Monocyclic Monomers

Various methylene derivatives of spiroorthocarbonates and spiroorthocstcrs have been reported to give double ring-opening polymerization e.g. Scheme 4.36). Like the parent monocyclic systems, these monomers can be sluggish to polymerize and reactivity ratios are such that they do not undergo ready copolymerization with acrylic and styrenic monomers. Copolymerizations with VAc have been reported.170 These monomers, like other acetals, show marked acid sensitivity. 

There are large numbers of naturally occurring representatives, especially of pyrrole that include the important polypyrroles (porphyrins and corrins), and the nitropyrrole antibiotics such as pyr-rolomycins and pyrroxamycin. Derivatives of furan have been used as fungicides and A-vinylpyr-rolidone is an important monomer for the production of blood plasma extenders and for cosmetic applications. On account of the similarity in the pathways for the aerobic degradation of monocyclic furan, thiophene, and pyrrole, all of them are considered here. Anaerobic degradation of furans is discussed in Part 2 of this chapter. 

By using a transition metal chloride catalyst and an iodine modified cocatalyst, ring-opening polymerization of C5 and C8 monocyclic olefins is controlled to prepare either cis polymers or trans products that are crystallizable. In copolymerization, the cis/trans units in the copolymers are regulated by adjusting the C5/C8 olefin monomer ratio. As the comonomer is increased, the copolymer becomes less crystalline and then completely amorphous at equal amounts of cis/trans units. Polymerization results are reported from WC16 and MoCl5 catalysts. 

Before discussing the polymerization of monocylic olefins, a brief review of the preparation of polymers from bicyclohep-tenes will acknowledge their historical contribution with respect to polymerization catalysts, polymer structure and properties. Their monomer reactivity in polymerization is much faster than the reactivity of the less strained monocyclic olefins. Anderson (1) and Truett (2) polymerized norbornene... 

In a later publication (16) the BE-4 monomer was analyzed by fast atom bombardment mass spectrometry. The authors concluded that the toxin has a molecular weight of 909 with an estimated molecular weight for the 20-carbon side chain of 313. It was also felt that the toxin was not a linear peptide as reported earlier (14,15) but a monocyclic peptide. The 20-carbon side chain was thought to be a novel 3-amino acid. 

The formation of a weak a-bond by overlap of two singly occupied 7i -orbitals is a characteristic feature of certain 7i-electron-rich inorganic systems. This structural feature can occur via an intramolecular process resulting in a transannular interaction that converts a monocyclic ring into a bicyclic system. Alternatively, it may involve an intermolecular contact in which two cyclic monomers are weakly associated to give a dimeric species. 

The most practically useful compound from oxepanes is -caprolactone, which is used as an important industrial monomer. Other oxepanes are considered following their structures from rather simple monocyclic to polyhetero-cyclic systems, the chemistry of the latter being now well developed in connection with investigation of complicated polycyclic natural products of marine origin. Below, only those data are cited that are absent in CHEC-II(1996). 

The anionic polymerization of 58 shows typical equilibrium polymerization behavior. From the temperature dependence of the equilibrium monomer concentration, the thermodynamic parameters for the polymerization of 58 in dimethyl sulfoxide were evaluated to be AHSS = -23.8 1.5 kJ/mol and ASss = — 71.5 + 4.2 kJ/mol deg (subscript ss refers to a solution state). [67] The ceiling temperature for 1 mol/L solution is about 60 °C. The enthalpy change in the polymerization of 58 is considerably larger than those for monocyclic lactams, pyrrolidone and piperidone, but no quantitative comparison of these data can be made, because the reported data refer to different experimental conditions. The significant entropy decrease in the polymerization is ascribable to the presence of the six-membered tetrahydropyran ring in the repeating unit. 

Kinetic data are shown. From the data, monomer reactivities are compared to monocyclic compounds. 

By using this method, they determined the rate constant of the propagation of endo-and exo-2-methyl-7-oxabicydo[2.2.1]heptaneZ1,22 and endo- and exo-2-tert-butyl-7-oxa-bicyclo[2.2.1]heptaneZ5. In these systems the polymerization proceeds via SN2 reaction between monomer and the propagating oxonium ion as was the case for the monocyclic ethers. They achieved the first case of a quantitative comparison of the polymerization reactivity between monocyclic and bicyclic ethers in the polymerization of exo-2-methyl-... 

These results indicate that the polymerization mechanism of bicyclic acetals is as complicated as that of monocyclic acetals184-188 and dependent on the monomer structure and the polymerization conditions. 

The question of whether a bi- or monocyclic molecule is present in these crystals was of major interest, but we have also sought possible factors that would cause an open side-chain in the monomer. 

Figure 5. Proposed structures of hydroperoxides formed in arachidonate (20 4) aqueous solutions (pH = 10.5) submitted to y-rays. Monohydroperoxides (6 isomers in positions 5, 8, 9, 11, 12, 15) are formed in micellar medium (high arachidonate concentration) whereas monocyclic and bicyclic hydroperoxides, together with dihydroperoxides are produced in dispersed monomers (low arachidonate concentration) [18],...

Attention in fundamental and applied research on shape-selective catalysis has been largely focused on open-chain and monocyclic compounds. However, we have observed the rapid developments in polymer materials containing multi-ring aromatic units and the need to develop the monomers and other specialty chemicals from polyaromatic hydrocarbons that are rich in coal-derived liquids [Song and Schobert, 1993, 1996]. Scheme 1 shows the structures of some advanced polymer materials containing aromatic ring in the main-chain. 

The formation of cyclic co-oligomers by backbiting reactions is to be expected when one or both monomers are monocyclic and the concentration of monomers is... 

The most practically important compound from oxepanes is e-caprolactone which is used as a monomer. Other oxepanes are considered following their structures from rather simple monocyclic to complicated polyheterocyclic systems. 

Other monocyclic monomers will imdergo ring-opening reactions cyclobutene and 1-methyl cyclobutene produce polybutadiene and cis-polyisoprene, respectively but this synthetic route cannot compete with estabhshed methods for preparing synthetic elastomers. Reactions are slower with the larger rings, as the strain decreases, but a useful elastomer with a high trans content and well-developed crystallinity (such as the product sold under the trade name Vestenamer) can be prepared from cis-cyclooctene (the trans compound is umeactive). 

In general, bi- and tricyclic monomers can be polymerized more easily than the monocyclic monomers, and this is reflected in the wider range of catalytic systems that can be used. 

Ability of internal double bonds of forming macromolecule to further transformations initiated by cationic initiators is the characteristic particularity of cationic polymerization. This character leads to reduction of polydienes unsaturation due to the formation of brunched and cyclic structures even at low monomer conversions [175]. Total unsaturation of resulting polypiperylene usually is about 60-90% from theoretical [243]. One supposes [244] that these chain units consist of monocycle units of type I-III ... 

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