Kinetics of phase separation of poly(styrene‐co‐methyl methacrylate) and poly(styrene‐co‐acrylonitrile) blends

The phase behavior and kinetics of phase separation for blends of the random copolymer poly(styrene‐co‐methyl methacrylate) (SMMA) and poly(styrene‐co‐acrylonitrile) (SAN) were studied by using small‐angle laser light scattering. The partially miscible SMMA/SAN blends undergo spinodal decomposition (SD) and subsequent domain coarsening when quenched inside the unstable region. For blends of SMMA and SAN, the early stages of the phase separation process could be observed, unlike a number of other blends where the earliest stages are not visible by light scattering. The process was described in terms of the Cahn–Hilliard linear theory. Subsequently, a coarsening process was detected and the time evolution of q_m at the beginning of the late stages of phase separation followed the relationship q_m∝t^?1/3, corresponding to an evaporation–condensation mechanism. Self‐similar growth of the phase‐separated structures at different timescales was observed for the late stage. Copyright © 2004 Society of Chemical Industry     

Nano‐AlN functionalization by silane modification for the preparation of covalent‐integrated epoxy/poly(ether imide) nanocomposites

Aluminum nitride nanoparticle (nano‐AlN) organically modified with the silane‐containing epoxide groups (3‐glycidoxypropyltrimethoxy silane, GPTMS) was incorporated into a mixture of poly(ether imide) (PEI), and methyl hexahydrophthalic anhydride‐cured bisphenol A diglycidyl ether grafted by GPTMS was prepared for nanocomposite. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were used to investigate the microscopic structures of nanocomposites. According to experimental results, it was shown that addition of nano‐AlN and PEI into the modified epoxy could lead to the improvement of the impact and bend strengths. When the concentrations of nano‐AlN and PEI were 20 and 10 pbw, respectively, the toughness/stiffness balance could be achieved. Dynamic mechanical analysis (DMA) results displayed that two glass transition temperatures (T_g) found in the nanocomposites were assigned to the modified epoxy phase and PEI phase, respectively. As nano‐AlN concentration increased, T_g value of epoxy phase had gradually increased, and the storage modulus of the nanocomposite at the ambient temperature displayed an increasing tendency. Additionally, thermal stability of the nanocomposite was apparently improved. The macroscopic properties of nanocomposites were found to be strongly dependent on their components, concentrations, dispersion, and resulted morphological structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Current Status and Future Prospect of Polymer‐Layered Silicate Mixed‐Matrix Membranes for CO2/CH4 Separation

The mixed‐matrix membrane (MMM), a state‐of‐the‐art polymer‐inorganic hybrid, is a relatively recent addition to the membrane family which adopts the synergistic advantages of the polymer and inorganic phase. Although marked improvement has been achieved by MMMs in CO₂/CH₄ separation, the development of a defect‐free structure to transcend the Robeson upper bound limit remains a challenge. In previous years, a number of inorganic materials with diverse nature have been studied for CO₂/CH₄ separation; however, layered silicates have not attracted much attention despite their superior thermal and mechanical properties. Analyses of the potential of using layered silicates as inorganic fillers in MMM fabrication for CO₂/CH₄ separation are reviewed. Additionally, the immediate challenges toward successful formation of layered silicate‐based MMM and future prospects are addressed.     

Kinetics of Phase Separation in Poly(ɛ-caprolactone)/Poly(ethylene glycol) Blends

The poly(ɛ-caprolactone)/poly(ethylene glycol) (PCL/PEG) blends reveal a miscibility window of upper critical solution temperature (UCST) character. The kinetics of liquid–liquid phase separation (LLPS) for the blends of PCL/PEG is investigated by time-resolved small angle light scattering (TRSALS). The time evolution of scattering profile is analyzed by linear Cahn–Hilliard theory for early stage of spinodal decomposition (SD). The evolution of the maximum intensity I_m(t) and the corresponding wavenumber q_m(t) obey the power-law scheme (I_m(t)∼t^β and q_m(t)∼t^−α). A relation of β=3α in late stage is obtained almost the same scaling exponents with β≅1 and α≅1/3 for various quenching depths. The α≅1/3 implied that a coarsening mechanism at the late stage of phase separation may proceed with Ostwald ripening or Brownian coalescence process. Besides, the intermediate and late stages of SD can be scaled into a universal from represented well by Furukawa’s structure factor. The percolation to cluster transition is accompanied with α∼0.13→1/3 from intermediate to late stage of SD for the off-critical mixture of PCL/PEG (4/6) blend. In this study, the experimental result demonstrates that the crystallization is a viable mechanism to lock phase-separated structure of the blends. The competition between phase separation and crystallization has been suggested to determine the final morphology.     

