The Influence Of Topological Structure On Nano-Scale Morphological Structures In The Thermosetting Blends Containing Block Copolymer And Study Correlative Properties

The study on the relation between the property and structure is an important topic in the thermosetting blends because of the relation between the structure and property of polymer. de Gennes ever proposed that ordered nanostructures of thermosets can be formed via locking-in preformed ordered mesoscopic structures of thermosets precursors via polymerization (i.e., crosslinking), consequently, the property of thermosets can be improved . The application of block copolymers in thermosets provides a convenient way for obtaining disordered and/or ordered nanostructures. It is recognized that the formation of nanostructures can be carried out via self-assembly or reaction-induced microphase separation mechanisms of amphiphilic block copolymers in thermosets.In the protocol of self-assembly, precursors of thermosets act as selective solvents of block copolymers and some self-assembly morphology, such as lamellar, bicontinuous, cylindrical, and spherical structures, are formed in the mixtures depending on blend composition before curing reaction. The micelle structures can be fixed with adding hardeners hardeners and subsequent curing. In other words, the role of curing reaction is to lock in the morphologies that are already present. From the point of view of the miscibility, one subchain of the block copolymer is miscible with thermosets while the others are not miscible with the matrix before and after curing reaction. For the formation of nanostructures via reaction-induced microphase separation mechanism, it is required that all the subchains of the block copolymer are miscible with precursors of thermosets before curing whereas only a part of subchains were phase-separated from the matrix of thermosets after curing. In other words, the nanostructures are formed by controlling the microphase separation of a part of subchains of block copolymers whereas the other subchains still remain miscible with the crosslinked thermosets. According to the structures of the thermosets ,miscibility between block copolymer and thermosets and the factor in influencing the nano-scale morphological structure, a series of AB, ABC and ABCBA type block copolymers were synthesized. And disordered and/or ordered nanostructured thermosets were obtained by the mixtures of block copolymer and thermosets, the mechanical properties of nanostructured thermosets were also investigated. The main researches are as follows:1. The effect of topological and sequential structures of block copolymer on the morphological structures and intermolecular interaction in polymer blendsWe design to synthesize three block copolymers with different topological structures (linear versus star-shaped) and sequent structures of blocks Linear poly(methylmethacrylate)-block-polystyrene (l-PMMA-b-PS) and tetra-armed PMMA-b-PS diblock copolymers with PMMA (and/or PS) subchains connected core molecules were synthesized via sequential atomic transfer radical polymerization (ATRP). Three block copolymers were further mixed with epoxy resin to prepare nanostructured epoxy thermosets. The purpose of the research is to investigate the effect of topological and sequential structures of block copolymer on the morphological structure and intermolecular interaction in polymer blends. By means of atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), the morphology of the thermosets was examined. It is found that the nanostructures were formed in the thermosets containing l-PMMA-b-PS and s-PS-b-PMMA block copolymers. It is noted that the long-range order of the nanostructures in the epoxy thermosets containing l-PMMA-b-PS is obviously higher than that in the system containing s-PS-b-PMMA. However, the macroscopic phase separation occurred in the thermosetting blends of epoxy resin with s-PMMA-b-PS block copolymer. The morphological difference is ascribed to the effect of topological structures on the intermolecular interaction and reaction induced microphase separation. In order to exclude the some kinetic factors(curing reaction) in interpreting the morphological differentce, in others words, for the purpose of testifying the effect of topological structure on the intermolecular interaction in polymer blends, the thermoplastic PVDF/PMMA blends were prepared to explore the topological structure of PMMA macromolecular chains on the intermolecular interaction between PVDF and PMMA. The results showed that the topological structure of PMMA macromolecular chains can enhance the intermolecular interaction between PVDF and PMMA.2. Study on the self-assembly behavior