Hildeberto Nava

Liquid crystalline copolymers of monomer-pairs containing mesogenic units which exhibit constitutional isomerism

SummaryThe synthesis and characterization of side-chain liquid crystalline copolymers obtained from a monomer pair containing a mesogenic unit which exhibits constitutional isomerism are presented. The particular example described refers to copolymethacrylates obtained from 4-hydroxy-4′-methoxy-α-methylstilbene and 4-methoxy-4′-hydroxy-α-methylstilbene containing six and eleven methylenic units in the spacer. The polymer containing six methylenic units presents a nematic mesophase, while the polymer containing eleven methylenic units presents a smectic A or C mesophase. None of these polymers exhibited side-chain crystallization.

Functional Polymers Based on p- and m-(Hydroxyphenyl)-2-Oxazolines

2-Oxazolines can be polymerized cationically with a variety of electrophilic initiators to produce linear poly(N-acylethyleneimine)s. In many cases their polymerization proceeds through a living mechanism and this allows not only the synthesis of polymers with well characterized molecular weights, but also the preparation of a variety of block and graft copolymers (Scheme 1). Because of a slow propagation rate compared to that of other heterocyclic monomers, the elemental reaction steps can be conveniently followed by carrying out the polymerization directly into a NMR sample tube. Poly(N-acylethyleneimine) is also an excellent starting polymer backbone on which a large variety of reactions have been performed to produce a number of unusual functional polymers. In addition to this, 1:1 alternating copolymerization and 2:1 periodic copolymerization of 2-oxazolines have opened several new, very fruitful areas of active research. All the above summarized information has been excellently reviewed by Kobayashi and Saegusa,1 the leaders of the most active group working in this field.