Macromolecular Reaction Engineering

Cover: Cp₂ZrCl₂ and Ni-diimine catalysts were supported on montmorillonite (MMT) to produce in-situ polyethylene-clay nanocomposites in a gas-phase reactor. The development of nanocomposite morphology was investigated with TEM, SEM, and XRD. During polymerization, the MMT layers were partially exfoliated by the growing polymer chains, starting from the opening of the clay gallery and proceeding towards its center. Further details can be found in the article by S.-Y. A. Shin, L. C. Simon, J. B. P. Soares,^* G. Scholz, and T. F. McKenna on page 543.

Ab initio prediction of chemical rate coefficients is on the way to become a useful tool for polymer reaction engineering. A strategy is presented as to how the strict accuracy requirements for this application can be fulfilled by currently available quantum chemical methods. A comparison of computed results to reliable PLP data for radical propagation in solution polymerization is given.

A polyelectrolyte composed of methylimidazolium salt with β-cyclodextrin complexed counterion and acrylic-functionalized poly(N-isopropylacrylamide) as grafted side chains has been elaborated via a three-step synthetic procedure. The aqueous solution of the system displays a noticeable thermosensitive behavior, where it exhibits enhancement of shear viscosity close to body temperature. For the first time, based on classically prepared poly(NIPAAm) bearing terminal amino groups, corresponding acryl- and methacrylamide macromonomers were easily obtained under microwave conditions.

A high-throughput analysis technique is described for studying photopolymerization kinetics using Fourier-transform infrared spectroscopy. Double bond conversion is monitored on samples with composition and exposure time gradients, producing a conversion map within one sample substrate, measuring the effects of monomer viscosity and diluent backbone chain structure.

A theoretical model for determining copolymer compositions and complete molecular weight distributions of block-like copolymers, obtained via continuous supported atom transfer radical polymerization in continuous flow reactors, was developed. An almost perfect match between the simulated and experimental kinetic data (first order kinetic plots, conversions, and polydispersity index) was observed.

In emulsion polymerization, the thermodynamic equilibrium between polymer particles and monomer droplets results in polymer particles that contain high concentrations of polymer, even at low conversion. This causes enhanced chain branching which is often detrimental in synthetic rubber processes. A mathematical model is used to show that a miniemulsion process for rubber polymerization may suppress branching.

Polyethylene–clay nanocomposites are produced with Cp₂ZrCl₂and Ni-diimine catalysts supported on montmorillonite in a gas-phase reactor. One-hour pre-polymerization at room temperature and atmospheric pressure (1: before, 2: after) increases the average particle diameter (5–15 to ≈50µm). If pre-polymerization continues for 24h, irregularly shaped particles with protruding polymer fibrils may form (3.a). Polymerization at high ethylene pressure yields particles with more regular morphology (3.b).

The continuous distribution kinetic modeling of photopolymerization of methyl, ethyl, butyl, and hexyl methacrylates is reported. The model predicts all the salient features of the photopolymerization, viz., time evolution of polymer molar and mass concentrations to equilibrium and the instantaneous increase of M_n and PDI to steady state. The rate coefficients were evaluated by fitting the model with the experimental data.