The polymerization of hexachlorocyclotriphosphazene (I) (also known as phosphonitrilic chloride trimer) to high molecular weight poly(dich1orophosphazene) (11) has been studied in the presence of phosphorus pentachloride, water, and hydrogen chloride. Phosphorus pentachloride is a powerful polymerization inhibitor, water is a polymerization catalyst or cocatalyst, and hydrogen chloride is a mild inhibitor. The results are discussed in terms of possible reaction mechanisms.
The Dandy-Walker malformation (DWM) is hydrocephalus that primarily affects the fourth ventricle, whose overdistention involves also the aqueduct and third ventricle. However, just the opposite is true in the Arnold-Chiari malformation (ACM) since the hydrocephalus is limited to the lateral ventricles which squeeze the third ventricle between them and compress the aqueduct and fourth ventricle. The evidence indicates that both result from hydrodynamic stresses in embryonal and early fetal life. This communication is offered in rebuttal to some statements in an otherwise authoritative and comprehensive article.
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