Various Degrees Of Conversion Research Articles

Investigation of the porous structure of polyvinylchloride by standard contact porometry

Standard contact porometry has been used for the first time to study the porous structure of polyvinylchloride. Features of the porous structure of polymer specimens formed during the polymerization of vinylchloride in bulk to various degrees of conversion have been clarified. A correlation has been observed between the porometric characteristics and known ideas about the formation of the polymer's morphological structure during the polymerization of vinylchloride in bulk.

Étude de la gélification d'un système triol/diacide/monoacide avec effect de substitution sur le triol

AbstractUsing a new general formulation of Flory's gelation criterion, a critical transition equation is derived for the trimethylolpropane (2,2‐bis(hydroxymethyl)‐1‐butanol)/adipic acid/lauric acid system having a substitution effect on the hydroxyl groups of the triol. The successive reactivity of the hydroxyl groups present in the trimethylolpropane has been formulated by the study of the condensation of the triol with the monoacid, lauric acid. From GPC measurements of the reaction medium for various degrees of conversion, the distribution curves of the different molecular species are plotted. Examination of these distribution curves has shown a non‐equireactivity of the sites of the polyol, which may be assigned to a positive substitution effect. Comparison of experimental distribution curves with the results of the kinetic analysis allows one to quantify the substitution effect. The gelation equation shows that a positive substitution effect on the hydroxyl groups of the triol decreases the extent of reaction necessary for the gelation. The difference between the experimental gelation curves and the theoretical curves with substitution effect may be assigned to intramolecular reactions.

The development of strength in reaction sintered silicon nitride

The development of strength in reaction sintered silicon nitride has been investigated by determining the elastic moduli, fracture mechanics parameters, strengths and critical defect sizes of silicon compacts reacted to various degrees of conversion using “static” or “flowing” nitrogen. The relationship between each property and the nitrided density is shown to be independent of the green silicon compact density but is influenced by the nitriding conditions employed. Young's moduli, rigidity moduli and strengths vary linearly with the nitrided density. After an initial period when increases may occur, the critical defect sizes in both “static” and “flow” materials decrease continuously with increasing nitrided density, although at any particular density they are larger in material produced under “flow” conditions. A model is suggested for the development of the structure of reaction sintered silicon nitride involving the development of a continuous silicon nitride network within the pore space of the original silicon compact. The experimental data are discussed in terms of the proportion of silicon nitride which contributes effectively to the continuous network.

The nature of the active centres and the stereospecific effect of benzyl derivatives of four valent titanium in polymerization of Butadiene

A study has been made of the stereospecific effect of tetrabenzyltitanium and its halide derivatives in polymerization of butadiene. The proportion of 1,2-units decreases and of 1·4- cis-units in the polymers increases in the order of the series of catalysts (C 6H 5CH 2) 4Ti, (C 6H 5CH 2) 3TiCl, (C 6H 5CH 2) 3TiBr and (C 6H 5CH 2) 3TiI. Tribenzyltitanium iodide has a high stereospecific effect for formation of 1·4- cis-units, the concentration of which reaches 94–97%. By determination of the number of benzyl groups attached to titanium at various degrees of conversion, it is shown that the active centre formed from tetrabenzyltitanium contains three benzyl groups and one polymer chain. In the case of tribenzyltitanium iodide the active centre contains two benzyl groups, an iodine atom and a polymer chain, attached to the titanium atom. Electron donors alter the stereospecific effect of tribenzyltitanium iodide considerably. In the presence of these the proportion of 1,2-units in the polymer increases to 68%.