Poly Relative Thermal

In another TG study, Chiu (45) compared the relative thermal stabilities of five polymers, as shown in Figure 4.40. These polymers, poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA), high-pressure polyethylene (HPPE), polytetrafluoroethylene (PTFE), and an aromatic poly-pyromellitimide (PI), were all heated under identical conditions in the... 

The rate constant for spontaneous decomposition was reported to be 40 x i0 s at 65 °C in cyclohexane [101, 103]. The rate of decomposition of PSLi in cyclohexane at 150 °C is 0.205 min corresponding to a 3.5-min half-life [104]. In the presence of 2 equivalents of n,sec-dibutylmagnesium at 100 °C, the rate of decomposition of PSLi is 1.9 X 10 min while it is 6.4 x 10 " in the absence of additive, corresponding to half-lives of 102 and 3 h, respectively [105]. Similar decomposition reactions have been observed for poly(styryl)sodium [102]. The thermal stability of poly(a-methylstyryl)lithium is much lower than that of poly(styryl)lithium. The observed half-lives for spontaneous termination are 5 h and a few minutes at 25 and 60 °C, respectively [106]. The relative thermal stability of styryl carbanionic chain ends follows the order K Na > Li for the alkali metal counterions. 

The thermal stability of poly(a-methylstytyl)lithium is much lower than that of PSIi. The observed half-lives for spontaneous termination are 5 h and a few minutes at 25 and 60 °C, respectively. " However, the chain ends were stabilized with respect to spontaneous decomposition by the addition of TMEDA. The relative thermal stability of styryl catbanionic chain ends follows the order K" Na >li for the alkali metal counterions. 

Polymer Solvent. Sulfolane is a solvent for a variety of polymers, including polyacrylonitrile (PAN), poly(vinyhdene cyanide), poly(vinyl chloride) (PVC), poly(vinyl fluoride), and polysulfones (124—129). Sulfolane solutions of PAN, poly(vinyhdene cyanide), and PVC have been patented for fiber-spinning processes, in which the relatively low solution viscosity, good thermal stabiUty, and comparatively low solvent toxicity of sulfolane are advantageous. Powdered perfluorocarbon copolymers bearing sulfo or carboxy groups have been prepared by precipitation from sulfolane solution with toluene at temperatures below 300°C. Particle sizes of 0.5—100 p.m result. 

Poly(A/-vinyl-2-pyrrohdinone) (PVP) is undoubtedly the best-characterized and most widely studied A/-vinyl polymer. It derives its commercial success from its biological compatibiUty, low toxicity, film-forming and adhesive characteristics, unusual complexing abiUty, relatively inert behavior toward salts and acids, and thermal and hydrolytic stabiUty. 

Seawater Distillation. The principal thermal processes used to recover drinking water from seawater include multistage flash distillation, multi-effect distillation, and vapor compression distillation. In these processes, seawater is heated, and the relatively pure distillate is collected. Scale deposits, usually calcium carbonate, magnesium hydroxide, or calcium sulfate, lessen efficiency of these units. Dispersants such as poly(maleic acid) (39,40) inhibit scale formation, or at least modify it to form an easily removed powder, thus maintaining cleaner, more efficient heat-transfer surfaces. 

Polymer-based microreactor systems [e.g., made of poly(dimethyl-siloxane) (PDMS)], with inner volumes in the nanoliter to microliter range (Hansen et al. 2006), are relatively inexpensive and easy to produce. Many solvents used for organic transformations are not compatible with the polymers that show limited mechanical stability and low thermal conductivity. Thus the application of these reactors is mostly restricted to aqueous chemistry at atmospheric pressure and temperatures for biochemical applications (Hansen et al. 2006 Wang et al. 2006 Duan et al. 2006). 

Kohori, F., Sakai, K., Aoyagi, T., Yokoyama, M., Sakurai, Y., and Oakano, T. Preparation and characterization of thermally responsive block copolymer micelles comprising poly(A-isopropylacrylamide-fc-DL-lactide). J. Contr. Rel, 1998, 55, 87-98. 

---