Vinylene carbonate polymerization

When ethylene carbonate is monochlorinated, the chloroethylene carbonate thus obtained is the starting material for the synthesis of vinylene carbonate which is used in radical polymerization to yield high-molecular weight polymers and copolymers or in Diels-Alder cycloadditions [Scheme 174 ] (Ref. 227). 

Early work by Buck and Davar89 examined the plasma polymerization of several monomer systems. Best results in terms of reverse osmosis performance were achieved with vinylene carbonate/acrylonitrile and vinyl acetate/acrylo-nitrile. 

Vinylene Carbonate—A Study of Its Polymerization and Copolymerization Behavior... 

Bulk polymerization of vinylene carbonate (VCA) initiated by 60Co y-rays was studied at 30°-110°C at a constant dose rate of 1 - 105 rad/hr. An overall activation energy of 5.0 kcal/mole and a maximum reaction rate of 1 10 3 mole/l-sec were obtained. As has been reported, purification of the monomer is a crucial point because inhibiting impurities are formed during the synthesis. From experiments with chlorine-substituted ethylene and vinylene carbonates, we tentatively conclude that, in addition to mono- and dichloroethylene carbonate, dichloro-vinylene carbonate is mainly responsible for the inhibition. The copolymerization behavior of VC A with some chlorine-substituted olefins was studied. Chlorotrifluoroethylene (CTFE) is an especially suitable comonomer the reactivity ratios found were rVCA = 0.42 and rCXFE = 0.48. 

Generally, 1,2-disubstituted ethylene derivatives have only a small tendency for radical homopolymerization. An exception is vinylene carbonate (VCA) which can be easily polymerized by chemical as well as radiation initiation. However, the reaction is strongly affected by traces of impurities formed during the synthesis. Inhibition experiments are discussed with regard to the nature of the inhibiting impurities. The copolymerization behavior of VCA with some halo-substituted olefins was studied with chlorotrifluoroethylene (CTFE), a statistical copolymer with a slight tendency for alternation was obtained. 

Field and Schaefgen (5) demonstrated that a high molecular weight poly (vinylene carbonate) (PVCA) was obtained if the first step of the synthesis, photochlorination of ethylene carbonate, was carried out in CC14 instead of bulk reaction and if the monomer was distilled from NaBH4 shortly before polymerization. On the other hand, bulk chlorination led invariably to poor quality VCA. 

Copolymerization of Vinylene Carbonate with Some Halo-Substituted Olefins. Copolymerization experiments were conducted using trans-dichloro-ethylene, vinylidene chloride, and CTFE since these monomers have a structural relation to the inhibiting impurities discussed above. With frans-dichloro-ethylene, no polymerization occurred, and only oligomers of VCA with a molecular weight of 300 were formed. Like dichlorovinylene carbonate, trans-dichloroethylene acts as an inhibitor, probably through degradative chain transfer by abstraction of a chlorine atom. 

Exploration of the template controlled free-radical oligomerization of other activated olefins began with standard monomers utilized in bulk polymer synthesis and the template 63. Vinyl acetate and acrylonitrile led only to uncontrolled polymerization, while vinylene carbonate did not react under the standard experimental conditions. More exotic monomers, such as vinyl trifluoroacetate and rert-butyl acrylate, were also unsuccessful. Only methyl acrylate polymerization was arrested by template 64 to provide the macrocyclized product 96 in modest yield as a mixture of five diastereomers (Scheme 8-25). Subsequent studies with the more effective thiophenyl-bearing template 63 at lower temperatures improved this yield to 35%. The diastereomer distribution was reminiscent of the methyl methacrylate-derived product, although no stereochemical assignments were made in this case either. 

TABLE IV Effect of Initiator (Azobisisobutyrontrile) Concentration on Polymerization at 60°C for 18 hr of Vinylene Carbonate in Bulk"... 

