Josefine Eilsø Nielsen - Department of Chemistry, University of Oslo, P.O. Box ۱۰۳۳, Blindern, N-۰۳۱۵ Oslo,Norway
Kaizheng Zhu - Department of Chemistry, University of Oslo, P.O. Box ۱۰۳۳, Blindern, N-۰۳۱۵ Oslo,Norway
Sverre Arne Sande - School of Pharmacy, Department of Pharmaceutics, University of Oslo, P.O. Box ۱۰۶۸,Blindern, N-۰۳۱۶ Oslo, Norway
Lubomír Kováčik - Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Albertov ۴, Prague, ۱۲۸ ۰۱, Czech Republic

This Thermoresponsive amphiphilic biodegradable block copolymers of the type poly(-caprolactone-co-lactide)-poly(ethylene glycol)-poly(-caprolactone-co-lactide) (PCLA-PEGn-PCLA) have great potential for various biomedical applications. In the present study, we have surveyed the effects of PEG-spacer length (n=1000 and 1500), temperature, and polymer concentration on the self-assembling process to form supramolecular structures in aqueous solutions of the PCLA-PEGn-PCLA copolymer. This copolymer has a lower critical solution temperature, and the cloud point depends on both concentration and PEG-length. Thermoreversible hydrogels are formed in the semidilute regime; the gel windows in the phase diagrams can be tuned by concentration and length of the PEG-spacer. The rheological properties of both dilute and semidilute samples were characterized; 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

Copolymer, self-assembling, structure, temperature responsive