Summary Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is the technique routinely used at high temperature to analyze the molar mass distribution in polyolefins. The distribution of comonomer along the molar mass distribution in a copolymer is a key microstructural feature that determines the macroscopic properties of the material, and thus, its range of possible applications and performance. The direct coupling of a modern filter‐based infrared (IR) detector to a high temperature GPC instrument, by means of a heated flow‐through cell, is here described. The analyses are carried out by recording the continuous IR absorbance chromatograms at selected bands, which show different sensitivities to the different monomer units. A slice‐by‐slice ratio of the IR bands is further calculated to determine the average chemical composition of each molar mass fraction, after GPC separation. The high sensitivity of this IR detection method allows the injection of low concentrations of sample and the use of standard GPC analysis conditions, so that chromatographic quality is not compromised even in cases where very high molar mass fractions are present. The analysis of comonomer variations along the molar mass distribution in polyolefin copolymers is discussed. Selected applications of the method to polyethylene and poly(propylene) copolymers are presented.

Functionalized titanium dioxide (TiO 2 ) nanospheres with pimelic acid (TiO 2 -PA) were synthesized through a novel and effective route, where the goal was to promote a high percentage of b-crystal into a matrix of isotactic polypropylene (iPP) by the use of low amount of nucleating agent. The successful chemical attachment of pimelic acid onto the TiO 2 surface was indicated by the presence of a new band at 1575 cm -1 and an increase in the thermal stability of the PA of approximately 200°C, which were observed through infrared spectra and thermogravimetric techniques, respectively. The iPP nanocomposite was analyzed by differential scanning calorimetry and wide-angle X-ray diffraction in order to identify b-crystals. An exothermic peak at 152°C and a diffraction peak at 2h = 16.2°confirmed the ability of the TiO 2 -PA nanoparticles to promote the b-crystal phase in the iPP nanocomposite even at low percentages (0.1 % w/w).About 85 % of b-crystal content was promoted with the TiO 2 -PA particles, that was significantly higher than the 25 % obtained by unmodified TiO 2 particles. Moreover, from visco-elastic analysis, it is evident that TiO 2 -PA particles help to improve the dissipation energy by effect of the promoted b-crystal phase in the polymer composites. Likewise, the AFM images provide evidence of the incompatibility of TiO 2 particles with the iPP matrix showing protruding reliefs in comparison with the homogeneous topography of the iPP/TiO 2 -PA composite. This results were confirmed by SEM, where the exclusion of TiO 2 particles was evident.

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Summary: An infrared detector based on a set of narrow band optical filters was coupled to a high temperature Gel Permeation Chromatograph (GPC) producing continuous chromatograms of absorbance after the molar mass fractionation. A multiple linear regression (MLR) model was established to relate the measured absorbance to the average octene weight percent in industrial ethylene-octene copolymer samples. This method is compared to univariate and multivariate band ratio models. The application of these models to produce molar mass compositional distributions is also outlined.

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The results of an investigation concerning a mechanism of brittle fracture in glass reinforced plastic (GRP) rods used in non-ceramic insulators (NCI) are presented. Commercial grade GRP rods and GRP rods from actual insulators were exposed to ultra-pure water (UPW) and acids while being subjected to mechanical stresses. The experimental results revealed that water has the potential of inducing stress corrosion cracking on the fibers and hence brittle fracture in the rods. It is observed that the fracture proceeded faster when the rods were exposed to UPW than when exposed to acids. Furthermore, a brittle fracture in an epoxy cross-arm, which was installed in a region where the formation of acids in the atmosphere can be neglected, is analyzed. Based on these evidences, it is postulated that the failure of in-service NCI in the brittle mode can occur under the influence of water and mechanical stresses, and that the failure is more likely to happen with water than with acids.

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