A Study on the Interfacial Compatibility, Microstructure and Physico-Chemical Properties of Polyimide/Organically Modified Silica Nanocomposite Membrane

Polyimide-silica (PI-Silica) composites are of tremendous research interest as high-performance materials because of their excellent thermal and mechanical properties and chemical resistance to organic solvents. Particularly, the sol-gel method of fabricating such composites is popular for manipulating their properties. In this work, PI-silica composite films are synthesized by the sol-gel method and thermal imidization from the solution mixtures of hydrolyzed tetraethoxysilane (TEOS) (or glycidoxypropyltrimethoxysilane (GPMS)) modified silica and an aromatic polyamic acid (PAA) based on 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA)-p-phenylenediamine (PDA). The phase morphology of composites is found to be controlled by the substitution of TEOS with GPMS. Solid-state NMR spectroscopy is used to confirm the structural components of silica and GPMS-modified silica, whereas FT-IR results confirm the complete imidization of polyimide and composite film and suggest successful incorporation of Si-O-Si bonds into polyimide. The thermal, optical transmittance, and dielectric constant characterizations of pure polyimide and composite films are also carried out. Thermal stability of pure polyimide is found to be increased significantly by the addition of silica, whereas the partial substitution of TEOS with GPMS decreases the thermal stability of the composite, due to the presence of the alkyl organic segment of GPMS. The optical transmittance and dielectric constant of the composite films are controlled by manipulating the GPMS content.

Structure-Property Relationships of Soluble Poly(ester-urea)s containing Naphthyl Groups

The preparation of new types of polyureas with good thermal properties and improved solubility was investigated. Two new bulky diamines as new monomers for the preparation of polyurea were synthesized via two steps. First, a nucleophilic reaction of 1-naphthol and 2-naphthol with 3,5-dinitrobenzoyl chloride and then the reduction of the nitro groups by hydrazine hydrate/Pd-C to produce the corresponding diamines (1NA and 2NA). The poly(ester-urea)s were synthesized through the polyaddition reaction of the diamines with various commercially available diisocyanates. The polymers were characterized using IR and 1H NMR spectroscopy, elemental analysis, viscometry, thermal analysis, gel permeation chromatography (GPC), and X-ray diffraction. The copolymers were amorphous and readily soluble in a wide range of organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethyl sulfoxide, N, N-dimethylformamide, and m-cresol. Thermal analysis showed a glass transition temperature between 146 and 178 °C. Their decomposition temperatures were more than 180 °C, and their 10% weight losses were in the range 281—315 ° C in air. The weight average molecular weights ( Mw) of the polymers were about 32 200—40 500 g/mol.

Silica core-polystyrene shell nanoparticle synthesis and assembly in three dimensions

Monodisperse silica nanoparticles (SiNPs) grafted with well-defined and highly dense polystyrene brushes are used as building blocks for the formation of three-dimensional (3D) colloidal crystals. By adjusting the refractive indices and the density of the hybrid particles with those of mixed solvents, iridescent microcrystals were formed throughout the entire suspension which were characterised by confocal laser microscopy. These core-shell hybrid particles are not charged and the driving force of the crystallization relies on repulsive forces between the polymer brushes with high grafting density. The interparticle distance is correlated to Bragg's Law and can be controlled by manipulating the grafting density and the length of the polymer brushes. Finally, the uniformity of these unique core-shell particles was exploited to generate 3D assemblies by a rapid and simple process based on centrifugation.

Well-defined colloidal crystal films from the 2D self-assembly of core–shell semi-soft nanoparticles

Silica core–polymer shell particles are obtained from surface mediated RAFT polymerisation and assembled into ordered 2D colloidal crystals.