Poly(p-phenylene butylene):  A New, Processable, High-Melting Hydrophobic Polymer

Abstract

With the objective to produce processable, high-melting, hydrophobic, and crystalline polymers, we embarked on the synthesis of poly(p-phenylene butylene) (PPPB) as a new representative of the class of polymers that contain only aromatic and aliphatic hydrocarbon units in their backbone. Acyclic diene metathesis (ADMET) polymerization of p-diallylbenzene followed by catalytic reduction of the resulting unsaturated polymer was used as the primary synthetic route to PPPB. For the ADMET polymerizations, Schrock's alkylidene molybdenum complex, Grubbs' benzylidene ruthenium catalyst, and two classical systems (WOCl2(OAr)2/Bu4Sn and WCl6/Bu4Sn) were employed, and different reaction conditions were compared. WOCl2(OAr)2/Bu4Sn in refluxing toluene proved to be the most appropriate catalyst system to produce the crystalline and high-melting poly(p-phenylene but-2-enylene) precursor polymer in high molecular weight and chemically pure form. Catalytic hydrogenation of the latter led to poly(p-phenylene butylene) with number-average molecular weights of up to 14 000 g mol -1 . The latter polymer was found to have a melting temperature of between 200 and 215°C and to be highly crystalline and melt-processable. Thus, PPPB indeed represents a high-melting, hydrophobic polymer that permits conventional processing technologies as opposed to its "homologue" poly(p-xylylene) (PPX).

Poly(p-phenylene alkylene)s – A forgotten class of polymers

“…In analogy to the synthesis of PPPO, the Suzuki crosscoupling condensation and acyclic diene metathesis (ADMET) polymerization of p-diallylbenzene (4) followed by catalytic reduction of the resulting unsaturated polymer were used as the primary synthetic routes to PPPB (Scheme 6) 28) . In contrast to P1 (the ADMET-precursor polymer of PPPO, see above), precursor polymer P2 was found to be only soluble at elevated temperatures, which arises from the rigidity of its backbone and the lack of favorable enthalpic interactions with solvents.…”

“…Consequently, the thermal application range of different ADMET catalyst systems, such as Schrock's alkylidene molybdenum complex, Grubbs' benzylidene ruthenium catalyst, and two classical systems (WOCl 2 (OAr) 2 /Bu 4 Sn and WCl 6 /Bu 4 Sn) was systematically investigated, and different reaction conditions were compared. While the applicability of Schrock's Mocatalyst and Grubbs' Ru-catalyst was found to be restricted to temperatures below 75 8C, the classical system WOCl 2 (OAr) 2 /Bu 4 Sn in refluxing toluene proved to be the most appropriate catalyst system to produce the crystalline and high-melting poly(p-phenylene but-2-enylene) precursor polymer P2 in high molecular weight and chemically pure form 28) . Catalytic hydrogenation of the latter led to poly(p-phenylene butylene) with numberaverage molecular weights of up to 14 000.…”

“…Driven by the goal to produce polymeric materials which combine the unique properties of PPX with the outstanding processability of, for example, polyethylene (PE), we undertook the exploration of the family of poly(p-phenylene alkylene)s (Fig. 2), which we refer to as alkarotic polymers, because they contain only alkane and an aromatic units [26][27][28][29][30] . Our approach is based on the notion that adjusting the number of rigid and flexible units in the polymer backbone allows the control of flexibility of the polymer chain and, therewith, the melting temperature and processability.…”

“…The reason for this may be the lack of appropriate synthetic routes to produce these polymers: While the synthesis of high-molecular weight PPX and its derivatives is enabled by a rather special intermediate (see below), efficient and high-yield coupling reactions that allow for the formation of the phenylene alkylene repeat unit are rare. Thus, with the above-discussed technological potential of high-melting, melt-processable, hydrophobic polymers in mind, we have embarked on exploring the family of poly(p-phenylene alkylene)s and summarize here our initial studies regarding the synthesis and structure-property relationships of these materials [26][27][28][29] . In the first section, an overview of potentially useful synthetic approaches for the preparation of poly(p-phenylene alkylene)s is given.…”

Synthesis of poly(sulfonate ester)s by ADMET polymerization

“…18,19 Unlike the related ring-opening metathesis polymerization (ROMP), which is a chain-growth process driven by the release of ring strain, ADMET is driven by the removal of the ethylene gas generated as a by-product. ADMET chemistry has been used recently in the synthesis of both all-carbon polyolefins [20][21][22] as well as polyethylene-like polymers containing heteroatoms [23][24][25][26][27][28][29] or aromatic rings [30][31][32] in the main chain. ADMET offers an interesting alternative for the incorporation of aliphatic sulfonate esters into the polymer backbone, which are rare in the literature.…”