Unusual Phase Separation Kinetics in Poly(Methyl Methacrylate)/Poly(Styrene-co-Acrylonitrile) (PMMA/SAN) Blends with PMMA of Different Molecular Weights

The influence of molecular weight of poly (methyl methacrylate) (PMMA) on the thermodynamics and dynamics of phase separation in PMMA/poly (styrene-co-acrylonitrile) (SAN) blends was investigated via optical microscopy, time-resolved small-angle light scattering (SALS), and dynamic rheological measurements. It was found that the cloud point temperature of the blends decreased with an increase in the molecular weight of the PMMA. The phase separation rates of PMMA 48K/SAN and PMMA 85K/SAN blends with the near-critical composition were almost the same at small quench depths due to the limited mobility of molecular chains at low temperatures. However, an unexpected phase separation dynamics was observed at larger quench depths. Not only the morphology evolution but also the apparent diffusion coefficient D_app calculated from SALS revealed that the phase separation rate was faster in the PMMA 85K/SAN blend than in the PMMA 48K/SAN blend. The possible reasons for this unusual rapid kinetics of phase separation observed in the higher molecular weight blend were discussed in terms of molecular mobility and viscoelasticity.     

Effect of Individualized Cellulose Fibrils on Properties of Poly(Methyl Methacrylate) Composites

Cellulose fibrils were manufactured from flax fibers using chemical treatments followed by cryo-crushing and ultrasonication techniques. The fibrils, consisting mainly of cellulose free from lignin, pectin and hemicellulose, were exploited as a biofiller in preparing poly(methyl methacrylate) (PMMA) matrix composites. The effects of incorporating cellulose fibrils on the physical and mechanical properties of the polymer matrix were investigated. In particular, the influence of the fibrils on the thermal stability and degradation of the composites was studied by means of thermogravimetric analysis carried out in both inert and oxidative atmospheres. The runs performed under air flow revealed the efficiency of the cellulose fibrils in delaying the polymer decomposition during thermal oxidation. The weight loss was slowed down in the composites of all compositions and the temperature of degradation increased with increasing the amount of the fibrils. The combustion properties of the fibril-based composites were evaluated by means of pyrolysis combustion flow calorimetry. The addition of cellulose fibrils into the PMMA matrix resulted in a noticeable decrease of the primary combustion parameters.     

聚甲基丙烯酸甲酯中乙酰丙酮铕水合物掺杂形成的差异化发光中心

制备了均匀且透明的乙酰丙酮铕水合物掺杂的聚甲基丙烯酸甲酯(PMMA)。Judd-Ofelt强场参数Ω2(19.73×10-20 cm2)和Ω4(2.19×10-20 cm2)表明在掺杂样品中三价铕离子周围环境具有较强共价性和反演非对称性。计算得5 D0→7 FJ(J=1,2和4)跃迁的最大发射截面分别为0.38×10-21,4.90×10-21和0.36×10-21 cm2。在365nm紫外光的激发下样品发出紫红色荧光,在254nm紫外光激发下则呈现明亮的红色,表明样品可作为紫外光敏感元件用于光学传感器。掺杂样品折射率与纯PMMA的折射率之间存在合理的差值,当其作为纤芯材料与包层材料纯PMMA结合制成标准尺寸9μm/125μm光纤时支持多模光传输,为进一步研发医疗照明光纤、柔性通讯光纤和光纤传感器提供基础。     

Phase Ordering and Crystallization Kinetics in Ultrathin Poly(ethylene oxide)/Poly(methyl methacrylate) Blend Films

Crystallization in ultrathin Poly(Ethylene Oxide)/Poly(Methyl Methacrylate) (PEO/PMMA) blend films with thickness of ca. 10 nm was investigated by means of microscopic and in situ spectroscopic methods. It was revealed that the blend films undergo a phase ordering in a humid atmosphere before or during crystallization, with PEO de-mixing with PMMA and segregating to the free film interface on the PMMA layer. The de-mixed PEO chains crystallize into a fractal-like morphology by a diffusion-limited process, and the crystal growth is 1-dimensional with Avrami exponent n ≈ 1, resulting in flat-on crystal lamellae with the PEO chains oriented normal to the film plane.     

Effect of Molecular Architecture on Physical Properties of Tree-Shaped and Star-Shaped Poly(Methyl Methacrylate)-Based Copolymers

The synthesis of star-like A(B)_n copolymers based on the hydrophilic poly(ethylene glycol) monomethyl ether (m-PEG, block A) and the hydrophobic poly(methyl methacrylate) (PMMA, blocks B) is reported. We obtained copolymers made of one m-PEG chain and 2 or 4 PMMA blocks using a combined “arm first”—“core first” approach. Such structures were called tree-shaped copolymers where the m-PEG was considered as the trunk and PMMA arms as the branches. Star-like copolymers (B)_nA-A(B)_n built by two tree-shaped fragments with a poly(propylene oxide) (PPO) as the central junction, were also synthesized according to a previously reported procedure. The latter were called star-shaped structures and the synthesis was performed to obtain architectures different from the tree-shaped one but characterized by a similar length of the PMMA arms. Microstructural analysis was carried out through ¹H-NMR and GPC, and the thermal and transport properties (sorption and diffusion) to liquid water were investigated and correlated to the molecular architecture of the two classes of copolymers.     

