Tri-functional monomer

Branched and crossiinked condensation polymers are produced when the reaction mixture includes tri-functional monomers as well as bi-functional ones. The incorporation of a single tri-functional monomer into a chain generates a branch point. As we increase the fraction of tri-functional monomers, branching becomes more prevalent and the resulting molecules more complex. When sufficient tri-functional monomers are present we create a three-dimensional crossiinked network. Figure 1.12 shows the general outline of the effects of tri-functional monomers on condensation polymers. 

Figure 1.12 General outline of the effects of tri-functional monomer content on condensation polymers...

These are usually formed from bi-functional and tri-functional monomers and eontaln strong covalent bonds between various linear polymer chains, e.g. bakellte, melamine, etc. These polymers are depicted as follows ... 

For simplicity, we start with a single tri-functional monomer RA3, the functional groups of which react with each other with the first shell substitution effect. It is now convenient to write down six types of reactions [44], one for each pair of reacting units of substitution degree 0,1, and 2. They are presented in Table 6 together with the appropriate rate constants. Similarly as in previous sec-... 

Fig. 3. Transfonnation of the molecular forest of trees (a) into a forest of rooted trees (b) for a tri-functional monomer. node representing a monomer unit, O terminal node representing an unreacted functionality...

The DA synthesis (nnder the same conditions as for linear polymerisations) of non-linear counterparts called upon various combinations of di- and tri-functional monomers, including trismaleimides. However, self-condensation of A2B and AB2 homologues (see Chapter 6) [11] also gave various branched and crosslinked products depending on the monomers used and their initial stoichiometry. Interesting materials were obtained and characterised fully, including their thermal reversibility. One of these systems is shown in Scheme 7.4. 

In the condensation reaction between a trifunctional alcohol and a difunctional isocyanate, gel formation is marked by significant changes in the velocity and attenuation in the MHz region. The relaxation in the isolated monomers can be ascribed to a combination of intra- and inter-molecular processes. Intermolecular relaxation occurs in the hydrogen-bonded structure formed as a result of hydroxyl interactions. Reaction between the isocyanate and alcohol leads to the possibility of normal mode contributions to the relaxation spectrum and consequent increase in the ultrasonic attenuation. Detailed analysis of the data is difficult because of the complex topography generated by the reaction of di- and tri-functional monomers. This study does however once more illustrate the possibility of using ultrasonic techniques to monitor polymerization processes. 

UV curing of coatings and printing inks is based on photocrosslinking by photoinitiated radical and cationic polymerization." Whereas monofunctional monomers polymerize to linear polymers, multifunctional, e.g. di- and tri-functional, monomers and oligomers are required to produce a crosslinked polymer network. 

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