Kinetics and Molecular Weight Distributions for Unsteady‐State Polymerizations Involving Termination by Chain Transfer with the Monomer

1959 ◽  
Vol 30 (2) ◽  
pp. 363-368 ◽  
Author(s):  
W. T. Kyner ◽  
J. R. M. Radok ◽  
M. Wales
Keyword(s):  
Molecular Weight ◽  
Chain Transfer ◽  
Unsteady State ◽  
Molecular Weight Distributions ◽  
Weight Distributions

TERTIARY MERCAPTANS AS MODIFIERS IN GR-S POLYMERIZATIONS

1947 ◽  
Vol 25b (2) ◽  
pp. 159-182 ◽  
Author(s):  
Maurice Morton ◽  
R. V. V. Nicholls
Keyword(s):  
Molecular Weight ◽  
Rate Equation ◽  
Slow Rate ◽  
Chain Transfer ◽  
Transfer Reactions ◽  
Molecular Weight Polymer ◽  
First Order ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Order Rate Equation

Tertiary octyl, decyl, dodecyl, and hexadecyl mercaptans were investigated as modifiers in GR-S polymerizations.The rate of disappearance of these modifiers followed a first-order rate equation during the first half of the polymerization, in accordance with the theory of chain-transfer reactions. During the latter part of the reaction, an increased rate of disappearance generally occurred. A mechanism is suggested.The rate of disappearance increased with decreasing chain-length of the mercaptan. The intrinsic viscosities and molecular weight distributions of the polymers obtained at different conversions were related to the activity of each mercaptan as a modifier. Values for the regulating index of each mercaptan were calculated.The slow rate of disappearance of tertiary hexadecyl mercaptan leads to the formation of polymer that is relatively homogeneous in molecular weight, and this mercaptan is therefore a desirable modifier. However, after 50% polymerization, the regulator action shows a marked acceleration, leading to the formation of progressively lower molecular weight polymer and resulting in a spread in the molecular weight distribution.

scholarly journals Further Effects of Chain-Length-Dependent Reactivities on Radical Polymerization Kinetics

2007 ◽  
Vol 60 (10) ◽  
pp. 754 ◽  
Author(s):  
Johan P. A. Heuts ◽  
Gregory T. Russell ◽  
Gregory B. Smith
Keyword(s):  
Molecular Weight ◽  
Radical Polymerization ◽  
Chain Length ◽  
Chain Transfer ◽  
Transfer Constant ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
A Chain ◽  
Chain Transfer Constant ◽  
Independent Chain

In the present paper, we finalize some threads in our investigations into the effects of chain-length-dependent propagation (CLDP) on radical polymerization kinetics, confirming all our previous conclusions. Additionally, and more significantly, we uncover some unexpected and striking effects of chain-length-dependent chain transfer (CLDTr). It is found that the observed overall rate coefficients for propagation and termination (and therefore the rate of polymerization) are not significantly affected by whether or not chain transfer is chain-length dependent. However, this situation is different when considering the molecular weight distributions of the resulting polymers. In the case of chain-length-independent chain transfer, CLDP results in a considerable narrowing of the distribution at the low molecular weight side of the distribution in a chain-transfer controlled system. However, the inclusion of both CLDP and CLDTr yields identical results to classical kinetics – in these latter two cases, the molecular weight distribution is governed by the same chain-length-independent chain transfer constant, whereas in the case of CLDP only, it is governed by a chain-length-dependent chain transfer constant that decreases with decreasing chain length, thus enhancing the probability of propagation for short radicals. Furthermore, it is shown that the inclusion of a very slow first addition step has tremendous effects on the observed kinetics, increasing the primary radical concentration and thereby the overall termination rate coefficient dramatically. However, including possible penultimate unit effects does not significantly affect the overall picture and can be ignored for the time being. Lastly, we explore the prospects of using molecular weight distributions to probe the phenomena of CLDP and CLDTr. Again, some interesting insights follow.

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