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.     

Thermal Stability and Degradation Kinetics of Poly(Methyl Methacrylate)/Sepiolite Nanocomposites by Direct Melt Compounding

Poly(methyl methacrylate) (PMMA) nanocomposites based on sepiolite modified with trimethyl hydrogenated tallow amine by an adsorption process were prepared by melt compounding using a corotating twin screw extruder. The morphology and dispersion of sepiolite in the PMMA were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal stability and the activation energies were investigated by thermogravimetric analysis/differential thermogravimetric (TGA/DTG). The XRD and TEM results show that the sepiolite was dispersed homogeneously in the PMMA matrix at a nanometer scale. The TGA analysis revealed that the addition of sepiolite improved the thermal stability of PMMA. The apparent activation energies were calculated by the method of Flynn–Wall–Ozawa in nitrogen at four different heating rates, showing that sepiolite increased the apparent activation energies by about 20 kJ/mol within the degree of conversion (α) of 0.35–0.9, as compared with the reference PMMA sample.     

聚甲基丙烯酸甲酯(PMMA)微流控芯片DNA分析系统的研制

生物分析是微流控芯片分析最具进一步发展及商品化前景的分支领域之一。报道了基于聚甲基丙烯酸甲酯(PMMA)微流控芯片DNA分析系统的研制。采用简易热压法自制的PMMA芯片,以小型光纤式激光诱导荧光为检测器,以四触点可切换1 800 V高压电源为电驱动系统,以2%羟乙基纤维素(HEC)为筛分介质,通过用于DNA分析的TO-PRO-3荧光染料和激光诱导荧光检测器670 nm截止滤光片的选择,构建了微流控芯片DNA分析系统。芯片凝胶电泳分离φX174-HaeⅢRF DNA片段, 以603 bp片段计算理论塔板数n为1.14×106·m-1, 271/281 bp的分离度R为1.2。建立的PMMA微流控芯片DNA分析系统具有制作和运行成本低,芯片可重复使用,分析重现性好等特点。该研究可用于制作微型化便携式DNA分析仪,应用于临床诊断、疾病筛查等领域。     

Preparation of Poly(vinylidene fluoride)/Poly(methyl methacrylate) Blend Microporous Membranes via the Thermally Induced Phase Separation Process

The thermally induced phase separation (TIPS) process was employed to prepare poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend microporous membranes. The effect of PMMA content on the dynamic crystallization temperature of the PVDF/PMMA/sulfolane system was analyzed. The effects of PMMA weight fraction and cooling rate on the cross-sectional morphology, crystallinity, crystal structure, thermal stability, and porous structure of the resulting membranes were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a mercury porosimeter, respectively. The mechanical properties of the membranes were evaluated by tensile tests. It was found that solid–liquid phase separation occurred in the PVDF/PMMA/sulfolane system. Scanning electron microscopy revealed that either increasing PMMA weight fraction or decreasing cooling rate will lead to a macroscopical phase separation between PVDF and PMMA. PMMA weight fraction and cooling rate had some influence on the crystallinity, porous structure, and mechanical properties, but no influence on the polymer crystal structure of the membranes. PMMA weight fraction influenced thermal stability of the final membranes but cooling rate did not.     

Parametric Studies on the Grafting of Poly(Methyl Methacrylate) onto Organophilic Montmorillonite Using Silylated Clay Platelets

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (Cloisite 30B) nanocomposites were synthesized by the chemical grafting of PMMA onto Cloisite 30B via solution polymerization of methyl methacrylate (MMA) with vinyl-modified organoclay. The effects of different parameters such as clay weight percent (CWP), solvent per monomer volume ratio, and dispersion time on the properties of the PMMA grafted Cloisite 30B were investigated using the Taguchi experimental design method. This method gives a much-reduced variance for the experiments with optimum setting of control parameters and provides a set of minimum experiments compared to the conventional methods. Qualitative evidence for the chemical grafting of the PMMA onto Cloisite 30B was confirmed by Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) was used to investigate interlayer changes of the clay in the grafted nanoplatelets. The exfoliated/intercalated morphology of the nanocomposites was confirmed by XRD. Furthermore, thermal properties were measured by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). Statistical analysis of results revealed that clay weight percent and solvent per monomer ratio had significant effects on the properties of final products. The percent of grafted PMMA and storage modulus of PMMA/30B nanocomposites decreased with increasing clay content due to better dispersion of the clay at lower loadings. On the other hand, because of a tendency to formation of homopolymer and oligomers at higher solvent loadings; the percent of grafted PMMA, storage modulus and glass transition temperature of PMMA/30B nanocomposites decreased with an increase in solvent per monomer volume ratio. However, the obtained PMMA/30B nanocomposites at the optimum conditions, was exhibited a higher glass transition temperature, higher storage modulus and better thermal stability than the pure PMMA.     

