Effects of kinetics and optical attenuation on the completeness, uniformity, and dynamics of monomer conversion in free-radical photopolymerizations

Guillermo Terrones, Arne J Pearlstein

Research output: Contribution to journalArticle

Abstract

For free-radical photopolymerizations with a photobleaching initiator in an initially uniform layer illuminated from one direction, we incorporate nonuniform photoinitiation into a simple kinetic model to show how the degree of monomer conversion varies spatially and temporally with the incident light intensity (I0), the absorption coefficient (αA) and initial concentration (CA,0) of the photoinitiator, and the propagation (kp) and termination (kt) rate constants (taken to be independent of the degree of conversion). We show that the spatiotemporal variation of monomer conversion depends on two dimensionless parameters: the initial absorbance γ = αACA,0L, where L is the layer thickness, and β = kp[fCA,0/(φαA I0kt)]1/2, where φ is the quantum yield of photoinitiator consumption, and O ≤ f ≤ 2 is the number of primary radicals produced for each photoinitiator molecule consumed. For each value of γ, there is a minimum value of β beyond which a specified layer-averaged extent of monomer conversion is assured. As β decreases, so does the extent of monomer conversion, with the final degree of conversion being lowest near the optical "front" of the layer, where the light absorption and photoinitiation rates are initially highest. The extent of nonuniformity decreases with increasing β until β ≈ 2, beyond which monomer conversion is essentially complete regardless of the initial absorbance. The results are discussed in terms of the spatiotemporal distributions of the primary radical and radical chain concentrations.

Original languageEnglish (US)
Pages (from-to)8894-8906
Number of pages13
JournalMacromolecules
Volume34
Issue number26
DOIs
StatePublished - Dec 18 2001

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

Fingerprint Dive into the research topics of 'Effects of kinetics and optical attenuation on the completeness, uniformity, and dynamics of monomer conversion in free-radical photopolymerizations'. Together they form a unique fingerprint.

  • Cite this