synopsisExperimental evidence is presented that describes the mechanism of formation of macroreticular styrene-divinylbensene copolymers in which phase separation occurs during a suspension polymerization. The mode of formation of the macroreticular structure is described as a three-stage process in which each droplet of the organic phase behaves as an individual in a bulk polymerization that results in a bead of copolymer. Macroreticular structure formation is described by changes in copolymer swelling ratios, infrared absorption spectra of vinyl groups pendent to the polymeric matrices, surface area, total porosity, and pore-size distribution. The proposed mechanism of formation is also substantiated by electron micrographs of the copolymers during various stages of the copolymerization.
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1191 ber of the first column. The third member of the new column is the sum of the second member of the new column and the third member of the first column. Thus the mth member of the new column is the sum of the preceding member of the new column and the mth nember of column I.5. Summing column II gives Si.6. A third column is obtained from column II just as column II was obtained from I. The sum of column III is St. 7. Calculate xm 605i -blSi -j-12S3 245i -1852 4S3 8. The peak position is given now by Pm = Po + (xm)(A P) (5) (6)where P" is the position of the first reading, x" is calculated according to step 7, and AP is the size of the equally spaced interval in the usual units.
EXAMPLEThe intensity of x-ray spectrometer lines is measured precisely by measuring automatically the time required to accumulate a fixed number of counts. The number of counts per unit of time is then the measure of intensity. Determining a peak position may be done by taking measurements at equal intervals of 26 about the expected point. (For this type of measurement, P is 26.) If the intensity is a maximum, the time is a minimum. Such times were determined for the cobalt Ka line by the follow-ing data taken with a lithium fluoride analyzing crystal. The various steps are indicated.Observations other than seven are permissible but the expression for xm is not as simple as that shown in step 7. The corresponding expressions may be derived by carrying out the standard orthogonal polynomial method. The expressions for x" when n = 5, 6, 7, 8, or 9 were all computed and that for seven points was the simplest. It must be emphasized that the peak must be symmetric in the form used. By decreasing AP and limiting the measurements to a small region around the peak, departure from symmetry may sometimes be reduced to a negligible magnitude. For the illustrative data (Table I), the orthogonal polynomial method was used to determine that the cubic and further terms beyond x2 were not statistically significant.The usefulness of the method consists in its simplicity which results in a great saving of time. For example, these data were computed in about 4 minutes. Using the same data but the more usual method involving squaring, cubing, etc., took 20 minutes. If uneven intervals had been used, the long method would probably have taken from 30 to 60 minutes.
LITERATURE CITED(1) Snedecor, G. W., "Statistical Methods," 4th ed., pp. 388-97,
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