SIMULTANEOUS POLYMERIZATION AND FORMATION OF POLYPHENYLACETYLENE FILMS BY RARE-EARTH COORDINATION CATALYSIS Ⅳ.KINETICS AND MECHANISM OF POLYMERIZATION

The CO_2 quenching method has been used for the first time to determine the active complex concen- tration in Nd(naph)_3-Al(i-Bu)_3 catalyst system for polymerization of phenylacetylene into polyphenylacetylene(PPA)films.The kinetics and mechanism of this polymerization have been investigated by CO_2 quenching and IR,UV analytical methods.The kinetic equation can be expressed as Rp=k[M][Cp],and the apparent activation energy is about 13.6 kJ/mol.There is self-termination of chain propagating.Models for formation of the active complex and polymerization mechanism are proposed.

THE STUDYOF SYNTHESIS AND CHARACTERISTICS OF POLYPHENYLACETYLENE USING WOBr_4AS CATALYST

A new kind of catalyst WOBr_4,which can be used in the polymerization of phenylacetylene(PhA),has been synthesized.The obtained polyphenylcetylene(PPhA) using WOBr_4 as catalyst is soluble、fusible、with brown-red colour and has 1831(M n).The analysis of the stucture of PPhA shows that the polymer has cis-transoidal structure,therefore,the reaction mechanism is via complex catalysis.

Visualized thermoresponsive helix-helix switch of polyphenylacetylene with a wide-range tunable transition temperature

Polymers with tunable helicity and naked-eye structural change under external stimuli are valuable for fabricating smart materials. Herein, we report a novel thermoresponsive color and fluorescent polyphenylacetylene switch with a tunable critical temperature. It relies on the temperature and solvent sensitivity of intramolecular n→π* interactions between the vicinal carbonyl groups of ester substituents located at 3,5-positions, which are indispensable for forming the cis-cisoid helical conformation of polyene backbones. In a properly chosen solvent, a compressed cis-cisoid helix is stabilized by n→π* interactions at low temperatures and yields a colorless solution. Increasing temperature causes the conformational transition toward an extended cis-transoid helix due to the disruption of n→π* interactions and produces a yellow solution. Reducing the hydrogen bond donating ability or polarity of solvents increases the switching temperature. By introducing a fluorogenic pendant, this conformational transition can also be read out by fluorescence quenching. This work may open a new window for developing intelligent materials through precisely tuning conformational transitions.

Electroabsorption spectrum of substituted polyphenylacetylenes

Electroabsorption (EA) measurements on thin films of poly[ o (trimethylsilyl) phenylacetylene] and poly[ o (trimethylsilylmethyl) phenylacetylene] have been performed. The spectral change induced by an exernal electric field (EA spectra) has been observed, which shows the similar shape of the second derivative of the optical absorption spectra. The change in the absorption Δ α is obtained from the EA spectrum, and Δ n is calculated through Kramers_Krong transformation. The optical properties of substituted polyphenylacetylenes (PPAs) were discussed.

UV LASER INITIATED STEREOSELECTIVE HOMOGENEOUS CATALYSIS POLYMERIZATION OF PHENYLACETYLENE

In this paper, the stereoselective homogeneous catalysis polymerization of phenylacetylene by using two kinds of catalysts W(CO)_5CH_3I and W(CO)_4I_2 produced from UV laser photolysis of W (CO)_6 in CH_3I, I_2—C_6H_6 and CHI_3—C_6H_6 respectively was studied. The effects of laser energy, laser irradiation time and lifetime of catalyst on the polymerization of phenylacetylene were discussed. The photoproducts of W (CO)_6 in CH_3I, I2—C_6H_6 and CHI_3—C_6I_6 were determined by IR spectra. The structures of polyphenylacetylene obtained by W (CO)_5CH_3I and W (CO)_4I_2 catalysts were characterized by IR spectra and ~1H NMR spectra.

Tunable Cis-cisoid Helical Conformation of Poly(3,5-disubstibuted phenylacetylene)s Stabilized by Interaction

A series of novel cis poly(phenylacetylene)s(PPAs)substituted at meta-position(s)by two alkoxycarbonyl pendants,Le.,sP-Me-C8/rP-Me-C8,P-Me-C12,sP-Et-C4,sP-2C4 and sP-Oct-C4,were synthesized under the catalysis of[Rh(nbd)Cl]2(nbd=norbornadiene).The dependence of elongation,screw sense,and stimuli response of helical polyene backbone on the structure of pendant,solvent,and temperature was systematically investigated in both solution and solid states.Because of n→π*interaction between vicinal carbonyl groups,sP-Me-C8/rP-Me-C8 could adopt contracted cis-cisoid helix in THF,toluene,CH2Cl2,and CHCl3.Such an intramolecular interaction was sensitive to the hydrogen bond donating ability of solvent and temperature,but insensitive to the dielectric constant and polarity of solvent.In poly(3-methoxycarbonyl-5-alkoxycarbonylphenylacetylene),the longer the chiral alkyl chain was,the easier the stable cis-cisoid helix could be achieved.However,when the methoxycarbonyl was changed to ethoxycarbonyl,sec-butyloxycarbonyl,and octyloxycarbonyl pendant groups,only cistransoid helix was obtained at room temperature due to the increased steric hindrance.Moreover,lowering temperature was found to facilitate the stabilization of n→π*interactions,and reversible temperature-dependent stereomutations were achieved in sP-Me-C8 and sP-Et-C4depending on the solvent where they were dissolved.These results suggested that the long alkyl chain,small pendant size,and lower temperature favored the stabilization of intramolecular n→π*interactions and the formation of contracted,cis-cisoid helices for poly(3,5-diestersubstituted phenylacetylene)s.