In this communication, the preparation of crosslinked polydicyclopentadiene (PDCPD) nanoparticles via ring‐opening metathesis polymerization (ROMP)‐induced self‐assembly approach is reported. For the ...ROMPs, the macromolecular chain transfer agents (Macro‐CTAs) are synthesized via the ring‐opening polymerization (ROP) of ε‐caprolactone (CL) with cis‐2‐butene‐1,4‐diol as the initiator. The ROMPs are performed with chloroform, tetrahydrofuran, toluene, 1,4‐dioxane, and N,N‐dimethylacetamide as the solvents, respectively, which are catalyzed with Grubbs second generation catalyst. It is found that the crosslinked PDCPD nanoparticles are obtained with spherical, cylindrical to planar morphologies, depending on the molecular weights of Macro‐CTAs, the concentrations of DCPD and the natures of solvents. The polymerization induced self‐assembly (ROMPISA) by the use of a non‐norbornene‐based macromolecular chain transfer agent provides a new and efficient approach to prepare crosslinked polymer nanoparticles.
In this communication, the preparation of crosslinked polydicyclopentadiene (PDCPD) nanoparticles via ring‐opening metathesis polymerization (ROMP)‐induced self‐assembly approach is reported.
Octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) was used as a crosslinking agent together with 4,4′‐methylenebis‐(2‐chloroaniline) to prepare polyurethane networks containing POSS. ...Fourier transform infrared spectroscopy (FT‐IR), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were employed to characterize the POSS‐reinforced polyurethane. The POSS‐containing PU networks displayed enhanced glass transition temperatures (Tgs) and the storage moduli of the networks of the glassy state and rubber plateaus were also observed to be significantly higher than that of the control polyurethane although only a small amount of POSS was incorporated into the systems. The results can be ascribed to the significant nanoscale reinforcement effect of POSS cages on the polyurethane matrix. TGA results showed the thermal stability was also improved with incorporation of POSS into the system.
Dynamic mechanical spectra of PU and PU nanocomposites containing POSS.
In this work, a novel curing-induced fluorescence (FL) enhancement phenomenon in the nanostructuring process of epoxy thermosets was investigated. Toward this end, a diblock copolymer composed of ...poly(ethylene oxide) and poly(((4-vinylphenyl)ethene-1,1,2-triyl)tribenzene) (PTPEE) blocks was introduced into epoxy thermosets. Before curing reaction, the mixtures of epoxy precursors with the diblock copolymer only emitted feeble FL under ultra-visible (UV) irradiation. However, photoluminescence was significantly enhanced after the curing reaction was carried out. It was found that the novel FL enhancement phenomenon resulted from the aggregation-induced emission behavior of PTPEE blocks, which was triggered by curing reaction. In the nanostructured thermosets, the fluorophore blocks (viz. PTPEE) of this diblock copolymer were segregated into aggregates, that is, a reaction-induced microphase separation occurred. Owing to the generation of PTPEE microdomains, the epoxy nanocomposites significantly displayed the enhanced dielectric constants due to the promoted contribution from electron polarizations via π–π conjugation in the materials.
We report an investigation of the influence of block copolymer architectures on formation of nanophases in epoxy thermosets via reaction-induced microphase separation approach. Toward this end, three ...binary block copolymers composed of polystyrene (PS) and poly(ε-caprolactone) (PCL) were synthesized via the combination of ring-opening polymerization (ROP) and atomic transfer radical polymerization (ATRP). These block copolymers possess PS-b-PCL diblock, PS-b-PCL-b-PS triblock, and PCL-b-PS-b-PCL triblock architectures; they were carefully controlled to have the identical composition and overall molecular weights. It was found that the block copolymers with different architectures in epoxy thermosets displayed quite different reaction-induced microphase separation behavior as evidenced with the results of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and dynamic mechanical thermal analysis (DMTA). The morphological transition from spherical to cylindrical to lamellar nanophases occurred with increasing the content of the block copolymer in the thermosets containing PS-b-PCL diblock copolymer. In the thermosets containing PS-b-PCL-b-PS triblock copolymer, unilamellar and multilamellar nanophases were formed depending on the content of the triblock copolymer. In contrast, the macroscopic phase separation occurred in the thermosets containing PCL-b-PS-b-PCL triblock copolymer. The behavior of nanophases in these thermosetting blends have been accounted for the demixing behavior of the miscible blocks (viz. PCL) during the reaction-induced microphase separation and the influence of copolymer architectures on the morphologies of PS microdomains.
In this contribution, we reported the synthesis of a novel trifunctional POSS cyclic carbonate POSS-3(5CC). With a difunctional five-member cyclic carbonate and a trifunctional polyetheramine as the ...precursor, the nanocomposites of polyhydroxyurethane (PHU) with POSS were synthesized. Transmission electron microscopy (TEM) showed that the nanocomposites of PHUs with POSS were microphase-separated; the spherical POSS microdomains via POSS-POSS interactions were generated with the size of 20~40 nm in diameter. After the introduction of POSS microdomains, the nanocomposites displayed improved thermal and mechanical properties. More importantly, the nanocomposites still displayed the reprocessing properties of vitrimers.
