Star‐Like Structure of Oligocarbonate‐Fluorene End‐Functionalized Poly(ethylene glycol) ABA Triblock Copolymers Below the Gel Point

Abstract

SummaryABA‐type oligocarbonate‐fluorene end‐functionalized poly(ethylene glycol) s form micelles with star‐like correlations in dilute solutions where water solvates the middle (B) poly(ethylene oxide) block. Using small‐angle neutron scattering (SANS), the star‐arm aggregation number and arm radius of gyration were characterized by Benoit's star‐polymer form factor under θ‐solvent conditions and by Alessandrini and Cargnano's renormalization group theory in good solvent. Model‐independent SANS Zimm plots provide the radius of gyration, micelle aggregation number, and second virial coefficient (A2) as a function of temperature. In comparison to unfunctionalized poly(ethylene glycol) A2 is consistent with predictions for self‐assembling polymers below the gelation point with a theta temperature of ≈ 75 °C.

Self-Assembly and Dynamics Driven by Oligocarbonate–Fluorene End-Functionalized Poly(ethylene glycol) ABA Triblock Copolymers

“…For F 2 E 445 F 2 and F 1.2 E 445 F 1.2 , the aggregation number, N agg , calculated from the extrapolated M w , corresponds well to the aggregation number of micelles and is consistent with previous estimates. 29 For F 15.3 E 445 F 15.3 and F 5.6 E 445 F 5.6 the value of N agg is too high for isolated micelles. We will show that the high N agg of F 15.3 E 445 F 15.3 and F 5.6 E 445 F 5.6 is due to kinetically frustrated clusters without clear separation into free micelles by DLS.…”

“…Filled circles (●) represent the CMC obtained from eq . Open squares (○) represent the CMC by fluorescence quenching from ref . The overlap concentration ( c *) of the unassociated PEG is shown.…”

“… a CMC obtained from eq . b CMC by pyrene fluorescence-quenching method c Berry plot from R vv (Figure S1).…”

“…This avoids confusion from prior notation of the series as ABA-F1, ABA-F2, ABA-F3, and ABA-F4. These notations are provided in Table for cross-consistency with previous work , along with polymer characteristics. These polymers, with the hydrophobic group number m = 15.3, 5.6, 2.0, and 1.2, are named as F 15.3 E 445 F 15.3 , F 5.6 E 445 F 5.6 , F 2 E 445 F 2 , and F 1.2 E 445 F 1.2 , respectively.…”

“…We provide a systematic study of model aqueous solutions of oligocarbonate-fluorene (F-TMC) end-functionalized poly­(ethylene glycol) triblock copolymer, P­(F-TMC) m –P­(EG) n –P­(F-TMC) m . In these systems, the driving force for association is due to π–π stacking interactions that induce micelle formation not formed in PEO . It is shown that the closed assembly formation common to micelles occurs in the presence of enhanced clustering driven by F-TMC.…”