Molecular Weight and Particle Size Distributions

Theoretical considerations indicate that compartmentaUzation of radicals in polymer particles does not change the polydispersity index PDI(— in emulsion polymerization 

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The range of the (molecular) size of the analytes usually exceeds that which can be determined by classical laboratory analytical methods such as size exclusion chromatography, etc. [351]. Reports on investigated substances are widespread and cover applications such as the separation and characterization of proteins [450] and enzymes [240, 241], of viruses [132], the separation of human and animal cells [50, 51], the isolation of plasmid DNA [367], and the molecular weight and particle size distribution of polymers [216,217]. The approach is relatively new in biotechnology therefore, practical experiences are not yet abundant. Langwost et al. [229] have provided a comprehensive survey of various applications in bio-monitoring. 

Poehlein and Degraff [336] extended the derivation of Gershberg and Long-field [330] to the calculation of both molecular weight and particle size distribution in the continuous emulsion polymerization of St in a CSTR. On the other hand, Nomura et al. [163] carried out the continuous emulsion polymerization of St in a cascade of two CSTRs and developed a novel model for the system by incorporating their batch model [ 14], which introduced the concept that the radical capture efficiency of a micelle relative to a polymer particle was much lower than that predicted by the diffusion entry model (pocd -°). The assumptions employed were almost the same as those of Smith and Ewart (Sect. 3.3), except that the model did not assume a constant value of p. The elementary reactions and their rate expressions employed in the first stage are as follows ... 

Co,C.C.,Cotts, P.,Burauer,S., deVries, R. and Kaler, E.W. (2001) Microemulsion polymerization 3. Molecular weight and particle size distributions. Macromolecules, 34, 3245-3254. 

Gelation and fusion of PVC plastisols can be studied by different techniques classified as statical and dynamic methods. Among the dynamic methods, rheological characterization has shown to be a reliable technique of study. Using dynamic methods the influence of plasticizer concentration and type and the influence of the resin type (characteristic molecular weight and particle size distribution) were analyzed. The most relevant findings are discussed below. 

When the molecular weight (or particle size) distribution was revealed. by chromatography after 2 and 48 hr, it was evident that after the longer time, larger particles with a narrower size distribution were obtained. 

Plastisol Viscosity and Viscosity Stability. After the primary contribution of the resin type in terms of its particle size and particle size distribution, for a given PVC resin, plastisol viscosity has a secondary dependence on plasticizer viscosity. The lower molecular weight and more linear esters have the lowest viscosity and hence show the lowest plastisol viscosity, ie, plastisol viscosity for a common set of other formulation ingredients... 

Many factors contribute to the toughness of a polyphase BMI/thermoplastic system, such as solubility parameters, phase adhesion, phase morphology, particle size and particle size distribution. Another important factor is the molecular weight of the thermoplastic modifier. It has been demonstrated for a particular poly(arylene-ether) backbone that high molecular weights increase the toughness of the blend system more than the low molecular weight counterparts (92). 

Precrosslinked" or "intramolecularly crosslinked" particles are micronetworks [1]. They represent structures intermediate between branched and macroscopically crosslinked systems. Their overall dimensions are still comparable with those of high molecular weight linear polymers, the internal structure of micronetworks (p-gels), however, resembles a typical network [2]. Synthesis is performed either in dilute solution or in a restricted reaction volume, e.g., in the micelles of an emulsion. Particle size and particle size distribution can be controlled by reaction conditions. Functional groups can be... 

Second, the number of polymer particles, TV, was found to increase continuously with the conversion [75,83,93,100] (Fig. 6b). Comparing these results with those obtained for inverse microemulsions (cf. Fig. 6a), one observes a downward curvature of N (conversion) in the case of O/W systems that correlates well with the increase in rip with time. It must be stressed that the determination of tip is subject to a large uncertainty, because it is based on the combined knowledge of the polymer molecular weight and the size of the polymer particle. The latter can be determined by either TEM or QELS. At low conversion, the polymer particles are swollen to a certain extent by monomer, and the diameter measured by QELS is not that of the dry particle. This has not always been appreciated by the researchers and can be at the origin of some significant differences between the rip values reported for similar systems. Another difficulty arises from the increase in both particle size distribution and particle diameter with time [75,93] (Fig. 7). This increase was explained by the same considerations as those given above. 

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