Polymer characterization sampling

Figure 7.10 Nuclear magnetic resonance spectra of three poly(methyl methacrylate samples. Curves are labeled according to the preominant tacticity of samples. [From D. W. McCall and W. P. Slichter, in Newer Methods of Polymer Characterization, B. Ke (Ed.), Interscience, New York, 1964, used with permission.]...

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

AppHcations of soHd-state nmr include measuring degrees of crystallinity, estimates of domain sizes and compatibiHty in mixed systems from relaxation time studies in the rotating frame, preferred orientation in Hquid crystalline domains, as weU as the opportunity to characterize samples for which suitable solvents are not available. This method is a primary tool in the study of high polymers, zeoHtes (see Molecular sieves), and other insoluble materials. 

Applications polymer characterization, preparative-scale fractionations, sample preparation, ultraquick separations, separations with highest efficiency... 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

Figure 12.9 Typical pyrolysis chromatogram of fraction from a styrene-acTylonitiile copolymer sample obtained from a miciocolumn SEC system 1, acrylonitrile 2, styrene. Conditions 5 % Phenylmetliylsilicone (0.33 p.m df) column (50 m X 0.2 mm i.d.) oven temperature, 50 to 240 °C at 10 °C/min carrier, gas, helium at 60 cm/s flame-ionization detection at 320 °C make-up gas, nitrogen at a rate of 20 mL/min. P indicates tlie point at which pyrolysis was made. Reprinted from Analytical Chemistry, 61, H. J. Cortes et ai, Multidimensional cliromatography using on-line microcolumn liquid cliromatography and pyrolysis gas cliromatography for polymer characterization , pp. 961-965, copyright 1989, with permission from tlie American Chemical Society.

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

NIR (near-infrared) imaging has also been well introduced into polymer characterization, mainly because no laborious sample preparation is necessary. Spatial resolution approaches the range of mid-infrared imaging. 

If one assumes that, in this case, ion abundances are (approximately) proportional to chain abundances in the polymeric sample, it can be concluded that chains terminated with phenolcarbonate on both sides are the most abundant ones (since peaks labeled as A are the most intense ones). In this way, a full polymer characterization is achieved. 

Polymer Characterization. Melt-pressed films of the nylon samples were examined using a Nicolett 5DX FTIR. The samples were pressed at 240° C - 260° C at 4,000 to 20,000 psi. Samples in 88% formic acid were precipitated into methanol and also examined as KBR pellets. All samples were scanned a minimum of 100 times. 

A recent survey has shown that our first polymer standard samples are widely distributed and used in research and industry for the calibration of a variety of characterization instruments, particularly gel-permeation chromatographs. They also serve as materials with well defined properties for research in many areas. These properties should become better defined with time as results accrue in the literature. 

One of the major applications of SEC is polymer characterization. As many of the properties that characterize a polymer, including hardness, brittleness, and tensile strength, are related to the molecular weight distribution, GPC can be used to identify subtle differences between polymer materials. The GPC technique can also be used as an alternative to reversed-phase LC for samples, such as creams, ointments, and lotions. These samples contain high levels of hydrophobic materials, such as triglycerides, which could bind strongly to the reversed-phase column and cause column fouling. 

Characterization of the crosslinked polymer in the dry state [apparent density (16), surface measurement by N2-ad sorption (17,18), Hg-intrusion for measurement of the pore volume (iS)] is not conclusive for the properties as polymeric reagent, However, extensive knowledge about the porous structure and the accessibility of different regions in the polymer network can be obtained by gel-permeation chromatography (GPC) (20). GPC is used in an inverse mode. Well-characterized samples are keys for the pore structure. 

In the literature, there exist many papers on the properties of epoxy glasses, but most of them are difficult to generalize due to incomplete characterization of the chemical and topological structure of the investigated samples. Sometimes, the difficulties of polymer characterization arise from the industrial origin of uncured resins and curing agents. 

Characterizing the Stereosequence Length of Propylene Oxide Polymers. The samples used in this study were the crystalline fractions of propylene oxide polymers made with various catalysts. Two methods were used to separate the fraction showing crystalline order (as judged from x-ray diffraction patterns) from the amorphous fraction ... 

If a concentration-selective detector, such as a DRI, is connected on-line with the viscosity detector, the ratio of the two signals yields the intrinsic viscosity distribution of the polymer sample. In polymer characterization, the intrinsic viscosity can be a property just as important as the molecular-weight distribution. Furthermore, polymer intrinsic viscosity follows the Mark-Houwink relation to the molecular weight, M, where K and a are Mark-Houwink viscosity constants ... 

Four examples of polymer characterization by SEC will be discussed a dextran sample with branching transitions, a pair of brominated polystyrene (PS) samples, aggregation in chitosan, and a PS star polymer. SEC numerical results for dextran, chitosan, and star-branced PS are listed in the corresponding figure captions. 

An important aspect of the use of analytical pyrolysis is its capability to provide complementary information to other analytical techniques used for polymer characterization. One such technique is IR analysis of polymers. Although IR spectra can be used as fingerprints for polymer identification, the success of this technique can be questionable when the polymer is not pure or is in a mixture with other compounds. The IR spectra are particularly difficult to use when a polymer is present only at a low level in a particular material and cannot be easily separated. The use of Py-GC/MS allows identification of polymers even in low concentration in specific mixtures because it couples pyrolysis with a chromatographic technique. On the other hand, some polymers generate by pyrolysis a low proportion of easily identifiable molecules, producing mainly char and small uncharacteristic molecules such as HF, H2O, CO2, etc. In these cases, IR is the technique of choice. Since for an unknown sample each technique can be misleading, the use of both types of information is always beneficial. 

Polymer characterization. The thermotropic behaviors of the polyester-carbonates prepared were examined under a polarized hot stage microscope (Sybron Co.). Normally the sample became softer at 120-150°C and melted with birefringence afterwards, depending on the molecular weight and composition of the polymer. The samples stayed bire-fringent until 350°c or higher. 

Preliminary data on MMD of our samples are given in Table IV. It is evident that equimolar concentrations of activator and initiator produce PCL polymers characterized by a regularly decreasing polymolecularity index Q, from ca. 2.6 to 2.0. In Figure 1 the number of polymer molecules formed per acyllactam molecule is plotted as a function of initiator concentration. The actual values should be compared to the theoretical value of 1, which corresponds to the assumption that the number of macromolecules would be equal to the number of acyllactam molecules (26J, as in the ideal case of a step-addition of lactam anions to a constant number of growth centers. 

As indicated in the previous sections, the antioxidant content in plastic material is often determined by chromatographic methods. Another widely used technique for polymer characterization is thermal analysis with differential scanning calorimetry (DSC). When the oxygen induction time (OIT) for a sample containing a phenoHc antioxidant is measured, a significant oxidative exothermic response is obtained in the DSC when all the phenolic antioxidant in a sample is consumed. The OIT is thus directly related to the antioxidant content in the material and to the stabihzing function, i.e. the antioxidant efficiency in the sample, if the consumption of phenolic antioxidants obeys zero-order kinetics at the temperature used [44]. Table 1 shows the amount of the antioxidant Irganox 1081 in polyethylene (PE) determined by HPLC and extraction by microwave assisted extraction (MAE),... 

---