Dispersion of the sedimentation boundary

Lavrenko, P. N.; Горбунов, А.А.; Urinov, E. U.

doi:10.1016/0032-3950(76)90087-3

Cited by 7 publications

(3 citation statements)

References 15 publications

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“…The first v-average weight (M 1 ) is the number-average molecular weight (M.). Using eq 4 it is easy to obtain the expressions for the corresponding average molecular weights and polydispersity prameters,…”

Section: Resultsmentioning

confidence: 99%

“…As a result, the distributions of sedimentation coefficients g(S) were obtained at four concentrations for each sample. The exclusion of concentration dependence S(c) led to the distribution curve of sedimentation constant g(S 0 ) the relative width of which as/S (see Table I 4 This also made possible avoiding the distorting effect of concentration and diffusion spreading of the concentration boundary on the g(S 0 ) shape.…”

Section: Methodsmentioning

confidence: 99%

“…4 Distributions of shifts g(x) were converted into those of sedimentation coefficients g(S). Several distributions g(S) obtained at different times were converted into a single distribution corresponding to infinite time.…”

Section: Methodsmentioning

confidence: 99%

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Polymerization of Oxetanes with Organoaluminium Catalysts. II. Analysis of Molecular-Weight Distributions in the Polymerization of 3-Methyl-3-chloromethyloxetane with the Al(i-C4H9)3–H2O Catalyst System

Aleksiuk

Шаманин

Podolsky

et al. 1981

Polym J

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ABSTRACT:Molecular-weight distributions and polydispersity parameters of the polymers formed in the polymerization of 3-methyl-3-chloromethyloxetane with the Al(i-C4 H9h-H2 0 catalyst system have been investigated. It was shown that the main feature of this process is the ability of macromolecules to regulate their own size in the formation of a polymer of high molecular weight ( 10 6 ) and narrow molecular-weight distribution (MwiM.= 1.30±0.05) without any dependence on conversion, and the initial monomer and catalyst concentrations. Proceeding from the suggestion that the ratio of the termination to propagation-rate constants (k,l kp) depends on the size of the macromolecules, equations for the unnormalized weight molecular-weight distribution (MWD), and polydispersity parameters were derived. The experimental and calculated values of weight MWD and polydispersity parameters are in satisfactory agreement. On the basis of these data, a model for polymerization is proposed, assuming the formation of an active centre in the form of an ion-pair of the polymer zwitter-ion solvated by its own polymer chain. This model explains adequately the dependence of the k,lkP ratio on the degree of polymerization and the observed molecular-weight characteristics of the polymer.KEY WORDS Molecular-Weight Distribution I Polydispersity Parameters I 3-Methyl-3-chloromethyloxetane I Organoaluminium Catalyst I Zwitter-lon Active Centres I Ring-Closure during Polymerization I in ref 1). It was shown in the preceding paper 1 that the polymerization of 3-methyl-3-chloromethyloxetane (MCMO) with the Al(i-C 4 H 9 h-H20 catalyst system involves not only the initiation and propagation reactions but also the termination of growing chains and the deactivation of the catalyst by the polymer. The propagation, termination, and initiation constants can be arranged in the following order: kP>pk,>pki. The lifetime of each macromolecule is much shorter than the time of the entire process and quasi-monomolecular reactions dominate the termination stage. After a relatively short induction period, a situation typical of the "equilibrium" polymerization could be observed: M" and the width of the unimodal molecular-weight distribution (MWD) do not change with conversion (see Table I However, in this case the Mw/Mn and Mz/Mw ratios are much lower than the "most probable" ratio (Mw/Mn=2.0) or the "recombination" ratio (Mw!Mn= 1.5) 2 and are nearly equal to each other. The systematic increase in the Mw/Mn ratio as compared to the Mz/ M w ratio does not exceed 5.0%. EXPERIMENTAL ProceduresPolymerization was carried out by a previously described method. 1 The number-average molecular weight was determined by osmometry with a HighSpeed Membrane Osmometer, Hewlett-Packard, model-502 automatic apparatus in toluene solution 33

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%