Infrared spectroscopy crystallinity, determination

T. Norris, PK. Aldridge and S.S. Sekulic, Determination of end-points for polymorph conversions of crystalline organic compounds using on-line near-infrared spectroscopy. Analyst, 122, 549-552 (1997). 

Note 4 The degree of crystallinity can be determined by several experimental techniques among the most commonly used are (i) X-ray diffraction, (ii) calorimetry, (iii) density measurements, and (iv) infrared spectroscopy (IR). Imperfections in crystals are not easily distinguished from the amorphous phase. Also, the various techniques may be affected to different extents by imperfections and interfacial effects. Flence, some disagreement among the results of quantitative measurements of crystallinity by different methods is frequently encountered. 

The investigation of the 300 MHz spectrum of poly(3-methyl-l -butene) indicates that the conclusions drawn by previous workers (2—4) concerning the structures of the crystalline and amorphous polymers are essentially correct the crystalline polymer being almost entirely of the 1,3-structure and the amorphous polymer being a mixture of both 1,2- and 1,3-structures. Further, it has indicated that this method is useful for analysis of the composition of the polymer. Quantitative composition determination, however, has not been carried out, since it is felt that the accuracy of the previous estimates utilizing near infrared spectroscopy were satisfactory. 

The four methods commonly used to determine the percent crystallinity of a partially crystalline polymer are dilatometry, X-ray crystallography, infrared spectroscopy, and calorimetry. 

Norris, T. Aldridge, P.K. Sekulic, S.S., Determination of End-Points for Polymorph Conversions of Crystalline Organic Compounds Using On-Line Near-Infrared Spectroscopy Analyst 1997, 122, 549-552. 

Conversion of the as-deposited film into the crystalline state has been carried out by a variety of methods. The most typical approach is a two-step heat treatment process involving separate low-temperature pyrolysis ( 300 to 350°C) and high-temperature ( 550 to 750°C) crystallization anneals. The times and temperatures utilized depend upon precursor chemistry, film composition, and layer thickness. At the laboratory scale, the pyrolysis step is most often carried out by simply placing the film on a hot plate that has been preset to the desired temperature. Nearly always, pyrolysis conditions are chosen based on the thermal decomposition behavior of powders derived from the same solution chemistry. Thermal gravimetric analysis (TGA) is normally employed for these studies, and while this approach seems less than ideal, it has proved reasonably effective. A few investigators have studied organic pyrolysis in thin films by Fourier transform infrared spectroscopy (FTIR) using reflectance techniques. - This approach allows for an in situ determination of film pyrolysis behavior. 

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

Raman spectroscopy is by no means a new technique, although it is not as widely known or used by chemists as the related technique of infrared spectroscopy. However, following developments in the instrumentation over the last 20 years or so Raman spectroscopy appears to be having something of a rebirth. Raman, like infrared, may be employed for qualitative analysis, molecular structure determination, functional group identification, comparison of various physical properties such as crystallinity, studies of molecular interaction and determination of thermodynamic properties. 

The decomposition of the ZSM-5 lattice at high temperatures can also be followed by monitoring the structure sensitive infrared bands. Figure 1 shows a set of spectra from the recent paper of Tallon and Buckley (ref. 11) in which the kinetics of ZSM-5 decomposition were investigated by using FTIR spectroscopy to determine the crystallinity of samples subjected to isothermal annealing. 

By sequential copolymerization of styrene and propylene using a modified Ziegler-Natta catalyst, MgCl2/TiCl4/NdClc(OR) //Al(iBu)3, which was developed in our laboratory, a styrene-propylene block copolymer is obtained. After fractionation by successive solvent extraction with suitable solvents, the copolymer was subjected to extensive molecular and morphological characterization using 13C-NMR, DSC, DMTA, and TEM. The results indicate that the copolymer is a crystalline diblock copolymer of iPS and iPP (iPS-fo-iPP). The diblock copolymer contains 40% iPS as determined by Fourier transform infrared spectroscopy and elemental analysis. 

The absorption bands belong to the crystalline oxide, which requires a separation of water content, degree of crystallinity and film thickness. Nevertheless, infrared spectroscopy can be useful to determine the degree of crystallinity or the number of surface states [69]. 

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