Investigation of Phase Separation in a Partially Miscible Polymer Blend by Rheology

The phase boundary and phase‐separation dynamics of a binary poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase‐separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase‐separation mechanisms.     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.     

基于新型聚合物碳糊复合电极的电致化学发光研究

以甲基丙烯酸甲酯(MMA)预聚物作为石墨粉的粘合剂,完全聚合固化,制备并表征了聚合物碳糊复合电极.基于此电极考察了鲁米诺体系的电致化学发光行为.在最优条件下,鲁米诺在聚合物碳糊电极上的电化学响应比在传统的碳糊电极上明显增强,电致化学发光的稳定性和发光强度也大大增加.利用尿酸对该体系发光的强抑制作用,建立了尿酸的电致化学发光检测方法,线性范围为8×10-11-3×10-8mol/L,检出限为1.2×10-11 mol/L,应用于体液测定,结果满意.     

Bonding at Compatible and Incompatible Amorphous Interfaces of Polystyrene and Poly(Methyl Methacrylate) Below the Glass Transition Temperature

Abstract

Films of high‐molecular‐weight amorphous polystyrene (PS, M _w = 225 kg/mol, M _w/M _n = 3, T _g‐bulk = 97°C, where T _g‐bulk is the glass transition temperature of the bulk sample) and poly(methyl methacrylate) (PMMA, M _w = 87 kg/mol, M _w/M _n = 2, T _g‐bulk = 109°C) were brought into contact in a lap‐shear joint geometry at a constant healing temperature T _h, between 44°C and 114°C, for 1 or 24 hr and submitted to tensile loading on an Instron tester at ambient temperature. The development of the lap‐shear strength σ at an incompatible PS–PMMA interface has been followed in regard to those at compatible PS–PS and PMMA–PMMA interfaces. The values of strength for the incompatible PS–PMMA and compatible PMMA–PMMA interfaces were found to be close, both being smaller by a factor of 2 to 3 than the values of σ for the PS–PS interface developed after healing at the same conditions. This observation suggests that the development of the interfacial structure at the PS–PMMA interface is controlled by the slow component, i.e., PMMA. Bonding at the three interfaces investigated was mechanically detected after healing for 24 hr at T _h = 44°C, i.e., well below T _g‐bulks of PS and PMMA, with the observation of very close values of the lap‐shear strength for the three interfaces considered, 0.11–0.13 MPa. This result indicates that the incompatibility between the chain segments of PS and PMMA plays a negligible negative role in the interfacial bonding well below T _g‐bulk.     

Comparison of Various Solvents for Poly(Phenylene Sulfide) Microporous Membrane Preparation via Thermally Induced Phase Separation

Six different solvents, i.e., diphenyl sulfone (DPS), diphenyl isophthalate (DPIP), benzoin (BZ), epsilon-caprolactam (CPL), hydrogenated terphenyl (HTP), and cyclohexyl pyrrolidinone (CHPN), were selected as diluents for poly(phenylene sulfide) (PPS) microporous membranes development via the thermally induced phase separation (TIPS) method. Phase separation behaviors for the various solvents were first identified through thermal analysis of their PPS solutions. Liquid-liquid separation behavior was identified for a group of solvents including DPS, DPIP, and BZ, whereas systems with the solvents CPL, HTP, and CHPN underwent solid-liquid separation during the cooling process. A newly designed casting device, which well simulated the industrial film casting process, was then used to produce films; it consisted of a side-by-side high-temperature plate and room-temperature plate. The different cooling conditions able to be produced by this casting device were found to greatly affect the TIPS process and the properties of the final membranes. The properties of PPS membranes prepared on this device from 30 wt.% binary solutions with the six solvents were investigated. The morphology of PPS membranes was also observed on the samples prepared under different cooling processes for the six solvents.     

