The disorderly exfoliated LDHs/PMMA nanocomposites synthesized by in situ bulk polymerization: The effects of LDH-U on thermal and mechanical properties

The disorderly exfoliated layered double hydroxides/poly(methyl methacrylate) (LDHs/PMMA) nanocomposites were obtained in a two-stage process by the in situ bulk polymerization of methyl methacrylate (MMA) in the presence of 10-undecenoate intercalated LDH (LDH-U). The dispersed behavior of the LDH-U in the PMMA matrix was identified by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/visible transmission spectroscopy. All these nanocomposites showed significantly enhancement of glass transition temperature (T_g) and the decomposition temperatures compared to pristine PMMA, as identified in differential scanning calorimetry (DSC) and thermogravimetric (TGA) analysis. The tensile modulus of these nanocomposites was also enhanced by incorporating the LDH-U into the PMMA matrix and increased as the amount of LDH-U increased. According to the analytical method of Ozawa-Flynn, the degradation activation energies of these nanocomposites are higher than that of pristine PMMA.     

半导体纳米复合材料ZnS/PMMA制备及其光学性质的研究

采用预聚法和溶胀法制备了具备光学透明性和可加工性的半导体纳米复合材料ZnS/PMMA. 用透射电镜(TEM)观察了ZnS纳米粒子在聚合物基体中的形貌. 结果表明， 基体中ZnS为六方晶型. 比较了分别以含锌微凝胶(ZnP)和ZnCl2为Zn2+源时,ZnS在基体中的生长情况. 紫外吸收和荧光光谱表明,掺杂了ZnS后的PMMA基体在280 nm处出现了一个新的吸收峰和强的荧光峰.     

PS-PMMA嵌段共聚物/PMMA在选择性溶剂中的自组装行为

用动态光散射和透射电镜研究了嵌段共聚物聚苯乙烯-聚甲基丙烯酸甲酯(PS-b-PMMA)和其对应的均聚物聚甲基丙烯酸甲酯(PMMA)在选择性溶剂四氢呋喃/环己烷(THF/CYH)中的自组装行为.选择性溶剂对PS嵌段是良溶剂,对PMMA嵌段和均聚物PMMA是非良溶剂,实验结果表明,在适当的分子量及组成条件下,PS-PMMA/PMMA在选择性溶剂中形成了单分散的纳米胶束,均聚物PMMA与PMMA嵌段一同形成了胶束的核,通过控制均聚物PMMA的量可以在较大的范围内调整胶束的尺寸.     

Preparation and characterization of microporous PVDF/PMMA composite membranes by phase inversion in water/DMSO solutions

PMMA/PVDF composite membranes were prepared by isothermal immersion-precipitation of dope solutions consisting of PMMA, PVDF, and DMSO into both harsh and soft nonsolvent baths. The effects of PMMA and DMSO contents on the membrane morphology, crystal structure, thermal behavior and tensile strength of the formed membrane were investigated. For a PMMA-free casting dope immersed in a harsh bath, such as pure water, the formed membrane exhibited a typical asymmetric morphology characterized by skin, finger-like macrovoids, and cellular pores. In contrast, when a soft 70% DMSO bath was adopted, PVDF crystallized to form a membrane packed by spherulitic globules. Incorporation of PMMA gave rise to interesting morphological features; e.g., PVDF globules were observed to adhere to the interlocked polymer branches coexisting with the continuous porous channels, as revealed by high resolution FESEM imaging. XPS analysis of the surfaces of the composite membranes suggested the occurrence of a surface segregation phenomenon, wherein PVDF preferentially migrated to the top surface region of the membrane such as to minimize the interfacial energy. XRD analyses indicated that PVDF crystallized into ‘α’ structure in both PVDF and PMMA/PVDF composite membranes. The crystallinity of the membranes was found to decrease with increasing PMMA content, which was confirmed by DSC thermal analyses. The latter results also indicated a significant decrease in membrane’s melting temperature as the PMMA content was increased. Tensile strengths of the membranes were improved by inclusion of PMMA in either harsh or soft baths. However, elongation at break showed a reversed trend.     

Investigation of flexural properties and failure behaviour of biaxial braided CFRP

In this research, the experimental tests of quasi-static three-point bending and three-point bending fatigue were carried out for a ±25° biaxial braided carbon fibre reinforced polymer (CFRP) manufactured using vacuum assisted resin transfer moulding (VARTM). A finite element (FE) model was also set up for quasi-static testing and the prediction results revealed that local fibre volume fraction (FVF) is a primary source affecting the mechanical properties of braided CFRP. The fatigue of the braided CFRP was defined as three different stages according to the flexural modulus results. The damage modes of the test specimens were observed via a digital microscope and scanning electron microscope (SEM) and the process-induced defects were summarised. With compiled results and observations, this study provides a better understanding of failure and fatigue behaviour of biaxial braided composites and their flexural properties which offers a good basis for any further research in fibre volume fractions, structure design and manufacturing for braided CFRP.     