Studying the degradation of polyhydroxybutyrate‐co‐valerate during processing with clay‐based nanofillers

Polyhydroxybutyrate‐co‐valerate (PHBV) is attracting interest as a new material for packaging applications and nanoparticulate layered silicates are being increasingly explored as a way to improve PHBV film properties. In this context, it is essential to understand how different types of nanofillers could influence polymer properties. PHBV was processed with three‐layered clay types using different mixing methods, and we examined the effect of processing time, clay type, and clay content on polymer molecular weight and composite morphology. PHBV molecular weight (M_w) decreased by 38% after extrusion processing and was further reduced in the presence of montmorillonite (MMT). However, when PHBV was processed with kaolinite as the additive, no further reduction in polymer molecular weight was observed. Molecular weight also decreased as the MMT clay content increased from 1 to 5 wt %. The results suggest that release of tightly bound water from clay surfaces at elevated temperature may be responsible for PHBV degradation during processing. Evidence also points to the possibility that the surface modifier present in organically modified MMT may catalyze PHBV degradation in some way. X‐ray diffraction studies indicated an intercalated morphology in the presence of modified montmorillonite but good dispersion was also achieved when unmodified kaolinite was blended with PHBV. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical properties of poly(urethane‐imide)/epoxy/silica hybrids

Improving properties of polyurethane (PU) elastomers have drawn much attention. To extend the properties of the modified PU composite, here a new method via the reaction of poly(urethane‐imide) diacid (PUI) and silane‐modified epoxy resin (diglycidyl ether of bisphenol A) was developed to prepare crosslinked poly (urethane‐ imide)/epoxy/silica (PUI/epoxy/SiO₂) hybrids with enhanced thermal stability. PUI was synthesized from the reaction of trimellitic anhydride with isocyanate‐terminated PU prepolymer, which was prepared from reaction of polytetramethylene ether glycol and 4,4′‐diphenylmethane diisocyanate. Thermal and mechanical properties of the PUI/epoxy/SiO₂ hybrids were investigated to study the effect of incorporating in situ SiO₂ from silane‐modified epoxy resin. All experimental data indicated that the properties of PUI/epoxy/SiO₂ hybrids, such as thermal stability, mechanical properties, were improved due to the existence of epoxy resin and SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Later-stage spinodal decomposition in polymer solution under high pressure—analyses of qm and Im

Later-stage spinodal decomposition (SD) of polymer solutions (polypropylene/trichlorofluoromethane) induced by pressure-jump was examined in situ as a function of pressure P by using time-resolved light scattering method with the cell designed for high pressure and high temperature. The time-evolution of the magnitude of scattering vector q_m(t,P) at maximum scattered intensity and the maximum scattered intensity I_m(t,P) were analyzed in order to characterize the coarsening processes of the later-stage SD, where t refers to time after the onset of pressure-jump. The changes in q_m(t,P) and I_m(t,P) with t at different P's were found to fall onto the respective master curves on the reduced plots, indicating that the scaling postulate is valid not only for the coarsening behaviors at different temperatures but for those at different P's.     

