Chain-length dependence of free-radical termination rate deduced from laser single-pulse experiments

Easy Access to Chain-Length-Dependent Termination Rate Coefficients Using RAFT Polymerization

“…For example, Olaj and Vana [7,22] reported b-values for styrene bulk polymerizations of close to 0.16 at 25 8C, ambient pressure, and b % 0.1 and k t 0 % 3 Á 10 8 L Á mol À1 Á s À1 at 70 8C. Buback et al [23] reported a b-value of 0.16 at 80 8C and 2200 bar. (iv) The obtained hk t i,i i value finally shows a strong decrease for P > 100, with the onset of the decrease shifting with varying RAFT agent concentration.…”

“…To date, studies to elucidate this chain-length dependence are sophisticated and include analysis of molecular weight distributions [6] of pulsed laser polymerization experiments [7,8] and conversion vs time profiles of single-pulse polymerizations. [9] The aim of this Communication is to present a novel and extremely simple approach to chainlength-dependent k t values, utilizing the RAFT process.…”

Modeling Termination Kinetics of Non-Stationary Free-Radical Polymerizations

“…Several authors [16,17] used chain-length dependent expressions for k t also at low conversion. Using Equation (4 d) instead of Equation (4 c) allows to include a chainlength dependence of k t also in the non-entangled region:…”

“…Inhibitor species may even be formed during photo-initiator decomposition. The widely used initiator 2,2-dimethoxy-2-phenylacetophenone (DMPA), for example, decomposes into a propagating and a non-propagating free-radicals, [17] with the latter species acting as an inhibitor in the absence of further irradiation. In time-resolved SP-PLP initiated by DMPA, both types of free radicals are instantaneously produced in equal amounts during the primary decomposition step.…”

Complications in the 355 nm Pulsed-Laser Polymerization ofN-Vinylcarbazole

“…However, both photo initiators have very similar UV absorption characteristics and both fragment into two free-radical species (which display different reactivities) upon irradiation. [9,10] During the PLP-SEC experiments of NVC in toluene solution we encountered some noteworthy difficulties: (i) it was very difficult to identify reaction and pulsed-laser conditions where a reliable reproducibility of the results could be obtained; (ii) we observed frequent PLP tube cracking and clear evidence of charred polymer at laser energies where no such problems are observed using other monomers, such as styrene or methyl methacrylate; (iii) we had difficulties during the SEC analysis of some samples, which were caused by increased back pressure on the columns despite all samples being subjected to thorough filtering prior to injection. These initial experimental observations gave additional rise to suspicions that the PLP of NVC at 355 nm (or 351 nm) may be subject to significant difficulties and side reactions.…”