degree of ionization, the half-life of the LSI decrease became longer. This is shown in Figure 7.In conclusion, the results obtained in this work appear to indicate that chain expansion of PMA in methanol induced by a sudden increase in the degree of ionization does not occur as a cooperative process but instead as a stepwise process involving initially only the outer regions of the coils. This takes place in the microsecond time range. Subsequently, a statistical distribution of ionized sites is established in a rather slow equilibration process. The relaxation process observed by Morawetz et al.3 in the time range of seconds probably corresponds to this equilibration process. Attempts to detect the slow process in the present work were not successful because the light scattering setup did not allow measurements of small LSI changes at long time scales.Acknowledgment. The polyfmethacrylic acid) samples were synthesized and characterized by R. Zuch, U.Fehrmann, and M. Weller at the Hahn-Meitner-Institut.The valuable assistance of Dr. G. Beck during the flash photolysis experiments is gratefully acknowledged.
The Tennessee Eastman copolyester of poly(ethylene terephthalate) with 60 mol % p‐oxybenzoate units was spun with various capillaries using a constant shear rate at the wall. Variables examined were the length‐to‐diameter ratio L/D of the capillary, the spin draw ratio Vf/V0, and the spinning temperature. Fibers spun at 260°C showed improved homogeneity of orientation through the cross section, better crystallite orientation, and higher initial moduli as L/D was increased. The spin draw ratio required to optimize these fiber properties decreases as L/D is increased. For example, when L/D = 49.44, the initial modulus has nearly reached its plateau value at a spin draw ratio of 10. However, in contrast to the results of Sugiyama, Lewis, White, and Fellers, we find that some spin draw is always required to optimize fiber properties. Fibers spun with a spin draw ratio of approximately unity showed very poor crystallite orientation and initial moduli. It is suggested that loss of orientation under these conditions may be due to the different velocity profiles in the spinneret and in the solidifed fiber. Fibers were also spun at five temperatures using a capillary having L/D = 49.44. Shear in the capillary is more effective in introducing orientation when the spinning temperature is 260°C or above. At spinning temperatures of 240 and 250°C, the initial modulus increases more slowly with spin draw ratio, and appears to have a lower plateau value. Acierno, La Mantia, Polizzotti, Ciferri, and Valenti spun the same polymer under conditions in which essentially all the orientation was introduced by spin draw. They used a very low extrusion velocity at the spinneret, a small L/D, and spin draw ratios up to 3000. They reported that the initial modulus increased with decreasing spinning temperature, in contrast to our results. Thus the optimum spinning conditions may depend upon whether most of the orientation is introduced by shear in the capillary, or by a high spin draw ratio.
We have previously reported two studies of the rheology and fiber properties of one sample of the copolymer of polyethylene terephthalate having 60 mol% of p‐oxybenzoate (PHB) units. The DSC curve of that sample exhibited crystalline melting transitions, and the sample appeared to contain PHB blocks. Here we compare those results with observations for a second sample that, although nominally the same polymer, appears to be more random because it exhibits little PHB crystallinity. We had previously reported that the flow of the copolymer containing PHB blocks was non‐Newtonian at all temperatures, and that it exhibited a thermal history effect. We find the flow of the more random polymer is Newtonian above the melting temperature, and the melt viscosity of the more random copolymer exhibits no thermal history effect. Fibers were spun from the more random copolymer with a capillary rheometer using a capillary having a length/diameter ratio of 14.1 and a shear rate at the wall of 6.4 sec−1. Spinning temperatures were 250, 260, and 280°C, and the spin draw ratio was examined as a variable. The initial modulus increased with spin draw ratio but exhibited no dependence upon the spinning temperature. For the copolymer containing PHB blocks, the initial modulus increased as the spinning temperature was raised. These differences are due to the larger amount of PHB crystallinity in the more blocky sample. When chips of the more random sample were heated for 1 h at 235°C, the melt viscosity increased and the initial modulus of the fibers decreased. These changes are due to the crystallization of longer PHB blocks produced by melt interchange.
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