Xanthates (MADIX agents) are an important class of RAFT agents. Currently, they are the only "living" agent that can be successfully used in a classical ab inito emulsion polymerization (i.e., where surfactant micelles are used as mircoreactors for polymerization), in which novel nanostructures can be prepared. The composition and molecular weight distribution (MWD) controls to a large extent the morphology of these nanostructures. A key factor that controls the MWD is the chain transfer ability of the MADIX agents. Three MADIX agents with different leaving groups (methyl benzyl or ethyl propionyl) and different activating moieties (O-ethyl or O-trifluoroethyl) were examined for their chain transfer ability in the homopolymerization of styrene. The chain transfer constants, C tr, were determined using both the Mayo and chain length distribution methods. This is the first comprehensive study in which accurate activation parameters for MADIX agents have been elucidated for styrene polymerizations. The activation parameters from both methods showed that changing the Z group on the MADIX agent from a OCH 2CH3 (Ctr ) 0.69) to a OCH2CF3 (Ctr)3.5) lowered the Ea,tr by at least 5 kJ mol -1 . This suggests that when the electron-withdrawing power on the Z group is increased, the reactivity of polystyrene radicals toward the SdC bond is also increased. This is opposite to what is found when electron-donating Z groups are used (e.g., phenyl or benzyl groups), in which the C tr values are actually orders of magnitude greater than for OCH2CF3, suggesting that the radical reactions to RAFT agents is more complex than to CdC bonds. It is postulated that the transition state of the intermediate radical plays an important role in the overall Ctr value. The confidence contour plots showed that the activation parameters for the O-ethyl xanthates with different leaving groups (C(CH3)Ph and C(CH3)CO2Et) were completely overlapping, suggesting that these leaving groups have little or no effect on the Ctr values. The O-trifluoroethyl xanthate allows the preparation of polymers with controlled molecular weights and low polydispersities close to 1.4 to be prepared, which is a distinct improvement on the first generation MADIX agents, O-ethyl xanthates (polydispersity close to 2).

Polymeric nanocapsules were synthesized by encapsulating extruded vesicles of dimethyldioctadecyl ammonium bromide (DODAB) using a reversible addition-fragmentation chain transfer (RAFT)-based encapsulation approach. Random copolymers containing acrylic acid and butyl acrylate units were first synthesized by RAFT in solution using dibenzyl trithiocarbonate (DBTTC) as the RAFT agent. These anionic copolymer chains were subsequently adsorbed onto the surface of cationic DODAB vesicles and then chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryogenic transmission electron microscopy (cryo-TEM) characterizations demonstrate the successful formation of nanocapsules.

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.

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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.