Molecular weight development in free-radical polymerization with polyfunctional chain-transfer agents, 1 - Equal reactivity model

Citation
H. Tobita et M. Hayashi, Molecular weight development in free-radical polymerization with polyfunctional chain-transfer agents, 1 - Equal reactivity model, MACROMOL TH, 10(6), 2001, pp. 573-580
Citations number
25
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
MACROMOLECULAR THEORY AND SIMULATIONS
ISSN journal
1022-1344 → ACNP
Volume
10
Issue
6
Year of publication
2001
Pages
573 - 580
Database
ISI
SICI code
1022-1344(20010803)10:6<573:MWDIFP>2.0.ZU;2-G
Abstract
The analytic expression for the weight-average molecular weight development in free-radical polymerization that involves a polyfunctional chain-transf er agent is proposed. Free radical polymerization is kinetically controlled ; therefore, the probability of chain connection with a polyfunctional chai n-transfer agent as well as the primary chain-length distribution changes d uring the course of polymerization. We consider the primary chains, and the heterochain branching model is used to obtain the weight-average chain len gth at a given conversion level in a matrix formula, described as (P) over bar (w) = W{D-w + (I + T)SP(I-TSP)D--1(f)}. Because the primary chains are formed consecutively, the number of chain types N is extrapolated to infini ty, but such extrapolation can be conducted with the calculated values for only three different N values. The criterion for the onset of gelation is s imply described as a point at which the largest eigenvalue of the produce o f matrixes, TSP reaches unity, i.e., det(I-TSP)=0. The present model can re adily be extended for the star-shaped polyfunctional initiators and the rel ationships between the model parameters and kinetic rate expression for suc h reaction systems are also shown. [GRAPHICS] Extrapolation method to obtain P-w at N --> infinity for C2 at x = 0.5. The curve is a quadratic regression determined from the values at N = 50, 70 a nd 100.