= Michael Hess
{c}
\b[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.<Terminology for biorelated polymers and applications (IUPAC Recommendations 2012) by Michel Vert and others>[full byline and recommendation scope]{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:
$$
M_n=\frac{\sum_iN_iM_i}{\sum_iN_i},\qquad
M_w=\frac{\sum_iN_iM_i^2}{\sum_iN_iM_i}.
$$
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 $30\,\mathrm{kg\,mol^{-1}}$. Then $M_n=20\,\mathrm{kg\,mol^{-1}}$ and $M_w=(10^2+30^2)/(10+30)=25\,\mathrm{kg\,mol^{-1}}$. Their ratio is $1.25$. Reversing to equal \i[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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