Synthesis And Self-assembly Of Amphiphilic (Fluoro-)Siloxane Graft Copolymers

Polysiloxanes have extensive applications in the textiles and chemical industries due to their high hydrophobicity, flexibility, biocompatibility and excellent surface properties. The self-assembly of amphiphilic polysiloxanes in solution is used innumerous applications or potential applications such as the separation technology, the preparation of low surface tension materials, and controlled drug delivery and release. Despite the many applications, not much investigation has been taken on the self-assembly of amphiphilic (fluoro-)siloxanes graft copolymers in solution. Our work focuses on the synthesis and self-assembly of modified poly(dimethylsiloxane)- graft-polyether copolymers by using different side chain. And the main results were shown as follows:(1) Controlled synthesis of vinyl-terminated fluorosiloxane (V-PMTFPS).A series of vinyl-terminated fluorosiloxane macromonomers were synthesized by anionic ring-opening polymerization (ROP) of 1,3,5-trimethyl-1,3,5-tris(3',3',3'- trifluoropropyl) -cyclotrisiloxane (F3). The polymerization was carried out in tetrahydrofuran (THF) with n-butyllithium (n-BuLi) as the initiator, and then vinyl dimethylchlorosilane was introduced into the reactor by means of a syringe. The obtained macromonomers have controlled molecular weight and narrow molecular weight distribution (DPI≤1.13). The molecular structure of V-PMTFPS was also conformed by 1H NMR measurement.(2) Controlled synthesis of vinyl-terminated polystyrene (V-PS).In this paper, a two-step procedure was performed to prepare vinyl-terminated polystyrene macromonomers:①The living polystyrene (PS) were prepared by the anionic polymerization of styrene (St) in toluene using n-butyllithium (n-BuLi) as the initiator.②The of polymerization active center was transformed from carbon anion (C-) to oxygon anion (O-) by the addition of hexamethylcyclotrisiloxane (D3)/ tetrahydrofuran (THF) solution, and then vinyl dimethylchlorosilane was introduced into the reactor by means of a syringe. The obtained macromonomers have controlled molecular weight and molecular weight distribution (DPI≤1.22). The molecular structure of V-PS was also conformed by 1H-NMR measurement.(3) A series of amphiphilic (fluoro-)siloxane graft copolymers were synthesized via hydrosilylations. The conditions of hydrosilylation reactions were determined by the methods of hydrogen measurement, FTIR and 1H-NMR. Then a series of amphiphilic siloxane graft copolymers were prepared by hydrosilylation in tetrahydrofuran (THF) using Karstedt's catalyst. The side chain of amphiphilic siloxane graft copolymers were modified by V-PMTFPS (FS), perfluoroalkyl group (Rf) and V-PS, respectively. The obtained copolymers have high macromonomer conversion and the structure of graft copolymers were also conformed by 1H-NMR measurement.(4) The self-assembly of amphiphilic (fluoro-)siloxane graft copolymers in solutionThe critical micellization concentration (CMC) in solution was measured by pyrene fluorescence. The structural transitions of the self-assembled aggregates from spheres (vesicles) to big vesicles or composite vesicles were found. It was also found that the self-assembled aggregates could be triggered by a variety of parameters including copolymer concentration, copolymer compositions, solvent properties and other preparation conditions. In addition, the mechanism of morphology transition is discussed.