Formation Of Nanostructures In Thermosets Containing Block Copolymers

The study on the nanostructured thermosets is an important topic in the polymer materials because of the relation between the structure and property of polymer. 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, self-organized nanostructures are formed prior to curing and these disordered and/or ordered nanostructures are further locked in with the subsequent curing reaction. And for the self-assembly, some self-assembly nanostructured morphologies are formed in the precursor of thermosets before curing reaction. 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.We designed and sythesized a series of amphilic block copolymers according to the structures of the thermosets and miscibility between block copolymer and thermosets. And disordered and/or ordered nanostructured thermosets were obtained by the mixtures of block copolymer and thermosets. The main researches are as follows:1. Study on the nanostructure in epoxy thermosets containing poly(ε-caprolactone)-b- poly(butadiene-styrene)-b-poly(ε-caprolactone) (PCL-b-PBS-b-PCL): an evidence of reaction-induced microphase separationThe block copolymer PCL-b-PBS-b-PCL was synthesized by the ring-opening polymerization ofε-caprolactone. The triblock copolymer was further mixed with epoxy resin to prepare nanostructured epoxy thermosets. Further study illustrated that PCL subchains were miscible with epoxy after and before curing while PBS subchains and diglycidyl ether of bisphenol A (DGEBA) had the upper critical solution temperature (UCST). Then PBS subchains occurred reaction-induced microphase separation during curing reaction and formed nanostructures in epoxy thermosets.2. Lamellar nanostructures in epoxy thermosets containg poly(ε-caprolactone)-b-poly(butyl acrylate) (PCL-b-PBA) via reaction-induced microphase separationThe diblock copolymer PCL-b-PBA was synthesized via the ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The diblock copolymer was incorporated into epoxy thermosets to access the nanostructures in the thermosets. The nanostructures were investigated by means of field-emission scanning electron microscope (FESEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). It was found that depending on the concentration of the diblock copolymer in the thermosets, the nanostructures changed from spherical particles to lamellar objects of PBA nanophases. In terms of the miscibility of the PCL/PBA subchains of the block copolymer with epoxy resin after and before curing reaction, it was judged that the nanostructures were formed via the mechanism of reaction-induced phase separation.3. Effect of topological structures of block copolymers on nanostructures in thermosetsThe four arms star-shape block copolymer fa(PCL-b-PS)4 was synthesized. Then the star-shape block copolymer was mixed with epoxy resin and the nanostructures were obtained. The results showed that the lamellar nanostructures were formed in epoxy thermosets containing four arms shar-shape block copolymer fa(PCL-b-PS)4 while the lattice with simple cubic nanostructures were in epoxy thermosets containing diblock copolymer PCL-b-PS. FTIR and DSC results illustrated that the precursor of epoxy (DGEBA) could rip into the outer PS subchains and come into the inner PCL subchains of the star-shape block copolymer. This resulted in the miscibility of PCL subchains and epoxy matrix. In terms of the miscibility of the PCL/PS subchains of the block copolymer with epoxy resin after and before curing reaction, it was judged that the lamellar nanostructures were formed via reaction-induced phase separation.4. Study on the self-assembly nanostructures in the cross-linked epoxy thermosts containing poly(ε-caprolactone)-b-poly(dimethylsiloxane)-b-poly(ε-caprolactone)The triblock copolymer PCL-b-PDMS-b-PCL was synthesized via the ring-opening polymerization ofε-caprolactone in the presence of dihydroxypropyl-terminated PDMS (HTPDMS) initiator, and was incorporated into epoxy resin and the nanostructured thermosets were successfully obtained. The morphology of the epoxy thermosets containing PCL-b-PDMS-b-PCL triblock copolymers were investigated by means of atomic force microscopy, transmission electronic microscopy and small angle X-ray scattering. The spherical PDMS microphase with the diameter as 10-20 nm was dispersed in epoxy thermosets containing 10 wt % block copolymer; and wormlike PDMS microphase was formed when the content of block copolymer more than 20 wt %. The formation was judged to follow the self-assembly mechanism in terms of the difference in miscibility of the PDMS and PCL subchains with epoxy resin after and before curing reaction.5. Study on the surface properties and structures of the triblock copolymer PCL-b-PDMS-b-PCL and linear epoxy resin mixturesThe binary polymer blends were obtained by mixing triblock copolymer PCL-b-PDMS-b-PCL and Phenoxy. FTIR and DSC results illustrated that PCL blocks in the triblock copolymer are miscible with Phenoxy. The contact angle of Phenoxy blends containing 10 wt % triblock copolymer was significantly increased and the contact angles increased with increasing the content of triblock copolymer while the surface free energy decreased. XPS results showed that the PDMS block aggregated on the surface to minimize the surface free energy of the polymer blends. Microphase separation of the triblock copolymer occurred in binary Phenoxy blends and phase separation on the surface of the Phenoxy blends was proved by atom force microscope via the different friction force of the surface of the polymer blends.6. Study on the self-assembly ordered nanostructures in phenolic resin containing poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) diblock copolymerThe diblock copolymer PEO-b-PS was synthesized by ATRP. Then the PEO-b-PS diblock copolymer was used to incorporate into phenolic resin to afford the long-range ordered nanostructured phenolic resin by self-assembly. And the changes of the nanostructures in phenolic resin before and after curing reaction were studied by SAXS. The results showed that the PS microdomains arranged into hexagonal cylinder when the content of PEO-b-PS diblock copolymer was 40 wt %. In views of the difference in miscibility and phase behavior for the blends of the PEO/PS subchains of the diblock copolymer with phenolic resin after and before cuing, the formation of the ordered nanostructures was judged to be via the mechanism of self-assembly.