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SynopsisThe influence of molecular weight on thermal transitions and on their thermodynamic parameters is discussed for a random thermotropic liquid crystalline copolyether based on the reaction of a 1 : 1 molar mixture of 1,5-dibromopentane and 1,7-dibromoheptane with 4,4'-dihydroxy-a-methylstilbene. Optimum phase transfer catalyzed polyetherification reaction conditions were established for the synthesis of polymers containing bromoalkane chain ends only over a wide variety of molecular weights. All these copolyethers present a crystalline and an enantiotropic nematic mesophase over the entire range of molecular weights studied. Both the thermal transitionFand their thermodynamic parameters are strongly molecular weight-dependent up to M, = 10,OOO-12,OOO, after which they remain constant. The enthalpies and entropies of isotropization of the copolyethers are higher than those of melting. This is in contrast to the same thermodynamic parameters of the corresponding homopolyethers. The enthalpies and entropies of isotropization of both homopolymers and copolymers present similar values, suggesting that copolymerization does decrease the degree of order in the crystalline phase but does not significantly change the alignment degree of the mesogenic units in the nematic mesophase.

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Unsupported nickel-molybdenum-tungsten sulphide catalysts were prepared from tri-metallic Ni-Mo-W alkyl precursors by in situ activation during the hydrodesulphurization (HDS) of dibenzothiophene (DBT). The tri-metallic Ni-Mo-W precursors were prepared by reaction of tetraalkylammonium thiomolibdotungstates salts, (R 4 N) 4 MoWS 8 (where R = H, methyl, propyl, butyl, cetyl-trimetyl), with NiCl 2 in water at a Ni/Mo(W) molar ratio of 2. These precursors are named Ni/(NH 4 ) C 1 , NiMoW-C 3 , NiMoW-C 4 and NiMoW-C C catalysts respectively. These catalysts exhibit a ''Swiss-cheese''-like morphology, a wide distribution of specific areas (from 46.9-194.07 m 2 /g) and high content of carbon (C/Mo = 2.5-8.9). The in situ activation of these tetraalkylammonium thiotrimetallates precursors leads to a mesoporous structure with pore size ranging from 10-40 Å and type IV adsorption-desorption isotherms of nitrogen. X-ray diffraction showed that the structure of unsupported nickelmolybdenum-tungsten sulphide catalysts corresponds to a typical structure of 2H-MoS 2 poorly crystalline with low-stacked layers. The nature of the alkyl group strongly affects both the specific area and the HDS activity. The catalytic activity is strongly enhanced when using carbon-containing precursors; the NiMoW catalysts prepared by in situ activation present high HDS activity. The lowest specific area of the catalysts was observed for the NiMoW-H sample.

SynopsisA novel synthetic method for the preparation of high molecular weight aromatic polyethers is presented. I t consists in the Scholl reaction of di(1-naphthyl) ethers of aromatic derivatives exhibiting lower nucleophilicity and higher oxidation potential than the 1-naphthoxy groups. The examples described in this paper refer to the synthesis of aromatic polyether sulfones and aromatic polyether ketones by the polymerization of 4,4'-di(l-naphthoxy)diphenyl sulfone and respectively 4,4'-di(l-naphthoxy)benzophenone. Both polymerization reactions are performed at room temperature in nitrobenzene, using anhydrous FeC1, as catalyst, and apparently follow a "reactive intermediate polycondensation" polymerization mechanism. is the Scholl r e a~t i o n .~-~ According to Balaban and Nenitzescu' the Scholl reaction can be defined as "the elimination of two aryl-bound hydrogens accompanied by the formation of an aryl-aryl bond under the influence

A novel and convenient synthetic method for the preparation of α,ω‐bis(2,6‐dimethylphenol)–poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO‐2OH) is presented. It is based on the oxidative copolymerization of 2,6‐dimethylphenol (DMP) with 2,2′‐di(4‐hydroxy‐3,5‐dimethylphenyl propane) (TMBPA) in a mixture of water–methanol or chlorobenzene–methanol. By using a 4/1 mole ratio of DMP to TMBPA and different solvent mixtures, it was possible to obtain bifunctional PPO‐2OHs with number average molecular weights between 1000 and 5000. A phase‐transfer‐catalyzed etherification of PPO‐2OH chain ends with a mixture of m‐ and p‐chloromethylstyrene was used to synthesize α,ω‐bis(vinylbenzyl)‐poly(2,6‐dimethyl‐1,4‐phenylene oxide)s (PPO‐2VBs). The thermal polymerization of the PPO‐2VBs was studied by differential scanning calorimetry, and has demonstrated a very high thermal reactivity for this new class of reactive oligomers.

SynopsisThe influence of molecular weight on thermal transitions and on the thermodynamic parameters was studied for two polymers based on 4,4'-dihydroxy-a-methylstilbene with either 1,9dibromononane (HMS-C9 polyethers) or 1,ll-dibromoundecane (HMS-C11 polyethers). HMS-C9 polyethers present an enantiotropic nematic mesophase over the entire range of molecular weights and a monotropic smectic mesophase for polymers of number average molecular weights higher than 17,000. The low molecular weight HMS-C11 polyethers are only crystalline. On increasing their molecular weight, the polymers become monotropic nematics, and at higher molecular weights, enantiotropic nematics. Up to a composition containing as little as 20 mol 4& nonane structural units, the random copolyethers based on 1,9-&bromononane, 1,ll-dibromoundecane, and 4,4'-dihydroxy-a-rnethyktilbene (HMS-C9/11 copolyethers) exhibit on cooling a phase diagram resembling that of HMS-C9 polyether. HMS-C9/11 containing about a 1/1 mole ratio between the two spacers presents both smectic and nematic enantiotropic mesophases. These results suggest that the phase diagram of random liquid crystalline copolymers is controlled by the shorter spacer. The thermodynamic parameters of isotropization for both polyethers and copolyethers are compared and suggest that copolymerization does not significantly decrease the degree of order of the mesogenic units in the mesomorphic phase.'For the previous paper in this series, see Ref. 1.

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