Cyclobutene polymerization

This process is quite unexpected for another reason. The cyclobutene ring is highly strained, making this monomer one of the most easily polymerized of all the cycloolefins. Thus, the variety of catalysts effective for cyclobutene polymerization is much broader than that effective for metathesis of low-strained cycloolefins and acyclic olefins (73). Therefore, the recovery of monomeric cyclobutene rather than its respective polymer is remarkable and indicates the lack of substantial metathesis activity in the above retrocarbenation system. 

Starting with the n = 4 case, the desired polymer can be obtained by polymerization of either cyclobutene (16, n = 4) or butadiene. Using the cyclobutene polymerization enthalpy from Reference 16 and of the enthalpy of formation of monomer from Pedley, we find the enthalpy of formation of [— CH=CH—(CH2)2—] is 12 kJmol-1. We conclude that the enthalpy of hydrogenation is —116 kJmol-1. 

Scheme 7.5 Aqueous cyclobutene polymerization by an insertion mechanism (a) and by ring opening polymerization (b) SDS= sodium dodecyl sulfate.

Crotonaldehyde, hydrogenation of, 43-48 Cubane, isomerization of, 148 Cyclic dienes, metathesis of, 135 Cyclic polyenes, metathesis of, 135 Cycloalkenes, metathesis of, 134-136 kinetic model, 164 ring-opening polymerization, 143 stereoselectivity, 158-160 transalkylation, 142-144 transalkylidenation, 142-144 Cyclobutane configuration, 147 geometry of, 145, 146 Cyclobutene, metathesis of, 135 1,5,9-Cyclododecatriene, metathesis of, 135... 

Most ruthenium-initiated ROMP studies have been performed using (233) and strained cyclo-olefinic monomers such as norbornene688 and cyclobutenes,689 although several reports on the polymerization of 8-membered rings have also appeared.690-692 A wide range of functionalities are tolerated, including ethers, esters, amines, amides, alcohols, carboxylic acids, and ketones. 

The optimum catalyst for a given reaction depends primarily on (a) the energetics of the reaction and (b) the functional groups present in the substrate. If, for instance, a strained cycloalkene such as norbomene or cyclobutene is to be polymerized, a catalyst of low activity will be sufficient to attain acceptable reaction rates. RCM... 

As expected, the metathesis polymerization of more strained cycloalkenes, such as cyclobutene, occurs more rapidly than less strained structures such as cyclopentene. 

Mit geringer Ausbeute konnten Natta und Mitarbeiter 53) das erythro-diisotaktische Polycyclobuten auch durch Polymerisation mittels Rheniumchlorid in Wasscr bei 50 °C nach dcr Methode von Rinehart 81) crhalten. Ein Polymeres mit Cyclobuten-Grundbausteinen ist auch mit dem TT-Allyl-Ni-bromid-Komplex in athanolischem Medium zu ge-winnen 56). 

The photochemistry of 1,3-dienes can be highly dependent on the diene structure and reaction conditions. Important variables include the ground state conformation [22,23], the reaction concentration, the use (or not) and properties of a triplet sensitizer [14] or an electron acceptor [18], and solvent polarity. The simplest dienes also often yield the most complex chemistry. For example, 1,3-butadiene 3 undergoes unimolecular isomerization in dilute solution to give only cyclobutene 4 and bicyclobutane 5 (Sch. 2), and polymerization in concentrated solution [24]. At intermediate... 

In the following years, a number of other monocyclic, bicyclic and polycyclic olefins including cyclobutene, [4] cyclopentene [3 a, 5] and cyclooctene [6] were found to undergo ring-opening polymerization. 

Discotic SCLCPs were synthesized by the group of Grubbs [82]. For this purpose, norbornenes XXVIII-n (n=5, 10) and cyclobutenes XXIX-n (n=5, 10) with alkoxy-substituted triphenylenes as mesogenic units (see Fig. 18) were prepared. Polymerization was carried out with initiator 6. The resulting polymers had a narrow PDI between 1.09 and 1.17. Physico-chemical data for poly-XXVIII and poly-XXIX are listed in Table 18. 

Table 4 shows polymerization conditions and properties of crystalline polymers of cyclobutene, cyclopentene, norbomene, and tetracyclododecene produced by zirconocenes. The activities for the polymerization of cycloalkenes are significantly lower than for ethylene. The melting points are surprisingly high they were found to be 395 °C for polycyclopentene and over 400 °C for the others the decomposition temperatures lie in the same range. 

Ethylene has been co-polymerized with a range of cycloolefms, including cyclobutene,596 cyclopentene,596 cyclohexene,597 norbornene (NB),596 5-phenyl-2-norbornene,598 5-vinyl-2-norbornene,599 5-ethylidene-2-norbornene,600 dimethano-octa-hydro-naphthalene,601 phenyldimethano-octahydro-naphthalene,598 and norbornadiene.602 Several non-conjugated cyclodiolefins have been co-polymerized as well.603... 

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