“…Comparison of this expression with Equation (3) shows that monomer renewal from macromonomer strongly influences the polymerization rate at higher catalyst concentrations. However, Equation (6) still predicts an increase of the polymerization rate with increasing cobalt concentration (though this increase is now expected to be not higher than a factor of two), in contrast to experimental data 2, 13–16…”
Section: Introductionmentioning
confidence: 74%
“…This expected increase of the polymerization rate is attributed to monomer consumption due to reaction (1e). However, instead of an increase, experiments show a decrease of polymerization rate with cobalt catalyst 2, 13–16. One contributing factor to this decrease is that Equation (3) does not take into account the fact that macromonomer with a chain length of one is simply monomer, as expressed by the transformation “reaction”: …”
Section: Introductionmentioning
confidence: 99%
“…For a chain transfer controlled system (as for CCT polymerization), it has been shown that this decrease does not occur, if chain transfer shows a similar chain‐length dependence 22. Smirnov et al13 have previously suggested that the rate coefficient of catalytic chain transfer is chain‐length dependent. This dependence is also introduced into the proposed model of CCT copolymerization.…”
Batch experiments were carried out to investigate the kinetics of catalytic chain transfer copolymerization of methyl methacrylate and n‐butyl methacrylate. The Predici® model developed to represent the system describes the numerous experimental data measured at high concentrations of Co(II) catalyst, taking into account the chain‐length dependencies of termination, propagation and catalytic chain transfer. The constants for catalytic chain transfer are determined as 2.3 × 104 for both methyl methacrylate and n‐butyl methacrylate from fitting the experimental data. Two inhibition mechanisms are shown to describe the decrease of the polymerization rate in the presence of catalyst equally well, with an unknown impurity dissolved in initiator introduced to explain experimental profiles measured at high initiator concentrations.
“…Comparison of this expression with Equation (3) shows that monomer renewal from macromonomer strongly influences the polymerization rate at higher catalyst concentrations. However, Equation (6) still predicts an increase of the polymerization rate with increasing cobalt concentration (though this increase is now expected to be not higher than a factor of two), in contrast to experimental data 2, 13–16…”
Section: Introductionmentioning
confidence: 74%
“…This expected increase of the polymerization rate is attributed to monomer consumption due to reaction (1e). However, instead of an increase, experiments show a decrease of polymerization rate with cobalt catalyst 2, 13–16. One contributing factor to this decrease is that Equation (3) does not take into account the fact that macromonomer with a chain length of one is simply monomer, as expressed by the transformation “reaction”: …”
Section: Introductionmentioning
confidence: 99%
“…For a chain transfer controlled system (as for CCT polymerization), it has been shown that this decrease does not occur, if chain transfer shows a similar chain‐length dependence 22. Smirnov et al13 have previously suggested that the rate coefficient of catalytic chain transfer is chain‐length dependent. This dependence is also introduced into the proposed model of CCT copolymerization.…”
Batch experiments were carried out to investigate the kinetics of catalytic chain transfer copolymerization of methyl methacrylate and n‐butyl methacrylate. The Predici® model developed to represent the system describes the numerous experimental data measured at high concentrations of Co(II) catalyst, taking into account the chain‐length dependencies of termination, propagation and catalytic chain transfer. The constants for catalytic chain transfer are determined as 2.3 × 104 for both methyl methacrylate and n‐butyl methacrylate from fitting the experimental data. Two inhibition mechanisms are shown to describe the decrease of the polymerization rate in the presence of catalyst equally well, with an unknown impurity dissolved in initiator introduced to explain experimental profiles measured at high initiator concentrations.
“…The curvature in Figure 1a may be due to several reasons: (i) there may be errors in the SEC analysis originating from too few low molecular weight calibration standards and the differential refractive index detector response is chain length dependent for low molecular weight chains 32 (so it is difficult to ascertain whether the curvature is real or an artifact of the analysis); (ii) it has been shown previously that C S is chain length dependent for short chains 7,33 (i.e., the region of interest in this case), which can introduce curvature in the ln P(M) vs M plots; [33][34][35] (iii) as previously mentioned, eq 1 gives approximate character in the case of short chains. 21 The Mayo 30,36 method was not suitable for measuring the C S of COBF with AMS since the molecular weights produced were very low, causing difficulty in determining accurate values of the number average molecular weight, M n .…”
Copolymerizations of styrene (STY) and α-methylstyrene (AMS) have been performed at
different monomer feed compositions and temperatures (40−70 °C) in the presence of the catalytic chain
transfer agent bis(boron difluorodimethylglyoximate)cobaltate(II) (COBF). The average chain transfer
constant, 〈C
S〉, was found to increase approximately 3 orders of magnitude upon going from pure STY
to pure AMS. The addition of only 10% AMS increased the 〈C
S〉 by 1 order of magnitude. This behavior can be predicted from the relative fractions of growing radical end groups, which results in
the majority of polymer chains being formed with an unsaturated AMS end group. No significant
penultimate unit effects in the chain transfer reaction were observed. The addition of 10−20% AMS
results in the majority of the growing radicals having AMS end groups, and hence AMS dominates
the catalytic chain transfer reaction. The 〈C
S〉 values continue to increase as the AMS content is increased beyond 20%; however, this can be mostly attributed to a decrease in 〈k
p〉 rather than an increase in 〈k
tr〉. The expected end groups in the homopolymerization of AMS in the presence of COBF
were confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry
(MALDI-TOF-MS).
“…In 1975, Boris Smirnov and Alexander Marchenko discovered a method in which they could control the molecular weight in a methacrylate polymerization by introducing catalysts that could greatly enhance the process of chain transfer to monomer . They found that substituted cobalt porphyrins, 1 , or benzoporphyrins, 2 , provided dramatic reductions in the molecular weight of the methacrylate polymers during radical polymerization with little to no reduction in overall yield of polymer. − …”
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