Reaction-induced microphase separation in epoxy thermosets containing an amphiphilic diblock copolymer was investigated in this work. To this end, the diblock copolymer ...poly(ε-caprolactone)-block-poly(n-butyl acrylate) (PCL-b-PBA) was synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The block copolymer was incorporated into epoxy thermosets. Before the curing reaction all the subchains of the diblock copolymer were miscible with the precursors of epoxy resin. After curing, only the PBA blocks were separated out whereas the PCL blocks remained miscible with epoxy resin. Such a reaction-induced microphase separation results in the formation of ordered nanostructures in the thermosets. The nanostructures in the thermosets were investigated by means of field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA). It is found that, depending on the concentration of the diblock copolymer, the thermosets can displayed spherical particles or lamellar nanostructures. The SAXS curves with the multiple scattering maxima suggests that the thermosets possess long-range ordered nanostructures.
In this study, we synthesized poly(ethylene oxide)-block-poly(ε-caprolactone)-block-polystyrene (PEO-b-PCL-b-PS) triblock copolymer via the combination of ring-opening polymerization (ROP) and atomic ...transfer radical polymerization (ATRP). The ABC triblock copolymer was incorporated into epoxy to access the nanostructured thermosets. It is found that the nanophases of the epoxy thermosets can be modulated by using different hardeners. While cured with 4,4′-methylenebis(2-chloroaniline), the thermosets displayed the long-ranged ordered nanostructures in which the spherical nanophases were arranged into body-centered cubic (bcc) lattice at the compositions investigated. While 4,4′-diaminodiphenylsulfone was used as the hardener, the thermosets displayed the lamellar nanostructure. The formation of nanostructures in the thermosets has been evidenced by atomic force microscopy and small-angle X-ray scattering. The morphological transition from spherical to lamellar nanophases has been interpreted in terms of the microphase separation of different subchains of the ABC triblock copolymer out of the epoxy–amine matrix during the curing reactions owing to the dependence of miscibility of epoxy networks with PCL subchain of the triblock copolymer on types of hardeners. The kinetics of curing and microphase separation shows the tandem reaction-induced microphase separation occurred while DDS was used as the hardener, which gave rise to the formation of lamellar nanostructures in the epoxy thermosets containing the ABC triblock copolymer.
Hepta(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS)-capped poly(ethylene oxide) (PEO) was synthesized via the reaction of hydrosilylation between ...hepta(3,3,3-trifluoropropyl)hydrosilsesquioxane and allyl-terminated PEO. The POSS-capped PEO was characterized by means of Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The organic−inorganic amphiphile was incorporated into epoxy resin to prepare the organic−inorganic nanostructured thermosetting composites. The morphology of the hybrid composites was characterized with field emission scanning electronic microscopy (FESEM) and transmission electronic microscopy (TEM). The formation of nanostructures was addressed on the basis of miscibility and phase behavior of the sub-components (viz. POSS and PEO chains) of the organic−inorganic amphiphile with epoxy after and before curing reaction. The static contact angle measurements indicate that the organic−inorganic nanocomposites displayed a significant enhancement in surface hydrophobicity as well as reduction in surface free energy. The atomic force microscopy (AFM) showed that there is significant migration of the POSS moiety at the surface of the thermosets. The improvement in surface properties was ascribed to the enrichment of the POSS moiety on the surface of the nanostructured thermosets, which was evidenced by X-ray photoelectron spectroscopy (XPS).
The one-dimensional (1D) polyethylene (PE) nanocrystals were generated in epoxy thermosets via crystallization-driven self-assembly. Toward this end, an ABA triblock copolymer composed of PE midblock ...and poly(ε-caprolactone) (PCL) endblocks was synthesized via the ring opening metathesis polymerization followed by hydrogenation approach. The nanostructured thermosets were obtained via a two-step curing approach, i.e., the samples were cured first at 80 °C and then at 150 °C. Under this condition, the one-dimensional (1D) fibrous PE microdomains with the lengths up to a couple of micrometers were created in epoxy thermosets. In contrast, only the spherical PE microdomains were generated while the thermosets were cured via a one-step curing at 150 °C. By the use of the triblock copolymer, the generation of 1D fibrous PE nanocrystals is attributable to crystallization-driven self-assembly mechanism whereas that of the spherical PE microdomains follows traditional self-assembly mechanism. Compared to the thermosets containing the spherical PE microdomains, the thermosets containing the 1D fibrous PE nanocrystals displayed quite different thermal and mechanical properties. More importantly, the nanostructured thermosets containing the 1D fibrous PE nanocrystals displayed the fracture toughness much higher than those only containing the spherical PE nanocrystals; the KIC value was even three times as that of control epoxy.
Double-decker silsesquioxane (DDSQ) and hindered urea bonds were simultaneously introduced into the main chains of linear segmented polyurethane (PU) to synthesize organic–inorganic linear segmented ...poly(urea urethanes) (PUUs). The organic–inorganic PUUs were microphase-separated, and the POSS cages were aggregated into the microdomains with the size of 10–20 nm. The organic–inorganic PUUs had the improved thermomechanical properties in comparison to those of the control PU. Notably, the strong physical cross-linking was formed in the organic–inorganic PUUs, and thus the materials could display the properties of thermoset elastomers. The physical cross-linking was attributable to the formation of POSS microdomains, which acted as the nano-cross-linking sites. Owing to the formation of physical cross-linking, the shape memory properties have been imparted to the organic–inorganic nanocomposites; the fixing of temporary shapes and the recovery of original shapes were significantly improved. The inclusion of hindered urea bonds provided the organic–inorganic PUUs with the solid-state plasticity at room temperature (i.e., self-healing properties) via the dynamic exchange of hindered urea bonds. It was found that the nanoreinforcement of POSS microdomains did not significantly decrease the self-healing properties of the organic–inorganic PUUs. This work reports an approach simultaneously to optimize the shape memory and self-healing properties of polyurethanes.