超微粒介孔分子筛Ti-MCM-41的合成及应用

超微粒分子筛;苯乙烯;催化氧化;超微粒介孔分子筛Ti-MCM-41的合成及应用     

Bottlebrush‐shaped copolymers with cellulose diacetate backbone by a combination of ring opening polymerization and ATRP

Graft copolymers with cellulose diacetate (CDA) backbone and both the poly(ε‐caprolactone) and polystyrene, or poly(butyl acrylate) or PMMA grafts were prepared by two‐step process. First, ε‐caprolactone (CL) was polymerized by ring‐opening polymerization (ROP) initiated with CDA, partly funcionalized with 2‐bromo‐isobutyryl groups (degree of functionalization was 0.5). The p(CDA‐g‐CL) copolymers were used in the second step as polyfunctional macroinitiators of ATRP of the vinyl monomer, giving densely grafted copolymers with polyester and PSt, or PBuA, or PMMA grafts. The prepared copolymers were characterized by SEC, some of them also by FTIR spectroscopy and atomic force microscopy (AFM). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 564–573, 2008     

Sulfonation of metallocene‐based polyolefinic elastomers and its influence on physicomechanical properties: Effect of reaction parameters,styrene grafting,and pendant chain length

Direct sulfonation and styrene‐mediated sulfonation were carried out onto metallocene‐based poly(ethylene‐co‐octene) (POE) and poly(ethylene‐co‐butene) (PBE) elastomers to impart polarity on the completely nonpolar rubbery matrices and to prepare a new class of elastomer. The influence of styrene‐grafting and pendant chain length on the degree of sulfonation was also studied. The effects of sulfonation, styrene grafting and styrene‐mediated sulfonation at their optimized levels on various physicomechanical properties were thoroughly investigated, and the resultant properties were correlated with structures of the modified elastomers. Higher extent of sulfonic acid groups were introduced through direct sulfonation in comparison with the styrene‐mediated sulfonation, whereas better thermal and mechanical properties were obtained through styrene‐mediated sulfonation in comparison with the direct sulfonation process. PBE had shown higher degree of sulfonation and percentage grafting than POE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8023–8040, 2008     

Styrene polymerization with nickel complexes/methylaluminoxane catalytic system

Polymerization of styrene using β‐diketiminate nickel (II) bromide complexes CH{C(R)NAr}₂NiBr (R = CH₃, Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; R = CH₃, Ar = 2,6‐Me₂C₆H₃, 2 ; R = CF₃, Ar = 2,6‐ⁱPr₂C₆H₃, 3 ; R = CF₃, Ar = 2,6‐Me₂C₆H₃, 4 ) in the presence of methylaluminoxane was studied. Compound 3 is the most active styrene polymerization catalyst of all the nickel complexes tested. The activity of these catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. Weight‐average molecular weight of the prepared polystyrene ranges from 21 000 to 72 000, with polydispersity indexes of 1.95–2.78. The microstructure of the obtained products is atactic polystyrenes from NMR analyses. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of optically active helical vinyl polymers via free radical polymerization

A facile synthetic route to prepare the dual‐functional molecule, 2,5‐bis(4′‐carboxyphenyl)styrene, was developed. The esterification of this compound with chiral alcohols, that is, (S)‐(+)‐sec‐butanol/(R)‐(?)‐sec‐butanol, (S)‐(+)‐sec‐octanol/(R)‐(?)‐sec‐octanol, and D ‐(+)‐menthol/L ‐(?)‐menthol, respectively, yielded three enantiomeric pairs of novel vinyl monomers, which underwent radical polymerization to obtain helical polymers with an excess screw sense. These polymers exhibited optical rotations as large as fourfold those of the corresponding monomers. Their helical conformations were quite stable as revealed by the almost unchanged chiroptical properties measured at different temperatures. The polymers with linear alkyl tails in the side‐groups formed irreversibly columnar nematic phases in melt although the corresponding monomers were not liquid crystalline. Whereas, the polymers with cyclic tails generated no mesophase. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2408–2421, 2009     

New azo-peroxidic initiators in the radical polymerization of styrene and methyl methacrylate

Two new azo-perester compounds, di-tert-butyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tBu) and di-tert-amyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tAm), synthesized on the basis of 6,6′-azobis-(6-cyanoheptanoic acid) (ACHpA), were investigated for their use in the radical polymerization of styrene (S) and methyl methacrylate (MMA). Their characteristics are given, including chemical (IR spectra), thermal (DSC) and kinetic, i.e., thermal decomposition studied by volumetric and gas chromatographic methods. The rate constants and activation energies of the decomposition of both the azo and perester bonds were determined. The new azo-peresters were utilized to initiate the radical solution polymerizations of S and MMA at 60 °C. The kinetic parameters of the processes, i.e., polymerization rate and overall rate constant, were determined. Subsequently, the polymerization products were characterized by IR and DSC. It was found that the perester groups were present in the obtained polymers, and hence, the polymers are “active” for further polymerization.     

“Living” radical polymerization of styrene catalyzed by cyclometalated ruthenium(II) complexes bearing nonlabile ligands

Cationic substitutionally inert cyclometalated ruthenium (II) and osmium (II) complexes, ([Mt(o‐C₆H₄‐2‐py)(LL)₂]PF₆), where LL‐1,10‐phenanthroline (phen) or 2,2′‐bipyridine (bipy), were used for radical polymerization of styrene. Gradual modification of the complexes within the series allowed comparison of the catalytic activity and the redox properties. There was no correlation between the reducing powers of the complexes and their catalytic activities. The osmium compound of the lowest reduction potential was not active. All the ruthenium complexes catalyzed the polymerization of styrene in a controlled manner; but the level of control and the catalytic activity were different under the same polymerization conditions. [Ru(o‐C₆H₄‐2‐py)(phen)₂]PF₆ demonstrated the best catalytic performance though its redox potential was the highest. It catalyzed the “living” polymerization with a reasonable rate at a catalyst‐to‐initiator ratio of 0.1. 1 equiv. of Al(OiPr)₃ accelerated the polymerization and improved the control, but higher amount of Al(OiPr)₃ did not speed up the polymerization and moved the process into the uncontrollable regime. Under the most optimal conditions, the controlled polymerization occurs fast without any additive and the catalyst degradation. Added free ligands inhibited the polymerization suggesting that the catalytically active ruthenium intermediates are generated via the reversible dechelation of bidentate phen or bipy ligands. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3814–3828, 2009     

聚苯乙烯的催化裂解研究

由于塑料性质稳定,难以自然降解,其废弃物不仅严重污染环境,更造成了资源浪费.因此,废旧塑料的再资源化对环境保护和可持续发展有着重要意义.废塑料再资源化回收技术是指将废塑料热裂解或催化裂解、回收燃料油和化工原料的技术~([1,2]).     

Thermal stability of poly(styrene) containing no head-to-head units

General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer. This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques. A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.