REACTIVITY RATIOS FOR COPOLYMERIZATION WITH THE PARTICIPATION OF A CHARGE-TRANSFER COMPLEX

The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by H-1-NMR spectroscopy, and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50 degrees C was determined to be 0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions for copolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios is presented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained. They are r(12) = 0.034, r(21) = 0.012, r(1C) = 0.0030, r(2C) = 0.0034, and k(1C)/k(12) = 11.34, k(2C)/k(21) = 3.42.

Mortality weighting-based method for aggregate urban air risk assessment

This paper deals with a mortality-weighted synthetic evaluation (MWSE) method for evaluating urban air risk. Sulphur dioxide (SO2), nitrogen oxide (NOx), and particulate matter (PM10) were used as pollution indices. The urban area of Hangzhou, China is divided into 756 grid cells, with a resolution of 1 km×1 km, and is evaluated using the MWSE and the air quality index (AQI), a widely-used method to evaluate ambient air quality and air risk. In an evaluation of one day in April 2004, the surface areas categorized as levels I and III, as defined by the integrated air risk evaluation, were 27.3% and 3.3% lower, respectively, than grades I and III defined by the AQI evaluation. Meanwhile, the areas classified as level II or above level III by the integrated air risk evaluation were 55.1% and 101.1% higher, respectively, than grade II or above grade III when using the AQI evaluation. From this comparison, we find that the MWSE method is more sensitive than the AQI method. The AQI method uses a single index to assess integrated air quality and is therefore unable to evaluate integrated air risks due to multiple pollutants. The MWSE method overcomes this problem, providing improved accuracy in air risk assessment.

Effect of Carbon Particles with Different Topological Shape on the Rheological Behavior of PVA Aqueous Dispersion

Poly(vinyl alcohol)(PVA)is usually processed and used in a form of aqueous dispersion.A large number of inter-and intramolecular hydrogen bonds make it very difficult to obtain suitable rheological behavior for processing.In this study,carbon particles with different topological shapes were added into PVA aqueous dispersion to tune the steady and dynamic rheological behavior.The results show that the zero-dimensional particles(carbon black,CB)increase monotonically the zero-shear viscosity of PVA dispersion,while the one-dimensional particles(carbon nanotubes,CNTs)make it first increase,and then decrease and rise again,like an N-shape,and the two-dimensional particles(graphene oxide,GO)can make it first decrease and then increase,exhibiting a U-shape.It is believed that the topological shape of the carbon particles brought about these discrepancies.The zero-dimensional particles mainly act as physical crosslinking points due to their small size.While at a certain content,both CNTs and GO can destroy the intermolecular hydrogen bonds between PVA chains because the PVA chains can twine around the slim CNTs and the large planar size of GO prevents the adsorbed PVA from forming hydrogen bond with other chains.The high hydroxyl value of carbon particle surface could strengthen this effect.It is expected that the viscosity of polymer dispersion can be regulated by particles with different topological shape and the surface characteristic,so as to widen the operable concentration range during preparing composite functional materials.

Temperature-dependent Crystallization and Phase Transition of Poly(L-lactic acid)/CO_(2) Complex Crystals

Semicrystalline polymers can crystallize in the unique crystalline polymorph and show different phase behaviors under the high-pressure CO_(2) treatment.Understanding such unique crystallization and phase transition behavior is of fundamental importance for the CO_(2)-assisited processing of semicrystalline polymers.Herein,we investigated the polymorphic crystalline structure,phase transition,and structure-property relationships of poly(L-lactic acid)(PLLA)treated by CO_(2) at different pressures(1-13 MPa)and crystallization temperatures(Tc's,10-110℃).PLLA crystallized in the PLLA/CO_(2) complex crystals under 7-13 MPa CO_(2) at TCS50℃but the common a crystals under the high-pressure CO_(2) at TC≥70℃.Solid-state nuclear magnetic resonance analysis indicated that the PLLA/CO_(2) complex crystals possessed weaker interactions between the PLLA chains than the common a crystals.The PLLA/CO_(2) complex crystals were metastable and transformed into the thermally stable a crystals via the solid-to-solid route during heating or annealing at the temperature above 50℃.The complex crystals of PLLA produced at low Tc was more ductile than the a crystals due to the lower crystallinity and the plasticizing effect of CO_(2).