Effects of the molecular weight of poly(ether imide) on the viscoelastic phase separation of poly(ether imide)/epoxy blends

The phase separation of diglycidyl ether of bisphenol A/methyl tetrahydrophthalic anhydride blends modified with three poly(ether imide)s (PEIs) of different molecular weights was investigated with scanning electron microscopy (SEM) and time‐resolved light scattering (TRLS). The morphologies observed by SEM for the three blends were all close to a cocontinuous structure with different periodic distances. The results of TRLS indicated that the phase separation for the PEI‐modified epoxy blends took place according to the spinodal decomposition mechanism and the onset time of phase separation, with the periodicity of the phase structure depending on the PEI molecular weight and cure temperature. The time‐dependent peak scattering vector was simulated with a Maxwell‐type viscoelastic relaxation equation, indicating that the coarsening process of epoxy droplets was mainly controlled by the viscoelastic flow. Relaxation times obtained at different temperatures for the three blends could be described by the Williams–Landel–Ferry equation. The effects of the PEI molecular weight on the processes of viscoelastic phase separation were investigated, and the observed trends could be explained qualitatively through thermodynamic analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of poly(styrene‐b‐butadiene‐b‐styrene)/montmorillonite nanocomposites

With some polymerizable small molecules grafting onto the montmorillonite surface, we disposed the clay through in‐situ emulsion polymerization, and the structure of the modified montmorillonites were studied through Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD). The nanocomposites of poly(styrene‐b‐butadiene‐b‐styrene) (SBS)/montmorillonite with excellent mechanical properties were prepared by mixing SBS and the modified montmorillonite on the double rollers at 150°C. The exfoliation of the layered silicates was confirmed by XRD analysis and transmission electron microscopy (TEM) observation. After mechanical kneading of the molten nanocomposites, the exfoliation structure of the silicates is still stable for polystyrene macromolecules grafting onto the silicates. Upon the addition of the modified montmorillonite, the tensile strength, elongation at break and tear strength of the nanocomposites increased from 22.6 MPa to 31.1 MPa, from 608% to 948%, from 45.32 N/mm to 55.27 N/mm, respectively. The low‐temperature point of glass‐transition temperature (T_g) of the products was about −77°C, almost constant, but the high‐temperature point increased from 97°C to 106°C. In addition, the nanocomposites of SBS and modified montmorillonites showed good resistance to thermal oxidation and aging. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of granulometry and organic treatment of a Brazilian montmorillonite on the properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites prepared by miniemulsion polymerization

The influence of granulometry and organic treatment of a Brazilian montmorillonite (MMT) clay on the synthesis and properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites was studied. Hybrid latexes of poly(styrene‐co‐butyl acrylate)/MMT were synthesized via miniemulsion polymerization using either sodium or organically modified MMT. Five clay granulometries ranging from clay particles smaller than 75 μm to colloidal size were selected. The size of the clay particles was evaluated by specific surface area measurements (BET). Cetyl trimethyl ammonium chloride was used as an organic modifier to enhance the clay compatibility with the monomer phase before polymerization and to improve the clay distribution and dispersion within the polymeric matrix after polymerization. The sodium and organically modified natural clays as well as the composites were characterized by X‐ray diffraction analysis. The latexes were characterized by dynamic light scattering. The mechanical, thermal, and rheological properties of the composites obtained were characterized by dynamical‐mechanical analysis, thermogravimetry, and small amplitude oscillatory shear tests, respectively. The results showed that smaller the size of the organically modified MMT, the higher the degree of exfoliation of nanoplatelets. Hybrid latexes in presence of Na‐MMT resulted in materials with intercalated structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Layered Silicate‐Induced Enhancement of Fracture Toughness of Epoxy Molding Compounds over a Wide Temperature Range

Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T_g of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.

     

Viscoelastic effects on the phase separation in thermoplastics modified cyanate ester resin

A high temperature thermosetting bisphenol-A dicyanate, BADCy was blended with a thermoplastic poly(ether imide) (PEI). The phase separation behavior of the blend was investigated by scanning electron microscopy (SEM) and time resolved light scattering (TRLS). It was found by SEM that the blend with 20 and 25 wt% PEI had a phase inversion structure. The results of TRLS displayed clearly that the phase separation took place according to a spinodal decomposition (SD) mechanism and the evolution of both scattering vector q_m and the maximum scattering intensity I_m followed Maxwell-type relaxation equation. The temperature-dependent relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in PEI/BADCy blends were affected by viscoelastic effect.     

