End-group functionalization of poly(2-oxazoline)s using methyl bromoacetate as initiator followed by direct amidation

• Published in: European polymer journal Vol. 120; p. 109273
• Main Authors: Podevyn, Annelore, Arys, Koen, de la Rosa, Victor R., Glassner, Mathias, Hoogenboom, Richard
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-11-2019; Elsevier BV
• Subjects: Acetonitrile; Amidation; Amines; Aromatic compounds; Cationic polymerization; Chemicals; Copolymers; End-group functionalization; Hydrogen bonding; Hydroxyl groups; Initiation (polymerization); Kinetics; Methyl bromoacetate; Organic chemistry; Poly(2-oxazoline)s; Polymerization; Polymers; Polyoxazolines; Reagents; Ring opening polymerization; Studies; Temperature; Transition temperature; Kinetics; End-group functionalization; Methyl bromoacetate; Amidation; Poly(2-oxazoline)s
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2019.109273

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•MeBrAc as functional initiator to prepare well-defined methyl ester end-functionalized poly(2-oxazoline)s.•Easy access to a broad range of end-group functionalized poly(2-oxazline)s by amidation.•PAOx side chain and chain length hardly influences rate of end-group modification.•Profound impact of end-group functionality on thermoresponsive properties.
Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are an alluring class of polymers for many applications due to the broad chemical diversity that is accessible for these polymers by simply changing the initiator, terminating agent and the monomer(s) used in their synthesis. Additional functionalities (that are not compatible with the cationic ring-opening polymerization) can be introduced to the polymers via orthogonal post-polymerization modifications. In this work, we expand this chemical diversity and demonstrate an easy and straightforward way to introduce a wide variety of functional end-groups to the PAOx, by making use of methyl bromoacetate (MeBrAc) as a functional initiator. A kinetic study for the polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile (CH3CN) at 140 °C revealed relatively slow initiation and slower polymerization than the commonly used initiator, methyl tosylate (MeOTs). Nonetheless, well-defined polymers could be obtained with MeBrAc as initiator, yielding polymers with near-quantitative methyl ester end-group functionality. Next, the post-polymerization modification of the methyl ester end-group with different amines was explored by introducing a range of functionalities, i.e. hydroxyl, amino, allyl and propargyl end-groups. The lower critical solution temperature (LCST) behavior of the resulting poly(2-ethyl-2-oxazoline)s was found to vary substantially in function of the end-group introduced, whereby the hydroxyl group resulted in a large reduction of the cloud point transition temperature of poly(2-ethyl-2-oxazoline), ascribed to hydrogen bonding with the polymer amide groups. In conclusion, this paper describes an easy and fast modular approach for the preparation of end-group functionalized PAOx.