Macromolecular Reaction Engineering

Cover: This work demonstrates that the glass transition temperature of an in situ polymerized carbon nanotube/polyimide (CNT/PI) nanocomposite can vary non-monotonically with the concentration of the reactive CNT added. This is due to its influence on the polycondensation reaction stoichiometry and thus on the molecular weight of the matrix PI polymer. Further details can be found in the article by D. H. Kim, and Y.-Y. Won* on page 45.

Block copolymers are synthesized using a RAFT agent in conjunction with emulsion polymerization via stage-wise operations. Living macromonomers from the first stage are chain-extended to produce styrene-, butyl-acrylate-, and methyl-acrylate-based copolymers. The semi-batch mode produces polymers of improved purity and polydispersity as shown by NMR and SEC data.

Not the slow fragmentation model (SFM) but the intermediate termination model (ITM) is shown to be applicable for styrene RAFT polymerization with dithiobenzoate via comparison of miniemulsion polymerization rate with bulk polymerization rate. The ITM gives a significantly higher measured rate of miniemulsion polymerization (average diameter = 107 nm) than bulk polymerization, while SFM does not.

A detailed kinetic model is developed and applied to the heterogeneous free-radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical carbon dioxide. The model, accounting for polymerization occurring in both the dispersed polymer-rich and in the continuous supercritical phase, compares favorably with experimental results of conversion and molecular weight distribution.

It is demonstrated that the glass transition temperature of an in situ polymerized carbon nanotube/polyimide nanocomposite can vary non-monotonically with the concentration of the reactive CNT added. This fact is attributed to the influence of the CNT concentration on the polycondensation reaction stoichiometry and thus on the molecular weight of the matrix PI polymer.

Methods for the preparation of Ziegler-Natta catalysts with controlled particle morphology are evaluated. They differ in the dealcoholation agents and processes. The catalyst with the highest Ti content, whose support has the largest pores, shows the best performance in both ethylene and propylene polymerization. The polymers particles have a spherical morphology.