Polyetherimide‐modified bismaleimide resins. II. Effect of polyetherimide content

A novel polyetherimide was prepared and used to improve the toughness of bismaleimide resin composed of bis(4‐maleimidediphenyl) methane and O,O′‐diallyl bisphenol A. The morphologies of the modified resins change from spherical particles to an inverted phase structure, depending on the modifier's content based on the scanning electronic microscopy results. Dynamic mechanical analysis is also used to characterize morphologies of the modified resins. The phase‐separation process of the modified system is traced by time‐resolved light scattering. The change in the light‐scattering profile with curing time showed that the phase separation mechanism depended on the modifier concentration. Phase separation took place via the spinodal decomposition mechanism in the PEI 15‐phr‐ and 20‐phr‐modified system. The fracture energy (G_IC) increased with PEI content in the modified system; in the PEI 15‐phr‐modified system, the G_IC value was three times greater than that of the unmodified BMI resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 350–358, 2001     

Synthesis and liquid‐crystal‐aligning properties of novel aromatic poly(amide imide)s bearing n‐alkyloxy side chains

Novel aromatic poly(amide imide)s (m‐PAIs, m = 8, 12, 16) containing preformed isophthalamide unit and pendent n‐alkyloxy (‐O‐n‐C_mH_2m+1, m = 8, 12, 16) side chains were prepared in thin films by polymerization of pyromellitic dianhydride (PMDA) with N,N′‐bis(4‐aminophenyl)‐5‐(n‐alkyloxy)isophthalamides (m‐DAs) obtained from N,N′‐bis(4‐nitrophenyl)‐5‐(n‐alkyloxy)isophthalamides (m‐DNs). The m‐PAI films were tough, flexible and transparent with inherent viscosities in the 1.25–1.67 dL/g range in DMAc and soluble in DMAc and NMP on heating. In TGA m‐PAIs began to degrade around 440°C and in DSC no phase transitions were detected. In X‐ray diffractometry the m‐PAIs appeared amorphous with loosely developed layered crystalline structure. In liquid crystal (LC)‐aligning performance measured using 4‐n‐pentyl‐4′‐cyanobiphenyl (5CB) on thin film surfaces rubbed with standard velvet fibers, the m‐PAIs showed homogeneous LC alignment parallel to the rubbing direction with 2.5–17.5° pretilt angles, depending on the rubbing density and n‐alkyloxy side chain length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and Characterisation of Anhydride‐Cured Epoxy Nanocomposites Containing Layered Silicates Modified with Phenolic Alkylimidazolineamide Cations

Summary: Phenolic alkylimidazolineamides were prepared and applied as modifiers in order to render layered silicates organophilic and to prepare polymeric nanocomposites. The imidazolineamine, 2‐{2‐[heptadec‐8‐enyl]‐4,5‐dihydro‐1‐imidazol‐1‐yl}‐1‐ethaneamine (IA), was reacted in bulk with one of the two phenolic compounds, ethyl 4‐hydroxybenzoate (P) or methyl 3‐[3,5‐di(tert‐butyl)‐4‐hydroxyphenyl]propionate (HP), which is an intermediate for antioxidants, to prepare the two phenolic imidazolineamides, PIA and HPIA. During protonation in water, both phenolic imadazolineamides were used successfully to exchange interlayer sodium cations of sodium bentonite and fluorohectorite, thus producing organophilic layered silicates with an increased interlayer distance of around 3.3 nm. The new phenolic organophilic layered silicates represent a novel class of phenolic organic/inorganic hybrid materials. They were applied as fillers in hexahydrophthalic anhydride‐cured bisphenol‐A diglycidyl ether (BADGE). Thermal analysis (DSC), transmission electron microscopy (TEM), wide angle X‐ray scattering (WAXS), and mechanical tests were used to evaluate the thermal, mechanical, and morphological properties. Although fracture toughness, measured as the stress intensity factor, K_Ic, and the energy release rate, G_Ic, increased by around 50% with increasing silicate content without sacrificing glass temperature, both tensile strength and Young's modulus increased only marginally. Low matrix reinforcement was attributed to inadequate compatibility matching, as evidenced by the slightly lower interlayer distances of the layered silicates encapsulated in the epoxy matrix.

Representative TEM micrographs of the sample ER‐bent‐PIA/10.     

