Xylene backbone

Figure 3.116 Synthesis of a bis-imidazolium cyclophane on a xylene backbone and its...

Figure 3.117 Synthesis of transition metal complexes of bis-carbene cyciophane ligands with a xylene backbone.

The mechanism of these reactions has been studied in detail by Goldman for the pincer ligand based on the xylene backbone and by Brookhart for the pincer ligand based on the resorsinol backbone. -" These reactions have also been studied intensively by computational methods. - The most revealing studies include entropy terms in the calculations of energies and include a treatment of the steric effects on the pincer ligands. ... 

Benzene, toluene, and xylene are made mosdy from catalytic reforming of naphthas with units similar to those already discussed. As a gross mixture, these aromatics are the backbone of gasoline blending for high octane numbers. However, there are many chemicals derived from these same aromatics thus many aromatic petrochemicals have their beginning by selective extraction from naphtha or gas—oil reformate. Benzene and cyclohexane are responsible for products such as nylon and polyester fibers, polystyrene, epoxy resins (qv), phenolic resins (qv), and polyurethanes (see Fibers Styrene plastics Urethane POLYiffiRs). 

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen sensitive. In order to study the oxidation products, a xylene solution of poly(phenylhydrosilane)(Mw = 2340, Mw/Mn = 1.72) was refluxed (140 °C) for 12 h in a system exposed to the air [15]. Only minor changes were observed by GPC analysis whereas FTIR showed characteristic absorptions due to siloxane-type structures on the polymer backbone. A detailed NMR analysis, based on H NMR, Si INEPT and H- Si HMQC spectroscopies, indicated that the oxidized material contains the units 7-10 shown in Scheme 8.2. In particular, units 7,8 and 9+10 were present in relative percentages of 27%, 54% and 19%, respectively, which mean that more than 70% of the catenated silicons were altered. It has also been reported that silyl hydroperoxides and peroxides are not found as products in the autoxidation of poly(phenylhy-drosilane) [16]. 

The lithiated polyethylene copolymer was then suspended in hexane or THF solvent. The graft-from reactions were carried out in slurry solution by reacting the lithiated polyethylene copolymer with anionic polymerizable monomers, such as styrene and p-methylstyrene. After certain reaction time, 10 ml of isopropanol was added to terminate the graft-from reaction. The precipitated polymer was filtered and then subjected to fractionation. Good solvents for backbone and side chain polymers were used during the fractionization, using a Soxhlet apparatus under N2 for 24 hours. The soluble fractions were isolated by vacuum-removal of solvent. Usually, the total soluble fractions were less than 5 % of the product. The major insoluble fraction was PE graft copolymer, which was completely soluble in xylene or trichlorobenzene at elevated temperatures. 

The soluble and insoluble fractions were examined separately. The insoluble fraction, which made up 35% of the total, had the NMR spectrum expected of a DPP-rich block copolymer, with a sharp methyl proton signal and only one strong signal, at 8 6.46 ppm (PPP), in the aromatic backbone region. The composition, from comparison of the integrated intensities of the methyl and backbone proton signals, was 82 mole % DPP and 18% MPP. The soluble fraction had the spectrum expected of a block copolymer with about 65% MPP units. Since a coprecipitated blend was separated almost quantitatively into the pure homopolymers with m-xylene under these conditions, the copolymer is characterized as a block copolymer. 

Firstly, Aharoni et al. [128] described a process of ozonization of polymers or copolymers containing unsaturations in a mixture of two solvents. One of them is inert to ozone and the other one is less reactive than polymer double bonds but more reactive than the single C-C bonds of this polymer. A typical solvent mixture is composed of toluene and 1,1,2,2,-tetra-chloroethane, or xylene and decaline. This mixture permits one to control the attack of polymer only onto unsaturations and not to produce unstable sites in the polymer backbone (as peroxides or hydroperoxides coming from single bond C-C attack) which could decompose in a second step producing undesirable by-products. In this way, only unsaturations are reacted and... 

Xylene-soluble highly grafted artlexldant functions on polyolefin backbone... 

Fig. 1 Sketch of a polymer single crystal and electron micrograph of polyethylene single crystals (Marlex 50) grown from hot xylene. Chain backbones in the crystals are mostly aligned with the c-crystallographic axis. (From Ref...

These data indicate that the intramolecular interactions which prevailed in dilute solution and which remained "locked in" the solid polymer upon freeze drying are still maintained upon dissolution in xylene. The resulting "solutions" in xylene remain unchanged at ambient conditions over periods of months. It appears that equilibration of inter/intra associations readily occur upon dissolution or dilution in dioxane with S-PS at 1.7% sulfonation levels. However, with the same sample dissolved in a solvent of lower polarity, such as xylene, equilibration upon dilution either does not occur or is very slow. The addition of cosolvents such as alcohols expedites this equilibration. At different sulfonate levels, with different cations or different backbone molecular weights the situation may be different. 

Effect of Functionalization on the Backbone Polymer Molecular Weight. It is important that the functionalization of PS s in the experimental section be demonstrated to have no substantial effect on backbone polymer molecular weight in order for the comparisons that follow to have the desired significance. The PS used in these studies has an intrinsic viscosity of about 0.7 in xylene solvent or in xylene/methanol mixed solvent systems. It is a basic assumption of these studies that if... 

To determine an initiation efficiency of each polymerization condition, the PMMA branches were cleaved from the PP backbone and analyzed by GPC. As reported previonsly 12), PMMA branches were successfully detached from the PP backbone through an ester exchange reaction in a methanol/o-xylene mixed solvent in the presence of sodium methoxide. After the cleavage reaction, PMMA was easily extracted from the mixture by dissolution in chloroform. 

The ethanol spiropyrane showed a higher response than the hA-p-xylene and n-methyl spiropyrane. However, the response is no greater than that shown by hA-decyl spiropyrane, suggesting that there is a compromise between the dipolar formation, spatial disruptance and the effect obtained by attaching the photochromic material to the polymer backbone. 

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