Chain‐Length‐Dependent Termination of Vinyl Acetate and Vinyl Pivalate Bulk Homopolymerizations Studied by SP‐PLP‐EPR. Issue 12 (11th May 2014)

• Record Type: Journal Article
• Authors: Kattner, Hendrik; Buback, Michael
• Is Part Of: Macromolecular chemistry and physics. Volume 215:Issue 12(2014:Jun.)
• Page Start: 1180
• Page End: 1191
• Publication Date: 2014-05-11
• Subjects: Polymers -- Periodicals; Polymerization -- Periodicals; Synthetic products -- Periodicals; Macromolecules -- Periodicals; 547.7
• DOI: 10.1002/macp.201400095
• Languages: English
• ISSNs: 1022-1352

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Bulk homopolymerizations of vinyl acetate and vinyl pivalate are studied by EPR experiments between −65 °C and 60 °C with dicumyl peroxide acting as the photoinitiator. No mid‐chain radicals are seen, which demonstrates that backbiting plays no role. The chain‐length dependence of the termination rate coefficients measured up to 13% monomer conversion is adequately represented by the composite model. The power‐law exponents <italic>α</italic><sub>s</sub> and <italic>α</italic><sub>l</sub> for short‐chain and long‐chain radicals are: <italic>α</italic><sub>s</sub>(VAc) = 0.57 ± 0.05, <italic>α</italic><sub>s</sub>(VPi) = 0.67 ± 0.15, <italic>α</italic><sub>l</sub>(VAc) = 0.16 ± 0.07, and <italic>α</italic><sub>l</sub>(VPi) = 0.16 ± 0.07. The crossover chain lengths differ largely: <italic>i</italic><sub>c</sub>(VAc) = 20 ± 10 and <italic>i</italic><sub>c</sub>(VPi) = 110 ± 30. The rate coefficient for termination of two radicals of chain length unity, <inline-formula><alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pghmh7tjw1" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley:dummy:macp201400095:equation:macp201400095-math-0001" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>k</mml:mi><mml:mi mathvariant="normal">t</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>, </mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:mrow></mml:math></alternatives></inline-formula>, which is the fourth composite‐model parameter, depends on temperature, as does the monomer fluidity. <boxed-text content-type="graphic" position="anchor" orientation="portrait"><graphic position="anchor" mimetype="image" xlink:href="ark:/27927/pghmh7tkkv" orientation="portrait" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></boxed-text></p> </abstract>