Preparation of cyclic oligomeric alkylene phthalates via pseudo-high dilution condensation of alkylene diols with iso- and terephthaloyl chlorides and conversion to high molecular weight polyesters via ring-opening polymerization is described. Sterically unhindered amines such as quinuclidine or 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyze the condensation significantly faster than other tertiary amines and are useful for carrying out this conversion in high yield, in the first direct reaction of diol and diacid chloride to form cyclic polyesters. The mixtures of oligomeric cyclics melt at 150-200 degrees C, providing liquids of low viscosity. Ring-opening polymerization using tin or titanate catalysts affords high molecular weight polymers within minutes. Complete polymerization of PBT oligomeric cyclics can be achieved at 180-200 degreesC, significantly below the polymer's melting point of 225 degreesC, and with molecular weights as high as 445 x 10(3). Polymers formed via such a process are more crystalline than conventionally prepared polyesters.
Cyclic oligomers of engineering plastics such as polycarbonate and aromatic polyesters have been known for some time, being formed at very low levels during commercial manufacture. At GE Global Research, we have devised methods for high-yielding and selective preparation of such cyclic oligomers, that are amenable to commercial manufacture. The mixtures of cyclic oligomers have melting points significantly lower than individual ring sizes, and have very low viscosities in the melt. Ring-opening polymerization using appropriate initiators affords rapid reactions (2-6 min) without measurable exotherm, providing very high-molecularweight polymers and without reaction byproducts. These materials have been scaled to commercial quantities, and have shown to be extremely useful for fabrication of glass and carbon fiber composites with high-fiber fractions.
A selective, high-yielding procedure for the preparation of Bisphenol A cyclic oligomeric carbonates via a triethylamine-catalyzed hydrolysis/ condensation reaction of bis (chlorof ornate) is described. The reaction produces cyclic oligomers in 80-90% yield, along with about 15 % high molecular weight polymer, but with almost total exclusion of linear oligomers. The structure of the amine catalyst controls the selectivity of cyclic vs linear vs polymer formation. Use of other amine catalysts can lead to different products. Use of pyridine as catalyst, for example, affords linear oligomers in 99% yield, with very low yields of cyclics. Polymerization of the cyclic oligomers to polycarbonate with Mv = 50 000-300 000 is achieved by heating at 300 °C for 15 min in the presence of various basic catalysts. The preparation of authentic oligomeric linear and cyclic materials is also described.
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