Poly(p-phenylene butylene): A new, processable, high-melting hydrophobic polymer

With the objective to produce processable, high-melting, hydrophobic, and c rystalline polymers, we embarked on the synthesis of poly(p-phenylene butyl ene) (PPPB) as a new representative of the class of polymers that contain o nly aromatic and aliphatic hydrocarbon units in their backbone. Acyclic die ne metathesis (ADMET) polymerization of p-diallylbenzene followed by cataly tic reduction of the resulting unsaturated polymer was used as the primary synthetic route to PPPB. For the ADMET polymerizations, Schrock's alkyliden e molybdenum complex, Grubbs' benzylidene ruthenium catalyst, and two class ical systems (WOCl2(OAr)(2)/Bu4Sn and WCl6/Bu4Sn) were employed, and differ ent reaction conditions were compared. WOCl2(OAr)(2)/Bu4Sn in refluxing tol uene proved to be the most appropriate catalyst system to produce the cryst alline and high-melting poly(p-phenylene but-2-enylene) precursor polymer i n high molecular weight and chemically pure form. Catalytic hydrogenation o f the latter led to poly(p-phenylene butylene) with number-average molecula r weights of up to 14 000 g mol(-1). The latter polymer was found to have a melting temperature of between 200 and 215 degrees C and to be highly crys talline and melt-processable. Thus, PPPB indeed represents a high-melting, hydrophobic polymer that permits conventional processing technologies as op posed to its "homologue" poly(p-xylylene) (PPX).