Abstract
The rate coefficient (k1) for the reaction of OH radicals with perfluoro ethyl vinyl ether (PEVE, C2F5OCF[double bond, length as m-dash]CF2) has been measured as a function of temperature (T = 207-300 K) using the technique of pulsed laser photolysis with detection of OH by laser-induced fluorescence (PLP-LIF) at pressures of 50 or 100 Torr N2 bath gas. In addition, the rate coefficient was measured at 298 K and in one atmosphere of air by the relative-rate technique with loss of PEVE and reference reactant monitored in situ by IR absorption spectroscopy. The rate coefficient has a negative temperature dependence which can be parameterized as: k1(T) = 6.0 × 10-13 exp[(480 ± 38/T)] cm3 molecule-1 s-1 and a room temperature value of k1 (298 K) = (3.0 ± 0.3) × 10-12 cm3 molecule-1 s-1. Highly accurate rate coefficients from the PLP-LIF experiments were achieved by optical on-line measurements of PEVE and by performing the measurements at two different apparatuses. The large rate coefficient and the temperature dependence indicate that the reaction proceeds via OH addition to the C[double bond, length as m-dash]C double bond, the high pressure limit already being reached at 50 Torr N2. Based on the rate coefficient and average OH levels, the atmospheric lifetime of PEVE was estimated to be a few days.
Highlights
Desirable properties such as thermal and chemical resistance have led to the use of fluoropolymers in many industrial processes including the production of plastics, elastomers or membranes[1,2] and to their production in large quantities
In this work we have studied the kinetics of the reaction of PEVE with OH radicals (R1) using both the technique of pulsed laser photolysis with detection of OH radicals by laser-induced fluorescence as well as relative-rate measurements using FTIR detection of reactants to derive the rate coefficient, k1
The complete dataset, including data obtained using two different experimental setups for determination of the absolute rate coefficient and the relative rate study is summarised in Fig. 7 as an Arrhenius plot
Summary
Desirable properties such as thermal and chemical resistance have led to the use of fluoropolymers in many industrial processes including the production of plastics, elastomers or membranes[1,2] and to their production in large quantities. The most important commercial fluoropolymers are homopolymers based on only three main monomers; tetrafluoroethylene (TFE), vinyl fluoride and vinylidene fluoride.[3] In addition, smaller amounts of co-polymers with tailored properties are made with co-monomers like hexafluoropropylene and perfluoro vinyl ethers. From a physical chemical perspective, we note that the reaction kinetics of perfluoro substituted organic trace gases can differ greatly from the non-fluorinated analogues. Study of the OH reaction with a fluorinated ethyl vinyl ether (electrophilic addition of OH to the CQC double bond) allows us to analyse the electronic effects caused by the presence of a fluorinated alkyl
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