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca₃Al) and calcium iron undecenoate (Ca₃Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.     

Variation of benzyl anions in MgAl-layered double hydroxides: Fire and thermal properties in PMMA

Magnesium aluminum layered double hydroxides (MgAl-LDHs) intercalated with a range of benzyl anions were prepared using the coprecipitation method. The benzyl anions differ in functionality (i.e. carboxylate, sulfonate, and phosphonate) and presence or absence of an amino substituent. Various methods for preparing LDHs (i.e. ion exchange, coprecipitation and rehydration of the calcined LDH methods) have been compared with the MgAl-benzene phosphonate and their effect on fire and thermal properties was studied. After characterization, the MgAl-LDHs were melt-blended with poly(methyl methacrylate) (PMMA) at loadings of 3 and 10% by weight to prepare composites. Characterization of the LDHs and the PMMA composites was performed using FTIR, XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. FTIR and XRD analyses confirmed the presence of the charge balancing benzyl anions in the galleries of the MgAl-LDHs. Improvements in fire and thermal properties of the PMMA composites were observed. The cone calorimeter revealed that the addition of 10% MgAl-LDHs reduces the peak heat release rate by more than 30%.     

Rheological,mechanical and morphological properties of thermoplastic vulcanizates based on NR‐g‐PMMA/PMMA blends

Graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA) was prepared using semi‐batch emulsion polymerization technique via bipolar redox initiation system. It was found that the grafted PMMA increased with the increase of methyl methacrylate (MMA) concentration used in the graft copolymerization. The NR‐g‐PMMA was later used to prepare thermoplastic vulcanizates (TPVs) by blending with PMMA through dynamic vulcanization technique. Conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied. It was found that the CV system provided polymer melt with lower shear stress and viscosity at a given shear rate. This causes ease of processability of the TPVs via extrusion and injection molding processes. Furthermore, the TPVs with the CV system showed higher ultimate tensile strength and elongation. The results correspond to the morphological properties of the TPVs. That is, finer dispersion of the small vulcanized rubber particles were observed in the PMMA matrix. Various blend ratios of the NR‐g‐PMMA/PMMA blends using various types of NR‐g‐PMMA (i.e. prepared using various percentage molar ratios of NR and MMA) were later studied via dynamic vulcanization by a conventional sulphur vulcanization system. It was found that increasing the level of PMMA caused increasing trend of the tensile strength and hardness properties but decreasing level of elongation properties. Increasing level of the grafted PMMA in NR molecules showed the same trend of mechanical properties as in the case of increasing concentration of PMMA used as a blend component. From morphological studies, two phase morphologies were observed with a continuous PMMA phase and dispersed elastomeric phase. It was also found that more finely dispersed elastomeric phase was obtained with increasing the grafted PMMA in the NR molecules. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of inorganic components on the structure and thermo-oxidative degradation of PMMA modified metal alkoxide–EAA complex

Poly(methyl methacrylate) (PMMA) modified titanium and zirconium n-butoxide–ethyl acetoacetate (EAA) complex [M5-Ti(OBuⁿ)₂(EAA)₂ and M5-Zr(OBuⁿ)₂(EAA)₂] were obtained from trialkoxysilane-functional PMMA and EAA modified titanium and zirconium alkoxide via the sol–gel method. Infrared (IR), ¹³C nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to analyze the structures and properties of the hybrids with various proportions of metal oxide species. The effect of the complex of metal oxides and EAA ligands on structure and thermo-oxidative degradation of the M5-Ti(OBuⁿ)₂(EAA)₂ and M5-Zr(OBuⁿ)₂(EAA)₂ hybrids were investigated in this study. The ¹H spin–diffusion path length of the hybrids was in a nanometer scale as estimated from the spin–lattice relaxation time in a rotating frame (T_1ρ^H). The apparent activation energies (E_a), evaluated by van Krevelen’s method, for random scission of PMMA segments in hybrids decreased with increasing metal oxide content.     

