The amphiphilic triblock copolymer poly( -caprolactone)-b-polybutadiene-b-poly( -caprolactone) (PCL-PB-PCL) was synthesized via the ring-opening polymerization of -caprolactone in the presence of a hydroxyl-terminated polybutadiene (HTPB), which was catalyzed by stannous octanoate [Sn(Oct) 2 ]. The amphiphilic triblock copolymer was further used to prepare the nanostructured epoxy thermosets. The in situ polymerization of epoxy monomers in the presence of PCL-PB-PCL started from the homogeneous solutions composed of the block copolymer and the monomers of epoxy at the temperature above the upper critical solution temperature (UCST) of diglycidyl ether of bisphenol A (DGEBA) and HTPB blends. The transmission electronic microscopy (TEM), small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM) showed that the nanostructured thermosets were successfully obtained. Depending on the content of the block copolymer in the thermosets, the PB domains can display spherical and interconnected nanoobjects with the size of 10-20 nm. It is judged that the nanostructures are formed on the basis of the mechanism of polymerization-induced microphase separation, which is in a marked contrast to the approach in which some equilibrium self-organized structures were preformed and the microphases were fixed via subsequent curing reaction.

A polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer was synthesized via the atom transfer radical polymerization (ATRP) of styrene with mono-2-bromoisobutyryl-terminated PEO [PEO-OOCCBr(CH 3 ) 2 ] as a macroinitiator, and the polymerization was mediated by copper(I) bromide (CuBr) and 2,2′-bipyridine (BPY). The PS-b-PEO diblock copolymer was used to incorporate into epoxy resin to afford the nanostructured epoxy thermosets. Both atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) showed that the long-range ordered nanostructures were obtained via the approach of in situ polymerization in the presence of the diblock copolymer. It was found that the nanophases of PS were arranged into a simple cubic symmetry lattice while the content of diblock copolymer was 40 wt %. In view of the difference in miscibility and phase behavior for the blends of the subchains (i.e., PS and PEO) of the diblock copolymer with epoxy after and before curing, the formation of the ordered nanostructures was judged to be via the mechanism of reactioninduced microphase separation, which is in marked contrast to the mechanism of self-organization of block copolymers together with the subsequent fixation of the self-organized structures.

The block copolymers, poly(ε-caprolactone)-block-polystyrene (PCL-b-PS) with the linear and star-shaped topological structures were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The two block copolymers with the identical block compositions were incorporated into epoxy to access the nanostructured thermosets. The microphase-separated morphologies in the systems were investigated by means of atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). It is identified that the epoxy thermosets can display the long-ranged ordered nanostructures depending on the concentration of the diblock copolymers. By considering the miscibility of the subchains of the block copolymers with epoxy after and before the curing reaction, it is judged that the formation of the nanostructures followed the mechanism of reaction-induced microphase separation. It is noted that the nanoscaled morphologies of the thermosets are quite dependent on the macromolecular topologies of the block copolymers. For the epoxy thermosets containing the linear PCL-b-PS diblock copolymer, the spherical PS nanophases were arranged into cubic (e.g., bcc, fcc, or simple cubic) lattice whereas the PS nanophases into lamellar lattice while the thermosets contain the tetra-armed PCL-b-PS block copolymer. The difference in nanostructures for the epoxy thermosets has been interpreted on the basis of the restriction of topological structures of the block copolymers on the formation of nanophases.

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