Hydrogenated hydroxy-terminated

Another rubber which appears to be of interest for insulation of rocket motors is hydrogenated hydroxy-terminated polybutadiene (HHTPB). As this rubber is derived from HTPB, it is more compatible and would also have strong bond with the HTPB-based propellants. Further, as the quantum of unsaturahon is considerably reduced in HHTPB, the life of rocket motors insulated with HHTPB will also be more. In a nutshell, the use of HHTPB results in an increased stability to... 

Toluene solutions of Pd encapsulated within dendrimer-templated inverted micelles have been tested for catalytic activity by examining their effectiveness towards hydrogenation of allyl alcohol in organic solvents [19]. The reaction product was confirmed to be n-propanol by H NMR spectroscopy, and the turnover frequency, calculated from the rate of hydrogen uptake, was 760 mol H2 (mol Pd) h at 20 °C. This value compares favorably with the value of 218 mol H2 (mol Pd) h obtained for the same reaction carried out in water using Pd nanoparticles encapsulated in hydroxy-terminated dendrimers. 

Urethanes. The basis for urethane chemistry is the reaction of an isocyanate group with a component containing an active hydrogen. The first step in formulating a urethane sealant is to prepare what is commonly called (lie prepolymer, typically by reaction of a hydroxy-terminated polyether with a stoichiometric amount of a diisocyanate. 

Hydroxy-terminated liquid polybutadienes are prepared for reactions with diisocyanates to form elastomeric polyurethanes (see Chapter 6). Such materials can be prepared by anionic polymerizations as living polymers and then quenched at the appropriate molecular weight. These polybutadienes can also be formed by a free-radical mechanism. The microstructures of the two products differ, however, and this may affect the properties of the finished products. To form hydroxy terminated polymers by a free-radical mechanism, the polymerization reactions may be initiated by hydroxy radicals from hydrogen peroxide. 

Fig. 30. TGIC separation of PS samples with diiferent end groups (hydrogen terminated vs hydroxy terminated) by NP-TGIC. Top - colunm Nucleosil 100 A 250 x 2.1 mm, eluent isooc-tane/THF=55/45 (v/v) and RP-TGIC. Bottom - cxilunm Nucleosil C18 100 A 250 X 2.1 mm, eluent CH2Cl2/CH3CN=57/43 (v/v)). Flowrates are 0.1 ml/min. Temperature programs are also drawn in each figure. Reproduced from [118] with permission...

Ethylene polymerized with diethyl peroxydicarbonate contains terminal ester groups (41). Using C-labeled cyclohexane peroxydicarbonate, the fate of the primary radicals during the polymerization of methyl methacrylate (MMA) and styrene has been studied (42). Although this reference includes no detailed analysis of the products, it indicates that ROOCO-terminated polystyrene telechelics may be obtained by this technique. A similar method has been used for the preparation of telechelic polybutadiene (43). The carbonate end groups are easily modified into terminal hydroxyl groups by hydrolysis. Hydrogenation of the carbonate functionahzed telechelic polybutadiene, followed by hydrolysis, srields hydroxy-terminated polyethylene telechelics. 

Hydroxy-terminated polymers prepared in this manner were used to build more complex macromolecular architectures such as graft copolymers [50] or block copolymers [51]. Using a 1,3-dithiepine instead of a 1,3-dioxepine as sacrificial monomer, allylic thiol polymer end groups could be obtained [52]. The poly(l,3-dithiepine) block was cleaved (sacrificed) under hydrogenation conditions using Raney-Nickel. 

Hydroxy-terminal PMMA 11 can be prepared in a different way. Allylithium adds to 1,1-diphenyl ethylene to give initiator 12. Again, readily polymerizes MMA to give 13. 9-BorabicycTo-[3,3,l]nonane (9-BBN) reacts selectively witTTthe carbon-carbon double bond of to produce alcohol 11 after oxidation with basic hydrogen peroxide. HPLC analysis as above shows that hydroxy PW1A 11 is produced cleanly. This method is the easiest way to prepare hydroxy PMMA 11 because allylithium is prepared from commercially available affyl phenyl ether." ... 

The presence of alcohol in the medium leads to a reduction of the apparent polymerization rate the greater the proportion of alcohol introduced into the reaction medium, the lower the EO polymerization rate. It was proposed that the hydroxy-terminated chains contribute to decrease the polymerization rate by hydrogen-bonding interactions with alkoxide ends. The combination of alkoxide with the parent hydroxy compound has been used to initiate EO polymerization in various media (THE, DMSO). This was used for the preparation of multibranched poly(EO). Typically, a polyhydroxy compound to be used as multifunctional initiator is partially deprotonated by the addition of 0.2-0.8 molar equivalent of an alkali metal derivative. This limits aggregation of alkoxide species and preserves solubility, thus allowing a better control of the initiation and propagation of EO polymerization, but to the detriment of reaction kinetics. 

Even cationic species such as the (hydrated) hydrogen ion (H ) can be lured into the hydrophobic silicone films from water medium as long as they contain appropriate additives to allow penetration of the analyte. For instance, Nivens et al. [140,141] have reported fabrication of silicone/ sol-gel films using a hydroxy-terminated poly(dimethyl siloxane (PDMS-OH), tetraethoxysilane (TEOS) and 3-ami-nopropyltriethoxysilane (APTES) mixture in ethanol-water. Tetramethylammonium hydroxide (TMAOH) is added to the mixture to entrap the fluorescent pH indicator dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS) [102], after base-catalyzed polycondensation of the silanes and the PDMS-OH. Silica optical fibers are stripped from their jacket at the distal end and dip-coated with the indicator gel before the end of gelation (24 h). The optical fluorosensor is able to measure between pH 6.0 and 8.5 for 6 months if stored in buffer medium. 

Some of these questions have been addressed using hydroxyphenyl- and acetoxyphenyl-terminated hyperbranched polyesters. The phase behavior of blends of hydroxyphenyl- and acetoxyphenyl-terminated hyperbranched polyesters with linear polymers such as polycarbonate, polyesters, and polyamides indicated that the hydroxy-terminated hyperbranched polyester blend miscibility was identical to that of poly(vinylphenol), suggesting that strong interactions due to hydrogen bonding, more than chain architecture, dominate the blend miscibilily. The acetoxy-terminated hyperbranched polyester showed less miscibility than the hydroxy-terminated polymers owing to the absence of... 

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