Solvents, polymer analysis

Anionic and neutral polymers are usually analyzed successfully on Syn-Chropak GPC columns because they have minimal interaction with the appropriate mobile-phase selection however, cationic polymers adsorb to these columns, often irreversibly. Mobile-phase selection for hydrophilic polymers is similar to that for proteins but the solubilities are of primary importance. Organic solvents can be added to the mobile phase to increase solubility. In polymer analysis, ionic strength and pH can change the shape of the solute from mostly linear to globular therefore, it is very important to use the same conditions during calibration and analysis of unknowns (8). Many mobile phases have been used, but 0.05-0.2 M sodium sulfate or sodium nitrate is common. 

Detection is also frequently a key issue in polymer analysis, so much so that a section below is devoted to detectors. Only two detectors, the ultra-violet-visible spectrophotometer (UV-VIS) and the differential refractive index (DRI), are commonly in use as concentration-sensitive detectors in GPC. Many of the common polymer solvents absorb in the UV, so UV detection is the exception rather than the rule. Refractive index detectors have improved markedly in the last decade, but the limit of detection remains a common problem. Also, it is quite common that one component may have a positive RI response, while a second has a zero or negative response. This can be particularly problematic in co-polymer analysis. Although such problems can often be solved by changing or blending solvents, a third detector, the evaporative light-scattering detector, has found some favor. 

Apart from paints, electrokinetic separations find limited application for synthetic polymers [905], mainly because of solvent compatibility (CE is mostly an aqueous technique) and competition of SEC (reproducibility). Reasons in favour of the use of CE-like methods for polymer analysis are speed, sample throughput and low solvent consumption. Nevertheless, CE provides some interesting possibilities for polymer separation. Electrokinetic methods have been developed based on differences in ionisation, degree of interaction with solvent constituents, and molecular size and conformation. 

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

Cheung et al. [702] have evaluated various solvent evaporative high-temperature SEC-FTIR interfaces. This detection approach was initially employed only for qualitative analysis, but is recently also being used quantitatively. For that purpose the polymer film quality generated by the interface is of critical importance (thickness effects). Table 7.76 lists the main features of evaporative SEC-FITR for polymer analysis. 

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... 

This is used in polymer analysis, it involves the removal of solvent from a solvated polymer as it elutes down a drift tube and the isolated polymer particles then scatter fight from the light source allowing molecular weight to be calculated. 

In the first, the ratio cA/cB is kept constant and LS is conducted on solutions of varying total concentration c (= cA + cB). As for experiments on single polymers, dilution is effected with pure solvent. Theoretical analysis shows that ... 

To sum up, the choice of operating conditions for a specific FFF application is made in a way that recalls the general criteria used in chromatography. An accurate search of literature addressed to similar samples that have been already analyzed by FFF techniques is very useful. A number of specific reviews have been published concerning, for example, enviromnental, pharmaceutical, and biological samples (see Section 12.5). As previously mentioned above, one of the most important factors is the stability of the considered colloidal system, for which a great deal of information can be obtained from specialized literature, such as colloid, polymer, and latex handbooks [33], For example, the use of the proper surfactant (e.g., Fl-70) is common for SdFFF applications. Polymer analysis with ThFFF requires solvent types similar to those employed in size exclusion chromatography. 

Solvatochromism Solvent polarity Analysis, sensors, monitoring of polymers and polymerisation... 

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

HS-SPME is a very useful tool in polymer analysis and can be applied for absolute and semi-quantitative determination of the volatile content in polymers, for degradation studies, in the assessment of polymer durabihty, for screening tests and for quality control of recycled materials. For quantitative determination of volatiles in polymers, SPME can be combined with multiple headspace extraction to remove the matrix effects. If the hnearity of the MHS-SPME plot has been verified, the number of extractions can be reduced to two, which considerably reduces the total analysis time. Advantages of MHS-SPME compared to MAE are its higher sensitivity, the small sample amount required, solvent free nature and if an autosampler is used a low demand of labor time. In addition, if the matrix effects are absent, the recovery will always be 100%. This is valuable compared to other techniques for extracting volatiles in polymers in which the recovery should be calculated from the extraction of spiked samples, which are very difficult to produce in the case of polymeric materials. 

To form crosslinked coatings, the polymer must be free of unreacted functional monomer that would act as a chain terminator in the crosslinking reaction. The unreacted VEC could be easily removed from the acrylic copolymer by passing the resin solution through a wiped film still under vacuum, then redissolving the polymer in solvent. GC analysis indicated that the unreacted VEC had been totally removed. 

Sasanuma, Y., Conformational analysis of chain molecules in liquid crystalline phases by a rotational isomeric state scheme with maximum entropy method I. H— H dipolar couplings from n-alkanes dissolved in a nematic solvent, Polym. J., 32, 883-889 (2000a). 

Few studies have addressed finding ESI mass spectrometric conditions optimal to polymer analysis. Factors to be considered include mainly the composition (solvent and the agent promoting the formation of sample ions) of the spraying solution and the sampling or focusing of the gaseous ions within the ESI source. 

---