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

Johan P. A. Heuts; Gregory T. Russell; Gregory B. Smith

doi:10.1071/CH07214

RESEARCH ARTICLE

Previous Next Contents Vol 60(10)

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

Johan P. A. Heuts ^A ^C , Gregory T. Russell ^B ^C and Gregory B. Smith ^B

+ Author Affiliations

- Author Affiliations

^A Laboratory for Polymer Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.

^B Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.

^C Corresponding authors. Email: j.p.a.heuts@tue.nl, greg.russell@canterbury.ac.nz

Australian Journal of Chemistry 60(10) 754-764 https://doi.org/10.1071/CH07214
Submitted: 26 June 2007 Accepted: 1 August 2007 Published: 9 October 2007

Abstract

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.

References

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

Abstract

Subscriber Login