Isothermal crystallization of HDPE/octamethyl polyhedral oligomeric silsesquioxane nanocomposites: Role of POSS as a nanofiller

The isothermal crystallization of HDPE/POSS (polyhedral oligomeric silsesquioxane) nanocomposites (POSS content varying from 0.25 to 10 wt %) was studied using differential scanning calorimetry (DSC) technique. The Avrami model could successfully describe the isothermal crystallization behavior of the nanocomposites. The value of Avrami exponent (n) varies between 2 and 2.5 for all the compositions studied. For a given composition, the values vary with crystallization temperature and in general increased with POSS content up to 1 wt % POSS content and decreased thereafter. The presence of POSS was found to increase the rate of crystallization, which manifested itself in the increased value of the Avrami rate constant (K) and reduced value of crystallization half‐time (t_1/2). The rate of crystallization peaked at 1 wt % POSS content and was almost constant at higher POSS loadings. X‐ray diffraction studies revealed that POSS exists as nanocrystals in HDPE matrix while some POSS gets dispersed at molecular level too. It is observed that only the POSS dispersed at molecular level acts as a nucleating agent while the POSS nanocrystals do not affect the crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

微波辐射下活性炭固载固体酸催化合成乙酸环己酯

报道了利用颗粒状活性炭固载对甲苯磺酸作催化剂，在微波辐射下，快速合成乙酸环己酯。实验结果显示，当微波功率为400W。催化剂用量为0．8g，n(醇)：n(酸)=1．5：1，反应时间仅为30min，酯化率为96．7％。另外通过实验发现,微波辐射下，反应速率明显高于常规加热方式。     

环氧树脂/倍半硅氧烷共混材料的性能研究

通过三烷氧基硅烷水解缩聚反应制备了甲基倍半硅氧烷(MSSQ)单体和乙基倍半硅氧烷(ESSQ)单体,采用红外光谱、核磁共振、元素分析对其进行表征,证实了倍半硅氧烷(SSQ)的立体结构。采用共混法制备了环氧树脂(EP)/SSQ和EP/纳米SiO2共混材料,性能测试结果表明,相对于纯EP及EP/纳米SiO2共混材料,EP/SSQ共混材料具有较高的玻璃化转变温度、热变形温度、热稳定性及力学性能。     

Star-shaped poly(?-caprolactone) with polyhedral oligomeric silsesquioxane core

A readily available octa(3-chloropropyl) polyhedral oligomeric silsesquioxane (POSS) [(ClCH₂CH₂CH₂)₈Si₈O₁₂] framework was used to prepare octa(3-hydroxypropyl) POSS [(HOCH₂CH₂CH₂)₈Si₈O₁₂], which was further used as an initiator to synthesize star poly(?-caprolactone) with POSS core via ring-opening polymerization catalyzed by Stannous (II) octanoate [Sn(Oct)₂]. The organic-inorganic star PCLs were characterized by means of gel permeation chromatograph (GPC), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The wide-angle X-ray diffraction (WAXRD) experiments indicate that the presence of POSS cores did not alter the crystal structure of PCL. The star PCLs exhibited enhanced melting temperatures in comparison with the linear counterpart. The isothermal crystallization kinetics shows that both the overall crystallization rate and the spherulitic growth rate of the star PCLs increased with increasing the concentration of POSS (or with decreasing the arm lengths of the stars). The fold surface free energy of the star PCLs decreased with increasing the concentration of POSS. These results could be interpreted based on the effect of the heterogeneous nucleation of POSS cores, which accelerates the process of crystallization.     

氨基磺酸催化合成乙酸环己酯

研究了以氨基磺酸为催化剂 ,以乙酸和环己醇为原料合成乙酸环己酯的方法 ,讨论了影响酯化反应的各种因素 ,并得出了酯化反应的最佳工艺条件 :醇酸比为 1∶2 (0 .4mol∶0 .8mol)、1.9g氨基磺酸为催化剂、15ml环己烷为带水剂 ,反应时间 110min ,酯收率达 84 5 %。并与十二水合硫酸铁铵、氯化铁等催化剂作了比较。实验结果表明 :以氨基磺酸为催化剂具有催化剂用量少、重复使用效果好 ,反应时间短 ,酯收率高 ,方法简单等优点。     

