Calibration techniques polymerization

All three monomers were soluble In the chromatographic mobile phase and standard analytical techniques were used for calibration. Solutions containing known quantities of monomer were chromatographed to establish a peak area concentration relationship for the appropriate detector. The homopolymer of methylacrylate was also soluble In the mobile phase. Thus, both UV and refractometer detectors were calibrated for polymerized methylmethacrylate by chromatographing solutions of PM ... 

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

A modification of this technique, applicable to many step polymerizations, involves the continuous monitoring of the small-molecule by-product. For example, for polyesterification between a diol and diacid above 100°C, water distills out of the reaction vessel and its volume can be measured by condensation and collection in a calibrated trap. 

Dilatometric technique can also be used for determination of polymerization rate in the case of multimonomer polymerization. However, in this case calibration of the dilatometric method is more complex. The substrates and products are both polymers with similar molecular weights. Difference in density during the course of polymerization is connected only with the conversion of double bonds to the single bonds. It is difficult to obtain a macromolecular product in which double bonds are fully converted to single bonds. Calibration must be based on simultaneous measurements of Ah and independent method (e.g., IR spectroscopy) and calculation of (1/dp l/d]vi). 

In conclusion, TPM has proved to be a very efficient tool for the characterization of soft materials. The intense development of porous samples with very well controlled pore size distribution, as carried out in our group, allows determination of calibration curves for numerous solvents. In particular, calibrations for solvents able to swell polymeric materials are now available, making TPM a very attractive technique. The simplicity and the low cost associated with TPM are further arguments for extended use of this technique. 

Positronium lifetime spectroscopy is particularly well suited for stud)hng defects in crystals and structural fluctuations in amorphous materials and can give an estimate of free volumes in condensed matter [116]. It is a useful technique to estimate the free volume of polymeric membranes [117]. In a study on silica gels, the decay lifetime has been found (Fig. 4.16) to be proportional to the pore diameters (measured by N2 adsorption) between 30 and 100 A [118]. Information on pore size distribution and surface area may also be obtained by means of calibration curves. 

Sample Materials. Vinnol H 60d. Vinnol Y 60, and Vinnol E 6Qg are commercial polyvinylchlorides from Wacker. produced by suspension, bulk, and emulsion polymerization techniques, respectively. All materials have nearly the same molecular weight distribution (MWD) as Solvlc 226 which, (with our SEC calibration) gave M = 74.000, M = 35,000. The samples used in this investigation in the Vinnol 60 series had molecular weights in the range M = 72,000 2000 and... 

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