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11. |
Quasiliving Carbocationic Polymerization. X. Molecular Weight Averages and Polydispersity |
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Journal of Macromolecular Science: Part A - Chemistry,
Volume 18,
Issue 9,
1982,
Page 1339-1351
Tibor Kelen,
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摘要:
In quasiliving polymerizations with reversible chain transfer (QL0Rsystems), polymers with narrow molecular weight distribution can be obtained, It has been shown that while in true living systems (L00) R = 1, and in quasiliving systems with irreversible chain transfer (QL01) R = 2 is the limiting value of polydispersity, in QL0Rsystems r = 4/3 is the polydispersity to which the distribution of the polymer tends with increasing polymerization time. This limit is independent of the rate of reinitiation; the course of the R vs t curves is, however, determined by the various rate constants.
ISSN:0022-233X
DOI:10.1080/00222338208077227
出版商:Taylor & Francis Group
年代:1982
数据来源: Taylor
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12. |
Quasiliving Carbocationic Polymerization. XI. An Interpretation of Solvent Effects by Donor and Acceptor Numbers |
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Journal of Macromolecular Science: Part A - Chemistry,
Volume 18,
Issue 9,
1982,
Page 1353-1366
Judit Puskás,
Gábor Kaszás,
J.P. Kennedy,
T. Kelen,
Ferenc Tüdös,
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摘要:
Counteranion/solvent interactions (counteranion solvation) profoundly influence each and every elementary step of carbocationic polymerizations and are just as important as the commonly emphasized cation/solvent interactions (cation solvation). Counteranion solvation and carbocation solvation have been characterized by Gutmann' s acceptor number AN and donor number DN, respectively. Analysis of earlier data leads to the conclusion that the effect of monomer concentration on the rate, molecular weight, and molecular weight distribution obtained in cationic olefin polymerizations in “polar” solvents are in fact due to subtle changes in solvent concentration. Indeed, olefin monomers behave as “nonpolar” solvents and by changing the monomer concentration the character of the medium may profoundly change. It is further concluded that quasiliving polymerizations cannot be achieved in batch operations because the conditions that prevail in the initial charge, although possibly suitable for quasiliving polymerizations, must continuously change with the diminishing monomer concentration, i.e., by continuously changing the solvent character of the system. In contrast, in continuous systems initial conditions in the charge suitable for the attainment of living or quasiliving conditions can be maintained even for long periods of time by continuously replenishing the consumed monomer. By the use of these concepts, heretofore unexplained observations made in the course of quasiliving polymerization studies have been accounted for and, beyond this, new insight into solvation phenomena in cationic polymerizations is generated.
ISSN:0022-233X
DOI:10.1080/00222338208077228
出版商:Taylor & Francis Group
年代:1982
数据来源: Taylor
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13. |
Quasiliving Carbocationic Polymerization. XII. Forced Ideal Copolymerization of lsobutylene with Styrene |
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Journal of Macromolecular Science: Part A - Chemistry,
Volume 18,
Issue 9,
1982,
Page 1367-1382
Gábor Kaszás,
Miklós Györ,
JosephP. Kennedy,
Ferenc Tüdüs,
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摘要:
Forced ideal carbocationic copolymerization of isobutylene/styrene systems has been achieved by continuous addition of mixed monomer feeds to 2-chloro-2,4,4-trimethylpentane/TiCl4in n-hexane/methylene chloride charge by keeping the input rate equal to the overall rate of copolymerization. The composition of the copolymers was identical to that of the feeds over the entire monomer concentration range. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at higher isobutylene concentrations in the feed. The molecular weight increase was less pronounced at higher styrene concentration because more methylene chloride had to be used in the solvent system to keep the copolymer in solution. The micro-structure of the copolymers is uniform as determined by gel permeation chromatography (UV plus RI) and13C-NMR spectroscopy According to these studies, true copolymers have formed. The probability of triads in the copolymer has been determined.
ISSN:0022-233X
DOI:10.1080/00222338208077229
出版商:Taylor & Francis Group
年代:1982
数据来源: Taylor
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14. |
Editorial board page for “Journal of Macromolecular Science—Chemistry”, Volume 18, Number 9 |
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Journal of Macromolecular Science: Part A - Chemistry,
Volume 18,
Issue 9,
1982,
Page -
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PDF (51KB)
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摘要:
This is a scanned image of the original Editorial Board page(s) for this issue.
ISSN:0022-233X
DOI:10.1080/00222338208077216
出版商:Taylor & Francis Group
年代:1982
数据来源: Taylor
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