The copolymerizations of dihydrofuran or dihydropyran monomers with maleic anhydride or vinylene carbonate were carried out with different concentrations of monomers in the presence of radical initiators (AIBN) in DMF or in bulk at 70 - 100 °C and the polymerization results are given in Table I. The polymer yields were increased with the monomer concentrations (runs I and 2, 3 and 4, 5 and 6), and with the initiator concentrations (runs 5 and 6, 9 and 10) as well as with the polymerization time (runs 14 and 15). The bulk copolymerization (run 13) resulted in higher yield than the solution polymerization (run 14). 

Disubstituted ethylenes, RCH=CHR, are only polymerized to high-molar-mass products under certain conditions. For example, vinylene carbonate (I) polymerizes free radically to high-molar-mass products, whereas maleic anhydride (II) only yields low-molar-mass compounds under these conditions. 1,2-Diphenyl ethylene cannot be polymerized to poly(phenyl methylene) (III), but phenyl diazomethane, C6H5CHN2, can be. 

We have confirmed by an in-situ subtracfively normalized interfacial FTIR (SNIFTIR) that the polymer by VC begins to form at 4.3 V vs. Li /Li on Li CoO as shown in Fig. 4.12, where the upward peaks at 1,830, 1,805, and 1,750 cm below 4.3 V correspond to the consumption of VC, EC, and EMC, respectively. This resultant polymeric film formed at 4.3 V suppressed the further decomposition of EC and EMC above 4.3 V, where the downward peaks at 1,850-1,800 and 1,650-1,550 cm can be ascribed to the formation of decomposition products. The chemical structure of the polymer was assumed to be a poly(vinylene carbonate) by XPS. However, the reaction between Li jCoO and VC at 85°C did not show the existence of polymeric materials. These results indicate that the thermal stability... 

Figure 3.4 Vinyl lactone quenching, (top) Termination of a living ROMP with 3H-furanone yields a polymeric carboxylic acid end group, (bottom) Termination with vinylene carbonate resulting in a polymeric aldehyde end group.

Hindered amide derivative BF3n did not show the tendency towards spontaneous polymerization and the crystal structure of the complex BF3n-PTSA showed the interaction of electropositive =CH2 with the it-orbital of PTSA (Fig. 13, the distance between the centroid of PTSA toluene ring and vinylene carbon of BF3n was 3.802 A). This particular cation-x interaction was considered to support the proposed initiation mechanism in view of the fact that a similar interaction between the activated methylene group and the indene it-orbital could be the basis for the formation of the postulated zwitterionic dimer. 

In 1993, Scherf and Chmil described the first synthesis of a ladder-type poly(pflra-phenylene-czs-vinylene) (116) [138]. On the one hand, ladder polymer 116 represents, a planar poly(phenylene) containing additional vinylene bridges on the other hand, it is a poly(phenylenevinylene) with aryl-aryl linkages in the polymeric main chain. The target macromolecules, as fully aromatic ladder polymers, are composed of all-carbon six-membered rings in the double-stranded main chain (an example of angularly annelated poly(acene)s). 

The target structures in the final example are fully aromatic polymeric hydrocarbons, consisting of all-carbon six-membered rings - so-called angularly annulated polyacenes 91 [55]. The structural difference between those and the methylene-bridged poly(phenylene)s is the replacement of the benzylic methylene bridges by vinylene moieties. 

In polyethylene, the tertiary carbon atom, which dominated the chemistry of the oxidative degradation of PP, is present only at branch points. This suggests that there may be a difference among LDPE, LLDPE and HDPE in terms of the expected rates of oxidation. This is complicated further by the presence of catalyst residues from the Ziegler-Natta polymerization of HDPE that may be potential free-radical initiators. The polymers also have differences in degree of crystallinity, but these should not impinge on the melt properties at other than low temperatures at which residual structure may prevail in the melt. Also of significance is residual unsaturation such as in-chain tra s-vinylene and vinylidene as well as terminal vinyl, which are defects in the idealized PE strucmre. 

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