Morphological Control And Properties Of Nanostructured Thermosets Containing Block Copolymers

A series of amphiphilic block copolymers such as AB diblock, ABA triblock, ABC triblock and bottlebrush-like copolymers were synthesized via the combination of ring-open polymerization, reversible addition-fragmentation chain transfer polymerization(RAFT), atom transfer radical polymerization(ATRP) and click chemistry reaction. These block copolymers were used to modulate ordered and/or disordered nanostructures in several crosslinked polymers. The nanostructures and formation mechanisms of the crosslinked polymers containing block copolymers were characterized by means of transmission electron microscopy(TEM), atomic force microscopy(AFM) and small-angle X-ray scattering(SAXS). Furthermore, the properties of the nanostructured materials were investigated. The main results were summarized as follows:1. The poly(ethylene oxide)-b-poly(sodium 4-styrene sulfonate)(PEO-b-PSSNa) diblock copolymer was synthesized via RAFT polymerization. The PEO-b-PSSNa diblock copolymer was incorporated into epoxy to prepare the thermosets. The spherical nanostructured epoxy resins were successfully prepared. It was found that the formation of the nanostructures was in a self-assemble manner. The glass transition temperatures(Tg’s) and the initial thermal degradation temperatures decreased with increasing the content of the diblock copolymer. The dielectric permittivity(ε) increased with increasing the content of the diblock copolymer with the frequence(f) from 103 to 107 Hz.2. The ABC triblock copolymer poly(ε-caprolactone)-block-polystyrene-block-poly(2,2,2-trifluoroethyl acrylate)(PCL-b-PS-b-PTFEA) and ACB triblock copolymer poly(ε-caprolactone)-block-poly(2,2,2- trifluoroethyl acrylate)-block-polystyrene(PCL-b-PTFEA-b-PS) were synthesized via RAFT polymerization. Both PCL-b-PS-b-PTFEA and PCL-b-PTFEA-b-PS were incorporated into epoxy resin to obtain the tubular and spherical nanostructured epoxy resins. It was found that both of the formation of the nanophases in the thermosets containing PCL-b-PS-b-PTFEA and/or PCL-b-PTFEA-b-PS followed the combination of self-assembly and reaction-induced microphase separation mechanisms. The glass transition temperatures(Tg’s) decreased with increasing the content of the triblock copolymers.3. Bottlebrush-like copolymer poly(2-(2-bromopropanoyloxy)ethyl methacrylate)-g-(polystyreneb-poly(ε-caprolactone) [PBPEMA-g-(PS-b-PCL)] was synthesized via the combination of ATRP, Click and ROP. PBPEMA-g-(PS-b-PCL) was incorporated into epoxy resin to obtain the line-like nanostructured thermosets. It was found that the formation mechanism of the nanophases in the thermosets was reaction-induced microphase separation via single macromolecule. Bottlebrush-like copolymer poly(2-hydroxyethyl methacrylate-g-poly(ε-caprolactone))-r-poly(2-(2-bromopropanoyloxy) ethyl methacrylate)-g-polystyrene) [P(HEMA-g-PCL)-r-(BPEMA-g- PS)] was synthesized via the combination of RAFT, ROP and ATRP. The brush-like copolymer was incorporated into epoxy and the spherical and lamellar nanostructured thermosets were obtained. It was proved that the formation of the nanostructures followed the mechanism of reaction-induced microphase separation via single macromolecule(RIMPS).4. Two structurally similar triblock copolymers, poly(?-caprolactone)-block-poly(butadiene-costyrene)-block-poly(?-caprolactone)(PCL-b-PBS-b-PCL) and poly(?-caprolactone)-blockpoly(ethylene-co-ethylethylene-co-styrene)-block-poly(?-caprolactone)(PCL-b-PEEES-b-PCL) were synthesized via ROP and they possessed the identical compositions and close molecular weights. Both the triblock copolymers were incorporated into epoxy to obtain the nanostructured thermosets. It was found that the formation of the nanophases in the thermosets containing PCL-b-PBS-b-PCL followed a reaction-induced microphase separation mechanism whereas that in the thermosets containing PCL-b-PEEES-b-PCL was in a self-assembly manner. The quite different formation mechanisms of nanophases in the thermosets resulted in the quite different morphologies, glass transition temperatures(Tg’s) and fracture toughness of the nanostructured thermosets.5. The ABA triblock copolymers PNIPAAm-b-PVPy-b-PNIPAAm and PNIPAAm-b-PAA-bPNIPAAm were sythesized via RAFT/MADIX and RAFT polymerization, respectively. The nanostructured PNIPAAm-b-PVPy-b-PNIPAAm and PNIPAAm-b-PAA-b-PNIPAAm hydrogels were successfully obtained. It was found that the diffusion of water molecules in PNIPAAm-b-PVPy-bPNIPAAm block copolymer networks was in a non-Fickian and accelerating manner. The swelling ratios of the PNIPAAm-b-PVPy-b- PNIPAAm hydrogels were significantly higher than that of control PNIPAAm network. Compared to control PNIPAAm hydrogel, the PNIPAAm-b-PVPy-b-PNIPAAm hydrogels displayed an accelerated response to the external temperature changes in terms of deswelling and reswelling tests. It was also found that the PAA-blocked PNIPAAm hydrogels displayed accelerated thermal response to the external temperature changes compared to the control PNIPAAm hydrogel.