聚甲基丙烯酸甲酯热降解行为研究

采用热损失法研究了不同的工艺条件对聚甲基丙烯酸甲酯熟降解的影响和热降解动力学的研究,结果表明,聚甲基丙烯酸甲酯在氮气氛下热降解为1级反应.平均活化能为195.36 kJ/mol;在氧气氛下热降解分为2个阶段,反应前期为1.5级反应,反应中后期为1级反应.升温速率对2段式反应的温度划分有较大的影响.随着升温速率的提高,1.5级反应的温度区域增大.     

提高聚甲基丙烯酸甲酯热稳定性的研究

本文分析了聚甲基丙烯酸甲酯热稳定性差的产生原因及处理方法。聚甲基丙烯酸甲酯热稳定性差产生的原因是:①在聚合过程中由于歧化终止产生C=C双键,形成不稳定的终端基团;②氧气参与过程反应生成活泼的过氧自由基,在夺取聚合物中的氢原子,形成C=C双键,因而降低了聚甲基丙烯酸甲酯的热稳定性。解决方法是:通过与其它单体共聚,消除不稳定终端基团,以及使用抗氧剂消除氧气对有聚合物自由基的氧化作用。     

基于 FLUENT 的磁流变液的流动行为仿真

对磁流变液在不同条件下的流动行为进行分析,利用 Gambit 建立了磁流变液的俯视二维简化模型并对其进行了网格划分。应用 FLUENT 对不同入口速度和障碍物大小条件下磁流变液中基础油的流动行为进行了仿真模拟,得出不同障碍大小和入口速度下的速率变化云图,分析表明仿真效果能较好的模拟磁流变液的真实流动状态,能较好的解释磁流变液在不同剪切速率和链聚集程度下的流动行为。     

丙烯酸甲酯共聚单体对聚甲基丙烯酸甲酯物理老化行为的影响

通过差示扫描量热法(DSC)研究了聚甲基丙烯酸甲酯(PMMA)和甲基丙烯酸甲酯(MMA)-丙烯酸甲酯(MA)共聚物(P(MMA-co-MA))在40、60、80℃的物理老化行为.结果表明:二者的老化速率βH都随老化温度的升高而增大.通过计算得出,PMMA改变局部构象所需的自由能大于P(MMA-co-MA),并且参与到构象松弛的分子链段尺寸小于P(MMA-co-MA),这是由于在共聚物中丙烯酸甲酯链段的加入影响了临近甲基丙烯酸甲酯链段的运动能力.因此,在较低温度下PM-MA的老化速率远小于P(MMA-co-MA).但随着老化温度升高,参与到构象重排的分子链段逐渐增加,并且MMA链段的运动能力也有了很大提高,这时少量MA链段对分子链段整体运动能力的影响变得不再明显,PMMA与P(MMA-co-MA)的老化速率趋于相同.     

丙烯酸甲酯共聚单体对聚甲基丙烯酸甲酯物理老化行为的影响

通过差示扫描量热法(DSC)研究了聚甲基丙烯酸甲酯(PMMA)和甲基丙烯酸甲酯(MMA)-丙烯酸甲酯(MA)共聚物(P(MMA-co-MA))在40、60、80℃的物理老化行为。结果表明:二者的老化速率βH都随老化温度的升高而增大。通过计算得出,PMMA改变局部构象所需的自由能大于P(MMA-co-MA),并且参与到构象松弛的分子链段尺寸小于P(MMA-co-MA),这是由于在共聚物中丙烯酸甲酯链段的加入影响了临近甲基丙烯酸甲酯链段的运动能力。因此,在较低温度下PMMA的老化速率远小于P(MMA-co-MA)。但随着老化温度升高,参与到构象重排的分子链段逐渐增加,并且MMA链段的运动能力也有了很大提高,这时少量MA链段对分子链段整体运动能力的影响变得不再明显,PMMA与P(MMA-co-MA)的老化速率趋于相同。     

低吸水性聚甲基丙烯酸甲酯的研究

主要针对降低PMMA吸水率的要求,运用分子设计原理用苯乙烯、N-苯基马来酰亚胺进行PMMA共聚,并对其制备工艺进行改进,得到吸水率降低30％左右,力学性能变化不大,800nm透光率可达90％的PMMA共聚物。     

低吸水性聚甲基丙烯酸甲酯的研究

主要针对降低PMMA吸水率的要求,运用分子设计原理用苯乙烯、N-苯基马来酰亚胺进行PMMA共聚,并对其制备工艺进行改进,得到吸水率降低30％左右、力学性能变化不大、800nm透光率可达90％的PMMA共聚物。     

