Monomer vinylidene

This treatment can be extended without mrxlification to polymers obtained from vinylidene monomers with different substituents (CH2=CR R2) and from aldehydes (RCHO) in which the oxygen atom replaces the methylene group. 

Macromolecules having identical constitutional repeating units can nevertheless differ as a result of isomerism. For example, linear, branched, and crosslinked polymers of the same monomer are considered as structural isomers. Another type of structural isomerism occurs in the chain polymerization of vinyl or vinylidene monomers. Here, there are two possible orientations of the monomers when they add to the growing chain end. Therefore, two possible arrangements of the constitutional repeating units may occur ... 

Linear polymers prepared by step reaction polymerization, such as nylon 66, and linear, ordered polymers prepared by the chain polymerization of symmetrical vinylidene monomers, such as polyvinylidene chloride (PVDC), can usually be crystallized because of symmetry and secondary-bonding. Isotactic polymers, such as isotactic polypropylene (PP), usually crystallize as helices. 

Mino, G., and S. Kaizerman, American Cyanamid Company Process for polymerization of a vinylidene monomer in the presence of a ceric salt and an organic reducing agent. U. S. 2,922,768 (January 26, 1960). 

Radical anions from a vinyl (vinylidene) monomer undergo dimerization or they can add a molecule of the parent monomer to yield a dimeric radical ion. Using styrene as an example, these reactions can be illustrated by the equations... 

Vinyl and vinylidene monomers are basically unsymmetrical because the iwo ends of the double bond are distinguishable (ethylene and tetrafluorethylene are exceptions). One C of the double bond can be arbitrarily labeled the head and the other the tail of the monomer, as shown in the formula for vinyl fluoride (4-3). 

Radical reactions with the n bond of vinyl monomers are not nearly as selective as ionic attack, and free-radical initiators cause the polymerization of nearly all vinyl and vinylidene monomers. (Some of these polymerizations are not elTicient because of side reactions. Propylene is acase in point as described in Section 6.8.5.) Resonance stabilization occurs to some extent with most vinyl monomers but it is important in radical polymerizations only when the monomers contain conjugated C—C double bonds as in styrene, 1,3-butadiene, and similar molecules ... 

Steric hindrances prevent the polymerization of most 1,2-disubstituted ethylenes by any mechanism. However, 1,1 -disubstituted monomers and vinylidene monomers usually polymerize more readily than the corresponding vinyl analogs. 

Polymers of vinylidene monomers (1,1-disubstituted ethylenes) have lower Tg s than the conesponding vinyl polymers. Polyisobutene and polypropylene comprise such a pair and so do poly(vinylidene chloride) and poly(vinyl chloride). Symmetrical disubstituled polymers have lower Tg s than ihe monosubstituled macromolecules because no conformation is an appreciably lower energy form than any other (cf. the discussion of polyisobutene in Section 4..1). 

Table 3 lists some of the common vinylidene monomers. 

Strong bases (pKa > 11) also convert alkyl cobaloximes and alkyl cobalamins into -complexes such as 73. This is usually followed by further decomposition to olefins and alkanes. The stability of complexes such as 73 depends very much upon X and the nature of the axial ligand in the cobalt chelate.98-218-227 230 Strong nucleophiles such as RS or CN can cause decomposition of LCo—R as well.98-231 Under the normal conditions of radical polymerization, Markovnikov organocobaloxime should form whenever the hydride, LCoH, appears in the polymerization mixture. If 1,2-vinylidene monomers are being polymerized, then thermally unstable tert-alkyl-cobaloximes are obtained. These species are expected to undergo homolytic Co—C cleavage to yield tertiary radicals. 

Two kinds of linkages may join vinyl or vinylidene monomers into polymeric chains the head-to-tail bonds or head-to-head or tail-to-tail linkages. The head-to-tail enchainment... 

Let us consider now the problems of sterospedfidty of the addition step in anionic propagation of vinyl or vinylidene monomers. The predominant structure of the growing end-groups is depicted below ... 

Each of the polymers listed above is made from one monomer only. These polymers are called homopolymers. Any number of coreactive vinyl or vinylidene monomers can be polymerized together and the product is called a random copolymer. In a copolymer molecule, the different monomer units are combined together in a random way. As the polymer free radical grows, the next unit to be added is decided by chance it depends upon which monomer molecule encounters the right part of the chain first... 

Scheme 10 Renewable butyrolactone-based vinylidene monomers (M) MBL (R = H, Me) and polymers P(M)MBL vs MMA and PMMA...

To improve modulus of HDPE, it was blended with a graft copolymer of HDPE with vinyl or vinylidene monomer (e.g., styrene)... 

To improve modulus of high-density polyethylene, HDPE, it was blended with a graft copolymer of HDPE with vinyl or vinylidene monomer (e.g., styrene) H. Yui, T. Kakizaki, H. Sano, Japanese Patent 014,752, 09 Feb 1978, Appl. 27 July 1976, to Mitsubishi Petrochemical Co., Ltd. 

Circular dichroism is extensively employed in the stmctural study of biological polymers, but not in the study of synthetic polymers. This is because most biological polymers are optically active, whereas most synthetic polymers are not. However, if the optically active vinyl or vinylidene monomers are incorporated in a synthetic polymer, the synthetic polymr could become optically active. 

There is no reason why only one of the four hydrogen atoms can be replaced and it is quite normal to replace more than one of these atoms. When two atoms are replaced the resultant polymers are said to be derived from vinylidene monomers, where vinylidene refers to an ethylene molecule with two of its hydrogen atoms replaced with other atoms or molecules. When two hydrogen atoms are replaced they are both from the same carbon atom of the ethylene molecule. Some examples of linear polymers based on vinylidene monomers are shown below with their substituents. 

Two types of monomers A and B, have been distinguished on the basis of the relationship between their structure and polymer chirality. To the former type belong monomers, such as vinyl and vinylidene monomers, which need to be chiral in order to give optically active polymers, while monomers of the latter type such as suitably substituted dienes suffice to be prochiral. 

It is known that vinyl aromatic monomers when inserted in copolymer macromolecules with optically active vinyl or vinylidenic monomers become optically active and may or may not contribute to the optical rotation of the whole polymer measured at the sodium D line In particular, by mvestigating the electronic transitions of the aromatic chromophores, it is general found that both symmetry forbidden and... 

Whilst the glass transition is of very great importance in adhesives, crystalline melting is not. This is because the polymers in most adhesives are totally amorphous, which in turn is due to a lack of molecular regularity. Stereoregular polymers can be made from vinyl and vinylidene monomers with the employment of organometallic initiators, but these are not used when such monomers are converted into polymers which are used in adhesives. The latter are atactic and examples are MMA copolymers in structural acrylic adhesives, amorphous polypropylene, polyacrylic pressure-sensitive adhesives, and polycyanoacrylates. 

In order to be useful for structure analysis, the observed resonances must be assigned to chemical structures. Eor copolymer analysis, the enormity of the problem of assigning the observed resonances can be recognized by the following simple considerations. For the 21 most common vinyl and vinylidene monomers, there are a total of 210 possible binary copolymers and 1330 ternary copolymers [29]. These copolymer combinations can also have an alternating, random, or block sequence structure so that the total number of possible copolymers is quite large. Experimentally, only about 30 of these copolymers have been studied. This extremely complex situation suggests that computer simulation of the spectra of the copolymers is helpful in the interpretation of the NMR spectra [30]. 

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