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Author: Ganna Gryn'ova2
Entropy-Driven Selectivity for Chain Scission: Where Macromolecules Cleave

Abstract (Expand)

We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches … have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high‐temperature (HT) NMR spectroscopy of self‐assembled supramolecular diblock systems as well as temperature‐dependent size‐exclusion chromatography (TD SEC) of covalently bonded Diels–Alder step‐growth polymers.

Authors: Kai Pahnke, Josef Brandt, Ganna Gryn'ova, Ching Y. Lin, Ozcan Altintas, Friedrich G. Schmidt, Albena Lederer, Michelle L. Coote, Christopher Barner-Kowollik

Date Published: 22nd Jan 2016

Publication Type: Journal

Entropy-Driven Chain Effects on Ligation Chemistry

Abstract (Expand)

We report the investigation of fundamental entropic chain effects that enable the tuning of modular ligation chemistry – for example dynamic Diels–Alder (DA) reactions in materials applications – not … only classically via the chemistry of the applied reaction sites, but also via the physical and steric properties of the molecules that are being joined. Having a substantial impact on the reaction equilibrium of the reversible ligation chemistry, these effects are important when transferring reactions from small molecule studies to larger or other entropically very dissimilar systems. The effects on the DA equilibrium and thus the temperature dependent degree of debonding (%debond) of different cyclopentadienyl (di-)functional poly(meth-)acrylate backbones (poly(methyl methacrylate), poly(iso-butyl methacrylate), poly(tert-butyl methacrylate), poly(iso-butyl acrylate), poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl acrylate) and poly(isobornyl acrylate)), linked via a difunctional cyanodithioester (CDTE) were examined via high temperature (HT) NMR spectroscopy as well as temperature dependent (TD) SEC measurements. A significant impact of not only chain mass and length with a difference in the degree of debonding of up to 30% for different lengths of macromonomers of the same polymer type but – remarkably – as well the chain stiffness with a difference in bonding degrees of nearly 20% for isomeric poly(butyl acrylates) is found. The results were predicted, reproduced and interpreted via quantum chemical calculations, leading to a better understanding of the underlying entropic principles.

Authors: Kai Pahnke, Josef Brandt, Ganna Gryn'ova, Peter Lindner, Ralf Schweins, Friedrich Georg Schmidt, Albena Lederer, Michelle L. Coote, Christopher Barner-Kowollik

Date Published: 2015

Publication Type: Journal

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