Preparation Of Poly(Ionic Liquid) Brushes With Reversible Wettability Via Reverse Surface-Initiated Radical Polymerization

Wettability is an important property for solid surfaces. In the recent years, super-hydrophobic surfaces have been investigated extensively, especially, smart surfaces with reversible wettability which were achieved under the stimulus of external environment (such as light, electric field, thermal and chemical) have attracted mor attention for their many potential applications. The control of surface wettability can be achieved in two ways: One is to construct appropriate surface microstructure, and the other is to obtain desired surface free energy. Through a stimulation of external environment to change the surface chemical composition and the surface free energy, surface wettability of the materials is expected to tunned reversibly. There are a variety of methods to control the free energy of solid surfaces, among which grafting the polymer brushes onto the surface of substrates by "Grafting from" technique is very effective method. At present there have been a large number of polymerization reactions can be applied to "Grafting from" technique. Reverse atom transfer radical polymerization(RATRP) has been studied more and more widely in preparation of polymers for it can acquire desired polymer structure, anticipated molecular weight and narrow molecular weight distribution.At the same time, because of structural tunability of room temperature ionic liquids they have become preferred surface modification materials for surface wettability control.Thesis includes three parts as follows:(1) Three double bond functional ionic liquid monomers including allyl pyridine hexafluorophosphate(ALPY-PF₆), (4-vinyl)-benzyl pyridine hexafluophosphate (VBPy-PF₆) and 1 - benzyl-1'- [4 -(vinyl)- benzyl]- 4,4' - bipyridine hexafluophosphate (BVBBP-PF₆ ) have been successfully synthesized through a two-step procedure their structures were confirmed by 1HNMR spectra.(2) The surface initiator monolayer of 2-bromo-2-methyl-N-(3-(triethoxysilyl) propyl propanamide (BTPAm) was successfully immobilized onto the pretreated silicon wafer surface by a self-assembly process, which ensures smooth finishing of subsequent RATRP.(3) Well-defined polymer brushes were successfully grafted onto the silicon surface by using reverse atom transfer radical polymerization (RATRP) under different polymerization temperature respectively with ALPY-PF₆, VBPy-PF₆ and BVBBP-PF₆ as the monomers, CuC_l2 as the catalyst, 2,2′-bipyridine as the ligand, 2-bromo-2-methyl-N-(3-(triethoxysilyl)propyl propanamide)(BTPAm) as the surface initiator, AIBN as the radical initiator and cyclohexanone as the solvent. Reversible switching between hydrophilicity and hydrophobicity can be easily achieved by exchanging their counteranions. Dynamic studies proved that polymer brush growth from the surfaces is a controlled process with a"living"characteristic.