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A large number of polypropylene samples, of isotacticities spanning the range 0.35 to 1.00 mm, have been examined by differential scanning calorimetry (DSC) in order to establish a calorimetric index for determining stereostructure. Crystallization studies show that the crystallization onset temperature decreases in step with reduced isotacticity. However, samples prepared with supported catalysts show significantly lower crystallization onset temperatures than those from conventional catalysts which is believed to be due to differences in the inter- or intramolecular distribution of stereodefects. Furthermore, whole and fractionated samples cannot be fitted by one calibration curve. However, the enthalpy of crystallization is found to be related to the isotacticity by an equation of the form: log ΔH = m log (isotacticity) + c. This relationship is found to be applicable to samples from all types of catalysts examined and to both whole and fractionated samples. Fusion curves have been determined for “as received” as well as conditioned and annealed samples but the melting temperatures are not found to be a reliable guide to isotacticity. The respective enthalpies of fusion are found to follow the same logarithmic relationship stated above and thus can also be used as a basis for a calorimetric isotactic index. Examination of glass transition and related heat capacity data does not provide any clear-cut alternative index.

Widely used radiotracer methods for active center determination, employing 14 CO tags and tritiated alcohol quench, generally provide conflicting results, thus casting doubt on the validity of both methods. This paper seeks to harmonize the apparent discrepancies by comparative studies on the polymerization of ethylene, propylene and 4-methylpent-1-ene, catalyzed by TiCl 3 .AA/AIR 3 , employing an innovative duel-labeling approach. It is concluded that quantitative 14 CO tagging of active site requires short contact times and high 14 CO concentrations to minimize interfering side reactions. The tritiated alcohol quench, after the tagging reaction, could provide information on the extent of transfer reaction. Under optimized conditions, tagging and quenching procedures can provide comparable and meaningful data.

A method is proposed for the determination of low levels of moisture in rubbers and other soluble polymers. The material for analysis is dissolved in an appropriate solvent and triethylaluminium is added to react with the water contained in the sample. The liberated ethane is analysed by a simple GC technique. The method is calibrated using an internal standard and by addition of known amounts of water. A series of natural and synthetic rubbers dried under varying conditions were found to have water contents in the range 0.01-2% w/w. Removal of proteinaceous material from natural rubber reduces the equilibrium water content of the stored rubber. Active hydrogen impurities in the rubbers are shown to interfere with the determination and consequently the observed water content must be assumed to represent the upper limit of water unless such impurities are known to be absent, or present only in negligible amounts.

This study examines the application of infrared (IR) spectrometry to the determination of polypropylene (PP) stereoregularity. The use of the absorption bands at 998 cm−1 and 841 cm−1 as indices of isotacticity and bands at 1167 cm−1 and 973 cm−1 as internal references have been explored. Calibration curves relating various absorption ratios to isotacticity as measured by 13C nuclear magnetic resonance are reported. The ratios A998/A973 and A841/A973 are the most useful and provide linear correlations with isotacticity. The effect of instrument type on the calibration has been investigated for both dispersive and Fourier transform type IR spectrometers. For samples annealed at room temperature the average of measurements on the same set of PP films by five instruments provide the calibrations: A998/A973 = 1.08 ± 0.02 (mm)−0.15 ± 0.03; and A841/A973 = 0.84 ± 0.06 (mm)−0.04 ± 0.02. High temperature annealing increases the crystallinity of the samples and the corresponding value of the absorption ratio but is not necessary for obtaining reproducible calibration curves.

The determination of polypropylene isotacticity is still of importance today in the evaluation of commercial catalysts and in the search for detailed mechanistic understanding of the stereoregulating process. Whereas, methods based on NMR measurements provide the most definitive information secondary techniques which are simpler and faster to carry out still Provide valuable information. This paper reviews the methods for tacticity determination based on solvent extraction, IR and recently proposed calorimetric techniques. The advantages and limitations of the methods are discussed. Some recent experimental results pertaining to the calibration of the IR method and to various aspects of the calorimetric measurements will also be presented.