Birefringence poly

Light Scattering Loss of Zero-Birefringence Copolymer. Table II shows the scattering parameters of zero-birefringence poly(MMA-co-BzMA) and those of the homopolymer glasses. The Vy and Hy intensities of all samples had no angular... 

The Tg, refractive indices (no) and Abbe numbers (vd) of zero-birefringence polymers are shown in Table IV. The zero-birefringence poly(MMA-co-3FMA) and poly(MMA-co-BzMA) have slightly lower Tg (the former 90.0 0, the latter 103.30) compared with PMMA, because the Tgs of P3FMA and PBzMA are 64 and 6lO, respectively. Furthermore, the Tg of zero-birefringence PMMA with dopant molecules was also decreased by plasticization. 

Poly(methyl methacrylate). PMMA offers distinct advantages over BPA-PC with respect to significandy lower birefringence, higher modulus, and lower costs, but has not been successhil as a material for audio CDs and CD-ROM as well as a substrate material for WORM and EOD disks because of its high water absorption (which makes it prone to warp) and its unsuitabiUty for metallising, and less so because of its low resistance to... 

Fig. 26. Qualitative compatison of substrate materials for optical disks (187) An = birefringence IS = impact strength BM = bending modulus HDT = heat distortion temperature Met = metallizability WA = water absorption Proc = processibility. The materials are bisphenol A—polycarbonate (BPA-PC), copolymer (20 80) of BPA-PC and trimethylcyclohexane—polycarbonate (TMC-PC), poly(methyl methacrylate) (PMMA), uv-curable cross-linked polymer (uv-DM), cycHc polyolefins (CPO), and, for comparison, glass.

Figure 17 Isothermal melting of Ziegler-Natta isotactic poly(propylene). (a) Spherulites with mixed birefringence at Tc = 148°C. The top middle figure displays the melting for the same thermal history, (b) Subsequent to crystallization, the temperature was raised to 171°C spherulites acquire negative birefringence, (c), (d) and (e) Isothermal melting at 171°C for 80, 200 and 300 min, respectively. Reproduced with permission from W.T. Huang, Dissertation, Florida State University, 2005. (See Color Plate Section at the end of this book.)...

Dynamic Light Scattering and Transient Electric Birefringence Study of Poly(vinyI chloride) Micrc els... 

Data of Dr were obtained for low molecular weight poly (y-benzyl-L-gluta-mate) (PBLG) samples in isotropic solutions by two methods. Mori et al. [129] used dynamic electric birefringence, while Zero and Pecora [130] and Kubota and Chu [131] applied depolarized dynamic light scattering. Figure 18 shows... 

Fig. 5.4. Ratio of Maxwell-constant to intrinsic viscosity as a function of molecular weight for linear oligomers of poly oxy-propylene glycol in cyclo-hexanol at 20° C (full circles). Ratio of birefringence to shear stress in the limit of zero shear stress for the same oligomers in bulk (temperatures 20—60° C) (open squares). The experimental point at the righthand side is obtained on a high molecular weight sample, Tsvetkov, Garmonova and Stankevich (166)...

Preliminary polarizing microscope studies on poly(/ -phenylethyl isocyanide) show the spontaneous reversible formation of a highly birefringent mesophase in concentrated solutions. These observations suggest that small differences in conformations due to concentration changes give rise to the occurrence of a phase separation and molecular ordering. 

From these measurements of linear dichroism, it can be concluded, that the linkage of l-l.c. s to a polymer backbone generally reduces the nematic order. This effect has been found so far for poly(acrylates), poly(methacrylates) and poly-(siloxanes) and is established by NMR 59,60), ESR61) and birefringence measurements. 

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