Robin A. Hutchinson

Studies of higher temperature polymerization ofn-butyl methacrylate andn-butyl acrylate

Free-radical acrylic polymerizations of n-butyl methacrylate and n-butyl acrylate at temperatures above 120°C show significant departure from classic free-radical kinetics. An extended model of depropagation, where the equilibrium monomer concentration varies with temperature and polymer content, is postulated and shown to adequately explain the data for n-butyl methacrylate. Intramolecular chain transfer and scission is postulated to explain the apparent reduction in molecular weight and rate of polymerization seen in n-butyl acrylate polymerization, with supporting experimental evidence found via electrospray-ionization mass spectrometry.

Critically evaluated rate coefficients in radical polymerization – 7. Secondary-radical propagation rate coefficients for methyl acrylate in the bulk

Propagation rate coefficient (kp) data for radical polymerization of methyl acrylate (MA) in the bulk are critically evaluated and a benchmark dataset is put forward by a task-group of the IUPAC Subcommittee on Modeling of Polymerization Kinetics and Processes. This dataset comprises previously published results from three laboratories as well as new data from a fourth laboratory. Not only do all these values of kp fulfill the recommended consistency checks for reliability, they are also all in excellent agreement with each other. Data have been obtained employing the technique of pulsed-laser polymerization (PLP) coupled with molar-mass determination by size-exclusion chromatography (SEC), where PLP has been carried out at pulse-repetition rates of up to 500 Hz, enabling reliable kp to be obtained through to 60 °C. The best-fit – and therefore recommended – Arrhenius parameters are activation energy EA = 17.3 kJ mol−1 and pre-exponential (frequency) factor A = 1.41 × 107 L mol−1 s−1. These hold for secondary-radical propagation of MA, and may be used to calculate effective propagation rate coefficients for MA in situations where there is a significant population of mid-chain radicals resulting from backbiting, as will be the case at technically relevant temperatures. The benchmark dataset reveals that kp values for MA obtained using PLP in conjunction with MALDI-ToF mass spectrometry are accurate. They also confirm, through comparison with previously obtained benchmark kp values for n-butyl acrylate, methyl methacrylate and n-butyl methacrylate, that there seems to be identical family-type behavior in n-alkyl acrylates as in n-alkyl methacrylates. Specifically, kp for the n-butyl member of each family is about 20% higher than for the corresponding methyl member, an effect that appears to be entropic in origin. Furthermore, each family is characterized by an approximately constant EA, where the value is 5 kJ mol−1 lower for acrylates.

Continuous controlled radical polymerization of methyl acrylate in a copper tubular reactor.

The use of copper tubing as both the reactor and as a catalyst source is demonstrated for continuous controlled radical polymerization of methyl acrylate at ambient temperature and at low solvent content of 30%. The high surface area provided by the copper walls mediates the reaction via the single electron transfer-living radical polymerization (SET-LRP) mechanism. The polymerizations proceeded quickly, reaching 67% conversion at a residence time of 16 min. Ligand concentration could also be reduced without a sharp drop in polymerization rate, demonstrating the potential for decreased raw material and post-process purification costs. Chain extension experiments conducted using synthesized polymer showed high livingness. The combination of living polymer produced at high polymerization rates at ambient temperature and low volatile organic solvent content demonstrate the potential of a copper reactor for scale up of SET-LRP.

Modeling of chain length and long-chain branching distributions in free-radical polymerization

The effect of long-chain branching and β- scission reactions on the complete molecular weight (MW) and branching density distributions of polymer pro- duced in a well-mixed continuous reactor has been sys- ematically studied. An improved statistical description of ow branch points on a scissioning chain distribute between the two resulting polymer fragments has been developed and implemented in the PREDICI® software package, Simulations are used to illustrate that the branching density distribution does not provide a good visual ndication of average brarching in the system; appropriate averaging aeross the chair, length distribution must be performed, It is shown that chain lengths tend to the most probable distribution even in the presence of branching when scission is the principle MW-controlling mechanιsm. Furthemore, a uniform branchingdensity distribution is obtained, provided that a sufficient number of sciston events occur per chain relative to its average residence time in the reactor. Smaller amounts of scission, when combined with another MW-controlling mechanism such as transfer to solvent, can lead to the formation of chain length distributions with asymmetric or bimodal features as well as reducing the high-MW tail and polydispersity.

Consideration of Macromonomer Reactions in n-Butyl Acrylate Free Radical Polymerization

n-Butyl acrylate (BA) starved-feed solution semibatch experiments with varying final polymer content and monomer feed times were carried out at 138 °C. A full mechanistic model of the system implemented in Predici includes intermolecular chain transfer to polymer and macromonomer propagation as well as backbiting, chain scission, and midchain radical propagation and termination. The importance of macromonomer propagation under these conditions of industrial interest is illustrated by experiment and simulation, with the macromonomer reaction responsible for the significant increase in polymer weight-average molecular weight (

Investigation of Free-Radical Copolymerization Propagation Kinetics of Vinyl Acetate and Methyl Methacrylate

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Continuous controlled radical polymerization of methyl acrylate with copper wire in a CSTR

) with time. Rate coefficients for macromonomer propagation (k(mac) ) and β-scission (k(β) ) of k(mac) /k(p)  = 0.55 and k(β)  = 12 s(-1) (with k(p) the rate coefficient for BA chain-end propagation) provide a good representation of experimental

Copper mediated controlled radical polymerization of methyl acrylate in the presence of ascorbic acid in a continuous tubular reactor

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The Effect of Hydrogen Bonding on Intramolecular Chain Transfer in Polymerization of Acrylates

and macromonomer end group data at 138 °C.

Free Radical Copolymerization Kinetics of γ-Methyl-α-methylene-γ-butyrolactone (MeMBL)

The free-radical copolymerization propagation kinetics of vinyl acetate (VAc) and methyl methacrylate (MMA) at 50 degrees C were investigated through an experimental study combined with a computational analysis based on quantum chemistry. Copolymer composition data, obtained using pulsed laser polymerization followed by size exclusion chromatography (PLP-SEC) and proton nuclear magnetic resonance (NMR), were well represented by the terminal model using monomer reactivity ratios obtained with the computational approach (r(VAc) = 0.001 and r(MMA) = 27.9). Concerning the composition-averaged copolymerization propagation rate coefficient k(p,cop), the differences between the terminal model and the implicit penultimate unit effect (IPUE) model (s(MMA) = 0.544 and s(VAc) = 0.173) are small for VAc/MMA, with the terminal model sufficient to describe the experimental k(p,cop) data measured by PLP-SEC. Monomer and radical charge distributions determined computationally are used to explain the reactivity exhibited by the VAc/MMA system.