of poly(dimethylsiloxane)-b-poly(ε-caprolactone) in the epoxy resinTwo diblock copolymers PDMS-b-PCL with different molecular weight were synthesized via the ring-opening polymerization ofε-caprolactone, and were incorporated into epoxy resin. The purpose is to investigate the effect of the molecular weight of PDMS-b-PCL on the self-assembly nanostructures in the thermosets. The AFM and SAXS results showed that self-assembly nanostructures in the thermosets were affected by the molecular weight of PDMS-b-PCL. DSC results illustrated that the difference in the morphological structures in thermosets was ascribed to the difference in the in hydrogen bonding interactions resulting from the difference in the molecular weight of PCL subchain.3. The effect of the constitute of ABC type triblock copolymer on the nanostructures in the epoxy thermosetsFirst, the triblock copolymer poly(dimethylsiloxane)-b-poly(ε-caprolactone)-b-polystyrene (PDMS-b-PCL-b-PS)was synthesized via the ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The PDMS-b-PCL-b-PS was incorporated into epoxy thermosets to access the nanostructures in the thermosets. The purpose of the research is to explore the restriction of self-assembly nanostructures of PDMS subchain on the reaction induced microphase separation of PS subchain. By means of atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), the morphology of the thermosets was examined. It is found that the ordered"flower"-like and lamellar nanostructures were formed in the thermosets containing PDMS-b-PCL-b-PS triblock copolymers. The DSC and FTIR results showed that the ordered"flower"-like and lamellar nanostructures were obtained based on the restriction of self-assembly nanostructures of PDMS subchain on the reaction induced microphase separation of PS subchain. Second, the triblock copolymer polystyrene-b-poly(ε-caprolactone)-b-poly(n-butyl acrylate) (PS-b-PCL-b-PBA)was synthesized via the ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP) and Click Chemistry. The PS-b-PCL-b-PBA was incorporated into epoxy thermosets for the preparation of the nanostructures in the thermosets. The AFM and SAXS results showed that the ordered lamellar nanostructures were accesssed in the thermosets containing PS-b-PCL-b-PBA triblock copolymers. The DSC and FTIR results illustrated that the mutual restriction of PS and PBA subchains should take the responsibility for the formation of the ordered lamellar nanostructures in the thermosets.4. Reaction-induced microphase separation in the thermosets containing poly(ethylene oxide)-b- poly(ε-caprolactone)-b-polystyrene triblock copolymer: the effect of curing agent on the nanostructures of thermosetsThe poly(ethylene oxide)-b-poly(ε-caprolactone)-b-polystyrene triblock copolymer (PEO-b-PCL-b-PS)was synthesized via the ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The sythesised product was further used to prepared nanostructred epoxy thermosets. The results showed different epoxy resin with different structures can be obtained depending on the kinds of hardners. For 4, 4'-methylenebis (2-chloroaniline) (MOCA)-crosslinked thermosetting system, ordered lamellar nanostructures were obtained. Nonetheless, the macrophase separation occurred in the thermosets when the blends were cured with 4, 4'-diaminodiphenylsulfone (DDS). The dependence of morphological structures on the types of aromatic amines for epoxy and 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 agents.5. Nano-effect of toughening and strengthening in the epoxy thermosets containing polystyrene-b-poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b-poly(ε-caprolactone)-b-polys-tyrene: the effect of nanostructures on the mechanical propertiesThe polystyrene-b-poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b-poly(ε-caprolactone)-b- polystyrene (PS-b-PCL-b-PDMS-b-PCL-b-PS) was synthesized via the ring-opening polymerization (ROP)and atom transfer radical polymerization (ATRP). The PS-b-PCL-b-PDMS-b-PCL-b-PS was incorporated into epoxy thermosets to access the nanostructures in the thermosets, and the mechanical properties of the blends were measured by the notched three-point test. The AFM and SAXS results showed that the spherical and/or worm-like nanostructures were obtained in the thermosets. And the results of the notched three-point bending test showed that the thermosets were toughened and strengthened because of nanostructes. For the epoxy thermoset containing 10 wt% PS-b-PCL-b-PDMS-b-PCL-b-PS, the KIC value is enhanced up to 5.71 MN/m3/2, which is 3.2 as that of the control epoxy thermoset. At the same time, the value of bending modulus is enhanced up to 3.12GPa, which is 1.13 as that of the control epoxy thermoset.