Controllable synthesis of nanosilica surface-grafted PMMA macromonomers via catalytic chain transfer polymerization

Catalytic chain transfer polymerization (CCTP) has emerged as an efficacious method to produce low-molecular weight polymers. In this paper, we reported the first controllable synthesis of nanosilica surface-grafted poly(methyl methacrylate) (PMMA) (SI-PMMA) macromonomers by using bis(aqua)bis((difluoroboryl)-dimethylglyoximato)cobalt(II) (CoBF) as a chain transfer catalyst via CCTP. In a typical run, we firstly prepared functionalized nanosilica by using 3-(trimethoxysilyl)propylmethacrylate (MPS) as the coupling agent, allowing naosilica containing unsaturated double bonds in end groups. Subsequently, SI-PMMA macromonomers were prepared by PMMA surface-grafted onto the functionalized nanosilica via CCTP. The as-prepared products were characterized by Fourier transforms infrared (FT-IR) spectrum, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transforms Raman (FT-Raman) spectrum and gel permeation chromatography (GPC). We also investigated the dependence of macromonomers on CoBF concentrations.     

Effect of inorganic phase on polymeric relaxation dynamics in PMMA/silica hybrids studied by dielectric analysis

Dielectric relaxation spectroscopy was used to investigate the effect of the inorganic phase on the polymeric relaxation dynamics in PMMA/silica hybrids synthesized in situ via sol-gel processes. It was found that the large-scale molecular motions of PMMA were influenced by the addition of silica, inducing longer mean relaxation times, more heterogeneous relaxing environments and the higher activation energy. Explanations based on hydrogen-bond interactions between two phases and a fraction of entrapped chain segments in silica networks were proposed to understand the influence of the silica.     

一种连接石英毛细管的聚甲基丙烯酸甲酯电泳芯片的制作及其应用

利用模拟仿真软件模拟了死体积对于电泳分离的影响,并提出了一种实现聚甲基丙烯酸甲酯(Poly-methylmethacrylate,PMMA)电泳芯片与毛细管的最小死体积连接方法.将紫外吸收检测的检测窗口设计在石英毛细管上,使该PMMA芯片上的电泳分析可以直接采用紫外吸收检测器进行检测.利用该芯片对维生素B2进行了电泳分析,理论塔板数为73000/m;联磺甲氧苄啶片中的3种组分的分离度为4.5和1.9,3个峰迁移时间的RSD依次为1.0%,1.4%和1.0%,峰高的RSD依次为4.1%,3.0%和4.1%(n=5).     

Ternary structure design based on hydrogen bonding for transparent and flame retardant PMMA with good mechanical properties

The synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present,but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas-phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V-1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties.     

Structure Characterization and Thermal Properties of PMMA／Montmorillonite Nanocomposites via Emulsion Polymerization

Montmorillonite(MMT) modified with sodium silicate can change the arrangement of its layers fromedge-face and edge-edge to face-face. With the fine dispersion of the modified MMT in water, the cation-ex-change reaction was carried out with cetyltrimethyl ammonium bromide (CTAB) to obtain organo-montmoril-lonite (OMMT). As OMMT was uniformly dispersed in methyl methacrylate (MMA) monomer, PMMA/OMMT nanocomposites were formed via a common emulsion polymerization. The products were extractedwith hot acetone and characterized by FTIR, molecular weight, X-ray diffraction(XRD), transmission elec-tron microscopy(TEM), DSC and TGA. These results show that most of the OMMT layers have been exfo-liated, while the thermal stability is increased obviously. By means of FTIR spectral analysis, the ratios ofthe macromolecular radicals‘ termination of disproportionation patterns to combination are increased with theaddition of OMMT. This result further confirms the increase of the thermal degradation temperatures andglass transition temperatures of the PMMA/OMMT nanocomposites.     

Effects of incorporation of modified silica nanoparticles on the mechanical and thermal properties of PMMA

Silica nanoparticles of various sizes have been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA) matrix to enhance its thermal and mechanical properties. In order to improve nanoparticles dispersion, PMMA grafted particles have been prepared by atom transfer radical polymerization (ATRP) from well-defined silica nanoparticles. This strategy was expected to ensure compatibility between both components of the PMMA nanocomposites. TEM analysis have been performed to evaluate the nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites thermal stability and mechanical properties have been investigated by both thermogravimetric and dynamical mechanical analysis.     

Co-continuous phase structure formed in melt processing inducing shear bands to prevent crack propagation: Significant improvement in impact toughness of PMMA

High toughened polymeric materials have a wide application in many fields. Poly(methyl methacrylate) (PMMA) is a typical brittle polymer and it has been difficult to prepare high toughened PMMA material for a long time. To work on this issue, co-continuous phase structure was devised in PMMA/chlorinated polyethylene (CPE) blends through controlling the interfacial tension and viscosity in this work, resulting in the pronounced enhancement of impact toughness. The notched impact strength of co-continuous blends with 40 wt% CPE was up to 28.5 kJ/m², increased by 26 times compared with pure PMMA. Selective extraction experiments, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) showed that the CPE network was thin and weak when CPE addition was low, but became dense and strong once the content was more than 20 wt%. Two toughening mechanisms, i.e. cavitation and shear yielding, were put forward based on the micrographs of impact-fractured surfaces and double-notch four-point-bending test. This work may broaden the application prospects of PMMA and provide a new strategy to prepare high toughened polymeric materials through fabricating co-continuous in polymer blends.     

