Behavior of primary radicals in vinyl polymerization

Abstract

The reciprocal of the viscosity‐average degree of polymerization (P̄v−1) vs. rate of polymerization (V) relation is expressed as: where [η] = K′P̄vα, β = ktd/kt, k = rate of primary radical formation out of cages/concentration of initiator, \documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot][{\rm M}] = {\rm rate of initiation of polymerization} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{ti} [R_i \cdot][{\rm M} \cdot] $\end{document} = rate of termination of growing chains M· by reaction with primary radicals Ri·. From this equation, several, important constants can be determined. In the polymerization of styrene at 60°C. with 2,2′‐azobisisobutyronitrile, the results obtained are as follows: kp2/kt = 5.52 × 10−4 (or 5.86 × 10−4) l.‐mole.−1‐sec.−1. ktrM/kp = 6 × 10−5, ktrS/kp 1.1 × 10−2 (carbon tetrachloride as solvent), k = 1.57 × 10−5 (or 1.48 × 10−5) sec.−1, \documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot]/\sum {_i k'} _{ti} [R_i \cdot] = 1.20 \times 10^{- 7} $\end{document}. These values agree well with those obtained by the other authors. The rate of initiation \documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot]{\rm -}[{\rm M}] $\end{document} and the rate of termination \documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{ti} [R_i \cdot][{\rm M} \cdot] $\end{document} between the growing chains and primary radicals are calculated, respectively, from the equations: The rate of disappearance of the primary radicals through the reaction among themselves is negligible in comparison with the other termination rates in the usual conditions. The ratio of concentrations of the primary radicals R· and growing chains M· is expressed under an ordinary condition as: where VR is the rate of primary radical formation and k′p the rate constant of initiation.

Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions Part I Modeling

“…In the analysis presented here the effects of primary radical recombination will be neglected, as it has been shown that these events are negligible when compared with other polymerization kinetic reactions [17,25].…”

“…1 ͑m͒ ͑t͒ and 1 ͑p͒ ͑t͒ are the time varying firstharmonic volume fraction components of monomer and polymer, respectively, values of which are obtained by solving Eqs. (22)- (25). At grating growth saturation, when there is no monomer left to be polymerized, i.e., 1 ͑m͒ =0, Eq.…”

Assessment of crosslink network and network defects of unfilled and filled ethylene‐propylene‐diene terpolymer using solid state nuclear magnetic relaxation spectroscopy

“…Second is that the radicals are formed in a cage of surrounding filler aggregates (i.e., cage effect) as depicted in Figure . It has long been known that a high local concentration of initiator gives a high concentration of primary radicals, leading to excessive primary radical termination before meaningful addition reaction …”

Kinetische untersuchungen zur lösungspolymerisation von vinylchlorid

“…Es mu13 namlich beriicksichtigt werden, da13 das monomere Vinylchlorid fur das entstehende Polymere ein Fallungmittel darstellt und da13 deshalb bei dem relativ hohen Monomergehalt der Ausgangslosung (20)(21)(22)(23)(24)(25) Val.-%) das Polymere auch schon nach geringen Umsatzen nicht mehr vollstandig gelost wird und die Mischung somit nicht mehr homogen ist. So konnten auch andere Autoren598) beobachten, da13 selbst in Chlorbenzol bei hohen Ausgangskonzentrationen in bezug auf das Monomere eine Phasentrennung bereits bei Beginn der Polymerisation gegeben ist.…”