Jorge R. Vega

EMULSION COPOLYMERIZATION OF ACRYLONITRILE AND BUTADIENE. SEMIBATCH STRATEGIES FOR CONTROLLING MOLECULAR STRUCTURE ON THE BASIS OF CALORIMETRIC MEASUREMENTS

A semibatch emulsion copolymerization of acrylonitrile and butadiene is theoretically investigated, with the aim of controlling the molecular structure of the produced NBR. An open-loop estimator based on calorimetric measurements is proposed for monitoring the chemical composition, the average molecular weights, and the average degree of branching. With little effect on the other quality variables, the intermediate addition of acrylonitrile allows to produce a polymer with a constant chemical composition. Similarly, the intermediate addition of the chain transfer agent produces a polymer with either a fixed or with a prespecified linear variation of the average branching. The required feed profiles are obtained from a numerical inversion of a discrete process model. By increasing the initiator loads, the semibatch strategies also allow to increase the final conversion between 3% and 6%, without altering the reaction time nor deteriorating the polymer quality with respect to the batch. The numerical procedures were tested by inputing (relatively noisy) heat measurements from an industrial batch reactor.

Emulsion polymerization of styrene. Use of n -nonyl mercaptan for molecular weight control

Abstract The unseeded emulsion polymerization of styrene with n-nonyl mercaptan (nNM) as chain transfer agent (CTA) was investigated, with the aim of producing a PS latex of a low molecular weight polydispersity at high conversion and in short reaction times. To this effect, starved and minimum time semibatch reactions were investigated and compared to equivalent batch polymerizations. The high reactivity of nNM with respect to the monomer makes it feasible to implement a minimum time policy with intermediate addition of CTA only. The MWDs of the minimum time runs were intermediate between the broader distributions of the batch reactions and the narrower distributions of the starved experiments. The conversion profiles of minimum time experiments almost coincided with those of equivalent batch polymerizations. For controlling MWDs through semibatch operations, it seems preferable to use nNM instead of other (less reactive and more common) CTAs like tert-dodecyl mercaptan or CCl4.

Emulsion Copolymerization of Acrylonitrile and Butadiene in an Industrial Batch Reactor. Estimation of Conversion and Polymer Quality from On-line Energy Measurements

ABSTRACTA method for monitoring an industrial emulsion copolymerization of acrylonitrile and butadiene for the production of two NBR grades is presented. From an on-line calculation of the reaction heat (proportional to the mass flow rate of evaporated refrigerant), three open-loop estimators of increasing complexity were developed for monitoring conversion, copolymer composition, and average molecular weights. A good agreement between on-line estimates and off-line measurements was obtained.

SEC OF SIMPLE POLYMERS WITH MOLAR MASS DETECTION IN PRESENCE OF INSTRUMENTAL BROADENING. COMPUTER SIMULATION STUDY ON THE CALCULATION OF UNBIASED MOLECULAR WEIGHT DISTRIBUTIONS

This theoretical work presents a correction procedure for calculating an unbiased MWD when analyzing a linear homopolymer by size exclusion chromatography with molar mass detection. The fractionation and the measurements are ideal, but the chromatograms are distorted by a nonuniform and skewed instrumental broadening (IB), and are contaminated with a zero-mean random noise. The main assumption is that the molecular weight calibration is linear in the chromatogram range. The following phenomenological procedure was proposed: (i) independently correct the mass- and molar mass chromatograms for IB through a robust inverse filtering technique; (ii) estimate the unbiased calibration from the ratio of the corrected chromatograms; (iii) adjust a straight line to the mid-values of that calibration; and (iv) estimate the unbiased MWD from the linear calibration and the corrected mass chromatogram. For the chromatogram inversions, a minimum sized broadening matrix was selected and a singular value decomposition technique was applied. The following effects were evaluated: of an increased measurement noise, of uncertainties in the range of the measured chromatograms, and of systematic errors in the IB function. The method fails for very narrow MWDs.

Immunodiagnosis of Chagas disease: Synthesis of three latex-protein complexes containing different antigens of Trypanosoma cruzi

This article describes the physical adsorption and the chemical coupling of 3 antigenic proteins of Trypanosoma cruzi onto polystyrene (PS) based latexes to be used as novel immunodiagnosis reagents for detecting the Chagas disease. The coupled proteins were a homogenate of T. cruzi, or a recombinant protein (either Ag36 or CP1). With the homogenate, between 30 and 60% of the total-linked protein was chemically coupled, showing a small dependence with the pH. For Ag36 and CP1, around 90% of the total-linked protein was chemically coupled, with a maximum coupling at pH 5 (i.e., close to the isoelectric point). The chemical coupling of CP1 was less affected by the pH than the coupling of Ag36.

