Four-Center Type Photopolymerization in the Solid State

Organic photochemistry. XVII. Polymerization of unsaturated compounds by photocycloaddition reactions

“…Irradiating monomer 192 with light of wavelengths >400 nm produced solely low molecular weight oligomers because the oligomers absorbed light only at wavelengths shorter than 380 nm. 57,68,104,109 This explanation was analogous to that described above for diester 68 (Scheme II). Irradiating monomer 192 or the as-formed oligomer with short wavelength light (<380 nm) produced higher molecular weight polymer.68,104,109 Recrystallized oligomer did not form higher molecular weight polymer when irradiated further, presumably because it changed to a more stable crystal form.…”

“…The bis(nitroethylene) derivative 98 was reported to polymerize by cycloaddition when irradiated in the crystal state (eq 35). 57 The polymer 99 was indicated 100 + 101 (xn = n) ---> 101 lxn = n* 1381 101 (x" = n) + 101 S" = m) ---^101 i;n = m+n) (39) the same wavelengths as the monomer, as occurred with the bis(maleimides) discussed in section UK.…”

“…84 The rate of polymerization as measured by consumption of monomer 192 increased slightly as the temperature increased from -20 °C to +50 °C. 57,73,84 At up to 50% conversion, this temperature dependence corresponded to an activation energy of ~3 kcal mol-1. 84 The rate was considerably slower at -42 °C.57, 84 The reduced viscosities at constant conversion were nearly equal for polymerizations carried out at -55 °C to 0 °C.…”

“…This situation was in contrast to that where the growing polymer molecules absorbed light at was given. 57 The bis(anthracene) derivative 104 could have polymerized via 4 + 4 cycloadditions of the anthracene moieties similarly to other anthracenes discussed in section VB. An appropriate arrangement of the monomer molecules 104 in the crystal lattice would have been required for this reaction.…”

Polymerization in liquid crystals. XIII. Copolymerization of mesogenic monomers

“…If the polymer has an isomorphic structure with the monomer it remains dissolved in the monomer and the structure of the polymerizing phase is unchanged during the reaction. This type of reaction is termed as homogeneous (28,33).…”