Abstract: An isobutylene is polymerized in the presence of an aromatic initiator and a catalyst under the conditions that either a chlorinated hydrocarbon or an aromatic hydrocarbon is used singly or in admixture with an aliphatic hydrocarbon so that the reaction solution has a dielectric constant of 1 to 5 and a solubility parameter of 7.5 to 9.0.

Abstract: There are described a phenoxybenzene derivative having the formula (I): ##STR1## wherein R.sup.1 is hydrogen atom; an alkyl group having 1 to 3 carbon atoms; --OR.sup.6 or a halogen atom,R.sup.2 is hydrogen atom, nitro group or amino group,R.sup.3 is hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 5 carbon atoms, allyl group, vinyl group or --(CH.sub.2)n.sup.1 R.sup.7R.sup.4 is hydrogen atom, an alkyl group having 1 to 3 carbon atoms or --(CH.sub.2)n.sup.3 R.sup.25R.sup.5 hydrogen atom; an alkyl group having 1 to 3 carbon atoms; or phenyl group,X is ##STR2## wherein Y is oxygen atom or sulfur atom; or --CHR.sup.27 -- and line means a single bond or a double bond provided that n is 2 in case that the line means a single bond and n is 1 in case that the line means a double bond, ora pharmacologically acceptable salt thereof,a cognition enhancer comprising the same as an effective ingredient andan antidepressant comprising the same as an effective ingredient.