Cyclic addition polymerization

The process proceeds through the reaction of pairs of functional groups which combine to yield the urethane interunit linkage. From the standpoint of both the mechanism and the structure type produced, inclusion of this example with the condensation class clearly is desirable. Later in this chapter other examples will be cited of polymers formed by processes which must be regarded as addition polymerizations, but which possess within the polymer chain recurrent functional groups susceptible to hydrolysis. This situation arises most frequently where a cyclic compound consisting of one or more structural units may be converted to a polymer which is nominally identical with one obtained by intermolecular condensation of a bifunctional monomer e.g., lactide may be converted to a linear polymer... 

In Section 3 of this chapter it was mentioned that polymers obtained by intermolecular condensation of bifunctional monomers may often be prepared alternatively by an addition polymerization of a cyclic compound having the same composition as the structural unit. Typical examples are shown in Table III. The processes indicated are appropriately regarded as addition polymerizations. Each of these polymers may also be prepared through the condensation of suitable bifunctional monomers. The dimethylsiloxane polymer, for example, may be prepared, as indicated in Table I (p. 45), through the condensation of dimethyl dihydroxysilane formed by hydrolysis of the di-chlorosilane... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

The free amino group of the amino ester may then react analogously with another molecule of the monomer, etc. The kinetics of the polymerization are in harmony with a mechanism of this sort. The final polypeptide may contain up to 300 or more structural units. While the polymerization of N-carboxyanhydrides is closely analogous to the addition polymerizations of ethylene oxide and of other cyclic substances, definition unfortunately classifies it as a condensation polymerization inasmuch as carbon dioxide is eliminated in the process. 

A corresponding anionic mechanism in the presence of a strong base (or electron donor) is plausible. Other cyclic compounds may be susceptible to polymerization by similar ionic mechanisms. Inasmuch as the growth step must be extremely rapid, a chain reaction is indicated and classification with vinyl-type addition polymerizations should be appropriate in such cases. 

Cyclopolymerization of Nonconjugated Dienes. Cyclopolymerization is an addition polymerization that leads to introduction of cyclic structures into the main chain of the polymer. Nonconjugated dienes are the most deeply studied monomers for cyclopolymerization and for cyclocopolymerizations with alkene monomers 66 In general, (substituted and unsubstituted) dienes with double bonds that are linked by less than two or more than four atoms cannot undergo efficient cyclization and result in crosslinked materials.12 In fact, efficient cyclopolymerization processes have been described, for instance, for a,oo-dienes like 1,5-hexadiene, 2-methyl-l,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene,67 73 which lead to formation of homopolymers and copolymers containing methylene-1,3-cycloalkane units. 

In the reaction of ethylene with sulfuric acid, several side reactions can lead to yield losses. These involve oxidation, hydrolysis—dehydration, and polymerization, especially at sulfuric acid concentrations >98 wt % the sulfur trioxide can oxidize by cyclic addition processes (99). 

Figure 2.2 Polymerization of Cyclic Monomers (9-11). (RO) ROMP, (VA) Vinyl Addition Polymerization, (R/I) Radical/Ionic Polymerization...

Dienes. The bifunctionality of dienes makes their hydroboration more complex than that of simple alkenes. Competing hydroboration of the two double bonds may lead to mixtures of products arising from mono- or diaddition. Additionally, cyclic or polymeric organoboranes may be formed. Differences in the reactivity of the two double bonds and the use of appropriate hydroborating agents, however, may allow selective hydroboration.29,330... 

Synthesis of Cyclic Polymers Using Addition Polymerization. 126... 

Ring-opening polymerization is different from the addition and condensation polymerizations described so far. It does not produce byproducts (e.g., water) as polycondensation does, and there is no unsaturated double bond in the monomers to lead to additional polymerization. However, some similarities do exist. Ringopening polymerization is initiated by the opening of a cyclic structure in the monomers and followed by polyaddition. As a result, a linear polymer with a chemical composition identical to that of the monomer is obtained. 

In poly silane formation by the previously mentioned route, the products were complex and contained high-molecular-weight materials (molecular weight > 10 ) after only 10% of the dichloride had reacted. In the presence of a twofold excess or a 10% deficit of sodium, an appreciable amount of high-molecular-weight polymer was formed. Attempts to isolate dimers after 50% of the dichloride had reacted failed. The product with the lowest molecular weight was a cyclic pentamer. The polymerization, in fact, demonstrates some of the characteristics of a chain reaction as found in addition polymerization. 

Rose [50] carried out one of the earliest, really thorough investigations of the kinetics of polymerization of a cyclic ether polymerization. He studied oxetane polymerizations initiated by BF3. Rose was aware from the work of Farthing and Reynolds [51] that polymerization does not occur when BF3 comes into contact with pure, dry monomer. However, simultaneous addition of water, ethanol or hydroxy terminated polymer is sufficient to initiate polymerization. Since Rose [50] observed polymerization in his sytem, he assumed that it was not completely dry and discussed his results assuming water is a co-catalyst. As the concentration of water increased, the rate of polymerization at first increased. The rate... 

Not only polyethylene can be synthesized, but also many kinds of copolymers and elastomers, new structures of polypropylenes, polymers and copolymers of cyclic olefins. In addition, polymerization can be performed in the presence of fillers and oligomerization to optically active hydrocarbons is possible. For recent reviews and books see [17-20]. 

The Addition Polymerization of Cyclic Olefins 1105 Fig. 4.3 Brookhart catalyst for cyclopentene polymerization. 

The Addition Polymerization of Cyclic Olefns 129 Tab. 4.2 Polymerization of norbornene using multicomponent catalyst systems. 

---