Kinetic analysis of AB2 polycondensation in the presence of multifunctional cores with various reactivities
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Abstract The application of interfacial polycondensation to the preparation of several polyurethanes and polyamides from AB type monomers is described. The monomers are salts of aminoalkyl chloroformates and aminoacid chlorides, respectively. Differences in method and mechanism from the AA plus BB type interfacial polycondensation are discussed. Several new ring‐containing polymers were synthesized.
Interfacial polymerization
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Linear polymer
Condensation reaction
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Reactivity
Linear polymer
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Abstract Characteristic similarities and differences in polycondensations of ‘a − b’ and ‘a 2 + b 2 ’ monomers are described including cyclic ‘a − b’ and cyclic ‘a 2 ’ monomers. Polycondensations of ‘ab 3 ’ monomers that yield (hyper)branched polymers are compared with polycondensations of ‘a 2 + b 3 ’ monomers that yield (hyper)branched, multicylic, or crosslinked polymers. In all cases the influence of cyclization reactions on structure and molecular weight of the reaction products is considered. Furthermore, the definitions of polycondensation and condensative chain polymerization are discussed along with a differentiation between kinetically controlled and thermodynamically controlled polycondensations. magnified image
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In addition to the usual, easily measurable parameters that normally characterize molecular weight distributions (MWD) of polymers: Mw, Mn, Mz, Mw/Mn, three other parameters were chosen for their sensitivity to the amount of high, medium, or low molecular weights present in the polymer. These parameters, related to the polydispersity, are of particular interest for improving information on MWD and for dealing with the real shape of the molecular distribution curve. “High molecular weight dispersity” is the polydispersity of a Gaussian curve having the same maximum as the experimental curve and fitting with it, as well as possible, in the high molecular weight zone. The same criteria are applied to medium and low molecular weight dispersities. Using a small computer for determination of parameters, this method is applied to the practical characterization of Natene, a polyethylene, and Napryl, a polypropylene. This method affords precise, detailed comparisons between polymers and can be used to understand the special shapes of distribution curves related to polymer applications.
Dispersity
Molar mass distribution
Gel permeation chromatography
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Polypropylene
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Abstract The Z transform method has been used to calculate the molecular weight distribution (MWD) of condensation polymers. The MWD obtained by using Z transform is explicitly discrete. The method is illustrated for two cases: (1) further polycondensation of AB prepolymers with certain initial MWD, and (2) polycondensation of AB and A r ( r is the number of A type functional groups) monomers where AB monomers are added in several batches. In the latter case, it is found that the resulting MWD is much narrower than that of one‐batch polycondensation. The trick of producing narrow MWDs of condensation polymers is merely a consequence of keeping AB monomer concentration as low as possible during the reaction in order to suppress the condensation reaction between monomeric AB molecules. The theoretical prediction has been confirmed by Monte Carlo simulation. Therefore, it provides a new possible technique for obtaining narrow MWD polymers through polycondensation reactions.
Molar mass distribution
Self-condensation
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In a reactive extrusion process a new approach - degrading only a portion of the input followed by a mixing process with unreacted portion - has been proposed as a method to control the molecular weight and molecular weight distribution (MWD). The number average molecular weight, M n , and the weight average molecular weight, M w , are studied through the Schulz-Zimm molecular weight distribution. The results indicate that M n , and M w can be regulated separately during degradation. M w and the polydispersity index (PDI) of a segregated degradation process are higher than the corresponding results of a uniform system. In the later stage of a segregated degradation the PDI can be higher than that of the original polymers. Starting from a narrow unimodal MWD it is possible to produce a bimodal MWD.
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The molecular weight distribution, polydispersity and the distribution of side chains within a GPC-slice have been calculated for coeluting comb-shaped polymers. It is assumed that the polymers were synthesized by grafting monodisperse side chains onto a backbone having a broad molecular weight distribution. Despite the broad polydispersity of the backbone the polydispersity within a GPC-slice is rather narrow, as is the distribution of side chains. Consequently the effect of polydispersity on properties, which can be obtained by GPC coupled with molar mass sensitive detectors is negligible. However, this result is true only for the specific branching mechanism investigated.
Dispersity
Molar mass distribution
Side chain
Branching (polymer chemistry)
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