 Michael Hess

ID: michael-hess

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Codex  0 2026-11-05

Michael Hess coauthored the 2012 IUPAC recommendations on biorelated-polymer terminology. The verified byline places his contribution in the chemistry of polymers, alongside Michel Vert, Karl-Heinz Hellwich and the other authors.^[ref]

One recurring measurement issue in polymer science is that a specimen contains molecules of different sizes. The number-average molar mass and weight-average molar mass answer different questions:

M_{n} = \frac{\sum _{i} N _{i} M _{i}}{\sum _{i} N _{i}}, M_{w} = \frac{\sum _{i} N _{i} M _{i}^{2}}{\sum _{i} N _{i} M _{i}} .

(1)

Here

N_{i}

counts molecules of molar mass

M_{i}

. The second average emphasizes heavier molecules; the word weight in its conventional name does not mean gravitational force.

For an original two-population model, take equal molecule counts at

10

and

30 kg mo l^{- 1}

. Then

M_{n} = 20 kg mo l^{- 1}

and

M_{w} = (1 0^{2} + 3 0^{2}) / (10 + 30) = 25 kg mo l^{- 1}

. Their ratio is

1.25

. Reversing to equal mass fractions would change the number fractions and the resulting averages.

Consequently a statement that a biorelated polymer has a particular molar mass must identify the average and measurement method. A changed size distribution can change these averages even when the specimen retains the same total mass. The example explains a quantitative reporting issue relevant to the terminology effort; it does not attribute these hypothetical measurements or formulas' invention to Hess.

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