Analysis of a Styrene—Butadiene Graft Copolymer by Size Exclusion Chromatography I. Computer Simulation Study for Estimating the Biases Induced by Branching Under Ideal Fractionation and Detection

Abstract This theoretical work estimates the deviations in the molecular weights distribution (MWD), the degree of branching distribution (DBD), and the chemical composition distribution (CCD) due to branching when a (chromatographically complex) styrenebutadiene graft copolymer is analyzed by ideal size exclusion chromatography (SEC). The copolymer was isolated from a high-impact polystyrene. A novel polymerization model was developed that predicts the MWD, DBD, and CCD for the total copolymer and for each of its different branched topologies. Copolymer topologies are characterized by the number of trifunctional branching points per molecule. To simulate the molecular weight calibrations in SEC, the Zimm — Stockmayer equation was applied to each copolymer topology. Negligible deviations due to branching were found in the MWD and the DBD with respect to the theoretical predictions provided by the polymerization model. In contrast, errors in the CCD are intolerably large and consequently the CCD cannot be estimated by SEC.

Synthesis of latex-antigen complexes from single and multiepitope recombinant proteins. Application in immunoagglutination assays for the diagnosis of Trypanosoma cruzi infection.

The physical adsorption and the chemical coupling of recombinant proteins of Trypanosoma cruzi onto polystyrene and core-shell carboxylated particles were respectively investigated with the ultimate aim of producing latex-protein complexes to be used in an immunoagglutination assay able to detect the Chagas disease. To this effect, two single proteins (RP1 and RP5) and a multiepitope protein derived from three antigenic peptides (CP2) were evaluated, and sensitizations were carried out at different pHs. The maximum physical adsorption was produced at pHs close to the protein isoelectric point (i.e., pH 6 for RP5 and pH 5 for RP1 and CP2). High fractions of antigens were chemically bound to the carboxyl groups, and the highest surface density of linked protein was also observed at pHs close to the protein isoelectric point. The three latex-protein complexes obtained by covalent coupling at such pHs were tested with sera from a panel of 16 infected and 16 non-infected patients. In the immunoagglutination assays, the latex-CP2 complex produced the best discrimination between positive and negative sera.

Optimisation and standardisation of an immunoagglutination assay for the diagnosis of Trypanosoma cruzi infection based on latex-(recombinant antigen) complexes.

To determine the conditions under which the immunoagglutination assay to detect Chagas disease, obtained from a novel latex‐(chimeric recombinant antigen) complex, shows greater discrimination between the responses of a positive control serum and a negative control serum.

DETERMINATION OF THE BAND BROADENING FUNCTION IN SIZE EXCLUSION CHROMATOGRAPHY WITH LIGHT-SCATTERING DETECTION

This work describes the determination of the band broadening function (BBF) in a size exclusion chromatograph fitted with 2 mixed-gel columns, a light scattering (LS) detector, and a differential refractometer (DR). The raw data were the chromatograms of 4 narrow polystyrene standards. First, the interdetector volume shift was indirectly estimated from its upper and lower limiting values. Then, for each of the standards, their “local” BBFs were estimated by application of an existing theoretical method. Each local BBF is an assumed elution-volume invariant in the narrow ranges of the analyzed standards and is represented by an exponentially-modified Gaussian of standard deviation σBB and exponential decay τBB. Finally, a “global” BBF (valid for the complete fractionation range) was interpolated from the local BBF parameters. For increasing elution volumes, the global BBF exhibits an increasing σBB and a decreasing τBB. In addition, the asymmetry factor [τBB/σBB] and the global variance [ ] both decrease with elution volume.

Physicochemical characterization of water-soluble chitosan derivatives with singlet oxygen quenching and antibacterial capabilities

New water-soluble chitosan derivatives (WSCh) were obtained by Maillard reaction (MR) between glucosamine (GA) with both low and medium molecular weight chitosans (Ch). The WSCh showed larger solubility than the respective Ch, while their deacetylation degree (DD) decreased by approximately 12%. Infrared spectroscopy experiments of WSCh confirmed the formation of imine bonds after MR with intensified pyranose structure, and sugar molecules as polymer branches. However, a 6-times reduction of the molecular weight of WSCh was measured, indicating the breakdown of the polysaccharide chain during the MR. The polysaccharides quenched singlet molecular oxygen (1O2), with rate quenching constants correlating with the DD value of the samples, suggesting the important role of amino groups (-NH2) in the deactivation of 1O2. Additionally, all polysaccharides presented antimicrobial activity against pathogenic bacteria, e.g. Staphylococcus aureus, Escherichia coli, Salmonella sp., Enterococcus faecalis and Listeria ivanovii, as tested by their minimum inhibitory concentration (MIC). This way we obtained new water-soluble polysaccharides, with similar functional properties to those presented by native Ch, enhancing its potential application as carrier material for bioactive compounds.