Page 24 - Biodegradable Polyesters

2 1 Biodegradable Polyesters: Synthesis, Properties, Applications

Figure 1.1 Hermann Staudinger who was born on 23 March 1881 at Worms, Germany and
died on 8 September 1965 at Freiburg, Germany [2].

tailored with high precision. But in his time, his concepts about macromolecules
were doubted by the scientific community, although he presented key experi-
mental evidence to support the existence of high-molecular-weight polymers.
Most scientists were very reluctant to accept the existence of large compounds
with molecular weights exceeding 5000 Da. Instead, micelle-type aggregates,
as observed for soap molecules, were considered to account for the unusual
properties of such materials. Moreover, some scientists were convinced that
the size of a molecule could never exceed the size of the unit cell, as measured
by X-ray crystallography [5]. A well-known effort was that of a natural rubber,
which was selected as the model system by Staudinger because Carl Harries and
Rudolf Pummerer had suggested that natural rubber consisted of aggregated
small cyclic polyisoprene units via “partial valencies” associated with the double
bonds. Such aggregates should have been destroyed when the double bonds were
removed by hydrogenation. Staudinger’s hydrogenation experiments showed that
hydrogenated rubber was very similar to normal unsaturated rubber, indicating
the existence of high-molecular-weight polymers whether the double bonds were
hydrogenated or not. During the late 1920s [6–9], Staudinger provided additional
evidence based on viscometry to confirm that molecular weights remained
unchanged during chemical modification of polymers. Staudinger continued
to encounter very strong opposition from leading organic chemists for nearly
two decades. For instance, Heinrich Wieland, 1927 Nobel laureate in chemistry,
wrote to Staudinger, “Dear colleague, drop the idea of large molecules; organic