Ring-opening metathesis polymerization of dicyclopentadiene and tricyclopentadiene

Abstract

Over the past few decades, cyclo-olefin polymers (COPs) prepared by ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation have received considerable attention because of their attractive properties such as high transparency, low fluorescence, and low birefringence, which are suitable for use as optical-grade materials. Nippon Zeon commercialized COPs with names of Zeonor and Zeonex. The cyclo-olefin monomers are Diels-Alder adducts of cyclopentadiene such as norbornene (NB), phenylnorbornene, dicyclopentadiene (DCPD), and 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (DMON). The glass transition temperature (Tg) is modulated in the range 75-160 C by choosing the appropriate monomer. Cyclopentadiene is a major constituent in the C5-stream of naphtha cracking. Up to now, most C5-streams have not been used as sources of chemicals, but have instead been incinerated as energy sources. Cyclopentadiene is transformed to dicyclopentadiene (DCPD) through its spontaneous Diels-Alder addition reaction. When DCPD is heated, tricyclopentadiene (TCPD) and higher oligocyclopentadienes are formed through successive Diels-Alder reactions (eq. (1)). By stopping the Diels-Alder oligomerization at an appropriate time (~17 h’ heating under reflux), a mixture containing ~40 wt% TCPD is attainable, which is fractionated through vacuum distillation. The distillate is composed of four stereoisomers. The major isomer amounts to ~80% of the total, and can be isolated by recrystallization in ethanol. Previously, we reported preparations of ethylene copolymers (COCs) of TCPD and its partially hydrogenated compound HTCPD. In this work, we report the preparation of a new COP employing TCPD as the monomer. The COP, prepared using solely DCPD, exhibits a low Tg of ~100 C. By further addition of bulky TCPD, we can increase Tg to a more attractive region. An advantage of the COP preparation is that the fed cyclo-olefin monomer can be fully converted to the polymer. In ethylene/cyclo-olefin copolymerizations, full conversion of the fed cyclo-olefin is practically impossible because of the drift in monomer concentrations during the polymerization, and so recovery of the unreacted bulky monomers may be problematic.