Micelle Formation and Gelation of (PEG−P(MA-POSS)) Amphiphilic Block Copolymers via Associative Hydrophobic Effects

Abstract

A series of well-defined amphiphilic di- and triblock copolymers have been synthesized, using atom transfer radical polymerization, with poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomeric silsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks, respectively. The detailed self-assembly behavior of the amphiphilic macromolecules in aqueous media was studied using both static and dynamic light scattering (SLS and DLS) techniques. The evolution of block copolymer micelle formation in THF/water mixture (20/80 v/v) was monitored as the THF evaporated from the solvent mixture. Initially the block copolymer chains existed as unimers in solution, followed by the formation of smaller aggregates (R(h) < 2 nm) after 30 min, eventually growing in size to reach an equilibrium size when all the THF evaporated within 24 h. The micelles formed by the block copolymers were found to be kinetically unstable (not frozen); i.e., they tended to revert to individual copolymer chains on dilution. The hydrodynamic radii, R(h), of the micelles varied with the degree of polymerization (DP) of the hydrophobic P(MA-POSS); for example, for PEG(5K)-b-P(MA-POSS), an increase from R(h) approximately 13.3 +/- 1.1 nm to R(h) approximately 17.5 +/- 1.4 nm was observed with a nominal change in the DP of P(MA-POSS) from 4 to 6. The micelles formed by the triblock copolymers (P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)) were comparable in size to the diblock copolymer micelles; e.g., R(h) approximately 14.0 +/- 1.3 nm was found for P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4). The micellar structures created by the triblocks in aqueous media were "flowerlike", where the PEG middle block adopted a loop conformation in the micelle corona. In addition to micelles, larger aggregates formed by P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS) were also detected in solution. The larger aggregates may suggest a contribution from some PEG blocks adopting an extended conformation with one end dangling in solution, causing gelation at higher copolymer concentrations via intermicellar interactions. The P(MA-POSS)(4)-b-PEG(10K)-b- P(MA-POSS)(4) formed a gel in water at approximately 8.8 wt % copolymer concentration. No gel formation by diblock copolymers was observed; however, the addition of a small amount of triblock copolymer to an aqueous solution of diblock copolymer results in gel formation. Finally, rheological behavior of the obtained gels was also investigated.

Synthesis and assembly of polyhedral oligomeric silsesquioxane end-capped amphiphilic polymer to enhance the fluorescent intensity of tetraphenylethene

“…As shown in Fig. 3a polymer, which is consistent with the results reported by Zhang and He et al [45,46].…”

Synthesis and Self‐Assembly Behavior of Organic–Inorganic Poly(ethylene oxide)‐block‐Poly(MA POSS)‐block‐Poly(N‐isopropylacrylamide) Triblock Copolymers

“…From the 1 H NMR spectrum, the ratios of integration intensity of phenyl to 3-methacryloxypropyl protons can be calculated and were in good agreement with values calculated according to the formula of the MA-POSS macromers. 29 Si and 1 H NMR spectroscopy indicates that the MA-POSS macromer was successfully obtained. diblock copolymer was subjected to gel permeation chromatography (GPC) to measure the molecular weight and the GPC curve is shown in Figure 4 .…”

“…Nuclear Magnetic Resonance Spectroscopy (NMR) 1 H NMR spectroscopy was performed on a Varian Mercury Plus 400 MHz NMR spectrometer at 25 ° C and 29 Si NMR spectroscopy was conducted on a Bruker Avance III 400 MHz NMR spectrometer. In all cases, deuterium chloroform (CDCl 3 ) and tetramethylsilane (TMS) were used as the solvent and the internal reference, respectively.…”

“…The 1 H NMR spectroscopy indicates that the product resulting from the ATRP of MA-POSS with PEO-OOCH(CH 3 )Cl as the macromolecular initiator combined the structural features from the method reported by Ohno et al [ 39 ] Thereafter, the "corner-capping" reaction between Na 3 O 12 Si 7 (C 6 H 5 ) 7 and 3-methacryloxypropyltrichlorosilane was carried out to afford MA-POSS. Shown in Figure 1 is the 29 Si NMR spectrum of the product. The resonances at −64.6, −77.7 and −78.0 ppm are assignable to the silicon nucleus, as indicated in this figure.…”

Rapid and reversible morphology control in thin films of poly(ethylene oxide)-block-POSS-containing poly(methacrylate)

“…This control is enabled by the distinctive properties of PEO-b-PMAPOSS (PEO-b-PMAPOSS). 34,35 Each PS and PMMA, as a hydrocarbon polymer segment in POSS-containing BCPs, exists in the amorphous state over a wide range of temperatures during thermal annealing. In contrast, crystalline PEO usually melts at relatively low temperatures o60 1C.…”