对甲苯磺酸铜催化合成乙酸环己酯

研究了对甲苯磺酸铜催化乙酸与环己醇的酯化反应,考察了物料配比、催化剂用量、反应时间和带水剂用量等因素对酯化率的影响。实验结果表明,反应的优化条件是乙酸用量为0·2mol,n(环己醇)∶n(乙酸)=1·4,甲苯磺酸铜用量为1·2g,带水剂环己烷为15mL,回流反应60min后酯化率可达96·7%,催化剂重复使用7次仍可保持较高活性。     

Epoxy Networks Modified by a New Class of Oligomeric Silsesquioxanes Bearing Multiple Intramolecular Rings Formed through Si?O?C Bonds

Summary: A new class of silsesquioxane (SSO), containing species with two to nine Si atoms bearing multiple intramolecular rings formed through Si? O? C bonds, was synthesized as a glassy powder. It was characterized by UV‐MALDI‐TOF MS, ²⁹Si NMR and FT IR. Solutions containing different amounts of SSO in the diglycidyl ether of bisphenol A (DGEBA), were homopolymerized in the presence of (4‐dimethylamino)pyridine (DMAP) as initiator, leading to SSO‐modified epoxy networks. SSO species were covalently bonded to the epoxy network without any evidence of phase separation. The SSO addition provoked an increase in the elastic modulus in the glassy state explained by an increase in the cohesive energy density. The SSO addition gave also place to an increase in the intensity of tan δ and a decrease in both the glass transition temperature and the elastic modulus in the rubbery state. This was explained by a decrease in crosslink density associated with the flexibility of SSO structures. DMAP was much more effective than other usual initiators (like benzyldimethylamine, BDMA), in increasing the crosslink density of the resulting epoxy network. This led to high values of the glass transition temperature and the elastic modulus in the rubbery state.

Schematic representation of the chemical structure of the most significant species containing three Si atoms, present in the silsesquioxane.     

Molecular dynamics simulation of mixed matrix nanocomposites containing polyimide and polyhedral oligomeric silsesquioxane (POSS)

Mixed matrix blends containing polyimide (PI) and polyhedral oligomeric silsesquioxanes (POSS) are studied with atomistic molecular dynamics simulation. To examine the effect of functional group, two types of POSS are considered, either octahydrido silsesquioxane (OHS) or octaaminophenyl silsesquioxane (OAPS). The glass transition temperature of the model PI-OAPS blends increases with the incorporation of OAPS, an observation consistent with recent experiments on these systems. A decrease in glass transition temperature is shown for the model PI-OHS blends. Radial distribution functions for both blends are presented to show how packing between the inorganic (POSS) and organic (PI) species in the mixed matrix varies as a function of POSS loading and POSS functionalization. In addition, we report the mobility of the PI chains and POSS molecules in the material by calculating the mean square displacement. These results provide molecular insight about thermal property enhancements afforded by POSS-based additives.     

Thermal properties of new bismaleimide resins containing hydrogen silsesquioxane and diallyl bisphenol A

Bismaleimide (BMI) resins modified with hydrogen silsesquioxane (HSQ) and diallyl bisphenol A (DABPA) (BMI‐HSQ‐DABPA resins) were prepared. DSC, FTIR, and TGA were used to characterize the curing behaviors, structures, and thermal properties of the BMI‐HSQ‐DABPA resins, respectively. The results showed that the glass transition temperatures and thermal stabilities of the cured BMI‐HSQ‐DABPA resins increased with the rise of the contents of HSQ. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of crystallisation and interfacial nature of polyhedral oligomeric silsesquioxane/polypropylene composites in the presence of β-nucleating agent

Polyhedral oligomeric silsesquioxane (POSS)/polypropylene (PP) composites in the presence of β-nucleating agent (β-NAs) were prepared by melt-blending, and the interfacial interaction and crystallisation behaviour were investigated. The experimental results indicated that strong hydrogen bonding interactions were generated between amino groups of β-NAs and silicon hydroxyl groups attached to POSS, allowing the absorption/anchoring of the former on the surface of latter. Compared to POSS, β-NAs exhibited higher nucleation effect on PP, as evidenced by an increment of the crystallisation temperature by 7°C in the presence of β-NAs. As a result, the absorbed β-NAs on the surface of POSS not only improved the interfacial interaction between POSS and polymer matrix using interfacial crystallisation but also promoted the formation of β-crystals with toughening effect, which is very important to prepare excellent-performance PP/POSS composite.