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Complex Temperature and Concentration Dependent Self-Assembly of Poly(2-oxazoline) Block Copolymers

Authors
  • Trinh Che, Loan
  • Hiorth, Marianne
  • Hoogenboom, Richard1
  • Kjøniksen, Anna-Lena2
  • 1 Supramolecular Chemistry Group, Centre of Macromolecular Chemistry (CMaC), Department of Organic and Macromolecular Chemistry, Ghent University, Krijgslaan 281 S4, B-9000 Ghent, Belgium
  • 2 Faculty of Engineering, Østfold University College, P.O. Box 700, 1757 Halden, Norway
Type
Published Article
Journal
Polymers
Publisher
MDPI AG
Publication Date
Jul 04, 2020
Volume
12
Issue
7
Identifiers
DOI: 10.3390/polym12071495
PMID: 32635506
PMCID: PMC7407653
Source
PubMed Central
Keywords
License
Green

Abstract

The effect of polymer concentration on the temperature-induced self-association of a block copolymer comprising a poly(2-ethyl-2-oxazoline) block and a random copolymer block consisting of 2-ethyl-2-oxazoline and 2- n -propyl-2-oxazoline (PEtO80- block -P(EtOxx- stat -PropO40-x) with x = 0, 4, or 8 were investigated by dynamic light scattering (DLS) and transmittance measurements (turbidimetry). The polymers reveal a complex aggregation behavior with up to three relaxation modes in the DLS data and with a transmittance that first goes through a minimum before it declines at high temperatures. At low temperatures, unassociated polymer chains were found to co-exist with larger aggregates. As the temperature is increased, enhanced association and contraction of the aggregates results in a drop of the transmittance values. The aggregates fragment into smaller micellar-like clusters when the temperature is raised further, causing the samples to become optically clear again. At high temperatures, the polymers aggregate into large compact clusters, and the samples become turbid. Interestingly, very large aggregates were observed at low temperatures when the polymer concentrations were low. The formation of these aggregates was also promoted by a more hydrophilic copolymer structure. The formation of large aggregates with an open structure at conditions where the solvent conditions are improved is probably caused by depletion flocculation of the smaller aggregates.

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