聚甲基丙烯酸甲酯的改性研究

本文综述了聚甲基丙烯酸甲酯(PMMA)在耐热性能、耐磨损性能、阻燃等方面改性研究的途径及国内外研究的最新进展,分析了各种改性方法的特点,并展望了PMMA改性研究今后的发展方向。     

磁流变液的研究

磁流变液是一种新兴的液体传动介质 ,它具有优越的性能 ,被广泛用于液压传动 ,汽车、制造、机械加工等领域。本文着重介绍了磁流变液的制备及其国内外进展情况     

磁流变液智能流体研究进展、应用及展望

通过回顾磁流变液智能流体的组成及制备方法,分析了磁流变液智能流体主要流变机理以及在工程中的应用前景,并着重介绍了磁流变液在油气田开发中的研究进展。基于磁流变液特点、应用环境以及使用成本等因素,指出了磁流变液智能流体未来向高温稳定、可循环利用以及环境友好发展的新趋势。     

Rheological properties of poly(methyl methacrylate)/rigid ladderlike polyphenylsilsesquioxane blends

A series of poly(methyl methacrylate) (PMMA) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared at weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20 by solution casting and then hot‐pressing. Their rheological properties have been studied under both dynamic shear and uniaxial elongation conditions. Their rheological properties depend on the compositions. The storage modulus, G′, loss modulus, G″, and dynamic shear viscosity, η*, of the PMMA/PPSQ 95/5 blend were slightly lower than those of pure PMMA. However, the values of G′, G″, and η* for the other PMMA/PPSQ blends are higher than those of PMMA. The G′ values increase with an increase in PPSQ content from 5% through 15% PPSQ at low frequencies and then drop as the PPSQ content increases to 20%. Uniaxial elongational viscosity (η_E) data demonstrate that PMMA/PPSQ blends exhibit slightly weaker (5% PPSQ) and much weaker (10% PPSQ) strain‐hardening than PMMA. In contrast, the PMMA/PPSQ 85/15 blend shows strain‐softening. Neither strain‐hardening nor strain‐softening was observed in the 80/20 blend. The special rheological properties for the 95/5 blend is probably due to a decrease in PMMA entanglements brought by the specific PMMA–PPSQ interactions. Rheological properties of PMMA/PPSQ blends with higher PPSQ content (≥10%) are mainly affected by formation of hard PPSQ particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 352–359, 2007     

Synthesis and properties of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites

PMMA/MMT nanocomposites were successfully synthesized via in situ intercalative polymerization, and characterized by means of wide‐angle X‐ray diffractometry, transmission electron microscopy, thermal gravimetric analysis, dynamic mechanical analysis and Fourier‐transform infrared analysis. The nanocomposites possess partially exfoliated and partially intercalated structure, in which the silicate layers are exfoliated into nanometre secondary particles with thickness of less than 20 nm and uniformly dispersed in the polymer matrix. In comparison with pure PMMA, the thermal stability, glass transition temperature, and mechanical properties of the polymer are notably improved by the presence of the nanometric silicate layers. It was found that part of the PMMA chains in the nanocomposites are well immobilized inside and/or onto the layered silicates and, therefore, the unique properties of the nanocomposites result from the strong interactions between the nanometric silicate layers and the polymer chains. Copyright © 2003 Society of Chemical Industry     

Optomechanical investigating the impact of grafting polyamide-6 fibers with PMMA on its intrinsic optical properties

An optomechanical characterization was carried out to investigate the influence of grafting polyamide-6 fibers with poly (methyl methacrylate) (PMMA) on their structural relationship properties. Intrinsic optical properties of the modified sample were determined using a method based on the cold drawing process. The Mach-Zehnder interferometer attached with mechanical drawing device was used to determine the refractive indices and birefringence of the polyamide-6 samples at different draw ratios. A graphical method was used to determine the intrinsic birefringence of modified polyamide-6 with PMMA and it was found to be 0.0673 which is less than pure polyamide-6. The resulting data was used to estimate some structural parameters such as the orientation function, optical orientation angle and structural constant. The drawing effect is more significant on the modified sample than on the pure sample. It was found that the grafting process produced a material with new properties that can be used in different applications.     

