Aromatic polymers obtained by precipitation polycondensation: 4. Synthesis of poly(ether ketone ketone)s☆
Abstract High molecular weight aromatic poly(ether ketone ketone)s were synthesized by the Friedel-Crafts polyacylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4-phenoxybenzoyl)benzenes. Depending on the monomers used for polycondensation, polyketones of regular structure with different iso-/tereisomer repeating unit ratio ( 100 0 , 50 50 , 0 100 ) in the main chain were obtained. Polymers of each repeating isomer unit were prepared in two different ways. All the polymer syntheses were performed as precipitation polycondensations and the resulting polymers were obtained in particle form. The influence of reaction conditions and preparation route on the polymer properties were examined. The monomer concentration and monomer stoichiometric ratio were found to affect the polymer viscosity. The size and shape of the polyketone particles obtained were also found to be governed by reaction conditions and preparation route.
A DFT study of the formation of xanthydrol motifs during electrophilic poly(aryl ether ketone) synthesis
The reaction pathway of the cyclization of 2-phenoxybenzophenone into 9-phenyl-9H-xanthen-9-ol in the presence of acid and an excess of AlCl33 was studied using density functional theory. This type of reaction is known to occur during the Friedel–Crafts polycondensation of poly(aryl ether ketones) following the undesired benzoylation of nucleophilic positions ortho- to the growing polymer’s ether groups. The formed defect acts as an undesired terminator of the polymer chain, causing severe problems in the polymer’s melt state. A branched, multistep mechanism reminiscent of the Friedel–Crafts acylation reaction is discovered; the reaction starts with the protonation of the carbonyl oxygen, followed by intramolecular electrophilic attack on the carbonyl carbon that determines the turnover frequency of the catalytic cycle and ends by deprotonation of the Wheland intermediate.
Exploring interculturally competent teaching in social sciences classrooms
Abstract This paper explores a grounded research-based framework for intercultural competence and discusses the implications of interculturally competent teaching in the classroom and beyond. Given the importance of teachers being interculturally competent in today’s diverse classrooms, a number of questions, based on the framework, are presented, which guide teachers in reflecting upon their own teaching practice and the ways in which they integrate aspects of intercultural competence into their classrooms. The paper also provides some examples from the USA of ways in which intercultural competence development is being addressed in teacher training.