Ultrahigh molecular weight bisphenol A polycarbonate (BPAPC) with nonlinear chain structures has been synthesized by solid-state polymerization in microlayers at 230°C. It has been found that the molecular weights of the microlayers of low molecular weight prepolymers with thickness ranging from 5 to 35 μm increased rapidly to ultrahigh molecular weight (300,000−600,000 g/mol) without any discoloration. The amorphous prepolymers exhibited much higher reaction rate than the partially crystallized prepolymers. Although the reactive end group mole ratios of the prepolymers prepared by semibatch melt polycondensation deviated significantly from the stoichiometric value, branching and partial cross-linking reactions have been found to occur to rapidly increase the polymer molecular weight. These nonlinear chain structures observed were due to Fries rearrangement, Kolbe-Schmitt rearrangement reactions, and radical-induced scission/cross-linking reactions. The microstructures of the high molecular weight polymers have been analyzed by 13 C NMR, 1 H NMR, pyrolysis-gas chromatography mass spectrometry, and atomic force microscopy.

The dispersion polymerization of methyl methacrylate (MMA) has been studied in a nonpolar hydrocarbon solvent at low temperature using N,N‐dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiation system. To explain the heterogeneous kinetic characteristics of the polymerization process, the reaction locus has been experimentally and theoretically investigated. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were measured throughout the polymerization. It was found that the significant preferences of LPO and DMA to accumulate in the polymer‐rich phase after the system phase separation are mainly responsible for both the uniformity of particle sizes and the broad polymer MWDs. It was observed that particle agglomeration and breakup mechanisms were enhanced under agitation, thus promoting the formation of broader particle size distributions. The observed kinetics and thermodynamics of the low‐temperature polymerization were also examined through a mathematical model where the distributions of initiators, solvent, and monomer between phases were considered. A good agreement between the experimental and theoretical results was observed and the model was used to estimate the conditions that promote bimodal MWDs. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

An experimental and theoretical modeling study is presented on the kinetics of reversible oligomerization of L-lactic acid and the formation of L-lactide in closed reactors with SnCl 2 •2H 2 O/p-toluenesulfonic acid as a binary catalyst mixture. The experimental data and model simulations indicate that about 10 wt % L-lactide is produced by the cyclization of two repeating units of poly(L-lactic acid) at the chain end during the oligomerization process. The effects of the catalyst and reaction temperature at 160−200 °C on the discoloration of the reaction mixture have also been investigated, and it was observed that the discoloration of the reaction mixture was quite significant in the presence of the catalyst at high temperatures. The relevant kinetic parameters for the chain-growth reaction as well as cyclic L-lactide formation reaction have been estimated for both noncatalyzed and catalyzed reversible oligomerization reactions.

Spherical silica particles with pseudo‐inverse opal structure are synthesized by using pomegranate‐like polymer microparticles as templates. A micro‐dispersion polymerization occurring in the suspended monomer droplets in the presence of a silica precursor leads to the formation of nearly monodisperse polymer sub‐particles of about 1 µm size, randomly‐packed within a 30–100 µm polymer particle. The polymerization is followed by an acid‐catalyzed reaction that induces formation of silica in the interstices between the sub‐particles within a polymer particle. Spherical PIOS particles are eventually produced by selectively removing the polymer template by pyrolysis. The PIOS particles show large specific surface areas with unique pore geometry and pore size distribution.magnified image

A detailed model is presented to analyze the phase inversion in the dispersion polymerizations of methyl methacrylate (MMA) in non‐polar solvents. The reaction conditions under which the polymer particles lose stability and the reaction system phase inverts are investigated. At high solvent/monomer ratios, well‐defined micron‐sized polymer particles are produced even in the absence of stabilizer. However, low solvent/monomer ratios or stabilizer concentrations yield porous structures after a massive agglomeration of the precipitating particles. To quantify the phase inversion, a population balance equation (PBE) is derived and combined with a kinetic/thermodynamic model to develop a procedure capable of predicting the system phase inversion curve. The model predictions agree well with the experimental results.