precursor of the Deutsche Forschungsgemeinschaft (DFG). Therefore, he intensified his efforts, aiming at finding a correlation between molecular weight and the
viscosity of non-spherical colloid particles. He tried to adapt Einstein’s viscosity
law, established for spherical particles, to polymer chains. This led him to a
relationship that became known as the Staudinger law, correlating the polymer
molecular weight with the specific viscosity of dilute solutions, and extrapolating it
to infinite dilution (“Staudinger index” or intrinsic viscosity) [16]. Using a calibration with polymer samples of known molecular weight, it became possible to
estimate the molecular weight. This concept was refined by Kuhn, Mark, Houwink
and others, who substantially improved this correlation. Today, this correlation is
known as the Mark–Houwink and also as the Kuhn–Mark–Houwink–Sakurada
equation. This valuable and robust viscosimetry technique is still in use today in
academia and industry. It is well known as very reliable and facile method for
molecular weight determination. Unlike ultracentrifugation and gel permeation
chromatography, no costly investment is needed. Moreover, using this method it
was possible to distinguish between spherical and rod-like conformations of macromolecules in solution. It should be noted that Staudinger clearly favored a
rod-like fully stretched polymer conformation, resembling a Mikado stick (see
Fig. 1). In his view, highly ordered polymers rather than spaghetti-like randomcoil polymers account for the specific functions of polymers in nature. For many
years and also for other reasons, he heavily opposed Werner Kuhn and Hermann
F. Mark, who pushed forward the concept of random-coil polystyrene. A detailed
description of the dispute between Staudinger, Mark, and Meyer concerning the
size and shape of macromolecules is given by Priesner [4]. During his “habilitation”
in Staudinger’s laboratory, in the 1930s, Gu ¨nter Victor Schulz introduced osmometry as an accurate measurement for molecular weights.
4 Imaging of Single Macromolecules
In Freiburg the Staudinger group successfully made early attempts at characterizing
the morphology of polymers using ultraviolet phase contrast microscopy and also
transmission electron microscopy (TEM), which was invented in 1931 by Max
Knoll and Ernst Ruska. It was Magda Staudinger who started research on microscopic imaging of polymers in Freiburg during the late 1930s. In 1940, Elfriede
Husemann in collaboration with Helmut Ruska, working at the laboratory of
electro-optics of Siemens & Halske AG, successfully employed TEM to visualize
a single spherical glycogen macromolecule with molecular weight of around 1.5
million, as determined by osmosis, and an average diameter of 10 μm [17].
They achieved substantial improvement of contrast when they examined the piodobenzoyl derivative of glycogen with a much higher molecular weight of six
million. From the molecular weight, using the Einstein viscosity law, they calculated an average diameter of the p-iodobenzoyl glycogen macromolecule to be
30 μm, which is in remarkably good accordance with the diameter measured by
26
H.-J. Cantow and R. Mu ¨lhaupt
viscosity of non-spherical colloid particles. He tried to adapt Einstein’s viscosity
law, established for spherical particles, to polymer chains. This led him to a
relationship that became known as the Staudinger law, correlating the polymer
molecular weight with the specific viscosity of dilute solutions, and extrapolating it
to infinite dilution (“Staudinger index” or intrinsic viscosity) [16]. Using a calibration with polymer samples of known molecular weight, it became possible to
estimate the molecular weight. This concept was refined by Kuhn, Mark, Houwink
and others, who substantially improved this correlation. Today, this correlation is
known as the Mark–Houwink and also as the Kuhn–Mark–Houwink–Sakurada
equation. This valuable and robust viscosimetry technique is still in use today in
academia and industry. It is well known as very reliable and facile method for
molecular weight determination. Unlike ultracentrifugation and gel permeation
chromatography, no costly investment is needed. Moreover, using this method it
was possible to distinguish between spherical and rod-like conformations of macromolecules in solution. It should be noted that Staudinger clearly favored a
rod-like fully stretched polymer conformation, resembling a Mikado stick (see
Fig. 1). In his view, highly ordered polymers rather than spaghetti-like randomcoil polymers account for the specific functions of polymers in nature. For many
years and also for other reasons, he heavily opposed Werner Kuhn and Hermann
F. Mark, who pushed forward the concept of random-coil polystyrene. A detailed
description of the dispute between Staudinger, Mark, and Meyer concerning the
size and shape of macromolecules is given by Priesner [4]. During his “habilitation”
in Staudinger’s laboratory, in the 1930s, Gu ¨nter Victor Schulz introduced osmometry as an accurate measurement for molecular weights.
4 Imaging of Single Macromolecules
In Freiburg the Staudinger group successfully made early attempts at characterizing
the morphology of polymers using ultraviolet phase contrast microscopy and also
transmission electron microscopy (TEM), which was invented in 1931 by Max
Knoll and Ernst Ruska. It was Magda Staudinger who started research on microscopic imaging of polymers in Freiburg during the late 1930s. In 1940, Elfriede
Husemann in collaboration with Helmut Ruska, working at the laboratory of
electro-optics of Siemens & Halske AG, successfully employed TEM to visualize
a single spherical glycogen macromolecule with molecular weight of around 1.5
million, as determined by osmosis, and an average diameter of 10 μm [17].
They achieved substantial improvement of contrast when they examined the piodobenzoyl derivative of glycogen with a much higher molecular weight of six
million. From the molecular weight, using the Einstein viscosity law, they calculated an average diameter of the p-iodobenzoyl glycogen macromolecule to be
30 μm, which is in remarkably good accordance with the diameter measured by
26
H.-J. Cantow and R. Mu ¨lhaupt