Thermoresponsive polymers that undergo reversible phase transition by responding to an environmental temperature change, in particular polymers showing lower critical solution temperature (LCST), are frequently used as smart materials that have found increasing applications. Recently, there has been a rapid growth in interest on LCST polymers and many new research groups are entering the field from a wide range of application areas. While it is great to see more researchers working on LCST polymers, the downside of this rapid growth is that the fundamentals of the LCST phase transition behavior are not always clearly known and respected. Hence, this focus article provides a systematic discussion of the key aspects of the LCST behavior of polymers starting from fundamentals of LCST behavior to practical determination of cloud point temperature (Tcp). Finally, we offer a basic set of recommended measuring conditions for determination of Tcp (10 mg mL−1; 0.5 °C min−1; 600 nm) to facilitate the comparison of the LCST behavior and Tcp values of polymers developed and studied in different laboratories around the globe, which is nowadays nearly impossible since various techniques and parameters are being utilized for the measurements. It should be noted that these recommended conditions serve as a robust tool for turbidimetry, which is one out of the many characterization techniques one should utilize to fully understand LCST behavior of polymers.

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Thermoresponsive polymers with lower critical solution temperature: from fundamental aspects and measuring techniques to recommended turbidimetry conditions

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. To fit functional demand, materials with desired physical, chemical, biological, biomechanical, and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

Biomedical applications of biodegradable polymers

The use of stimuli-responsive polymers in sensing technologies and for actuation has garnered tremendous interest over the past few decades. This is mainly due to the myriad responsivities that these polymers can possess, e.g., responsivity to temperature, pH, biomolecules, CO2, light, and electricity. As a result, these stimuli-responsive devices can be used to monitor human health and detect environmental analytes, for soft robotics and artificial muscles. In this review, we highlight state-of-the-art examples of the synthesis, and use of stimuli-responsive polymers in these fields that have been reported since 2016.

Stimuli-responsive polymers for sensing and actuation

https://backend.orbit.dtu.dk/ws/files/189967651/Hofmeister_JCIS.pdf

The Hofmeister series: Specific ion effects in aqueous polymer solutions

Funding Information: M.T.C. acknowledges support from the EPSRC (EP/T00813X/1). The University of Hertfordshire are thanked for funding the research project of P.H. Publisher Copyright: © 2020 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202008123

Polymers exhibiting lower critical solution temperatures as a route to thermoreversible gelators for healthcare

Poly(N-isopropylacrylamide) (PNiPAm) and poly(2-ethyl-2-oxazoline) (PEtOx) represent two polymer types that are well-known for their lower critical solution temperature (LCST) behavior in aqueous media. To synthesize triblock copolymers containing both polymers, a crossover of two different polymerization methods was applied using a bifunctional initiator for the living cationic ring-opening polymerization (CROP) of EtOx. Quantitative end-functionalization with a trithiocarbonate resulted in a bifunctional PEtOx macro chain transfer agent (CTA). A series of well-defined PNiPAm-b-PEtOx-b-PNiPAm triblock copolymers were obtained by subsequent reversible addition–fragmentation chain transfer (RAFT) polymerization of NiPAm. The influence of the PNiPAm to PEtOx ratio on the thermoresponsive properties was intensively investigated via turbidimetry, dynamic light scattering, cryo transmission electron microscopy, and 1H NMR studies, revealing hydrogen bonds between both copolymer segments that strongly lower the...

LCST Behavior of Symmetrical PNiPAm-b-PEtOx-b-PNiPAm Triblock Copolymers

In a two-step synthesis, five different alkyl-substituted morpholine-2,5-dione monomers were synthesized from the natural amino acids glycine, alanine, valine, leucine, and isoleucine. The heterocyclic compounds crystallize in a boat-like conformation and are polymerized via 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed ring-opening polymerization (ROP) in tetrahydrofuran. Well-defined polymers could be obtained from the monomers based on valine, leucine, and isoleucine at a feed ratio of M/I/TBD = 100/1/0.5. Kinetic studies of the ROP reveal that the molar masses and dispersities (Đ < 1.2) could be well controlled, as confirmed by size exclusion chromatography and 1 H NMR spectroscopy. At conversions above 50%, the polymerization rate decreases and the dispersity slightly increases, presumably due to transesterification. Matrix-assisted laser desorption time-of-flight mass spectrometry indicates the presence of polymer chains with α-end groups derived from the initiator.

Michael Dirauf

Papers

LCST Behavior of Symmetrical PNiPAm-b-PEtOx-b-PNiPAm Triblock Copolymers

TBD-Catalyzed Ring-Opening Polymerization of Alkyl-Substituted Morpholine-2,5-Dione Derivatives.

Recent advances in degradable synthetic polymers for biomedical applications – Beyond polyesters

Molecular Insights into Site-Specific Interferon-α2a Bioconjugates Originated from PEG, LPG, and PEtOx.

LCST behavior of poly(2-ethyl-2-oxazoline) containing diblock and triblock copolymers