The percentage of two types of free radicals occurring within n-butyl acrylate pulsed laser polymerization (PLP) has been measured via ESR spectroscopy. Polymerization in solution of toluene, at monomer concentrations between 0.50 and 2.53 mol L -1 and temperatures between -50 and 70°C, was induced by 351 nm excimer laser pulses applied at a repetition rate of 20 Hz. The ESR spectra obtained at low degrees of monomer conversion may be adequately represented by superimposing a six-component four-line spectrum assigned to secondary propagating radicals (SPRs) and a nine-line spectrum assigned to tertiary midchain radicals produced by backbiting (MCR1s). The percentage contribution to total radical concentration of the latter species, which is produced from an SPR by a 1,5-H shift backbiting reaction, is negligible at -50°C and is close to 80% at 70°C. The transition of an SPR to a MCR1 species invalidates the linear correlation of time t after applying a laser pulse with the size of the growing radical. The observed high concentration of MCR1 species explains the known severe limitations met in acrylate PLP-SEC experiments directed toward measuring the propagation rate of acrylate radicals with chain-end functionality.

The combination of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) and size exclusion chromatography (SEC) combined with pulsed laser polymerization has been used to evaluate propagation rate coefficients (kp) in bulk free-radical polymerization for the systems methyl methacrylate and styrene. By varying laser frequencies, the relation between polymer chain length and observed propagation rate coefficient (k p obs ) has been investigated in detail. It has been found that deviations between MALDI-ToF-MS and SEC at higher molecular weights are the result of instrumental effects in SEC. Moreover, using a model and taking into account experimental studies on the propagation of oligomeric species, it has been inferred that the relationship between k p obs and polymer chain length is the result of chain-length-dependent behavior of the true kp in the oligomeric range, therewith excluding any chain-length-dependent behavior at higher molecular weights.

MALDI-ToF-MS mass spectra of copolymers contain a lot of information on both chain length distribution (CLD) and chemical composition distribution (CCD). In this paper an approach for extracting detailed information from a MALDI-ToF-MS mass spectrum is presented that enables the study of microstructure for copolymers. More specifically, this paper is dealing with a polystyrene-block-polyisoprene copolymer, in which the growth of the second block is followed with MALDI-ToF-MS as a function of conversion. The technique is compared to 1H NMR for the evaluation of average chemical compositions, revealing that ionization efficiencies do not influence the obtained mass spectra. It is shown that MALDI-ToF-MS can extract detailed information on the chain length distributions (CLDs) for both polystyrene and polyisoprene blocks. Using random coupling statistics, it is shown that the proposed analysis yields results with a high accuracy.

The combination of MALDI-ToF-MS and pulsed laser polymerization has been used to study the propagation rate coefficients for the copolymer system styrene-methyl methacrylate. For the first time, complete information regarding mode of termination, reactivity of photoinitiator-derived radicals, copolymer molecular mass, chemical composition, and copolymerization rates is obtained interrelated. The polymerizations were carried out in bulk with varying styrene concentrations at a temperature of 15.2 degrees C by an excimer pulsed laser with varying frequencies. Both chemical composition distributions and molecular weight distributions were determined by MALDI-ToF-MS. The data were fitted to the implicit penultimate unit model and have resulted in new point estimates of the monomer and radical reactivity ratios for the copolymer system styrene-methyl methacrylate: r(St) = 0.517, r(MMA) = 0.420, s(St) = 0.296, s(MMA) = 0.262. Comparison between Monte Carlo simulations and the obtained results further confirmed the very successful combination of pulsed laser copolymerization experiments with MALDI-ToF-MS. The obtained results are believed to be the most accurate and complete set of copolymerization parameters to date.