Improving the Barrier Properties of Poly(Lactic Acid) by Blending with Poly(Ethylene-Co-Vinyl Alcohol)

Poly(lactic acid) (PLA)/poly(ethylene-co-vinyl alcohol) (EVOH) blends were prepared via melt blending to improve the barrier properties of PLA. The phase morphologies and final properties (rheological behavior, thermal and dynamical-mechanical features, barrier properties, and mechanical behaviors) of the blends were investigated as a function of the EVOH content. The results indicated that hydroxyl groups of EVOH promoted the degradation of PLA, and thus affected the viscosities and morphologies of the resulting blends. The intrinsic viscosities of PLA in the blends decreased with the content of EVOH. The PLA and EVOH presented typical phase-separated morphologies, with a relatively small domain size of the EVOH phase. The EVOH enhanced the cold-crystallization behavior of PLA. The barrier properties to water vapor and oxygen increased linearly with increasing EVOH content.     

Morphology and Fracture Toughness of Nanostructured Epoxy Resin Containing Amino-Terminated Poly(propylene oxide)

Amino-terminated poly(propylene oxide) (ATPPO) was incorporated into epoxy resin to toughen thermosets. It was found that nanostructured thermosets were obtained; the nanostructures were characterized by means of atomic force microscopy and small-angle X-ray scattering. The formation of the nanostructures is interpreted on the basis of the occurrence of the reaction of terminal groups of ATPPO with diglycidyl ether of bisphenol A; this reaction is suggested to result in the formation of star-shaped block copolymers composed of poly(propylene oxide) (PPO) and epoxy blocks. Due to the presence of the star-shaped block copolymer produced in situ, the phase separation of PPO induced by the reaction was confined to the nanometer scale. The glass-transition behavior and fracture toughness of the nanostructured thermosets were investigated by means of differential scanning calorimetry, dynamic mechanical thermal analysis, and the measurement of critical stress intensity factors. The epoxy thermosets were significantly toughened by the inclusion of a small amount of ATPPO. The thermal and mechanical properties of the nanostructured thermosets are compared to the binary blends of epoxy resin containing hydroxyl-terminated poly(propylene oxide) (HTPPO) with identical molecular weight. With the identical composition, the nanostructured thermosets displayed higher fracture toughness than that of their binary blends. The difference in morphology and properties is interpreted in terms of the formation of the nanostructures.     

Poly(vinylidene fluoride) Crystallization Behavior and Membrane Structure Formation Via Thermally Induced Phase Separation with Benzophenone Diluent

Microporous poly(vinylidene fluoride) (PVDF) membranes were prepared by thermally induced phase separation (TIPS) at different quenching temperatures with benzophenone as the diluent. The crystallization behavior and crystal structure of PVDF in PVDF/benzophenone systems were investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). The different PVDF concentrations had a remarkable effect on PVDF crystallization behavior and resulted in different membrane structures. Spherulitic structures were vague when the PVDF/benzophenone solution was quenched to ?8°C; however, discernable spherulitic structures were obtained when quenched to 34 and 49°C. Additionally, two phase separation mechanisms (solid–solid (S–S) and solid–liquid (S–L) phase separation) were observed during membrane preparation. It was revealed by scanning electron microscopy (SEM) that microporous membranes had more discernable spherulitic structures formed by S–L phase separation than by S–S phase separation, which induced macrovoids and irregular pores on the fracture surfaces of membranes.     

Eu(DBM)_3Phen掺杂聚甲基丙烯酸甲酯静电纺丝荧光纤维

通过静电纺丝技术获得直径约为700 nm,均匀且随机取向的亚微米级Eu(DBM)3Phen/PMMA纤维。在紫外光辐射下,亚微米级荧光纤维发出明亮的红色荧光。其激发光谱表明,荧光纤维有效激发波长范围为200~400 nm。利用积分球配以CCD探测器,在367 nm长波紫外LED激发下对荧光纤维开展绝对光谱功率测试。当LED泵浦功率为535.76#W时,厚度80#m的Eu(DBM)3Phen/PMMA纤维薄层对紫外辐射的吸收率高达89%,350~850 nm范围内发射的总绝对光谱功率、总光子数和总荧光量子产率分别为36.56#W、11.46×10~(13)cps和12.94%。亚微米级Eu(DBM)_3Phen/PMMA纤维薄层中,Eu~(3+)较高的跃迁发射几率及较大的发射截面使得纤维可以高效吸收紫外辐射并转变为可见光,在提高太阳能电池光电转换效率方面具有潜在应用价值。     

Electrical conduction mechanism of polyvinyl chloride (PVC)-polymethyl methacrylate (PMMA) blend film

The electrical conduction mechanism in polyvinyl chloride (PVC)-polymethyl methacrylate (PMMA) blend film has been studied at various temperatures in the range 313 K to 353 K. The results are presented in the form of I-V characteristics. Analysis has been made in the light of Poole-Frenkel, Fowler-Nordheim, Schottky, log(J) vs. T plots and Arrhenius plots. It is observed that, Schottky-Richardson mechanism is primarily responsible for the observed conduction.