Oligomer Extraction from Polymers

There are a number of studies in the literature that describe the use of supercritical fluids to extract cyclic and low molecular weight oligomers from polymers. U.S. Patent 4,306,058 (Copelin, 1981), assigned to E. I. du Pont, describes the removal of cyclic oligomers from polyoxyalkylene. For instance, bubbling supercritical propylene at conditions of 100°C and 80 bar through the 

The specific extraction test described in the paper is not strictly a fractionation into a number of narrow cuts, as suggested by the title of the paper. But the results given in the paper show that polyphenylmethylsiloxane polymers can be dissolved by supercritical carbon dioxide at quite modest pressures. Other work has been carried out on both extraction and fractionation of OV-17, and quite different results have been obtained (Krukonis, 1982b). The fractionation results are given later in this chapter (in the section on silicone oils and polymers). To summarize, the results show that carbon dioxide at 40-100°C and at pressure levels as high as 448 bar (6,500 psia) cannot dissolve the phenylmethylsiloxane polymer and that less than 5% of the material can be extracted at this pressure level. 

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In SEC analysis of additive extracts from polymers, the effect of the extraction solvent on the mobile phase is less critical than in HPLC analysis. The extraction solvents typically employed generally do not interfere with the SEC mobile phases. Moreover, the same solvents are often used both as extraction solvent and as mobile phase. Therefore, there is no need to evaporate the extract to dryness prior to analysis and then to redissolve it in a suitable solvent. Typical extraction procedures often produce extracts that generally contain a small amount of wax. Frequently, removal of such oligomers from an extract is necessary, e.g. by means of precipitation, centrifuging, precolumn filtration or protection (use of a reversed-phase guard column). In SEC separations the presence of polyolefin wax does not usually disturb provided that the MW of the wax is higher than that of the analysed compounds. 

Treatment of polymers by superheated water at high temperatures can result in their decomposition/hydrolysis to monomers or lower oligomers [6]. At lower temperatures the polymer is stable and the small amounts of monomers, initiators, low oligomers and other small compounds can be extracted from polymers with superheated water [6]. For example, at 200°C styrene, alkylbenzene contaminants and styrene dimers were extracted from polystyrene without destroying the polymer. Although stable at 200°C, at 250°C polystyrene was decomposed into substituted benzenes [6]. 

Figure 5.7 (a) GPC of cyclic PBT oligomers extracted from chip mixed with xylene isomers, (h) GPC of cyclic PBT oligomers from a solution ring-chain reaction in 1,2-dichlorobenzene with dibutyl tin as catalyst. Reproduced with permission from J.J.L. Bryant and J.A. Semiyen, Polymer, 1997, 38, 4531. 1997, Elsevier... 

Polymer Devolatilization, Eractionation, and Plasticization Supercritical fluids may be used to extract solvent, monomers, and oligomers from polymers, including biomaterials. After extraction the pressure is reduced to atmospheric, leaving little residue in the... 

Applications Although Soxtec combines the best qualities of reflux and Soxhlet extractions up to now fairly little evidence has been reported concerning the efficacy of this system for polymer and rubber analysis. Nevertheless, it appears that oligomers and other reaction residues, softeners, antioxidants (e.g. BHT) and several other additives used to modify polymers are easily extracted from PVC, PP, PE, PS, rubber and many other polymeric materials. Also, some leading international plastic, rubber and packaging companies have made Soxtec an integral part of their quality control routines. Some application examples where Soxtec has proved successful are [148] ... 

Applications Pressurised fluid extraction (ASE , ESE ) is still in its early stage of development, both for polymeric and other samples. At present, most applications are found in the environmental, food, pharmaceutical and nutraceutical areas. Few reports describe the application of PEE to the extraction of monomers, oligomers and additives from polymers and most work is very recent. An application note [488] has provided some guiding principles for ASE applied to additives in polymers, namely as follows ... 

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. 

PET contains about 2-3 % of short chain oligomers, which cause problems in the processing of the polymer. Oligomers can occur as linear or cyclic molecules and can be extracted by suitable solvents. Different compounds have been identified depending on the solvent and the analysis technique used [49-52], After their extraction from the polymer, oligomers will reform by thermal treatment of the extracted sample [49], and a dynamic equilibrium between polymer and oligomers has been proposed. 

Separation of flavans monomer and oligomers from polymers and anthocyanins can be achieved by using a polyamide (1.7g) column (Bourzeix et al., 1986). A volume of 2-10 mL of the sample (wine, seeds or skins extract) is passed through the column, and the more polar... 

Other potential contaminants are, however, less obvious and these include lubricants (e.g., silicone grease), plasticizers (e.g., phthalates, phenyl phosphates, sebacates, and bisphenol A), slip agents (e.g., oleamide, erucamide, and stearamide), biocides (e.g., quarternary ammonium compounds) and polymers extracted from laboratory consumables (e.g., silicones from laboratory tubing) and membrane filters (e.g., cyclic oligomers and Nylon 66).168 169... 

Enough groundwork on the generic nature of solubility behavior in SCF solvents has been developed in the previous chapters of this book for the reader to extrapolate from the idealized situation of separating a mixture of naphthalene and chalk dust to other, more practical systems. Other systems may include the extraction of oleoresins from spices where the desired product is the extract, or the extraction of monomers and oligomers from polymers where the desired product is the purified polymer, or the separation of a mixture of chemicals where both streams are valuable products. Many of these examples are enumerated in the following chapters. 

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