Preparation, Morphology And Properties Of Nanostructured Thermosets

A series of AB-type diblock copolymers and ABC triblock copolymers were synthesized via combination of reversible addition-fragmentation transfer polymerization (RAFT), atom transfer radical polymerization (ATRP), ring-opening polymerization (ROP) and click chemistry. Nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC) were employed to characterize these block copolymers. These block copolymers were incoporated into thermosetting polymers to access ordered and disordered nanostructures via self-assembly and reaction-induced micrphase separation mechanism. The morphorlogy and thermomechanical properties of the nanostructured thermosets were investigated by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared spectroscopy (FTIR). The surface properties were examined by means of surface elemental analysis, static contact angle analysis and energy dispersive X-ray spectroscopy (EDS). The main results are being summarized as below: 1. Formation of nanostructures in epoxy thermosets via self-assembly mechanismSeveral AB-type diblock copolymers such as poly(2,2,2 -trifluoroethyl acrylate)-block-poly(ethylene oxide) (PTFEA-b-PEO), poly(glycidyl methacrylate)-block-poly(2,2,2-trifluoroethyl acrylate) (PGMA-b-PTFEA) were defigned and synthesized through the approach of RAFT polymerization. These block copolymers were incoporated into epoxy resin to access the nanostructures in the thermosets via self-assembly mechanism. The nanostructured thermosets were obtained via non-reactive and/or reactive mixing of the block copolymers with the epoxy matrices. It was found that the formation of the nanostructures in thermosets can optimize the interactions between epoxy matrix and the modifiers and thus the fracture toughness of the materials were significantly improved. In addition, the enhancement in surface hydrophobicity of the thermosets was obtained with the inclusion of the amphiphilc block copolymers. The improved surface properties have been interpretated on the basis of the surface migration of the hydrophobic blocks of the copolymers.2. Effect of curing agent on nanostructured thermosets containing star miktoarm terpolymers poly(ethylene oxide)-block-poly(ε-caprolacton- -e)-block-polystyrene (star (PEO-b-PCL-b-PS)) The star miktoarm terpolymer, star (PEO-b-PCL-b-PS) was firstly synthesized by the combination of RAFT polymerization, ROP and click chemistry. The block copolymers and DGEBA were cured with 4, 4'-methylenebis (2-chloroaniline) (MOCA) or 4, 4'-diaminodiphenylsul- -fone (DDS) as curing agent, respectively. The morphology of the thermosets was examined by means of atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). It is found that different nanostructure appeared in all the samples. Spherical and lamellar structures appeared when MOCA as hadener, while vesicles were obtained when the the curing agent was DDS. The dependence of morphological structures on the types of aromatic amines for epoxy and star (PEO-b-PCL-b-PS) thermosetting blends were interpreted on the basis of the difference in hydrogen bonding interactions resulting from the structure of the curing.3. Study on the reaction-induced microphase separation in the present of self-organized nanostructurePoly(ε-caprolactone)-block-brush-poly(dimethylsiloxane)-block- polystyrene (PCL-b-brush-PDMS-b-PS) terpolymers were synthesized via sequential ATRP, Then the terpolymers was incorporated into epoxy to obtain nanostructure.The morphology of the thermosets was examined by AFM and SAXS.The results of the AFM and SAXS indicated that vesicles were formed in the thremosets.According to the miscibility between terpolymer and thermosets, it was judged that the nanostructure was obtained by the mechanism of the reaction-induced microphase separation in the present of self-organized nanostructure.4. Preparationof nanoporous materials according to the mechanism of reaction-induced microphase separation reported in thermosetsFirstly, Poly (methyl methacrylate)-block-poly (4-vinylpyridine) (PMMA-b-P4VP) block copolymer was synthesized by RAFT polymerization. Secondly, PMMA-b-P4VP was mixed with phenolic resin. It was found that nanostructure was formed via the reaction-induced microphase separation mechanism. The nanostructure thermosets were then carbonized under nitrogen atmosphere, and uniform nanoporous carbon materials were obtained. In addition, nanoporous silica material was prepared too. Firstly, poly (glycidyl methacrylate)-block-polystyrene (PGMA-b-PS) were synthesized through RAFT polymerization. Secondly, the triethoxysilane group was clicked to the PGMA segment by the reaction of PGMA-b-PS block copolymers with 3-aminopropyl-triethoxysilane. Thirdly, the improved block copolymer PGMA-b-PS, TEOS was blended and hydrolyzed under acidic conditions. After condensation, sol-gel and pyrolysised, the nanoporous silica material with uniform distribution were finally prepared. 5. Formation of hydrophobic microphase-separated morphology and study of thermo-responsive properties of PS block-containing PNIPAAm hydrogelsRAFT polymerization was employed to prepare the crosslinked poly (N-isopropylacrylamide)-graft-polystyrene copolymer networks (PNIPAAm-g-PS). Due to the immiscibility of PNIPAAm with PS, the PNIPAAm-g-PS crosslinked copolymers displayed the microphase-separated morphology. While the PNIPAAm-g-PS copolymer networks were subjected to the swelling experiments, it is found that the PS block-containing PNIPAAm hydrogels significantly exhibited faster response to the external temperature changes according to swelling, deswelling, reswelling experiments than the conventional PNIPAAm hydrogels. The improved thermo-responsive properties of hydrogels have been interpreted on the basis of the formation of the specific microphase-separated morphology in the hydrogels, i.e., the PS chains pendent from the crosslinked PNIPAAm networks were selfassembled into the highly hydrophobic nanodomains, which behave as the microporogens and thus promote the contact of PNIPAAm chains and water.