The Use of Monomers and Initiators

Of all the elementary reactions concurrent with functionalization (Fig. 10.1), the most important is the grafting of a monomer to macroradicals. A competitive reaction is the interaction of the monomer with primary free radicals that resulted from peroxide thermolysis (homopolymerization of the monomer). 

It is hardly possible that oligomers and polymers of the monomer can be grafted to macroradicals because of thermodynamic factors (6). This results in a product with low efficiency of grafting that includes impurities of oligomers as well as homopolymers of the monomer grafted. Therefore to obtain a functionalized polyolehn, it is advisable to use monomers that show a weak tendency to homopolymerization. 

Typical monomers that are most widely used for polyolehns functionalizahon are given in Table 10.1. 

As a rule, in their structure, monomers are monosubstituted (RCH=CH2), 1,1-disubstituted (RiR2C=CH2), or 1,2-disubstituted ethylenes (RiCH=CHR2). Most of monosubstituted and 1,1-disubshtuted ethylenes are capable of homopolymerization and form high molecular weight compounds. The exceptions are 1,1-disubsti-tuted ethylenes with huge substituents, which— because of steric obstacles—can form only low molecular weight ohgomers. An example is 1,1-diarylethylenes that solely form dimers (22). 

Unlike monosubstituted and 1,1-disubstituted ethylenes, 1,2-disubstituted ethylenes, as a whole, cannot undergo homopolymerization and form high molecular weight polymers (22). Maleic anhydride (MAH) and its mono- and diesters make an example of such compounds. 

---