Ultrahigh molecular weight grade

PVC (usually low to medium molecular grade but ultrahigh molecular weight PVC is also used)... 

Pylios T and Shepherd DET (2008), Wear of medical grade silicone rubber against titanium and ultrahigh molecular weight polyethylene , J Biomed Mater Res Part B Appl Biomater, 84B, 520-523, DOl 10.1002/jbm.b.30899. 

Baker DA. Macro- and microscopic evaluation offatigue in medical grade ultrahigh molecular weight polyethylene. Berkeley, CA UC Berkeley 2001. 

One drawback of the nucleophilic routes described so far is that they produce a metal salt and solid solvent residue which needs to be removed from the system. In many condensation polymerisations the small molecule produced is volatile and can be removed directly from the reaction. The KF residue leads to reversibility of the reaction and transetherification. However, the low solubility of KF in diphenylsulfone means that a high molecular weight can still be achieved and the KF can be removed by extraction with water. Indeed extraction with water at very high temperatures has recently been used to produce ultrahigh-purity grades of PEEK [10]. These materials can have less than 1 ppm residual potassium and sodium. 

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