Hexa solution processing

Ethylene-propylene (30-60 mole per cent) copolymers produce substances which are rubbery in nature. They are prepared by using Ziegler catalysts based on vanadium oxychloride/aluminium trihexyl by solution process at 40°C using chlorobenzene or pentane as a solvent. These can be vulcanised with peroxides. Ethylene-propylene-hexa 1, 4-diene terpolymers are rubbers which can be vulcanised with sulphur. 

A. Tracz, J.K. Jeszka, M.D. Watson, W. Pisula, K. Mullen, T. Pakula, Uniaxial alignment of the columnar super-structure of a hexa(alkyl) hexa-peri-hexabenzocoronene on untreated glass by simple solution processing. J. Am. Chem. Soc. 125, 1682-1683 (2003)... 

Wong WWH, Singh TB, Vak D, Pisula W, Yan C, Feng X, Williams EL, Chan KL, Mao Q, Jones DJ, Ma CQ, Mullen K, Bauerle P, Holmes AB (2010) Solution processable fluorenyl hexa-peri-hexabenzocoronenes in organic field-effect transistors and solar cells. Adv Punct Mater 20 927-938... 

Resoles. Like the novolak processes, a typical resole process consists of reaction, dehydration, and finishing. Phenol and formaldehyde solution are added all at once to the reactor at a molar ratio of formaldehyde to phenol of 1.2—3.0 1. Catalyst is added and the pH is checked and adjusted if necessary. The catalyst concentration can range from 1—5% for NaOH, 3—6% for Ba(OH)2, and 6—12% for hexa. A reaction temperature of 80—95°C is used with vacuum-reflux control. The high concentration of water and lower enthalpy compared to novolaks allows better exotherm control. In the reaction phase, the temperature is held at 80—90°C and vacuum-refluxing lasts from 1—3 h as determined in the development phase. SoHd resins and certain hquid resins are dehydrated as quickly as possible to prevent overreacting or gelation. The end point is found by manual determination of a specific hot-plate gel time, which decreases as the polymerization advances. Automation includes on-line viscosity measurement, gc, and gpc. 

Chaput, Jeminet and Juillard measured the association constants of several simple polyethylene glycols with Na", K", Cs", and Tl". Phase transfer catalytic processes and most biological processes are more likely to involve the first two cations rather than the latter two, so we will confine the discussion to these. Stability constants for the dimethyl ethers of tetra-, penta-, hexa-, and heptaethylene glycols were determined poten-tiometrically in anhydrous methanol solution and are shown in Table 7.1. In the third column of the table, the ratio of binding constants (Ks/K s) is calculated. Note that Simon and his coworkers have referred to this ratio as the selectivity constant. ... 

Important results and a detailed insight into aqueous chemical deposition processes have been reported and discussed elsewhere for CdSe [248, 249] and ZnS [250, 251] target products. We should note also the work of Davies et al. [252] who described an alternative method for the chemical growth of metal sulfides and selenides on the basis of polysulfide or polyselenide solutions (containing hexa- and tetra-chalcogen anions) formed by the dissolution of sulfur or selenium in hydrazine monohydrate. ... 

Although it is generally agreed that the thermal isomerization of bicyclo[2.2.0]hexanes to hexa-l,5-dienes takes place via diradical intermediates,113 118 121,123 125 experimental evidence has been obtained which implies otherwise.115,116 While a radical stabilization energy of approximately 4 kcal mol"1 was obtained for the pyrolysis of methyl 4-chlorobicy-clo[2.2.0]hexane-l-carboxylate (28 b) to methyl 5-chlorohexa-l,5-diene-2-carboxylate (29b),115116 as related to the parent 2-chlorohexa-1,5-diene (29a),115-l16-118 kinetic studies have indicated that there is a small but significant increase in activation energy of about 1 kcal mol-1 for the gas-phase and solution pyrolysis of l-chloro-4-methylbicy-clo[2.2.0]hexane (28c), as compared to l-chlorobicyclo[2.2.0]hexane (28a).115-116 In the light of this result, the commonly accepted diradical mechanism must be questioned and it is likely that the isomerization of these compounds occurs via a concerted process. 

As described in Vol. Ill Cyclonitc can be made by nitrating hexamine (hexa-metliylenetetramine) witli nitric acid. Tlie product is precipitated by pouring the solution into hot water in such a way that the concentration of the acid became 50-55% MNO3 and the temperature 70-90 C was maintained. All unstable products were decomposed and NOj was evolved. This was a degassing process. ... 

Electron photoemission from solvated electron solution (in solvents such as hexa-methylphosphotriamide and liquid ammonia the solvated electrons are fairly stable) to vapour phase has been studied by Delahay and co-workers (whose works are reviewed in Ref. ). According to them, this process proceeds in three stages solvated electron photoionization diffusion of generated delocalized electrons to the solution s surface and emission proper, i.e. transition of electrons to the vapour phase where they are transferred from the cathode surface (i.e., from the solution) to the anode by the external electric field. 

---