2.7 About Primary Valences and Secondary Valences
Heimlich [2, p. 79] summarises the situation in rather direct fashion: Staudinger
“was brutal in his destruction of the legend of small molecules and replaced it by his
convictions about giant molecules.” Heimlich [2, p. 83] says: “While molecules
with what is called a molecular weight of 300 were classified as huge [. . .] in classic
organic chemistry, Staudinger downgraded them to dwarfs in relation to the macromolecules he proposed that had molecular weights of 10,000 or more.” Looked at
from our current perspective, this was a scientific revolution and a paradigm shift,
with which Staudinger laid the foundations for plastics chemistry. Most of his
contemporaries failed to realise the significance, however: “The response to
Staudinger’s article was minimal [. . .]. At this time, Staudinger was still unable
to provide any proof of the existence of long-chain molecules” [19, p. 251]. Doubts
about the accuracy of Staudinger’s theory dominated; there was opposition primarily to his theories about the bonding forces that existed in high polymers. The
predominant view in organic chemistry at the time was that the basic molecules in
polymers did not lose their independence, i.e. they were only bonded to form a unit
by low electromagnetic attraction. In other words, the existence of high polymers
was no reason to give up the concept of low molecules and to postulate macromolecules, which many chemists claimed were nothing more than a figment of the
imagination.
Detailed information about this controversy and the people involved will be
provided later on. Before this is done, here is an outline of Staudinger’s antithesis
and the necessary preconditions. The basic rule is: electromagnetic attraction takes
place between all the atoms of a piece of material, but the degree of attraction
varies. The strongest interaction between the atoms is within the individual molecules. These inter-atomic and/or intra-molecular forces are called primary or
covalences (primary bonds). In contrast to them, weaker bonding forces known as
secondary or partial valences (secondary bonds) are responsible for inter-molecular
cohesion (cf. [15], p. 17). For his macromolecular model, Staudinger now excluded
the “assumption of secondary valences” from the outset as being “not necessary”
[20, p. 13]. This was a logical conclusion, because the claim was that a macromolecule was an independent entity of a size that had not been considered possible
before and was not just a loose collection of familiar small molecular units. With
respect to the existing bonding relationships in the macromolecule, Staudinger
therefore worked on the assumption of primary valences in the same way as with
any other molecule. Secondary valences would only be a subject requiring examination when the discussion moved on to inter-(macro)molecular attraction.
At the latest from 1920 onwards, Staudinger was certain “that standard valence
formulae explain the wide range of different polymerisation products sufficiently”
([19], p. 251 and cf. [15], p. 35). In other words: the “thousand to one million
atoms” that macromolecules consist of are “bonded via primary valences”
([1], p. 93; cf. p. 77). Since this was the case, the chemist had a stable building
Courageous Questioning of Established Thinking: The Life and Work of Hermann. . .
95
Heimlich [2, p. 79] summarises the situation in rather direct fashion: Staudinger
“was brutal in his destruction of the legend of small molecules and replaced it by his
convictions about giant molecules.” Heimlich [2, p. 83] says: “While molecules
with what is called a molecular weight of 300 were classified as huge [. . .] in classic
organic chemistry, Staudinger downgraded them to dwarfs in relation to the macromolecules he proposed that had molecular weights of 10,000 or more.” Looked at
from our current perspective, this was a scientific revolution and a paradigm shift,
with which Staudinger laid the foundations for plastics chemistry. Most of his
contemporaries failed to realise the significance, however: “The response to
Staudinger’s article was minimal [. . .]. At this time, Staudinger was still unable
to provide any proof of the existence of long-chain molecules” [19, p. 251]. Doubts
about the accuracy of Staudinger’s theory dominated; there was opposition primarily to his theories about the bonding forces that existed in high polymers. The
predominant view in organic chemistry at the time was that the basic molecules in
polymers did not lose their independence, i.e. they were only bonded to form a unit
by low electromagnetic attraction. In other words, the existence of high polymers
was no reason to give up the concept of low molecules and to postulate macromolecules, which many chemists claimed were nothing more than a figment of the
imagination.
Detailed information about this controversy and the people involved will be
provided later on. Before this is done, here is an outline of Staudinger’s antithesis
and the necessary preconditions. The basic rule is: electromagnetic attraction takes
place between all the atoms of a piece of material, but the degree of attraction
varies. The strongest interaction between the atoms is within the individual molecules. These inter-atomic and/or intra-molecular forces are called primary or
covalences (primary bonds). In contrast to them, weaker bonding forces known as
secondary or partial valences (secondary bonds) are responsible for inter-molecular
cohesion (cf. [15], p. 17). For his macromolecular model, Staudinger now excluded
the “assumption of secondary valences” from the outset as being “not necessary”
[20, p. 13]. This was a logical conclusion, because the claim was that a macromolecule was an independent entity of a size that had not been considered possible
before and was not just a loose collection of familiar small molecular units. With
respect to the existing bonding relationships in the macromolecule, Staudinger
therefore worked on the assumption of primary valences in the same way as with
any other molecule. Secondary valences would only be a subject requiring examination when the discussion moved on to inter-(macro)molecular attraction.
At the latest from 1920 onwards, Staudinger was certain “that standard valence
formulae explain the wide range of different polymerisation products sufficiently”
([19], p. 251 and cf. [15], p. 35). In other words: the “thousand to one million
atoms” that macromolecules consist of are “bonded via primary valences”
([1], p. 93; cf. p. 77). Since this was the case, the chemist had a stable building
Courageous Questioning of Established Thinking: The Life and Work of Hermann. . .
95