Preparation and characterization of modified‐clay‐reinforced and toughened epoxy‐resin nanocomposites

Epoxy–clay nanocomposites were prepared by the dispersion of an organically modified layered clay in an epoxy resin (diglycidyl ether of bisphenol A) and curing in the presence of methyl tetrahydro acid anhydride at 80–160°C. The nanometer‐scale dispersion of layered clay within the crosslinked epoxy‐resin matrix was confirmed by X‐ray diffraction and transmission electron microscopy, and the basal spacing of the silicate layer was greater than 100–150 Å. Experiments indicated that the hydroxyethyl groups of the alkyl ammonium ions, which were located in the galleries of organically modified clay, participated in the curing reaction and were directly linked to the epoxy‐resin matrix network. Experimental results showed that the properties of epoxy were improved, evidently because of the loading of organically modified clay. The impact strength and tensile strength of the nanocomposites increased by 87.8 and 20.9%, respectively, when 3 wt % organic clay was loaded, and this demonstrated that the composites were toughened and strengthened. The thermal‐decomposition and heat‐distortion temperatures were heightened in comparison with those of pure epoxy resin, and so were the dynamic mechanical properties, including the storage modulus and glass‐transition temperature. Moreover, experiments showed that most properties of the composites were ameliorated with low clay contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2649–2652, 2004     

Synthesis and characterization of epoxy/amine terminated amide‐imide‐imide blends

A new amine terminated amide‐imide (ATAI) was synthesized by the polycondensation reaction of tetrimide dicarboxylic acid containing bulky m‐chloro phenyl pendant with p‐phenylene diamine. The structure of all the prepared compounds were confirmed by FTIR,¹H‐NMR and ¹³C‐NMR techniques. This new diamine was then used to cure epoxy resin namely diglycidyl ester of bisphenol‐A and the cure reaction was studied by Differential scanning calorimetry. The cured blends show better thermal properties. The T_g of the epoxy resin was increased from 134°C to 156°C on addition of 6% of ATAI. The DMA results indicate that the polymer blend with 8% ATAI composition has higher storage modulus compared to 3% and 6% ATAI composition. The polymer blends with 3% and 6% ATAI composition have higher crosslinking density and lower intersegmental and intrasegmental friction coefficients than 8% ATAI composition. In the DMA curves an increase in the peak half‐width was observed with increasing ATAI composition, indicating the possibility of the existence of more than one phase with increasing ATAI concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Technological and processing properties of natural rubber layered silicate‐nanocomposites by melt intercalation process

Natural rubber nanocomposites were produced by melt‐mixing of natural rubber with organically modified silicates. For comparison, a pristine‐layered silicate and a nonlayered version [English Indian clay (EIC)] were also included in the study. The layered silicate used was sodium bentonite (BNT) and organoclays used were octadecylamine‐ modified montmorillonite (MMT‐ODA) and methyltallow bis‐2‐hydroxyethyl ammonium‐modified montmorillonite (MMT‐ TMDA). Accelerated sulfur system was used for the vulcanization of the nanocomposites. The dispersion of these silicates was studied by X‐ray diffraction and transmission electron microscopy. The organoclay‐incorporated composites exhibited faster curing and improved mechanical properties. The improvement in the mechanical properties of the composites followed the order MMT‐ODA > MMT‐TMDA > EIC > BNT. The property improvement was attributed to the intercalation/exfoliation of the organically modified silicates because of their high initial interlayer distance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2537–2543, 2006     

Blends of epoxy resin with amine‐terminated polyoxypropylene elastomer: Morphology and properties

A liquid diglycidyl ether of bisphenol A (DGEBA) epoxy resin is blended in various proportions with amine‐terminated polyoxypropylene (POPTA) and cured using an aliphatic diamine hardener. The degree of crosslinking is varied by altering the ratio of diamine to epoxy molecules in the blend. The mixture undergoes almost complete phase separation during cure, forming spherical elastomer particles at POPTA concentrations up to 20 wt %, and a more co‐continuous morphology at 25 wt %. In particulate blends, the highest toughness is achieved with nonstoichiometric amine‐to‐epoxy ratios, which produce low degrees of crosslinking in the resin phase. In these blends, the correlation between G_IC and plateau modulus (above the resin T_g), over a wide range of amine‐to‐epoxy ratios, confirms the importance of resin ductility in determining the fracture resistance of rubber‐modified thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 427–434, 1999