments, which also rationalize previous experimental results reported in the literature using different living mechanisms
Preparative weak cation-exchange chromatography of monoclonal antibody variants - I. Single-component adsorption
No full textThe retention behavior of a monoclonal antibody has been characterized on a weak cation exchanger, Fractogel ENID COO-(s). This new generation of resin materials comprise of a higher mechanical strength compared to softer gel-type matrices while maintaining elevated capacities, resulting in higher productivity and longer lifetimes. These parameters are extremely important when working with large bio-molecules such as proteins, and in particular monoclonal antibodies. In the first part of this work a parameter estimation strategy is presented to fully characterize the retention behavior of a single monoclonal antibody and determine suitable model parameters. Literature correlations were used for the estimation of mass transfer rates. The transport limiting parameter, pore diffusion, was regressed experimentally. Various methods for the adsorption isotherm determination have been applied, their combinations resulting in little experimental effort and accurate predictions of elution profiles. The process has been modelled with a complete pore diffusion model and the agreement between experimental and predicted profiles is good in general. However, a very marked sensitivity to changes in the effective pore diffusion coefficient has been observed. A correlation describing the effect of the separation conditions on the diffusion rate is therefore needed in order to have a fully predictive mathematical model. (c) 2008 Published by Elsevier B.V
Calculation of molecular weight distributions in free-radical polymerization with chain branching
No full textThe molecular weight distribution (MWD) of a branched polymer has been calculated by using approximate techniques based on the partition of the overall polymer chain population into classes according to molecular dimension or the number of branches. These techniques are especially useful in segregated systems, such as emulsion polymerization, where rigorous methods are too onerous. A comparison with the correct MWD obtained through a detailed solution method has shown that, of these techniques, 'numerical fractionation' predicts in some cases a marked shoulder at the high molecular weights that does not exist in the true MWD. On the other hand, besides offering an intelligent description of gel formation, 'numerical fractionation' permits to calculate quickly the correct average molecular weights and constitutes a significant improvement compared to the classical method of moments when a complete MWD is required. In the latter case, however, the most accurate approximate technique has been found to be based on the subdivision of the polymer chains according to the number of branches. This technique, though more time-consuming than 'numerical fractionation', provides also the branching distribution along with the MWD. A quick method is suggested to estimate the minimum number of branches required by this technique to calculate the correct complete MWD
PNIPAAM grafted polymeric monoliths synthesized by the reactive gelation process and their swelling/deswelling characteristics
No full textThe production of macroporous monoliths functionalized with a thermo-responsive polymer (PNIPAAM) is described. The surface functionalization was achieved by copolymerization of acrylic end capped atom transfer radical polymerization initiator (BPOEA) with divinylbenzene with or without styrene. Monoliths were generated by swelling them with styrene, BPOEA and divinylbenzene followed by gelation with salt and post polymerization. Subsequent grafting of these monoliths with PNIPAAM was achieved by atom transfer radical polymerization and their swelling deswelling characteristics quantified. The grafted monoliths provide a unique chromatographic stationary phase where adsorption/desorption can be driven by the use of temperature only
Modeling of the chromatographic solvent gradient reversed phase purification of a multicomponent polypeptide mixture
No full textA model for Calcitonin purification from an industrial peptide mixture using polymer-based reversed phase columns was developed. Regressed competitive bi-Langmuir isotherm parameters for pure calcitonin are strong functions of the eluent composition and were correlated to the overall Henry coefficient only. It is shown that, by keeping constant these correlations, the adsorption behavior of impurities can be predicted simply by estimating their Henry coefficient from the raw mixture. The same can be repeated with very good results when changing the stationary phase or the organic solvent in the eluent. In both cases, only the Henry coefficient must be re-estimated from pulse injections
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Synthesis of temperature responsive polymer brushes from polystyrene latex particles functionalized with ATRP initiator
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