many components of molecular weight significantly higher than 30,000. The early
work was roughly correct, even though it was based on little else but elemental
analysis and gravimetry of derivatives. Since all molecules known then with
generally accepted molecular weights were volatile and, hence, small, the reports
such as those by Engelhard and Mulder did not sound credible.
When Berzelius coined the term “polymer,” he did not intend for it to mean what
we today call a polymer [43] (although it may include the results of addition
polymerization). Pierre Eugene Marcellin Berthelot narrowed the definition to
only describe the results of addition polymerization
5 [49]; he had himself isolated
the first three oligomers of 1-pentene but he did not posit the existence of truly long
chains. Probably the first to suggest that much larger molecules could exist (and
could be found in the non-distillable fractions of the condensation mixtures) was
Agostinho Vicente Lourenc ¸o, who prepared several oligomers of ethylene glycol
and ethylene succinate and conceived copolymerization [50, 51]. He was followed
in his belief in large chain molecules by a number of other chemists, e.g., Heinrich
Hlasiwetz and Josef Habermann, [52] who considered proteins to comprise
condensed molecular fragments. After 1880, several other researchers obtained
molecular weights for natural substances in excess of 10,000, such as caoutchouc
and solubilized derivatives of carbohydrates. Alfred Werner postulated in 1896 [53]
that Magnus’ green salt, Pt(NH 3 ) 4 PtCl 4 [54, 55], contained platinum chains. But
their combined opinion was not sufficient to sway the position of the scientific
community.
Instead, the theory of a colloid state of matter gained ground – this was supposed
to be a fourth state like the solid, liquid, and gaseous states. At first there was the
discovery of Thomas Graham in 1861 that albumin and other natural substances had
extremely small rates of diffusion in solution and also only very slowly permeated
semipermeable membranes; this led him to conclude that these materials must exist
in an aggregated state, as “colloids” [56]. This interpretation became stronger with
time. The connections between the molecules in the aggregate were thought to be
labile due to “partial valences” and the apparent molecular weights were, therefore,
dependent on concentration, temperature, and composition of the solutions. The
structure of the aggregated molecules was most often assumed to be cyclic,
thereby avoiding the problems that the apparently non-existing molecular termini
posed. The determination of molecular weight in solution only began to be available in the 1880s (the ground-breaking contributions of Franc ¸ois-Marie Raoult and
Jacobus Henricus van’t Hoff on vapor pressure and cryoscopy have been described
many times [1, 2]) and the colloid theory seemed to provide very plausible
explanations for the strange behavior of what we know today to be macromolecular
substances. After the creation of ideal solution theory, colloid science neatly made
it possible to explain the unorthodox results of physical-chemical measurements on
macromolecular solutions, since the unexpected behavior could be described as the
5 “La polyme ´rie est l’isome ´rie des corps forme ´s par la re ´union de plusieurs mole ´cules identiques
en une seule.”
Why Was the Macromolecular Hypothesis Such a Big Deal?
67
work was roughly correct, even though it was based on little else but elemental
analysis and gravimetry of derivatives. Since all molecules known then with
generally accepted molecular weights were volatile and, hence, small, the reports
such as those by Engelhard and Mulder did not sound credible.
When Berzelius coined the term “polymer,” he did not intend for it to mean what
we today call a polymer [43] (although it may include the results of addition
polymerization). Pierre Eugene Marcellin Berthelot narrowed the definition to
only describe the results of addition polymerization
5 [49]; he had himself isolated
the first three oligomers of 1-pentene but he did not posit the existence of truly long
chains. Probably the first to suggest that much larger molecules could exist (and
could be found in the non-distillable fractions of the condensation mixtures) was
Agostinho Vicente Lourenc ¸o, who prepared several oligomers of ethylene glycol
and ethylene succinate and conceived copolymerization [50, 51]. He was followed
in his belief in large chain molecules by a number of other chemists, e.g., Heinrich
Hlasiwetz and Josef Habermann, [52] who considered proteins to comprise
condensed molecular fragments. After 1880, several other researchers obtained
molecular weights for natural substances in excess of 10,000, such as caoutchouc
and solubilized derivatives of carbohydrates. Alfred Werner postulated in 1896 [53]
that Magnus’ green salt, Pt(NH 3 ) 4 PtCl 4 [54, 55], contained platinum chains. But
their combined opinion was not sufficient to sway the position of the scientific
community.
Instead, the theory of a colloid state of matter gained ground – this was supposed
to be a fourth state like the solid, liquid, and gaseous states. At first there was the
discovery of Thomas Graham in 1861 that albumin and other natural substances had
extremely small rates of diffusion in solution and also only very slowly permeated
semipermeable membranes; this led him to conclude that these materials must exist
in an aggregated state, as “colloids” [56]. This interpretation became stronger with
time. The connections between the molecules in the aggregate were thought to be
labile due to “partial valences” and the apparent molecular weights were, therefore,
dependent on concentration, temperature, and composition of the solutions. The
structure of the aggregated molecules was most often assumed to be cyclic,
thereby avoiding the problems that the apparently non-existing molecular termini
posed. The determination of molecular weight in solution only began to be available in the 1880s (the ground-breaking contributions of Franc ¸ois-Marie Raoult and
Jacobus Henricus van’t Hoff on vapor pressure and cryoscopy have been described
many times [1, 2]) and the colloid theory seemed to provide very plausible
explanations for the strange behavior of what we know today to be macromolecular
substances. After the creation of ideal solution theory, colloid science neatly made
it possible to explain the unorthodox results of physical-chemical measurements on
macromolecular solutions, since the unexpected behavior could be described as the
5 “La polyme ´rie est l’isome ´rie des corps forme ´s par la re ´union de plusieurs mole ´cules identiques
en une seule.”
Why Was the Macromolecular Hypothesis Such a Big Deal?
67