Rheopectic behavior of the aqueous polymethacrylic acid (PMA) solution was investigated with a Zimm-Crothers type viscometer. Measurements were performed for the solutions of PMA ranging in molecular weight from 6 X 10 5 to 16 X 10 5 , at concentration of 0.05-5.0 wt% and shear rate of 0.5-7 .0 s -1 . The solution viscosities of high molecular weight PMA (Mv > lOX 10 5 ) increase linearly with the elapse of shearing time at early stage, reach a maximum and then fall off. Ratio of the maximum viscosity to the initial one, llmaJllinit, decreases with decreasing the concentration of polymer and increasing the rate of shear, indicating that rheopexy is attributed to a competition between growth and disruption of the molecular clusters in the shear field. The influences of four additives (HCl, NaOH, NaCl, and urea) on rheopexy were examined ; it was found that, regardless of the additive species, there is a correlation between rheopexy and the initial rate of shear. These results suggest that a particular balance of hydrophilic and hydrophobic bonding abilities of PMA molecule is essential for the occurrence ofrheopexy in the solution.
synopsisA study was carried to determine experimentally the crosslinking of irradiated polypropylene by ultraviolet rays in vacuo. Three methods of detecting crosslinking were used: measuring the degree of swelling in decalin at room temperature, measuring the gel fraction in a tetrachloroethylene solution of the irradiated sample, and comparing the infrared spectra before and after irradiation. It was found that as the time of irradiation increases, the degree of swelling decreases, whereas the gel fraction in tetrachloroethylene solution increases. This shows that the crosslinking reaction proceeds with time. On the other hand, the infrared spectra of the irradiated sample remained almost unchanged, which shows that different bond species can hardly be formed by irradiation in vacuo. From these facts it may be concluded that the measurements amply confirm the hypothesis. Furthermore, it is demonstrated that ash residue in polypropylene plays an important role in photocrosslinking; that is, the photochemical primary proccss of the reaction is the absorption of light by the ash residue.
reduce the average coefficients of variation to less than 10%, it is necessary to pay much attention to slight changes of operative conditions such as the resolving power of the column and the flow rate of solvent.
KEY WORDSGel Permeation Chromatography/Cooperative Test/Average Molecular Weight/ Standard Deviation/
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