Triply linked phosphate groups

There is then branched isopolyphosphate that contains a single triply-linked PO3 group as below. 

In an attempt to obtain direct evidence for the presence of cross-linking in potassium polyphosphates crystallized from ultraphosphates melts, two tools were chosen. Cross-linking should in theory be observed by either phase chemistry or X-rays. Also, the existence of end and middle group phosphorus is well established 

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The evidence for cross-linking in crystalline inorganic polyphosphates to convert them to crystalline ultraphosphates with small degrees of cross-linking is circumstantial rather than direct. This is not to question the triply-linked phosphate groups in the... 

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