A marine bacterial community capable of degrading poly(ethylene terephthalate) and polyethylene.

New polyolefin resins, in spite of their simple chemistry, just carbon and hydrogen atoms, have become by design complex polymers with improved performance for the desired application. Besides the fundamental molar mass distribution, there are many other features that can be controlled when dealing with copolymers and new multireactor/multicatalyst resins. The average properties measured by spectroscopic techniques are not enough to define the microstructure of the new resins; it is necessary to fractionate the polymer according to certain parameters such as molar mass, branching, or stereoregularity. Separation techniques have become essential for the control and characterization of these polymers; nevertheless, full characterization is not a simple task and has demanded the development of new separation methodologies in recent years, and in many cases multiple separation techniques are required to define the microstructure. A review of the most important separation techniques with emphasis on the new technologies is given and the applications of these new polyolefin resins discussed.

Polyolefin Characterization: Recent Advances in Separation Techniques

This anthology summarizes contributions to Ziegler–Natta catalysis that have led through novel experimental methods to well-founded results, to continuing conclusions, and to increasing knowledge about the course of this catalysis. The complex and manifold mechanism has been elucidated in extensive kinetic studies in a half continuous tank reactor, in a plug flow reactor with oligomer distribution analysis as an additional “measuring instrument,” by dynamic NMR spectroscopy with line shape analysis, through use of C-enriched reacting ethylene as a molecular surveyor, and by observation of the individual behavior of a large number of particles with supported catalysts by transmission electron microscopy and video microscopy. The synopsis of the results of the different experimental methods gives assurance that we are safely on the right path.

Polyolefins: 50 years after Ziegler and Natta I Polyethylene and Polypropylene

A marine fungus Alternaria alternata FB1 efficiently degrades polyethylene.

Accurate quantification of polymer distributions is one of the main challenges in polymer analysis by liquid chromatography. The response of contemporary detectors is typically influenced by compositional features such as molecular weight, chain composition, end groups, and branching. This renders the accurate quantification of complex polymers of which there are no standards available, extremely challenging. Moreover, any (programmed) change in mobile-phase composition may further limit the applicability of detection techniques. Current methods often rely on refractive index detection, which is not accurate when dealing with complex samples as the refractive-index increment is often unknown. We review current and emerging detection methods in liquid chromatography with the aim of identifying detectors, which can be applied to the quantitative analysis of complex polymers.

Detection challenges in quantitative polymer analysis by liquid chromatography

Summary


Since the introduction of high temperature interaction chromatography for the analysis of polyolefins the technique has demanded a particular interest in the analysis of elastomers where crystallization techniques will meet a limitation given the low crystallinity of these polymers. In this paper the introduction of non carbon adsorption supports such as molybdenum sulfide, boron nitride and tungsten sulfide with equivalent separation to graphitized carbon packing in TGIC analysis of polyolefins is presented. A mechanism for the separation of polyolefins by adsorption chromatography on layered substrates is proposed. The influence of solvent polarity in interaction chromatography is discussed.

Advances in Thermal Gradient Interaction Chromatography and Crystallization Techniques for Composition Analysis in Polyolefins

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.

Characterization of Chemical Composition along the Molar Mass Distribution in Polyolefin Copolymers by GPC Using a Modern Filter-Based IR Detector

Summary


Molar mass distribution (MMD) of polyolefins is routinely analyzed by gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), practiced in different methods and detector systems. The filter-based infrared detector (IR) has become a preferred alternative to the traditional use of differential refractive index detector (DRI) for high temperature GPC (HT-GPC) when applied to polyolefins. The main reason is that a modern multiple band filter-based IR detector can be used to determine the distribution of co-monomer along the molar mass distribution in a copolymer, in a single HT-GPC analysis directly without the need of additional analytical procedures. In addition to that, the performance of the modern IR detector when used as primary concentration detector in the HT-GPC instrument, in either the single or the multiple detection schemes, proves to be superior to that of DRI detector. This is due to the high signal-to-noise ratio achievable by the modern IR detector and its excellent baseline stability. Such high detection quality can be attributed to the inherent robustness of IR spectroscopy against external factors such as GPC temperature and flow rate variations. The impact of that higher detection performance on the final processed analytical results of polymer MMD and molar mass averages among others, is the focus of this current investigation. Different application scenarios of industrial interest have been selected to show a direct comparison of both the IR and DRI detectors installed on a same GPC instrument.

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Esther López

Papers

Advances in Thermal Gradient Interaction Chromatography and Crystallization Techniques for Composition Analysis in Polyolefins

Characterization of Chemical Composition along the Molar Mass Distribution in Polyolefin Copolymers by GPC Using a Modern Filter-Based IR Detector

Direct Comparison of IR and DRI Detector for HT-GPC of Polyolefins

Simplified Robust Triple Detection Methods for High Temperature GPC Analysis of Polyolefins