Activation by the Grignard reagent of the bis(2-phenylindenyl)zirconium dichloride—triisobutylaluminum catalytic system for propene polymerization

Polymerization of propylene with the three-component catalytic system bis(2-phenylindenyl)zirconium dichloride—alkyl magnesium chloride—triisobutylaluminum is studied. The annelated zirconocene is alkylated by the Grignard reagent. The three-component system is as good in activity as two-component systems with polymethylalumoxane as a cocatalyst. Stereoblock elastomeric polypropylene with a high molecular weight is formed.     

丙烯在Au/TiO2催化剂上的化学吸附与临氢环氧化反应

环氧丙烷;丙烯环氧化;丙烯在Au/TiO2催化剂上的化学吸附与临氢环氧化反应     

Sorption and Diffusion of Propylene and Ethylene in Heterophasic Polypropylene Copolymers

Summary: Sorption experiments of ethylene and propylene in different polypropylene powder samples, both homopolymer and heterophasic copolymers with different rubber content, have been carried out in a high-pressure magnetic suspension balance at 10 bars pressure and 70 °C. The gross solubilities measured can be well correlated with the rubber content of the polymer samples. Solubility of ethylene and propylene in the rubber phase differ from solubility in the amorphous fraction of the homopolymer, especially the concentration ratio of propylene to ethylene differs significantly between rubber phase and amorphous fraction of the homopolymer. From the slope of monomer uptake, information on kinetics of mass-transfer can be gained. No significant differences were observed in terms of mass-transfer for ethylene and propylene. With increasing rubber content, effective diffusion coefficients increased slightly. By combined sorption studies with powder samples and compressed films, information about both effective diffusion coefficients and the effective length scale of diffusion could be gained. It could be shown, that the particle radius is not the characteristic length of diffusion in the studied powder samples. Mass transfer of nearly all samples could be described by a constant diffusion length of 120 to 130 µm, independently on particle size. This indicates that the effective scale of diffusion in polymer particles is in between microparticle and macroparticle scale used in classical particle modeling.     

Halogen Free Flame Retardant Agents for Polypropylene in Wire Coating Process

the processing behaviour and physical properties of polypropylene/flame retardant blends were investigated in order to evaluate their use in the wire-coating process. In particular, the need of flame retardancy, suitable melt processability and good mechanical properties of blends was taken into account. Three types of halogen free flame retardants were chosen and were melt blended to the polypropylene matrix. Blends properties were analysed by rheological, mechanical, and thermal characterization including flame retardancy tests. The wire coating process was also performed by a laboratory wire coating apparatus. The results demonstrated that some of the blends are suitable for the purpose of flame retardancy of electrical household wires as an alternative to PVC.     

Alk‐1‐ene Polymerization in the Presence of a Monocyclopentadienyl Zirconium(IV) Acetamidinate Catalyst: Microstructural and Mechanistic Insights

Suitably activated, (Cp*){N(^tBu)C(Me)N(Et)}ZrMe₂ is known to initiate the ‘living’ and isotactic‐selective polymerization of alk‐1‐enes, and it can be used to synthesize block copolymers and stereoblock polymers. We report a full molecular kinetic investigation of propene, but‐1‐ene, and hex‐1‐ene polymerization with a MAO‐activated catalyst system. By combining NMR microstructural polymer analysis with QM modeling of the active species, the complicated regio‐ and stereochemistry of the polyinsertion process, as well as the active chain‐transfer pathways, are investigated. The perspectives and limitations of this catalyst for application in (stereo)block polymerizations are discussed.

     

Isothermal Crystallization of Isotactic Poly(propylene) Studied by Superfast Calorimetry

The isothermal crystallization behavior and the structure and morphology of isotactic poly(propylene) (iPP) and iPP/hydrogenated hydrocarbon resin (HR) 90/10 blend were analyzed. To cover the entire temperature range, isothermal crystallizations were studied using superfast calorimetry at a high cooling rate in the range 0 to 110 °C, and by conventional DSC at a low cooling rate in the range 120 to 140 °C. Structural and morphological changes due to the different thermal treatments were also analyzed. The complete crystallization curve ranging from T_g to T_m showed bimodal crystallization behaviors for both iPP and iPP/HR 90/10 blend. This result is explained by taking into consideration the polymorph properties of iPP. It is in fact assumed that the curve from T_g to 60 °C referred mainly to the crystallization kinetics of the iPP mesomorphic form by homogeneous nucleation, whereas the curve from 60 °C to T_m mainly represented the crystallization kinetic curve for the monoclinic α form by heterogeneous nucleation. This hypothesis is confirmed by the analysis of the structures obtained using wide angle X‐ray experiments. Moreover, the addition of HR to iPP causes a drastic reduction in the crystallization rate of iPP in both regions due to the diluent effect of the miscible resin.

     

Creep Resistant Polymer Nanocomposites Reinforced with Multiwalled Carbon Nanotubes

Poly(propylene) (PP) nanocomposites filled with shorter‐ and longer‐aspect‐ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin‐screw extruder and an injection moulding machine. It is shown that with only 1 vol.‐% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long‐term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1 000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications.

     

Construction of Glycosylated Surfaces for Poly(propylene) Beads with a Photoinduced Grafting/Chemical Reaction Sequence

Surface modification of commercial PPBs with different saccharides is described. Surface‐glycosylated PPBs were prepared through reaction between the hydroxyl groups of poly(HEMA) and acetylated saccharides such as α‐glucose pentaacetate, β‐galactose pentaacetate, and lactose octaacetate. The modified PPBs were characterized by XPS and water contact angle measurement. It was found that the grafting degree of poly(HEMA) increases with UV irradiation time, monomer concentration, and water content in solvent. The binding degree of monosaccharides is higher than that of disaccharides. The glycosylated PPBs can selectively recognize lectins, indicating potential for protein isolation.

     

Nucleating Effect and Dynamic Crystallization of a Poly(propylene)/Talc System

The addition of nucleating agents to semicrystalline polymersis largely used in the processing industry of plastic materials to improve some properties of polymers as well as for economical and technological reasons. In this work, the influence of talc concentration on the nucleation efficiency of poly(propylene) (PP), as well as on the non-isothermal kinetics of the crystallization of that system were determined by differential scanning calorimetry (DSC). The nucleating efficiency was determined by Fillon's method, and the dynamic nucleation by Ozawa's method at cooing rates of 2, 5 and 10°C min^–1. The results show that both the degree of crystallinity and the crystallization temperature increase with the filler content and decrease at higher cooling rates and that Ozawa's (n,) exponent and the nucleation efficiency increase with temperature and filler content. It was also shown that the nucleating efficiency of talc in poly(propylene) is comparable to the best heterogeneous nucleating agents available. This revised version was published online in August 2006 with corrections to the Cover Date.     

利用双水相体系的温度诱导效应萃取甘草酸

利用双水相分配技术结合温度诱导效应提取甘草酸，研究甘草酸单铵盐在环氧乙烷－环氧丙烷共聚物（EOPO）／混合磷酸钾（KHP）体系中的分配行为，通过实验确定了最佳体系：EOPO L64浓度为28（wt)%，K2HPO4浓度为32（wt）％。甘草酸单铵盐最大总收率达68.4%，为工业上采用双水相技术提取干草酸提供了一种新途径。