Determination of the molecular weight between cross-links for different ambers: Viscoelastic measurements of the rubbery plateau

While much is known about the chemistry of amber, there are, to our knowledge, no quantitative estimates of the molecular weight between cross-links or quantitative estimates of the amount of cross-linking. In the present study we provide new data that advances our understanding of ancient ambers through an investigation of the network structure based on measurements of the rubbery modulus. Then, using rubber elasticity theory, we provide semiquantitative insights into the network structure. The work provides direct mechanical evidence of the chemically cross-linked structure of a Burmese amber, a Dominican amber, a Fushun amber, and two Baltic ambers by quantifying the molecular weight between cross-links Mc. The values of Mc of the studied ambers ranges from 1800 to 3000 g/mol, and the number of monomers between two cross-link junctions is estimated to be between 6 and 10.

Automated summary

While much is known about the chemistry of amber, there lacks quantitative estimates of molecular weight and amount of cross-linking. This study investigates the network structure of ancient ambers through measurements of rubbery modulus and provides semi-quantitative insights using rubber elasticity theory. The research offers mechanical evidence of chemically cross-linked structures in multiple types of ambers, with molecular weight between cross-links ranging from 1800 to 3000 g/mol and an estimated number of monomers between cross-link junctions between 6 and 10.