Visualization and design of the functional group distribution during statistical copolymerization

Paul H. M. Van Steenberge,Richard Hoogenboom,Julio C. Hernández-Ortiz,Marie-Françoise Reyniers,Bart Verbraeken,Ondrej Sedlacek,Dagmar R. D’hooge

doi:10.1038/s41467-019-11368-6

Paul H. M. Van Steenberge, Richard Hoogenboom + Show 5 more

Open Access

https://doi.org/10.1038/s41467-019-11368-6

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Journal: Nature Communications	Publication Date: Aug 13, 2019
Citations: 48	License type: open-access

Affiliation: Ghent University

Abstract

Even though functional copolymers with a low percentage of functional comonomer units (up to 20 mol%) are widely used, for instance for the development of polymer therapeutics and hydrogels, insights in the functional group distribution over the actual chains are lacking and the average composition is conventionally used to describe the functionalization degree. Here we report the visualization of the monomer distribution over the different polymer chains by a synergetic combination of experimental and theoretical analysis aiming at the construction of functionality-chain length distributions (FUNC-CLDs). A successful design of the chemical structure of the comonomer pair, the initial functional comonomer amount (13 mol%), and the temperature (100 °C) is performed to tune the FUNC-CLD of copoly(2-oxazoline)s toward high functionalization degree for both low (100) and high (400) target degrees of polymerization. The proposed research strategy is generic and extendable to a broad range of copolymerization chemistries, including reversible deactivation radical polymerization.

Highlights

Even though functional copolymers with a low percentage of functional comonomer units are widely used, for instance for the development of polymer therapeutics and hydrogels, insights in the functional group distribution over the actual chains are lacking and the average composition is conventionally used to describe the functionalization degree
Chain initiation is realized by a nucleophilic attack of the nitrogen of a cyclic imino ether (2-oxazoline) monomer (M) to an electrophilic center of for instance an alkylating reagent (I; initiator) such as methyl tosylate, creating a low molar mass oxazolinium species (P1)
We show that inherent limitations exist due to the stochastic nature of chain-growth polymerization and that redesigning of the reaction conditions and the chemical structure of the comonomers allows the synthesis of highly functional PAOx chains

Summary

Introduction

Even though functional copolymers with a low percentage of functional comonomer units (up to 20 mol%) are widely used, for instance for the development of polymer therapeutics and hydrogels, insights in the functional group distribution over the actual chains are lacking and the average composition is conventionally used to describe the functionalization degree. Chain initiation is realized by a nucleophilic attack of the nitrogen of a cyclic imino ether (2-oxazoline) monomer (M) to an electrophilic center of for instance an alkylating reagent (I; initiator) such as methyl tosylate, creating a low molar mass oxazolinium species (P1) This cationic species exhibits a new electrophilic center on the 5-position, enabling the nucleophilic attack of monomer, inducing the isomerization of the existing oxazolinium from a cyclic imino ether to an amide. This results in the formation of a macro-oxazolinium species (Pi; i: chain length), being reactive for further nucleophilic attack and polymerization. Upon macropropagation (kpm) a living macrospecies is formed with a cationic centre in the middle of the chain, a so-called mid-chain cationic macrospecies, which upon further monomer addition leads to branch formation

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