Transfer constants from complete molecular weight distributions

Abstract

Transfer constants to chain-transfer agent (CTA) and to monomer can be obtained by consideration of the complete molecular weight distribution, using the slope of a plot of the natural logarithm of number-molecular weight distribution against molecular weight, in the limit of high molecular weight and low radical flux (P. A. Clay, R. G. Gilbert, MacromolecuIes28,552 (1995)). This method is applied to the bulk polymerisations of methyl methacrylate (MMA) with added triethylamine (TEA) and with added tert-dodecylmercaptan (mixture of 2,4,4,6,6-pentamethyIheptane-2-thiol and 2,2,4,6,6-pentamethylheptane-4-thiol, TDM). The transfer rate coefficients are found to be 74 (+20) dm3 * mol-' . s -l at 60°C for TEA, and 56 (+13) dm3.mol-' . s -l at 25°C for TDM.

Cross-Chain Transfer Rate Constants of Styrene-Terminated Radicals to Methyl Acrylate and Methyl Methacrylate

“…Whang et al 17 used this technique to determine the chain transfer coefficients to monomer of methyl methacrylate at 60°C using a high-conversion emulsion polymer sample and of styrene at 50°C using a low-conversion emulsion polymer sample. The technique has also been applied to the pulsed laser homopolymerization of styrene in microemulsions, 19 to the pulsed laser bulk polymerization of methyl methacrylate in the presence of two chain transfer agents, 20 and to the pulsed laser polymerization of styrene and methyl, ethyl, and butyl methacrylate with n-dodecanethiol. 21 Although most examples of the determination of chain transfer coefficients using the methods outlined above pertain to transfer to monomer or to a chain transfer agent in homopolymerizations, in a few cases the method has also been applied to transfer in copolymerization; see below.…”

Determination of Monomer Transfer Constants in Emulsion Polymerization

“…The plot, ln(N (r)) versus r, shows fluctuation at large chain lengths, as in the real experiments. [3,9,11,12] In SEC data, the signal at small chain lengths is also unreliable, and therefore, we determined the regression line from the data between r = 1 6 10 4 and 8 6 10 4 . Because 1/ k p [M] p " t t e = 5 6 10 -7 for the present condition, the slope would be -g = -5.05 6 10 -5 if the effects of finally formed chains were neglected.…”

“…Strictly, the CLD no longer conforms to the most probable distribution when the polymer transfer reaction exists. However, as shown in the experimental data, [3,9,11,12] the SEC curve always involves some amount of error, especially for both tails, and the straight lines in ln(N (r)) versus r are obtained only for a limited region. Therefore, if we can find the region where the C m -value can be extracted, the CLD method would be considered to be applicable.…”

“…In addition, linear extrapolation may not be guaranteed if bimolecular termination reactions are chain-length dependent. [3] Recently, Gilbert et al [3 -7] proposed a simple alternative method to determine chain transfer constants based on the chain length distribution (CLD). This method was used to determine the chain transfer constants of monomer [4, 8 -10] as well as chain transfer agents [3,11,12] and oligomers.…”

“…[3] Recently, Gilbert et al [3 -7] proposed a simple alternative method to determine chain transfer constants based on the chain length distribution (CLD). This method was used to determine the chain transfer constants of monomer [4, 8 -10] as well as chain transfer agents [3,11,12] and oligomers. [13] This method is claimed to be less sensitive to experimental noise and poor base line selection in size exclusion chromatography.…”