Lewis acid mediated polymerization of poly(dimethylsiloxane) polymers: investigating reaction kinetics using both NMR spectroscopy and cyclic voltammetry

Alistair Apedaile, John Liggat, John Parkinson, George Nikiforidis, Leonard Berlouis, Mogon Patel

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Abstract

Bulk condensation polymerization of (dimethylmethoxy)-m-carborane and (dichlorodimethyl)-silane occurs in the presence of an Mx+Clx Lewis acid catalyst. In the literature, FeCl3 is commonly used as the catalyst of choice but little is known about the activation energy and entropy of this polymerization. By monitoring using 1H-NMR the reaction of a methoxy-terminated poly(dimethylsiloxane) and (dichlorodimethyl)silane the rate determining step in the FeCl3 catalyzed system is determined. The activation energy was calculated to be +43.6 kJ mol-1 and the entropy of the reaction was also calculated. The calculated large entropy of reaction indicates that the transition step is highly ordered. The formation of the electrophile intermediate species in the first step of the reaction has also been investigated using cyclic voltammetry. To the cyclic voltammetry data Randles-Sevcik fits have been applied to the oxidation peaks to determine the diffusion coefficients for the oxidation of Fe2+ to Fe3+ . Also, the initial prediction of a reversible reaction Step 1 was shown to be incorrect as the normalized reduction peak maxima increase with scan rate, indicative of an electron transfer-chemical reaction mechanism.

LanguageEnglish
Pages2601-2608
Number of pages8
JournalJournal of Applied Polymer Science
Volume123
Issue number5
Early online date1 Sep 2011
DOIs
Publication statusPublished - 5 Mar 2012

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Lewis Acids
Polydimethylsiloxane
Reaction kinetics
Nuclear magnetic resonance spectroscopy
Cyclic voltammetry
Silanes
Polymers
Entropy
Polymerization
Acids
Activation energy
Oxidation
Catalysts
Polycondensation
Chemical reactions
Nuclear magnetic resonance
Electrons
Monitoring
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Keywords

  • poly(dimethylsiloxane)
  • carborane
  • Lewis acid catalysis
  • group transfer polymerization
  • kinetics
  • nuclear magnetic resonance
  • cyclic voltammetry
  • Randles-Sevcik

Cite this

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title = "Lewis acid mediated polymerization of poly(dimethylsiloxane) polymers: investigating reaction kinetics using both NMR spectroscopy and cyclic voltammetry",
abstract = "Bulk condensation polymerization of (dimethylmethoxy)-m-carborane and (dichlorodimethyl)-silane occurs in the presence of an Mx+Clx Lewis acid catalyst. In the literature, FeCl3 is commonly used as the catalyst of choice but little is known about the activation energy and entropy of this polymerization. By monitoring using 1H-NMR the reaction of a methoxy-terminated poly(dimethylsiloxane) and (dichlorodimethyl)silane the rate determining step in the FeCl3 catalyzed system is determined. The activation energy was calculated to be +43.6 kJ mol-1 and the entropy of the reaction was also calculated. The calculated large entropy of reaction indicates that the transition step is highly ordered. The formation of the electrophile intermediate species in the first step of the reaction has also been investigated using cyclic voltammetry. To the cyclic voltammetry data Randles-Sevcik fits have been applied to the oxidation peaks to determine the diffusion coefficients for the oxidation of Fe2+ to Fe3+ . Also, the initial prediction of a reversible reaction Step 1 was shown to be incorrect as the normalized reduction peak maxima increase with scan rate, indicative of an electron transfer-chemical reaction mechanism.",
keywords = "poly(dimethylsiloxane), carborane, Lewis acid catalysis, group transfer polymerization, kinetics, nuclear magnetic resonance, cyclic voltammetry, Randles-Sevcik",
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T1 - Lewis acid mediated polymerization of poly(dimethylsiloxane) polymers

T2 - Journal of Applied Polymer Science

AU - Apedaile, Alistair

AU - Liggat, John

AU - Parkinson, John

AU - Nikiforidis, George

AU - Berlouis, Leonard

AU - Patel, Mogon

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N2 - Bulk condensation polymerization of (dimethylmethoxy)-m-carborane and (dichlorodimethyl)-silane occurs in the presence of an Mx+Clx Lewis acid catalyst. In the literature, FeCl3 is commonly used as the catalyst of choice but little is known about the activation energy and entropy of this polymerization. By monitoring using 1H-NMR the reaction of a methoxy-terminated poly(dimethylsiloxane) and (dichlorodimethyl)silane the rate determining step in the FeCl3 catalyzed system is determined. The activation energy was calculated to be +43.6 kJ mol-1 and the entropy of the reaction was also calculated. The calculated large entropy of reaction indicates that the transition step is highly ordered. The formation of the electrophile intermediate species in the first step of the reaction has also been investigated using cyclic voltammetry. To the cyclic voltammetry data Randles-Sevcik fits have been applied to the oxidation peaks to determine the diffusion coefficients for the oxidation of Fe2+ to Fe3+ . Also, the initial prediction of a reversible reaction Step 1 was shown to be incorrect as the normalized reduction peak maxima increase with scan rate, indicative of an electron transfer-chemical reaction mechanism.

AB - Bulk condensation polymerization of (dimethylmethoxy)-m-carborane and (dichlorodimethyl)-silane occurs in the presence of an Mx+Clx Lewis acid catalyst. In the literature, FeCl3 is commonly used as the catalyst of choice but little is known about the activation energy and entropy of this polymerization. By monitoring using 1H-NMR the reaction of a methoxy-terminated poly(dimethylsiloxane) and (dichlorodimethyl)silane the rate determining step in the FeCl3 catalyzed system is determined. The activation energy was calculated to be +43.6 kJ mol-1 and the entropy of the reaction was also calculated. The calculated large entropy of reaction indicates that the transition step is highly ordered. The formation of the electrophile intermediate species in the first step of the reaction has also been investigated using cyclic voltammetry. To the cyclic voltammetry data Randles-Sevcik fits have been applied to the oxidation peaks to determine the diffusion coefficients for the oxidation of Fe2+ to Fe3+ . Also, the initial prediction of a reversible reaction Step 1 was shown to be incorrect as the normalized reduction peak maxima increase with scan rate, indicative of an electron transfer-chemical reaction mechanism.

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