Abstract
Abstract
The radiation‐induced polymerization of n‐butyl acrylate (nBuA) in the presence of small amounts of organic compounds containing heteroatoms has been investigated to evaluate the tentative explanations proposed to account for the differences in initiation rate observed between tripropyleneglycol diacrylate (TPGDA) and hexanediol diacrylate (HDDA), when subjected to electron‐beam (EB) polymerization. The progress of monomer conversion as a function of increasing dose was monitored by transmission infrared spectroscopy applied to thin films submitted to incremental exposure to EB radiation. Miscible organic additives expected to favour hydrogen abstraction, or free radical generation as a consequence of easy carbon–halogen bond scission, were thus introduced in nBuA at a concentration of 2 wt%. The kinetic changes were examined at low monomer conversion. The presence of di‐n‐butyloxide, diisopropyloxide or diisopropylsulfide was shown not noticeably to affect the conversion–dose dependence for EB‐irradiated nBuA. n‐Butyl chloride or bromide caused a noticeable reduction of nBuA reactivity; this was even greater for the iodide at the same 2 wt% concentration. n‐Butanol (nBuOH) was shown to sensitize nBuA consumption when present at a low concentration (2 wt%), but the enhancement of the polymerization rate was not as high for a larger nBuOH content (10 wt%). These results are discussed in the light of the radical anion mechanism for the radiation‐initiated polymerization of acrylate monomers. The absence of a significant sensitizing effect from additives known to enhance free‐radical formation supports the minor contribution of homolytic bond scission to the initiation mechanism. The observed effects of nBuOH at low concentration, indicate that trace amounts of protonic contaminants can exert a strong influence on the efficiency of initiation by the radical‐anion mechanism.
© 2001 Society of Chemical Industry