PMMA/SMA共混体系流变行为与温度依赖性的研究

研究了甲基丙烯酸甲酯/苯乙烯马来酸酐共聚物(PMMA/SMA)体系的流变行为,探讨了SMA中马来酸酐(MA)含量对于共混体系时温叠加和温度依赖性的影响。结果表明,MA含量为12%(质量分数,下同)的PMMA/SMA12体系符合时温叠加原理,在低温下松弛时间与组分的关系存在正偏差,随温度上升浓度涨落加剧而有负偏差的情况出现;MA含量为28%的PMMA/SMA28体系时温叠加原理由于动力学不对称性而失效,在低温区域松弛时间与组分符合对数线性关系,高温区域则出现正偏差;与PMMA/SMA12相比,PMMA/SMA28具有更强的温度依赖性。     

不同组成ABS对ABS／PMMA合金性能的影响

选用两种不同牌号的ABS树脂与PMMA共混，对其组成与性能的关系进行了详细的研究。试验结果表明，不同组成的ABS对ABS/PMMA混合物的光学性能、力学性能以及流变行为的影响都有显著的不同．     

Cosolvency,coil expansion and dimensions of PMMA in mixed solvents

Limiting viscosity numbers ([ν]) and Schulz-Blaschke constants (k_s) of PMMA samples (differing in molecular weight) have been determined at 25°C (as a function of mixed solvent composition) for the following mixtures: acetonitrile+1-butanol, acetonitrile+pentyl acetate, and 1-chlorobutane+pentyl acetate. The first two mixtures are powerful cosolvents of PMMA and the third one is a ‘co-nonsolvent’ of the polymer. The samples are predominantly heterotactic. Their k_s values at θ indicate some association tendency of the polymer. Unperturbed dimensions and coil expansion coefficients have been obtained from [ν], as a function of solvent mixture composition. All the pure liquids are poor or non-solvents of PMMA (at 25°C), but the cosolvent pairs behave as very good solvents for the polymer. The mechanism of such cosolvency is analysed in terms of the different molecular interactions present in these systems.     

Structural and optical properties of iodine-doped PMMA film

Poly(methyl methacrylate) (PMMA) film was cast from solution in benzene (4% W/V). Various samples of iodine-doped PMMA films were prepared by adding different amount of iodine, namely, 0.5, 1, 2, and 8% (w/w), respectively, to PMMA solution in benzene. The structures of pristine and doped PMMA were investigated using analysis of their infrared spectra and wide-angle X-ray diffraction analysis. The refractive index of pristine PMMA is almost equal to that of glass. Changes in the refractive index of various doped PMMA samples have been determined from their reflectance and transmission spectra in ultraviolet–visible range. It has been observed that the refractive index increases at low concentrations of doping, and it is maximum for 1% iodine doping. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1627–1631, 1998     

Human Gingival Fibroblasts Cell Viability of Poly(Lactic Acid) Powder Reinforced PMMA/Hydroxyapatite Biocomposites

The dental composites based on poly(methyl methacrylate)/hydroxyapatite (PMMA/HA) were prepared through heat-processing polymer powder-liquid method, in the presence of poly(lactic acid) powder (PLA; 5–20 phr). The PLA powder enhanced the flexural modulus and strength of PMMA/HA composites. The Alamar Blue assay results indicated the PMMA/HA/PLA composites were able to sustain human gingival fibroblasts (HGF) cells growth. The images of live/dead cells confocal showed the populations of living cells on the composites surface were confluent and the survival of HGF cells on the PMMA composites surface are assured. These features suggested that the PLA powder reinforced PMMA/HA composites demonstrated excellent biocompatibility.     

From a laboratory to a pilot scale production of natural rubber grafted with PMMA

Graft copolymers of natural rubber and poly (methyl methacrylate) (NR‐g‐PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.5 l. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50°C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR‐g‐PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and ¹H‐NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of ¹H‐NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological and mechanical characterization of a PMMA/CdS nanocomposite

Thick film of poly(methyl methacrylate) (PMMA)/CdS nanocomposite have been synthesized by the solution casting process. The nanostructure of the CdS particles has been ascertained through the small angle X-ray scattering (SAXS) technique. The surface morphological characterization of the PMMA/CdS nanocomposite has been done through scanning electron microscopy (SEM) analysis. The variation of mechanical loss factor (Tanδ) with temperature and tensile properties of prepared samples have been studied using Dynamic Mechanical Analyzer (DMA). This study reveals that the glass transition temperature (T_g), Young’s modulus, and fracture energy of the PMMA/CdS nanocomposite are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanoparticles and the matrix of PMMA.