Polymer matrix techniques

Zhang J, Poliakoff M, George MW (2003) Rhodium-catalyzed hydroformylatirai of alkenes using in situ high-pressure IR and polymer matrix techniques. Organmnetallics 22 (8) 1612-1618... 

High-pressure in situ ETIR and polymer matrix techniques were used to study the rhodium-catalyzed hydroformylation of 1-octene, 1-butene, propene, and ethene using Rh(acac)(CO)2 or Rh(acac)(CO)(PPh3) in a polyethylene matrix as the catalyst precursor. The acyl rhodium intermediates, RC(=0)Rh(C0)4 and RC(=0)Rh (CO)3(PPh3), were observed. It was found that the acyl rhodium tetracarbonyl intermediates easily react with ethene to form acyl rhodium tricarbonyl species RC(=0)Rh(C0)3(C2H4) [61]. Deuterioformylation of l-phenyl-l-(n-pyridyl)-ethenes in the presence of a phosphane-modified Rh4(CO)i2 as catalyst precursor was carried out at 100 bar of CO D2 = 1 1 and 80 °C at partial substrate conversion. On basis ofa direct NMR analysis of the crude reaction mixture, it was concluded that the branched alkyl rhodium intermediate is almost exclusively formed [62]. 

Truly porous, synthetic ion exchangers are also available. These materials retain their porosity even after removal of the solvent and have measurable surface areas and pore size. The term macroreticular is commonly used for resins prepared from a phase separation technique, where the polymer matrix is prepared with the addition of a hq-uid that is a good solvent for the monomers, but in which the polymer is insoluble. Matrices prepared in this way usually have the appearance of a conglomerate of gel-type microspheres held together to... 

A multidimensional system using capillary SEC-GC-MS was used for the rapid identification of various polymer additives, including antioxidants, plasticizers, lubricants, flame retardants, waxes and UV stabilizers (12). This technique could be used for additives having broad functionalities and wide volatility ranges. The determination of the additives in polymers was carried out without performing any extensive manual sample pretreatment. In the first step, microcolumn SEC excludes the polymer matrix from the smaller-molecular-size additives. There is a minimal introduction of the polymer into the capillary GC column. Optimization of the pore sizes of the SEC packings was used to enhance the resolution between the polymer and its additives, and smaller pore sizes could be used to exclude more of the polymer... 

The mechanical properties of plastics materials may often be considerably enhanced by embedding fibrous materials in the polymer matrix. Whilst such techniques have been applied to thermoplastics the greatest developents have taken place with the thermosetting plastics. The most common reinforcing materials are glass and cotton fibres but many other materials ranging from paper to carbon fibre are used. The fibres normally have moduli of elasticity substantially greater than shown by the resin so that under tensile stress much of the load is borne by the fibre. The modulus of the composite is intermediate to that of the fibre and that of the resin. 

A method has recently been described for wrapping polymers around metal atoms and very small metal clusters using both matrix and macroscale metal vapor-fluid polymer synthetic techniques. Significant early observations are that (i) the experiments can be entirely conducted at, or close to room temperature, (ii) the resulting "pol5aner stabilized metal cluster combinations are homogeneous liquids which are stable at or near room temperature, and (,iii) the methodology is easily extended to bimetallic and trimetallic polymer combinations. ... 

The simple catalyst embedding technique has been applied to ethylene polymcaization in slurry In this technique, active catalytic components are embedded into styrene polymer matrix. The resulting polyethylene shows better morphology and higher bulk density than those produced by homogeneous catalyst. No activity loss was also observed with the... 

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

HPLC methods of determining the amounts of different additives in polymeric materials are preceded by an extraction process or dissolution of the polymer matrix. Although extraction-HPLC is often observed to be superior to the traditional spectroscopic techniques (UV and IR) in analysing additives, it is frequently difficult to obtain reproducible results in view of the variability of the extraction yield. On the other hand, it is equally difficult to obtain quantitative data in the dissolution/reprecipitation-HPLC method because of entrapment of analytes in the polymer precipitate and the potential for high absorption of the additives on the polymer surface. 

