Polymer-based catalytic nanoreactors, with the characteristics of easy preparation, good dispersion, and facile modulation of molecular structures, have been widely applied for various organic transformations. Usually, polymeric nanoreactors are fabricated via the self-assembly of amphiphilic copolymers in water, while the disassembly and instability of the relevant nanoreactors often compromise their potential applicability. Molecular brushes (MBs), as a kind of polymer with high-density grafted side chains on the linear polymer main chain, can be rapidly self-assembled into highly ordered nanostructures even at low concentrations. This study reports the fabrication of catalytic nanoreactors from molecular brushes of poly[norbornene–poly(bromoethyl methacrylate-co-methyl methacrylate)]-co-poly[norbornene polyethylene glycol monomethyl ether] (P[NB-(BEMA-co-MMA)]-co-P[NB-PEG]). The amphiphilic molecular brush was synthesized by combining reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP) techniques. Homogeneous catalysts, such as triethylenediamine and 4-(dimethylamino)pyridine analogues, were introduced by nucleophilic substitution with alkyl bromide on the side chain of molecular brushes. Furthermore, micellar catalytic nanoreactors were fabricated via self-assembly in deionized water. The resulted nanoreactors display high catalytic activities toward the Knoevenagel condensation reaction and acylation reaction of alcohol in water, respectively. This contribution describes a general method for constructing highly efficient molecular brush-based catalytic nanoreactors utilizing postpolymerization modification (PPM) for aqueous catalysis.
The ternary blended cement with finer slag and silica fume (SF) could improve the packing density (PD) through the filling effect. The excess water (water more than needed for filling into voids between the cement particles) can be released to improve the fresh properties and densify the microstructure which is beneficial for improving the hardened properties. To verify the hypothesis and reveal how and why (cement + slag + SF) the ternary blends could bring such advantages, the binder pastes incorporating slag and SF with various water-to-binder ratios were produced to determine the PD experimentally. To evaluate the optimum water demand (OWD) for maximum wet density, the influence of the dispersion state of the binder on PD was investigated using the wet packing density approach. The effect of PD of various binary and ternary binder systems on water film thickness (WFT), fluidity, setting time, and compressive strength development of cement paste was also investigated. The results show that the ternary blends could improve the PD and decrease the water film thickness (WFT). The enhanced PD and altered WFT are able to increase fluidity and compressive strength. The ternary blends could improve the compressive strengths by increasing PD and exerting nucleation and pozzolanic effects.
Finding vicarious building materials for Portland cement and reducing the usage of cementitious materials is a key to reduce the carbon emission of cement production. Desulfurization (FGD) gypsum powder is a common solid waste which application is limited by its low mechanical strength and poor water resistance properties. This paper studies the effect of sodium methylsilicate on the mechanical performance and waterproofs of macro-defect free (MDF) gypsum involving pressurized processing. The compressive strength, flexural strength, water absorption rate, softening coefficient and water contact angle of the MDF gypsum are assessed. The results show that adding 1.6 wt% sodium methylsilicate achieves to the maximum strength of 7.5 MPa for flexural and 35.7 MPa for compressive, which increasing by 4.2% and 6.6% relative to the pure MDF gypsum, and increasing by 11.9 % and 138.0 % relative to traditional casting gypsum. With the increasing content of sodium methylsilicate, the waterproofs of MDF gypsum become better. When adding 1.6 wt% sodium methylsilicate, the water absorption rate, softening coefficient and water contact angle is 0.4 %, 0.78 and 93.5° for 2 h immersion, respectively. The pressurized production is recommended to prepare MDF gypsum.
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