A single active site metal center of neodymocene chloride for the ring‐opening polymerization of ε‐caprolactone

A germyl‐bridged lanthanocene chloride, Me₂Ge(^tBu‐C₅H₃)₂LnCl (Ln = Nd; (Cat‐ Nd ), was prepared and successfully used as single catalyst to initiate the ring‐opening polymerization of ε‐caprolactone (ε‐CL) for the first time. Under mild conditions (60°C,[ε‐CL]/[Ln] = 200, 4 h), Cat‐ Nd efficiently catalyzes the polymerization of ε‐CL, giving poly(ε‐caprolactone) (PCL) with high molecular weight (MW) (>2.5 × 10⁴) in high yield (>95%). The effects of molar ratio of [ε‐CL]/Cat‐Nd, polymerization temperature and time, as well as solvent were determined in detail. When the polymerization is carried out in bulk or in petroleum ether, it gives PCL with higher MW and perfect conversion (100%). The higher catalytic activity of this neodymocene chloride could be ascribed to the bigger atom in the bridge of bridged ring ligands. Some activators, such as NaBPh₄, KBH₄, AlEt_3, and Al(i‐Bu)₃, can promote the polymerization of ε‐CL by Cat‐ Nd, which leads to an increase both in the polymerization conversion and in the MW of PCL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1212–1217, 2012     

In Situ synthesis of multiblock copolymers of poly(ϵ‐caprolactone) with different poly(ether diols) based polyurethane by reactive extrusion

Polyurethanes with multiblock copolymers of poly(?‐caprolactone) (PCL) and poly(tetramethylene oxide) glycol (PTMG) or poly(ethylene glycol) (PEG) as a soft segment were synthesized in situ via reactive extrusion from ?‐caprolactone (CL) and 4,4′‐diphenylmethane diisocyanate (MDI). The titanium alkoxide mixture generated from an ester‐exchange reaction between titanium propoxide [Ti(OPr)₄], and excessive PTMG or PEG was used as an initiator and catalyst. Compared to the reported fabrication of polycaprolactone‐based polyurethane (PCLU), the in situ reactive extrusion preparation not only explored a new rapid route for the fabrication of PCLU but also offered a simplified, controllable approach for the production of PCLU in a successive mass scale. A series of PTMG–PCLUs and PEG–PCLUs with different PCL block‐average degrees of polymerization (DP_n's) were prepared by only an adjustment of the relative concentration of CL in the reaction system, with a certain constant molar ratio of MDI to titanium alkoxide. ¹H‐NMR, gel permeation chromatography, and differential scanning calorimetry results indicate that all of the CL monomers were converted in the polymerization, and the molecular weight of the copolymers was about 8 × 10⁴ g/mol with a polydispersity index of approximate 2.4. With an increase in the PCL block‐average DP_n in PTMG–PCLU from 25 to 40, the tensile strength increased from 16.5 to 22.7 MPa, and the melting point increased from 46.1 to 49.5°C. It was also verified by PEG–PCLU prepared with organic Ti of lowered content in the initiator mixture that the mechanical properties could be greatly affected and dropped with decreasing content of organic Ti in the initiator mixture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Controllable ring‐opening polymerization of trimethylene carbonate catalyzed by aliphatic tertiary amines in the presence of benzyl alcohol or F127

With the increased awareness of avoiding residue metals, the field of organocatalysts is attracting more attention. Aliphatic tertiary amines, such as triethylamine (TEA), N, N, N, N‐tetramethylethylenediamine (TMEDA) and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDTA), have low boiling points which allow their easy elimination after a chemical reaction. Here, we used these aliphatic tertiary amines to catalyze ring‐opening polymerizations (ROPs) of trimethylene carbonate (TMC). In the presence of benzyl alcohol, the catalytic activities of the tertiary amines were in the order of TEA < TMEDA < PMDTA. Correlation between the molecular weight of polycarbonates and monomer conversions was linear, suggesting the polymerization was controlled. The polymerization pathway was presumed to follow an alcohol‐activated mechanism according to the end‐group fidelity determined using ¹H NMR spectroscopy. The ROP of TMC was also successfully initiated by PEO₉₉‐PPO₆₅‐PEO₉₉ (F127) under the catalysis of the tertiary amines, producing well‐defined PTMC_n‐F127‐PTMC_n copolymers with narrow dispersity ( ca 1.2) and with thermosensitive properties in aqueous solution. Furthermore, copolymerizations of TMC with acryloyl‐containing cyclic carbonate were catalyzed by the tertiary amines in the presence of F127. No crosslinking reactions were detected. Our results demonstrate that the aliphatic tertiary amines have the potential to catalyze TMC homo‐ or copolymerization featuring controllable structure and composition under mild conditions. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of fluorine‐containing polysiloxanes obtained via ring‐opening copolymerization of trifluoropropyltrimethylcyclotrisiloxane with cyclotetrasiloxane catalyzed by rare earth solid superacid SO$_{4}^{2-}$/TiO2/Ln3+

