Preparation of Organic/Inorganic Hybrid Hollow Particles Based on Gelation of Polymer Vesicles

Abstract

In a previous communication, we have reported the study of novel organic/inorganic hollow particles based on a reactive amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PEO-b-PTMSPMA). The preparation of these novel particles involved the preformed vesicles of the block copolymers in a methanol/water solvent mixture, followed by a gelation process to fix the vesicular morphology. In this paper, the detailed conditions for the preparations of the hybrid vesicles, including water contents in the binary solvent, initial copolymer concentration (Cini) in methanol, compositions of the diblock copolymers, and gelation catalyst, have been explored in great detail. The results demonstrated that the robust vesicles could be prepared under a variety of conditions, such as over a broader range of the water content (from ca. 34 to 98.4 wt %) at the Cini of 5.0 mg/mL for PEO45-b-PTMSPMA59. Furthermore, exclusive vesicles were formed under the Cini ranging from 0.5 to 20 mg/mL of PEO45-b-PTMSPMA59 in methanol while the water content was kept constant at 55.8 wt %, whereas the average size of vesicles and the size distribution increased correspondingly. Before the exclusive vesicles appeared, spheres, short rods, and lamellae were observed as the coexisted morphologies when the water content increased gradually. For the block copolymers with a constant PEO length and different PTMSPMA lengths, i.e., PEO45-b-PTMSPMAx (x = 29, 42, and 180), only vesicles were produced under the conditions applied with the longer PTMSPMA blocks resulting in a thicker vesicle wall. The gelation catalyst plays a critical role in the morphological fixation. We have found that triethylamine (TEA) was the best gelation catalyst under the conditions used in this study, while the acid catalysts destroyed the vesicles. In addition, because of the inorganic components, the nanocapsule was very stable, and its morphology remained even after calcination at 450 °C.