Synthesis and Characterization of a Thermoresponsive Copolymer with an LCST-UCST-like Behavior and Exhibiting Crystallization

Natalie Solfrid Gjerde; Alessandra Del Giudice; Kaizheng Zhu; Kenneth D Knudsen; Luciano Galantini; Karin Schillén; Bo Nyström

doi:10.1021/acsomega.3c03162

Synthesis and Characterization of a Thermoresponsive Copolymer with an LCST-UCST-like Behavior and Exhibiting Crystallization

ACS Omega. 2023 Aug 17;8(34):31145-31154. doi: 10.1021/acsomega.3c03162. eCollection 2023 Aug 29.

Authors

Natalie Solfrid Gjerde¹, Alessandra Del Giudice¹, Kaizheng Zhu², Kenneth D Knudsen³, Luciano Galantini¹, Karin Schillén⁴, Bo Nyström⁵

Affiliations

¹ Department of Chemistry, "Sapienza" University of Rome, P.O. Box 34-Roma 62, Piazzale A. Moro 5, I-00185 Roma, Italy.
² Faculty of Engineering, Østfold University College, P.O. Box 700, 1757 Halden, Norway.
³ Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller, Norway.
⁴ Division of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
⁵ Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway.

Abstract

In this work, the diblock copolymer methoxy-poly(ethylene glycol)-block-poly(ε-caprolactone) (MPEG-b-PCL) was synthesized with a block composition that allows this polymer in aqueous media to possess both an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST) over a limited temperature interval. The value of the UCST, associated with crystallization of the PCL-block, depended on heating (H) or cooling (C) of the sample and was found to be CP_UCST^H = 32 °C and CP_UCST^C = 23 °C, respectively. The LCST was not affected by the heating or cooling scans; assumed a value of 52 °C (CP_LCST^H = CP_LCST^C). At intermediate temperatures (e.g., 45 °C), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM) showed that the solution consisted of a large population of spherical core-shell particles and some self-assembled rodlike objects. At low temperatures (below 32 °C), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) in combination with SAXS disclosed the formation of crystals with a cylindrical core-shell structure. Cryo-TEM supported a thread-like appearance of the self-assembled polymer chains. At temperatures above 52 °C, incipient phase separation took place and large aggregation complexes of amorphous morphology were formed. This work provides insight into the intricate interplay between UCST and LCST and the type of structures formed at these conditions in aqueous solutions of MPEG-b-PCL diblock copolymers.