Table 4.45 shows the main features of SEC. This technique has become an indispensable tool for polymer characterisation. SEC has some advantages over other LC methods, such as the predictability of the end of a chromatographic run and of the retention times in a calibrated chromatographic system. SEC is an attractive technique for prefractionation or sample clean-up prior to a more sensitive RPLC technique. This intermediate step is especially interesting for experimental purposes whenever polymer matrix interference cannot be separated from the peak of interest [647]. Disadvantages are that the whole separation must be eluted within the... 

Each spectroscopic technique (electronic, vibra-tional/rotational, resonance, etc.) has strengths and weaknesses, which determine its utility for studying polymer additives, either as pure materials or in polymers. The applicability depends on a variety of factors the identity of the particular additive(s) (known/unknown) the amount of sample available the analysis time desired the identity of the polymer matrix and the need for quantitation. The most relevant spectroscopic methods commonly used for studying polymers (excluding surfaces) are IR, Raman (vibrational), NMR, ESR (spin resonance), UV/VIS, fluorescence (electronic) and x-ray or electron scattering. 

Selection of a suitable ionisation method is important in the success of mixture analysis by MS/MS, as clearly shown by Chen and Her [23]. Ideally, only molecular ions should be produced for each of the compounds in the mixture. For this reason, the softest ionisation technique is often the best choice in the analysis of mixtures with MS/MS. In addition to softness , selectivity is an important factor in the selection of the ionisation technique. In polymer/additive analysis it is better to choose an ionisation technique which responds preferentially to the analytes over the matrix, because the polymer extract often consists of additives as well as a low-MW polymer matrix (oligomers). Few other reports deal with direct tandem MS analysis of extracts of polymer samples [229,231,232], DCI-MS/MS (B/E linked scan with CID) was used for direct analysis of polymer extracts and solids [69]. In comparison with FAB-MS, much less fragmentation was observed with DCI using NH3 as a reagent gas. The softness and lack of matrix effect make ammonia DCI a better ionisation technique than FAB for the analysis of additives directly from the extracts. Most likely due to higher collision energy, product ion mass spectra acquired with a double-focusing mass spectrometer provided more structural information than the spectra obtained with a triple quadrupole mass spectrometer. 

It is apparent from Chapter 3 that new sample preparation technologies generally are faster, more efficient and cost effective more easily automated and safer use smaller amounts of sample and less organic solvent provide better recovery and meet or exceed precision and accuracy compared to traditional sample preparation techniques. Conventional methods of the analysis of additives in polymers are mostly based on the separation of the polymer matrix and additives by means of extraction. Many extraction principles are... 

The best method or the most suitable combination of methods can be discussed only in regard to the actual analytical problem. The ideal method for polymer analysis in an industrial environment is often essentially that practical one which identifies and quantitates the desired components at the lowest acceptable total cost for the customer, compatible with the desired accuracy and time constraints. Three examples may illustrate the necessary pragmatic trade-off. Despite being old methods, classical polymer/additive analysis techniques, based on initial additive separation from the polymer matrix through solvent extraction methods followed by preconcentration, still enjoy great popularity. This... 

Metal atoms can be incorporated into polymers using two approaches. For probing new reactions between metal atoms and polymers a small-scale spectroscopic approach, sometimes referred to as the Fluid Matrix Technique (11), is used. The coreactant polymer matrix, containing on the order of 0.5 fll of polymer, is preformed on an optical surface. In the case of viscous fluids such as 2 the material is painted on the substrate and held at temperatures ranging typically from 200 to 270 K. The temperature is chosen to maintain low volatility but retain mobility. Under high vacuum [10 6 torr]... 

For detailed characterization and extensive studies of reactivity, multi-gram quantities are still needed and large-scale metal vapor synthetic routes are necessary. The equipment required for this is well-documented (4) and so will not be described in detail here. The principles are those of the Fluid Matrix Technique except that in order to accommodate 10-100 gram of polymer, the coreactant is contained within a rotating flask which serves to provide a continuously renewed film as metal atoms are produced under high vacuum. 

Focusing on reactions using the Fluid Matrix Technique, we have studied the interaction of chromium vapor with 2 at 200 K (13). The resulting film was found to contain metal complexes encapsulated within the polymer in which the isocyanide group adopts a well-defined octahedral arrangement around the chromium center, i.e. a species of type Cr(CN-[P])g. Since characterization of this metal complex within the polymer is not trivial we shall develop the analysis in a little detail. 

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