Traditional catalysts such as (CH₃)₄NOH, NaOH, KOH, n‐BuLi and CF₃SO₃H can catalyze the copolymerization of trifluoropropyltrimethylcyclotrisiloxane with cyclotetrasiloxane to afford fluorine‐containing polysiloxanes. However, use of these catalysts poses significant difficulties in handling and separation. In this work, fluorine‐containing polysiloxanes were synthesized through a novel and environmentally friendly method: ring‐opening copolymerization of trifluoropropyltrimethylcyclotrisiloxane with cyclotetrasiloxane catalyzed by rare earth solid superacid SO /TiO₂/Ln³⁺. The effects of reaction conditions were examined in detail. The yield sequence of various rare earth catalysts is Nd ～ La ～ Y ～ Sm > Gd, while the number‐average molecular weight sequence is Nd > La > Y > Sm > Gd. The optimum conditions for the ring‐opening copolymerization of trifluoropropyltrimethylcyclotrisiloxane with cyclotetrasiloxane are as follows: [Nd³⁺] = 0.05 mol L^?1 and mol L^?1 in the immersing solution, SO /TiO₂/Nd³⁺ calcined at 500 °C and the copolymerization conducted at 80 °C for 40 min. Structures of resulting copolymers were characterized using size exclusion chromatography, ¹H NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and contact angle measurements. According to the copolymerization features, a cationic equilibrium reaction mechanism is proposed. Copyright © 2012 Society of Chemical Industry     

基于ANSYS的某型载重子午胎成型机主轴箱的改进设计

针对一次法载重子午胎成型机主轴箱在轮胎生产厂家所出现的主轴轴承磨损严重问题进行改进,主轴支撑由单轴承改进为双轴承支撑.从生产中遇到的问题入手,分析了问题产生的原因,提出了改进方案,通过理论计算和有限元分析为改进的设计方案奠定了理论基础,同时也是对改进设计的有效验证.     

Preparation of waterborne hyperbranched polyurethane acrylate/LDH nanocomposite

A series of novel waterborne hyperbranched polyurethane acrylate (WHPUA)/layered double hydroxide (LDH) nanocomposites based on hyperbranched aliphatic polyester Boltorn H20 (H20) and MgAl-LDH were successfully synthesized by in situ polymerization approach. The MgAl-LDH was firstly modified by sodium dodecyl sulfate (SDS) through the coprecipitation method, and then grafted by isophorone diisocyanate (IPDI), forming a complex with NCO groups at the surface and interlayer of LDH (LDH-DS-NCO). The residual hydroxyl groups after modification with succinic anhydride were crosslinked by the semi-adduct of IPDI reacted with HEA, and LDH-DS-NCO, followed by a neutralization reaction with triethylamine. The resulting water dispersible hyperbranched polyurethane acrylate WHPUA/LDH hybrid oligomer was then exposed to a medium pressure mercury lamp, forming a partially exfoliated WHPUA/LDH nanocomposite in the presence of a fragmental photoinitiator. The chemical structure, crystal configuration, morphology of WHPUA/LDH nanocomposite were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and high resolution transmission electron microscopy. The experimental results indicated that both the intercalated and exfoliated structures were formed in the UV cured polymer/LDH nanocomposite. The TGA results showed that the thermal stability was improved. Moreover, the pencil hardness was greatly increased, and the flexibility remained at an acceptable level for the UV cured polymer/LDH nanocomposites.     

Removal of Chromium from Synthetic and Real Effluents Using Uncalcined MgAl-NO3 Layered Double Hydroxide: Column Study and Modeling

In this study, the sorption ability of MgAl-NO₃ layered double hydroxide prepared by coprecipitation method to remove Cr(VI) from aqueous solution was investigated in fixed-bed column. The sorbent was characterized by XRD, SEM, FTIR, BET surface area, and pH_zpc. The effects of bed height (2–5 cm), flow rate (5–20 mL/min), inlet Cr(VI) concentration (30–100 mg/L), and solution pH (3–8) on the breakthrough characteristics of the column were determined, and the optimum conditions were observed at 3.5 cm, 10 mL/min, 50 mg/L, and a pH of 6. Moreover, the performance of the sorbent to remove Cr(VI) from wastewater was also examined at optimum conditions. The results show high removal and good selectivity for Cr(VI) in wastewater containing large amounts of coexisting anions.     

A Novel Micro Ring Structured PPy/pTS Free Standing Film With Improved Actuation Stability

A free-standing PPy/pTS film with a novel micro ring structured surface morphology have been electropolymerized by using CTAB/SDBS catanionic vesicles as templates. Characterizations showed that the micro ring structured PPy/pTS film was chemically similar to typical PPy/pTS films, while some DBS anions were also incorporated into the film from the mixed surfactants solutions. The micro ring structured PPy/pTS showed a slightly lower conductivity than conventional PPy/pTS films, due to the incorporation of DBS anions. The micro ring structured PPy/pTS films showed improved actuation stability compared to the conventional PPy/pTS films.     

Stability of SiN<Subscript>X</Subscript>/SiN<Subscript>X</Subscript> double stack antireflection coating for single crystalline silicon solar cells

Double stack antireflection coatings have significant advantages over single-layer antireflection coatings due to their broad-range coverage of the solar spectrum. A solar cell with 60-nm/20-nm SiN_X:H double stack coatings has 17.8% efficiency, while that with a 80-nm SiN_X:H single coating has 17.2% efficiency. The improvement of the efficiency is due to the effect of better passivation and better antireflection of the double stack antireflection coating. It is important that SiN_X:H films have strong resistance against stress factors since they are used as antireflective coating for solar cells. However, the tolerance of SiN_X:H films to external stresses has never been studied. In this paper, the stability of SiN_X:H films prepared by a plasma-enhanced chemical vapor deposition system is studied. The stability tests are conducted using various forms of stress, such as prolonged thermal cycle, humidity, and UV exposure. The heat and damp test was conducted for 100 h, maintaining humidity at 85% and applying thermal cycles of rapidly changing temperatures from -20°C to 85°C over 5 h. UV exposure was conducted for 50 h using a 180-W UV lamp. This confirmed that the double stack antireflection coating is stable against external stress.