Polyurethanes were synthesized by reaction of a rigid molecule, 3,3 '-dimethyl4,4'-biphenyldiyl diisocyanate (DBD), with flexible molecules, oligoethylene glycols (di-, tn-, and tetraethylene glycol) or a,w-alkanediols, and some of their thermal properties were studied. Poly(DBD-oligoethylene glyco1)s are amorphous polymers which exhibit no mesomorphic phase. Poly(DBD-alkanedio1)s are found to show a mesomorphic phase depending on the number of methylene units in the alkanediol. The polymers having methylene units from five to twelve are crystalline and show a mesomorphic phase. On the contrary, polymers having less than four methylene units do not show a mesomorphic phase since thermal decomposition of the polymers occurs before melting. The transition temperature from the mesomorphic phase to the isotropic liquid decreases with increasing length of the flexible chain of alkanediol. Ternary polymers are obtained by reaction of DBD with a mixture of hexanediol (HD) and dodecanediol (DD). The ternary polymers containing a small amount of HD and DD give a clear mesomorphic phase.
Neutralization dialysis is a very effective deionization method and the transport of weak acids and bases is also facilitated by the neutralization reaction in the system. The transport rates of weak acids and bases increased with the increase of their dissociation constants.
SynopsisAllylation of sodium phenoxide in the presence of crown ethers produces a high ratio of 0/0 + C allylation when conducted in water, phenol, benzene, or diethyl ether. The striking increase in the product ratios is attributed to specific complexation of the crown ethers that facilitate the dissociation of the ion pair aggregate of the sodioderivative in benzene or diethyl ether. The crown ethers may act as a phase transfer catalyst when the reaction is run in water. Furthermore, the 0/0 + C ratios of the allylation strongly depend on the kind of crown ethers used. To examine their effect the allylation of sodium phenoxide was studied with various crown ethers, such as 18-crown-6, benzo-18-crown-6, benzo-15-crown-5, poly(vinylmonobenzo-15-crown-5), and poly(viny1monobenzo-18-crown-6), as catalysts. It was found that among these crown ethers poly(viny1rnonobenzo-15-crown-5) was the most effective catalyst.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.