Benzocyclobutenyl functionalized polymers of cyclotrimerized terminal diynes: synthesis and crosslinking

The monomers 1,13-tetradecadiyne, 1,11-dodecadiyne, 1,9-decadiyne and 1,7-octadiyne were cyclotrimerized, using niobium pentachloride as the catalyst, in the presence of 1,5-hexadiyne, which co-cyclotrimerizes to give a benzocyclobutene (BCB) capping group. Molecular weights of the BCB-capped oligomers were in the 3100-8000 range, with fairly narrow polydispersities. The oligomers were characterized by 1 H NMR and IR spectroscopy, along with GPC and DSC studies. DSC studies on the end-capped oligomers show that each exhibits an exotherm around 260°C, indicative of the formation of carbon-carbon bonds in a crosslinking reaction. The final, crosslinked materials may be regarded as thermosetting thermoplastics, since they are hard at room temperature and soft at 250°C.