Structural and rheological properties of temperature-responsive amphiphilic triblock copolymers in aqueous media

Nielsen, J.E. , Zhu, K.Z. , Sande, S.A. , Kovacik, L. , Cmarko, D. , Knudsen, K.D. , Nystrøm, B.
Journal of physical chemistry B, Vol 121, no. 18 (May 11, 2017), 4885-4899 Volume: 121 Issue: 18 Pages: 4885-4899
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ThetmoresponSive amphiphilic biodegradable block copolymets of the type poly(e-caprolatone-co-lactide)-poly(ethylene glycolYpoly(epsilon-caprolacton4-1-. co-lacfide) (PCLA-PEG(m)-PCLA) have great potential for kivarious biomedical appliqations. In the present study, we have surveyed the-effects of PEG spacer length (m = 1000 and 1500), temperature, and polymer concentration on the self-assembling process to form supramolecular structures in aqueous solutions of the PCIA-PEG(m)-PCLA copolymer. This copolymer has a lower critical solution, temperature, and the cloud point depends on both coricenttation and PEG length Therinoteversible hyclrogels are formed in the semidilute regime; the gel window's the phase diagrams can be tuned by the concentration and length of the PEG spacer. The rheological properties of both dilute and serrridllute samples were chatatterized; especially the sol-to-gel transition was examined. Small-angle neutron scattering (SANS) experiments reveal fundamental structural differences between the two copolymers for both dilute and semidilute samples. The intensity profiles for the copolymer with the long PEG spacer could be described by a spherical., core shell model over a broad temperature. domain, whereas the copolymer with the short hydrophilic spacer forms, rod-like species over an extended temperature range. This finding is supported by cryo-TEM images. At temperatures approaching macroscopic phase separation, both copolymers seem to assume extended rod-like structures.
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