Blends of oppositely charged PEG-PPG-PEG copolymers displaying improved physical thermogelling properties

Oppositely charged F127 copolymers with a substitution ratio >95% were synthesized by end group modification. Single succinic anhydride end-capped F127 (F127-SA) or triple (F127-Tris- SA) carboxylic acid groups were introduced to the distal ends via esterification. F127 was also end-capped with two types of amines, triethylenetetramine (F127-TETA) and ethylene diamine (F127-EDA). Oppositely charged copolymers were solution-blended to produce co-micellized nanostructures at the optimized blend compositions, as determined by j-potential measurement and the composition dependence of the sol-gel phase-transition temperature. F127 exhibited the approximate storage modulus of 40 000 Pa, while the 1:1w/w F127-SA/ F127-TETA and 1:3 w/w F127-Tris-SA/F127-EDA blend displayed a modulus of 90 000 and 170 000 Pa, respectively. Hydrogels from negatively charged F127-SA or positively charged F127-TETA homopolymer showed the lower storage modulus. The rheological properties of the thermogelling polymers were enhanced by simple modification of the distal ends of F127 copolymers as well as by the additional ionic interactions between oppositely charged micelles.