A PMMA composite as an optical diffuser in a liquid crystal display backlighting unit (BLU)

The effect of thermo-physical properties, relative humidity and stiffness on the warpage of a poly(methyl methacrylate) (PMMA) diffusing plate modified with glass fibers in a direct-lit backlight unit (BLU) of a liquid crystal display (LCD) was investigated. The warpage of the PMMA diffusing composites modified with a glass fiber were significantly reduced relative to that of a conventional PMMA diffusing plate. Luminance and scattering characteristics of the PMMA diffusing composites having 5, 10, 20 vol% of glass fibers were measured. Although the luminance of the composite was lowered as increasing the volume fractions of glass fibers in the PMMA composites, good brightness uniformity of the composites on a light source was obtained.     

PMMA-PEO共混体系的辐射交联

<正> 聚甲基丙烯酸甲酯(PMMA)是典型的辐射裂解型聚合物。经辐照后,PMMA主链发生无规断裂。在聚合物共混体系中,PMMA是否能发生交联,这是辐射化学中一个非常重要的研究课题之一,也是一项探索性工作。 PMMA-PEO共混体系是可以分子水平共溶的体系。本文试图将共混体系的相容性与共混体系中的裂解型聚合物的辐射效应联系起来,讨论PMMA-PEO共混体系的辐射交联。     

Influence of the nature of the porous confining network on the sorption, diffusion and mechanical properties of hydrogel IPNs

Two series of amphiphilic hydrogels of various compositions were prepared by sequentially interpenetrating two polymer networks, a poly(2-hydroxyethyl acrylate) (PHEA) network inside either a macroporous matrix of poly(methyl methacrylate) (PMMA) or a macroporous poly(ethyl acrylate) (PEA) network. In both cases poly(2-hydroxyethyl acrylate) (PHEA) served as network II, and the firstly formed porous network was a hydrophobic homonetwork, PMMA or PEA, that conferred mechanical strength to the hydrogel. In order to obtain hydrogels with high hydrophilic content, the first network was prepared in the presence of a solvent, thus yielding a macroporous network. The two families of IPNs thus obtained were: (net-PMMA)-ipn-(net-PHEA) and (net-PEA)-ipn-(net-PHEA), with a PHEA content ranging from 36% to 87% and from 64% to 94%, respectively. The novelty of the work consisted in comparing the effect of using as the first macroporous network a polymer which is glassy at room temperature (PMMA) and another of the same family (PEA) but which is in the rubber state at room temperature. Swelling studies showed that the specific equilibrium water content of PHEA falls from 1.6 for pure (unconfined) PHEA to values that range from 0.4 to 1, for the (net-PMMA)-ipn-(net-PHEA), whereas in the second IPNs family, the equilibrium water uptake of PHEA phase is, at least, the same as that of the pure PHEA (in some cases it is greater). This means that the expansion of the PHEA phase is not restricted by the confining hydrophobic component when this last is in the rubber state at room temperature. Whereas for the first IPNs the mechanical properties significantly increased (storage modulus at 37 °C from 0.25 to 2.5 GPa) compared with those of pure PHEA (25.12 MPa), little if any reinforcing effect was observed in the second type of IPNs. This is due to the fact that the glass transition of the PEA network takes place at a lower temperature than that of PHEA, so both components are in the rubbery state at room temperature. Both series behave differently also in dynamic water sorption experiments: the rigid PMMA network hinders the diffusion of water, yielding lower values of the apparent diffusion coefficients. By contrast, with the PEA polymer as network I this diffusion is similar to that of the pure PHEA homonetwork.     

Optical and microstructural studies on electron irradiated PMMA: A positron annihilation study

The effect of electron irradiation on the free volume related microstructural and optical properties of Poly(methyl methacrylate) have been studied using Positron Annihilation and other techniques. The FTIR spectral study on the irradiated films suggests the existence of CC group and is understood by invoking the carbonaceous clusters as a consequence of chain scission in PMMA. Using UV-Visible absorption spectra the optical parameters like optical energy bandgap and activation energy were determined and the variation of these parameters suggests the existence of defects within the irradiated sample. Following Robertson’s theory, the carbonaceous cluster size is estimated and it increases with increase in electron dose. The XRD study indicates the enhancement of amorphous nature of the film due to chain scission by irradiation. The Positron annihilation result shows that electron irradiation affects the free volume related microstructure and the carbonaceous clusters may act as positron scattering centers.