Vinyl-substituted monomers polymerization

Some of the vinyl monomers polymerized by transition metal benzyl compounds are listed in Table IX. In this table R represents the rate of polymerization in moles per liter per second M sec-1), [M]0 the initial monomer concentration in moles per liter (M) and [C]0 the initial concentration of catalyst in the same units. The ratio i2/[M]0[C]0 gives a measure of the reactivity of the system which is approximately independent of the concentration of catalyst and monomer. It will be observed that the substitution in the benzyl group is able to affect the polymerization rate significantly, but the groups that increase the polymerization rate toward ethylene have the opposite effect where styrene is concerned. It would also appear that titanium complexes are more active than zirconium. The results with styrene and p-bromostyrene suggests that substituents in the monomer, which increase the electronegative character of the double bond, reduces the polymerization rate. The order of reactivity of various olefinically unsaturated compounds is approximately as follows ... 

The propensity of the C5 site towards electrophilic substitution has been exploited to prepare functionalized oligomers by cationic polymerization. Thus monomers like isobutene, s ene, the vinyl ethers, etc. polymerize in the presence of simple furan derivatives such as 2-methyl furan to give essentially short chains (DP between 2 and 100 depending on the specific experimental conditions) with a terminal furan ring as a result of predominant transfer onto the C5 position of the added furan compound (20). 

Figure 4.3 Scheme illustrating the development of immobilized ionic liquids by thermally induced free radical polymerization of vinyl-substituted imidazolium-based monocationic and dicationic monomers. 

Poly(vinyl pyrrotidone). Another commercial polymer with significant usage is PVP. It was developed in World War II as a plasma substitute lor blood. This monomer polymerizes faster in 50 water than it does in bulk, an abnormality inconsistent with general polymerization kinetics. This may be due to a complex with water that activates the monomer it may also be related to the impurities in the monomer that are difficult to remove. See also Vinyl Acetal Polymers. 

A simple example of photopolymerization based on PET is realized, if the monomers polymerized are the electron donor (D) and electron acceptor (A) themselves [12]. Therefore, the electron densities of both compounds must be very different. With vinyl monomers, combinations of donor and acceptor substituted olefins are especially suitable systems. 

Finally, the polymerization of vinyl monomers usually proceeds as a practically irreversible reaction. Exceptions are heavily substituted monomers like a-methylstyrene for which propagation is clearly reversible. In the ring-opening polymerization, the driving force for polymerization comes from ring strain, thus it varies greatly for different monomers. 

Polymerization of vinyl monomers proceeds much slower than the natural polymerization of for example, phenolic compounds. This can be exploited for the chemoselective polymerization of vinyl-substituted phenols and aminophe-nols (see Chapter 7) [41, 43]. Kobayashi and coworkers reported the selective polymerization of methacrylate-esters [41]. Thus, phenol-esters were selectively polymerized via the phenolic moieties leaving the methacrylate functionality unmodified (Figure 6.9). The latter was only attacked in the absence of polymerizable phenols. 

Figure 3. Typical patterns of radical ring-opening polymerization of exomethylene-sub stttuted and vinyl-substituted cyclic monomers.

Substituting a chloride for one of the hydrogen atoms on ethylene gives you the vinyl chloride monomer that can polymerize to polyvinyl chloride (PVC), as shown in Figure 16-5. 

Although the properties of condensation polymers are often superior to those exhibited by vinyl addition polymerization, little attention has been directed toward the introduction of fnnctional groups by polycondensation using appropriately substituted monomer. Polycondensation polymers may contain the reactive functional groups as a part of the polymer backbone or as pendent substituents. 

Vinyl-substituted cyanoacrylates have been used from time to time, either as modifiers for alkyl cyanoacrylates or on their own as adhesives. These cyanopentadienoates (2) are less reactive toward anionic polymerization than are the cyanoacrylates. This feature allows their preparation from acrolein and a cyanoacetate ester using a Lewis acid catalyst such as zinc chloride. " The monomer can be isolated and purified without going through a depolymerization step. 

Variously substituted oxazoline monomers, 2-ethyl, 2-n-pro-pyl, and 2-vinyl oxazoline monomers for HA, were newly prepared and polymerized with HAase catalysis. The reactions proceeded with total control of regioselectivity and stereochemistry, to afford the corresponding HA and Ch derivatives (unnatural polysaccharides) possessing N-propionyl, N-butyryl, and N-acryloyl group in every hexosamine unit (Scheme 40). Similarly, Ch derivatives were also achieved. The resulting N-acryloyl HA and Ch are functional polymers having a reactive vinyl group. 

Included among the many types of vinyl monomers that have been subjected to photoinitiated cationic polymerization are styrene," substituted styrenes, a-methylstyrenes, N-vinylcarbazole, alkyl vinyl ethers, prop-l-en-l-yl ethers, ketene acetals, and alkoxyallenes. Most useful in the crosslinking photopolymerizations employed for UV curing applications are multifunctional vinyl ethers and multifunctional prop-l-en-l-yl ethers. A number of multifunctional vinyl ether monomers are available from commercial sources, while multifunctional prop-l-en-l-yl ethers can be readily prepared by catalytic isomerization from their corresponding allyl ether precursors. The photoinitiated cationic... 

Arcus [8] discussed the conditions of the optical activity of polymers in alternate copolymerizations and underlined that an asymmetry was brought into main chains in the polymerization between vinyl monomers and a,j3-substituted monomers. Accordingly, the main chains of the polymers obtained by vinyl homopolymerizations do not have optical activities since they are pseudo-asymmetric. 

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