LIVING CYCLOPOLYMERIZATION OF 1,6-HEPTADIYNE DERIVATIVES USING WELL-DEFINED ALKYLIDENE COMPLEXES - POLYMERIZATION MECHANISM, POLYMER STRUCTURE, AND POLYMER PROPERTIES

We report here the living cyclopolymerization of 1,6-heptadiyne deriva tives (usually 4,4-disubstituted) using well-defined alkylidene comple xes as initiators. Diethyl dipropargylmalonate (2a), di-tert-butyl dip ropargylmalonate (2b), optically active di-(1R,2S,SR)-(-)-menthyl dipr opargylmalonate (2c(-)), di-(1S,2R,5S)-(+)-menthyl dipropargylmalonate (2c(+)), di-(1R)-endo-(+)-fenchyl dipropargylmalonate (2d), ,4-bis[[p -tolylsulfonyl)oxy]methyl]-1,6-heptadiyne (3b), 4,4-bis[(trimethylsilo xy)methyl]-1,6-heptadiyne (3c), the cyclic silyl ether, PhEtSi(OCH2)(2 )C-(CH2C drop CH)(2) (3d), and N,N-dipropargyl-2,4,6-triisopropylbenza mide (5b) are polymerized to give soluble polymers in high yield using Mo(NAr)(CHCMe(2)Ph)(OR(F6))(2) (1a; Ar = 2,6-i-Pr2C6H3, OR(F6) = OCMe (CF3)(2)) as the initiator in 1,2-dimethoxyethane (DME). The polymers show a high degree of conjugation (lambda(max) > 500 nm) and have narr ow molecular weight distributions. Poly(2a) is soluble in most organic solvents (THF, C6H6, toluene, CH2Cl2, CHCl3, DME, DMF, MeCN). The mec hanism of the polymerization has been investigated-by H-1 NMR studies and by monomer, initiator, and solvent variations. Symmetric, diphenyl -capped polyenes, ''pull-pull'' polyenes containing p-cyanophenyl end groups, and ''push-push'' polyenes containing p-dimethylamino end grou ps have all been prepared, as have polyenes that contain optically act ive substituents and ''push-pull'' polyenes containing p-(dimethylamin o)-phenyl and p-cyanophenyl end groups. 4,4-Bis(carboxyethyl)cyclopent -1-ene and -vinyl-3-methylene-5,5-bis-(carboxyethyl)cyclohex- 1-ene we re employed as model compounds in order to quantify five- and six-memb ered ring structures in the polymer. The substituted polyenes are far more stable at room temperature and in air than unsubstituted polyenes of the same length. Random and block copolymers of 2a, 2,3-dicarbomet hoxynorbornadiene (DCMNBD) and 7,8-bis(trifluoromethyl)tricyclo[4.2.2. 0(2,5)] deca-3,7,9-triene (TCDT) were prepared and characterized. The solution electrochemistry, thin film electrochemistry, and UV/vis spec troelectrochemistry of several homopolymers and copolymers have been e xamined.