Timothy D. Shaffer

Noncoordinating anions in carbocationic polymerization

The initiation and catalysis of isobutylene polymerization from several new metallocene and nonmetallocene initiator-catalysts that contain the noncoordinating anions (NCA), B(C6F5)4− and RB(C6F6)3−, is reported. Application of these initiator-catalysts is extended to styrenics and vinyl ethers. The NCA does not contribute to termination and can be used in low concentrations compared with conventional Lewis acids. These qualities provide for isobutylene polymerizations that yield low Mn oligomers or high Mn polymer, dependent upon the initiator and polymerization conditions. Mechanistic aspects of initiation, transfer and termination as well as the participation of adventitious water are considered for each class of initiator-catalyst. The influence of the NCA on the stereoregularity of cationic styrene polymerization is also considered. NCAs do not cause the stereospecific carbocationic polymerization of styrene. We suggest that under conditions not conducive to carbocationic polymerization, NCA/metallocenes mediate the coordination polymerization of styrene.

Thermotropic polyketones: A new class of main-chain liquid crystalline polymers

SummaryThe first examples of thermotropic liquid crystalline (LC) polyketones have been synthesized by the Friedel-Crafts acylation of biphenyl, fluorene and terphenyl with α,ω-dicarboxylic acid alkanes in a phosphorous pentoxide/methanesulfonic acid (PMMA) condensing agent. Polyketones prepared from biphenyl and fluorene exhibit good solubility as well as low thermal transition temperatures due to the copolymeric nature of these polymers. Both molecular weight and the inherent copolymer composition appear to influence the mesophase behavior in these polymers. Optical polarization microscopy has revealed smectic textures for all the polyketones exhibiting LC behavior.

Thermotropic Polyethers and Copolyethers: A New Class of Main Chain Liquid Crystalline Polymers

In 1975 deGennes suggested that thermotropic liquid crystalline (LC) main chain polymers might be prepared by incorporating mesogenic and flexible segments in the polymer main chain repeating units.1 In the same year, Roviello and Sirigu provided the first example of thermotropic LC main chain polymers, i.e., poly-alcanoates of p,p′-hydroxy-α,α′-dimethyl benzalazine.2 Since then, several research groups have become actively engaged in the study of thermotropic LC main chain polymers. This new field of polymer chemistry has been recently reviewed.3