Effect of catalyst partitioning in Co(II) mediated catalytic chain transfer miniemulsion polymerization of methyl methacrylate

Abstract

The effect of catalyst partitioning over the organic and water phases in the catalytic chain transfer mediated miniemulsion polymerization was investigated and a mathematical model developed to describe the instantaneous degree of polymerization of the formed polymer. Experimental and predicted instantaneous degrees of polymerization prove to be in excellent agreement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5839–5849, 2008

A Study of Particle Nucleation in Dispersion Copolymerization of Methyl Methacrylate

“…Assuming that the j crit for MMA radicals is on the order of 20–30 monomer units, it can be estimated that less than 2% of the growth of an average MMA chain takes place in solution. Furthermore, the high MWs found with addition of 5 and 10 ppm CCTA, suggests that the cobalt compound plays a minor role in the dispersed phase (due either to mass transfer or solubility issues governing partitioning46) and that polymerization in the dispersed phase is the major loci of reaction for MMA, as has been suggested in the literature 18, 42, 48…”

“…CCT‐mediated polymerizations are a type of controlled radical polymerization where the degree of polymerization (thus MW) of the polymer is controlled by a cobalt(II) catalyst, known as a CCTA 32–34. CCT of MMA using COBF (the CCTA used in this study) is well described by Smeets et al46 In theory, with enough catalyst, the average chain length of MMA polymer produced can be reduced to a value below the critical chain length, and the polymerization characteristics in solution can be studied and compared to the solution‐like polymerization of the MeMBL copolymers. At lower levels of CCTA, particle formation will still occur.…”

Catalytic Chain Transfer in Continuous Emulsion Polymerization

“…This results in a situation where a certain fraction of the amount of CCTA is not active in the control of the MWD. The number‐average degree of polymerization ($\overline {DP} _{{\rm n}} $ ) in CCT‐mediated emulsion polymerizations can be predicted accurately by the classical Mayo equation,14 extended with CCTA partitioning 4 …”

“…COBF, COEtBF and COPhBF, displays a broad variety of partition coefficients and chain transfer activities. COBF is fairy water soluble ( m Co = 0.72)3a, 3c, 4, 17 and partitions predominantly towards the aqueous phase. COEtBF ( m Co = 19)17, 18 and COPhBF ( m Co = ∞)3c, 17 are more hydrophobic and partition predominantly and exclusively towards the polymer particle phase.…”

“…However, when applied in emulsion polymerization, the compartmentalized nature of the reaction system affects the performance of any catalytic chain transfer agent (CCTA). Partitioning of the CCTA3b, 3c, 3d, 4 between the aqueous phase and the polymer particles results in lower apparent activities,3a, 3b, 3d, 3e, 4 as only the amount of CCTA in the polymer particles is active in the control of the average molecular weight of the polymer. The course of the polymerization3b, 3g and the final latex properties3a, 3e, 5 [i.e.…”