Anhydrous melt polymerization

In an effort to investigate the incapability of clays to fully disperse in PA matrices derived from diamine and diacid monomers, during the solution-melt process [48, 67], Boussia et al. [30] studied the formation of PA n.6-clay nanocomposites (n = 2, 6, and 12) through applying an anhydrous melt polymerization process. The latter is characterized by the absence of water as solvent and benign time-temperature profiles, so as to minimize ionic conditions that have been considered to affect clays dispersability [67], as well as the risk of thermal degradation of organoclays surfactants. 

Properties. Antimony pentafluoride [7783-70-2], SbF, is a colorless, hygroscopic, very viscous liquid that fumes ia air. Its viscosity at 20°C is 460 mPa-s(=cP) which is very close to the value for glycerol. The polymerization of high purity SbF at ambient temperature can be prevented by addition of 1% anhydrous hydrogen fluoride, which can be removed by distillation prior to the use of SbF. The pure product melts at 7°C (11), boils at 142.7°C,... 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

The anionic polymerization of caprolactam is rapid and can be carried out below die melting temperature of the PA. Care should be taken to work under anhydrous conditions. 

In a 100 ml three-necked flask with stirrer and thermometer 1 mol% of p-toluenesul-fonic acid methyl ester (methyl tosylate) are added to 3 g (0.03 mol) of anhydrous 2-methyl-2-oxazoline.The reaction mixture is stirred under nitrogen at 100-120 °C.The bulk polymerization sets in immediately. After 30 min. the viscous polymer melt is poured in a dish where it solidifies within minutes. After cooling to room temperature about 2 grams are dissolved in 20 ml ethanol and precipitated in 500 ml THF.The collected precipitate is dried under vacuum. 

Caprolactam can also be polymerized under anhydrous conditions using strong bases as catalysts. This was already reported by Schlack in 1938 [l7j. r.m. Joyce and D.M. Ritter [32] at DuPont discovered in 1939 that this anionic polymerization proceeded with a much higher rate than the hydrolytic process and that it could be carried out below the melting point of the polymer to yield products of low residual monomer content, so that they needed no extraction. In spite of these obvious advantages this type of polymerization at first did not enter into commercial practice because of poor reproducability, unstable melt viscosity and poor product color [29]. 

---