What Is Polyethylene

For UHMWPE, the molecular chain can consist of as many as 200,000 ethylene repeat units. Put another way, the molecular chain of UHMWPE contains up to 400,000 carbon atoms. 

There are several kinds of polyethylene (LDPE, LLDPE, HDPE, UHMWPE), which are synthesized with different molecular weights and chain architectures. LDPE and LLDPE refer to low-density polyethylene and linear low-density polyethylene, respectively. These polyethylenes generally have branched and linear chain architectures, respectively, each with a molecular weight of typically less than 50,000 g/mol. 

HDPE is a linear polymer with a molecular weight of up to 200,000 g/mol. UHMWPE, in comparison, has a viscosity average molecular weight of up to 6 million g/mol. In fact, the molecular weight is so ultra-high that it cannot be measured directly by conventional means and must instead be inferred by its intrinsic viscosity (IV). 

In the early 1960s, UHMWPE was classified as a form of HDPE among members of the polymer industry (Chubberley 1965). Thus, Chamley s earlier references fo UHMWPE as HDPE are fechnically accurafe for his time (Chamley 1963), but they have contributed to some confusion over the years as to exactly what kinds of polyethylenes have been used clinically. From a close reading of Chamley s works, it is clear that HDPE is used synonymously with RCH-1000, the trade name for UHMWPE produced by Hoechst in Germany (Chamley 1979). With the exception of a small series of 22 patients who were implanted with silane-crosslinked HDPE at Wrighington (Wroblewski et al. 1996), there is no evidence in the literature that lower molecular weight polyethylenes have been used clinically. 

Typical Average Physical Properties of HDPE, UHMWPE 

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