Polymer formation pathways

This scheme suggests that monomer can be converted into reactive and nonreactive products through processes occurring in the plasma (reaction pathways 2 and 4) as well as entering into polymer formation (reaction pathway 1). The reactive products may further contribute to polymer deposition (reaction pathway 3) or be converted to non-reactive products (reaction pathway 5). The degradation of the polymer to form non-reactive products (reaction pathway 6) is also considered. 

Stepwise Polymerization. Although condensation polymers account for only about one-fourth of synthetic polymers (bulkwise), most natural polymers are of the condensation type. As shown by Carothers in the 1930s 2, ), the chemistry of condensation polymerizations is essentially the same as classic condensation reactions that result in the synthesis of monomeric amides, urethanes, esters, etc. the principle difference is that the reactants employed for polymer formation are bifunctional (or higher) instead of monofunctional. Although more complicated situations can occur, we will consider only the kinetics of simple polyesterification. The kinetics of most other common condensations follow an analogous pathway. 

Primary and secondary alcohols gave excellent yields of ester (35). However, tertiary alcohols gave poor results because the predominant pathway was dehydration followed by polymer formation. 

In 2005, Rana et al. further expanded the scope of methods for forming colloidal templates in situ by devising a reaction scheme that utilized multivalent anions (such as tetrasodium ethylenediamine tetraacetate, EDTA) over previously used Au or CdSe NPs. The governing synthesis parameter is the R ratio , defined as the total negative charge from the multivalent anion divided by the total positive charge from the polymer. This new formation pathway relies on the counteranion condensation of EDTA and other multivalent anions with polyamines, to form polymer/salt... 

Figure 6.1 Formation pathway of the p-cumylphenoxy end structure and its characteristic product (compound X) for the thermally treated FR-PC. TMAFi = tetramethylammonium hydroxide. Reproduced with permission from K. Hayashida, H. Ohtani, S. Tsuge and K. Nakanishi, Polymer Bulletin, 2002, 48,...

The examination of the formulas of many of the monomers used to make polymers reveals a common characteristic. What is this characteristic, and how does it enable polymer formation Does nylon illustrate a different pathway to monomer formation Explain. 

A number of mechanisms for thermal decomposition of persulfate in neutral aqueous solution have been proposed.232 They include unimolccular decomposition (Scheme 3.40) and various bimolecular pathways for the disappearance of persulfate involving a water molecule and concomitant formation of hydroxy radicals (Scheme 3.41). The formation of polymers with negligible hydroxy end groups is evidence that the unimolecular process dominates in neutral solution. Heterolytic pathways for persulfate decomposition can he important in acidic media. 

Even though the rate of radical-radical reaction is determined by diffusion, this docs not mean there is no selectivity in the termination step. As with small radicals (Section 2.5), self-reaction may occur by combination or disproportionation. In some cases, there are multiple pathways for combination and disproportionation. Combination involves the coupling of two radicals (Scheme 5.1). The resulting polymer chain has a molecular weight equal to the sum of the molecular weights of the reactant species. If all chains are formed from initiator-derived radicals, then the combination product will have two initiator-derived ends. Disproportionation involves the transfer of a P-hydrogen from one propagating radical to the other. This results in the formation of two polymer molecules. Both chains have one initiator-derived end. One chain has an unsaturated end, the other has a saturated end (Scheme 5.1). 

A comment on the properties of the base employed in reactions that involve the formation of the Vilsmeier-Haack adduct is in order, because several derivatives of cellulose are obtained by this route. Preparation of Cell-Tos has been attempted in LiCl/DMAc, by reacting the polymer with TosCl/base. Whereas the desired product was obtained by employing triethy-lamine, use of pyridine (Py) resulted in the formation of chlorodeoxycellu-lose. In order to explain these results, the following reaction pathways have been suggested [147] ... 

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