Die metatesepolimerisasie van alkyne
The alkyne, phenylacetylene was polymerized in the presence of molybdenehexacarbonyl and different phenolic cocatalysts via catalytic polymerization. The reaction was monitored using a gaschromatographic method. The structural and morphological entities of polyphenylacetylene as well as the role of the different cocatalysts on the proposed metal carbene reaction mechanism were obtained. The influence of the number of hydroxyl groups, the distance of the hydroxyl group from the aromatic centre, the variation of functional groups other than the hydroxyl group on the phenyl ring as well as the influence of the number of conjugated aromatic centres and the influence of aliphatic alcohols on the polymerization activity of the Mo(C0)6-catalytic system for phenylacetylene polimerization were investigated. The influence of an increasing number of hydroxyl groups on the phenyl ring shows that the Mo(C0)6-catalytic system has exactly the same activity in the presence of phenol than in the presence of resorcinol (CJ-i4(0H)2) as cocatalyst. Phloroglucinol (CJI3(0H)3) leads to a decrease in the activity of the Mo(C0)6-catalytic system. Both resorcinol and phloroglucinol undergo keto-enol tautomerism. The same catalyst activity is obtained when the ketone, cyclohexanone is used as a cocatalyst and in the absence of a cocatalyst. It is not possible for the ketonic compound to have any influence on the catalyst activity. A decrease in the activity of the Mo(C0)6-catalytic system is noted if the distance between the hydroxyl group and the aromatic centre increases. The reaction rate of polymerization in the presence of benzyl alcohol (CJ15CH20H) and phenetyl alcohol (CJ15(CH2) 20H) as cocatalysts is in the same order as the reaction rate due to the activity of the Mo(C0)6-catalyst system in the absence of the cocatalyst. When aliphatic alcohols are used as cocatalysts a Mo(C0)6-catalytic activity is observed which is lower than the catalyst activity obtained in the absence of any cocatalyst. Comparison between the different aliphatic alcohols tested shows that an increase in the chain length of the aliphatic alcohol leads to a decrease in the Mo(C0)6-catalytic activity. Replacement of the hydroxyl group on the phenolic ring with other functional groups leads to a slightly higher reaction rate if the functional group is benzosulphonic acid but groups like -COOH, -NH2 and -OCH3 lead either to a decrease in the Mo(C0)6-catalytic activity or to a total deactivation of the catalytic system. Results obtained strengthened the mechanistic idea that the phenolic compound does not interact with the metal centre but with the alkyne. A strong polarized hydroxyl group enhances the formation of an intermolecular hydrogen bond between the hydrogen atom of the hydroxyl group and the tripple bond of the alkyne. The alkyne bond is then polarized in such a way that interaction between the metal centre and the alkyne is facilitated. An increase in reaction temperature leads to an increase in polymerization rate. A maximum polymer yield is obtained in the region of 120 °C after which the yield is maintained at the same level. An increase in reaction temperature leads to a decrease in the cis-content of the polymer. The increase in temperature also leads to a decrease in the molecular weight of the polymer. A morphological change from a porous to an enamel like polymer structure occurs and with an increase in temperature the polyphenylacetylene change in colour from bright orange to light yellow. The polyphenylacetylene synthesized at 120°C in the presence of different phenolic cocatalysts is yellow and have a general porous morphology with a mixed cisl transstructure and a molecular weight between 2 500 and 30 000. This polymer was identified as polyphenylacetylene by IR-, UV- and NMR-spectroscopy and characterized by SEM- and GPC-analysis. The optimum results are obtained in the presence of the Mo(CO)J2,4,6-ChCJ120Hcatalytic system with a Mo/PhOH molar ratio of 1:100, a reaction temperature of 120 °C and chlorobenzene as solvent.