Role of slow phase separation in assessing the equilibrium phase behaviour of PC-PMMA blends

Segregation Behavior of Miscible PC/PMMA Blends during Injection Molding

Miscible blends composed of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA), in which one of them has low molecular weight, were employed to study the surface segregation behavior during flow. The blend samples showed typical rheological behaviors, such as simple polymer melts without a long-time relaxation mechanism ascribed to phase separation, demonstrating that they were miscible. After injection molding, the amounts of a low molecular weight component on the blend surface were found to be larger than the actual blend ratio. Because the injection-molded products were transparent despite a huge difference in refractive indices between PC and PMMA, they showed no phase separation. This result demonstrated that surface segregation of a low molecular weight component occurred under flow field, which expands the material design such as tough plastics with good scratch resistance and optical fibers with tapered refractive index.

Complicated Structure Change during Capillary Extrusion of Binary Blends of Polycarbonate and Poly(methyl methacrylate)

The effects of pressure and shear rate on the miscibility of binary blends comprising bisphenol-A polycarbonate (PC) and low molecular weight poly(methyl methacrylate) (PMMA) were investigated using a capillary rheometer. Both pressure and shear rate affected the miscibility. The examination of an extruded strand of the blend provided information about the cause of the phase change. Under high pressure, pressure-induced demixing occurred at temperatures below the lower critical solution temperature (LCST) of the blend. Consequently, the extruded strand became opaque throughout. During shear-induced mixing/demixing, a part of the strand became opaque because of the distribution of the shear rate in the strand. For example, during shear-induced demixing, only the exterior of the strand, i.e., the high shear rate region, became opaque. Above the LCST, shear-induced mixing occurred, and only the center region of the strand became opaque.

Does the Processing Method Resulting in Different States of an Interconnected Network of Multiwalled Carbon Nanotubes in Polymeric Blend Nanocomposites Affect EMI Shielding Properties?

Electromagnetic interference (EMI), an unwanted phenomenon, often affects the reliability of precise electronic circuitry. To prevent this, an effective shielding is prerequisite to protect the electronic devices. In this study, an attempt was made to understand how processing of polymeric blend nanocomposites involving multiwalled carbon nanotubes (MWCNTs) affects the evolving interconnected network structure of MWCNTs and eventually their EMI shielding properties. Thereby, the overall blend morphology and especially the connectivity of the polycarbonate (PC) component, in which the MWCNTs tend to migrate, as well as the perfectness of their migration, and the state of nanotube dispersion are considered. For this purpose, blends of varying composition of PC and poly(methyl methacrylate) were chosen as a model system as they show a phase diagram with lower critical solution temperature type of characteristic. Such blends were processed in two different ways: solution mixing (from the homogeneous state) and melt mixing (in the biphasic state). In both the processes, MWCNTs (3 wt %) were mixed into the blends, and the evolved structures (after phase separation induced by annealing in solution-mixed blends) and the quenched structures (as the blends exit the extruder) were systematically studied using transmission electron microscopy (TEM). Both the set of blends were subjected to the same thermal history, however, under different conditions such as under quiescent conditions (in the case of solution mixing) and under shear (in the case of melt mixing). The electrical volume conductivity and the evolved morphologies of these blend nanocomposites were evaluated and correlated with the measured EMI shielding behavior. The results indicated that irrespective of the type of processing, the MWCNTs localized in the PC component; driven by thermodynamic factors and depending on the blend composition, sea-island, cocontinuous, and phase-inverted structures evolved. Interestingly, the better interconnected network structures of MWCNTs observed using TEM in the solution-mixed samples together with larger nanotube lengths resulted in higher EMI shielding properties (-27 dB at 18 GHz) even if slightly higher electrical volume conductivities were observed in melt-mixed samples. Moreover, the shielding was absorption-driven, facilitated by the dense network of MWCNTs in the PC component of the blends, at any given concentration of nanotubes. Taken together, this study highlights the effects of different blend nanocomposite preparation methods (solution and melt) and the developed morphology and nanotube network structure in MWCNT filled blend nanocomposites on the EMI shielding behavior.

Evaluation of Structures and Morphologies of Recycled PC/PET Blends Fabricated by High-Shear Kneading Processing

We fabricated polymer blends of recycled-PC (PC) and recycled-PET (PET) using high-shear processing technology. We also assessed its structure, morphology, and physical properties. Results of DSC measurements show that Tg of PC and Tc of PET shifted to higher temperatures by kneading under high-shear conditions. Results show further that the Tm of PET shifted to a lower temperature. Moreover, compatibilization progressed. TEM observations show that the PET domain was not confirmed completely under the kneading condition of 1 000 min−1/10 s or more. Compatibilization progressed. Tensile test results show that the PET ratio of 30 wt% (1 000 min−1/10 s) has higher breaking strain than neat PC does. Chemical resistance test results obtained by good solvent of PC demonstrated that blending of PET makes PC elution difficult.

Preparation, characterization, and spectroscopic properties of PC/PMMA doped blends: study of the effect of rare-earth doping on luminescence, quenching rate, and lifetime enhancement

Optical properties of highly transparent blends formed by bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) and doped with either europium(III) thenoyltrifluoroacetone hydrate [Eu(TTA)(3)-hydrate] or terbium(III) acetylacetonate hydrate [Tb(ACAC)(3)-hydrate] were studied. From the absorption/emission spectra (200 to 800 nm), percolation limits of less than 0.4 wt/wt% for Eu and above 0.7 wt/wt% for Tb were found. Lifetimes for 20/80 and 60/40 Tb-doped blends were from 1.0 to 1.5 ms, respectively, about 5 times longer than for a similar blend prepared with Langmuir-Blodgett film. For blends doped with Eu, the lifetimes were from 0.4 to 0.8 ms, almost double that for the pure complex. The results indicated interactions between the PC/PMMA blends and the rare-earth ion complex. Particularly, photoluminescent spectra evidenced the incorporation of the Eu(3+) and Tb(3+) ions into the blend, with quenching observed near 1.0 wt/wt%, except for the 20/80 blend doped with Eu ion, in which luminescence increased to 5 wt/wt %.

Camouflaged Carborarods Derived fromB-Permethyl-1,12-diethynyl-para- andB-Octamethyl-1,7-diethylnyl-meta-carborane Modules

Rigid camouflaged carborarods constructed from the corresponding C,C'-diethynyl derivatives of B-decamethyl-1,12-dicarbadodecaborane(12) (6) and B-octamethyl-1,7-dicarbadodecaborane(12) (48) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p-carborane and m-carborane cages are linked through their carbon vertices by using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid-rod molecules. The oxidative coupling of bis(ethynyl) derivatives of 6 generates oligomers containing, on average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex para-carborane cages in a series of model C,C'-diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage C--C bond lengths with cage size was observed and was attributed to hybridization effects. B-Permethylation had no significant structural effect with either 10- or 12-vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B-permethylated derivatives were increased through the operation of a steric "bumper-car" process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina-carborarods using ethynyl derivatives of 6 as precursors is described.