Reactive Polymer Intermediates

Figure 1 provides an overview of the two step synthesis process, pioneered by Allcock (4) and In use today by a number of workers and laboratories formation of a soluble reactive polymer Intermediate (II) from which is derived a large number of polymers via substitution reactions. 

The typical synthesis of the polymeric material involves the chlorophospho-nilrilic trimer, which is heated to form a reactive polymer intermediate and then... 

In another development, the use of diketenes as polymer intermediates that are similar in reactivity to the aromatic diisocyanates has been described. A particularly interesting diketene is anthracene-9,10-diketene, shown in Equation 4. Polymers, polyamides and polyesters, especially those from polyetherglycols and polyesterglycols, have been prepared. These diketenes, as reactive polymer intermediates, are also of potential interest for chain extension reactions on hydroxyl-terminated polyesters. 

The alternative approach is to add a photodegradant which is an ultraviolet light absorber. However, instead of dissipating the absorbed energy as heat (as with conventional ultraviolet absorbers) the aim is to generate highly reactive chemical intermediates which degrade the polymer. One such material is iron dithiocarbamate. 

The synthesis of poly(organophosphazenes) represents probably the best example of a central theme of Inorganic macromolecules Preparation of a reactive polymeric intermediate, poly(dichlorophos-phazene), and subsequent use in a wide variety of side group replacement reactions (Figure 1). This concept has been demonstrated in a number of laboratories (3) and has provided a wide variety of polymers with different properties. 

Because the opportunities for controlled chain growth are more restricted in inorganic than in organic systems, an alternative approach to polymer synthesis becomes appealing. This involves the use of substitution processes carried out on a preformed reactive polymeric intermediate. In this way molecular diversity can be introduced by different substitution reactions rather than by a diversification of the polymerization process. 

Protonation of pyrrole, furan and thiophene derivatives generates reactive electrophilic intermediates which participate in polymerization, rearrangement and ring-opening reactions. Pyrrole itself gives a mixture of polymers (pyrrole red) on treatment with mineral acid and a trimer (146) under carefully controlled conditions. Trimer formation involves attack on the neutral pyrrole molecule by the less thermodynamically favored, but more reactive, (3-protonated pyrrole (145). The trimer (147) formed on treatment of thiophene with phosphoric acid also involves the generation of an a-protonated species. 

Early attempts at producing dialkyltin compounds yielded polymers. More recently, Neumann has found several synthetic routes to reactive R2Sn intermediates which can be trapped by oxidative-addition reactions (J). In the absence of trapping agents the divalent tin compound polymerizes. Lappert and co-workers have shown that the bulky bistri-methylsilylmethyl ligand stabilizes the divalent tin species toward polymerization. This stable divalent tin species thus provides an excellent starting material for investigating a wide variety of oxidative-addition reactions, as shown in Fig. 10 (78). 

PPS doped with AsFs dissolves readily in AsFs, but cast films are no longer soluble. Frommer has suggested that the solubilization mechanism involves solvation of both reactive radical intermediates and dopant counterions.f In addition, dialkyl esters of phosphoric acid dope PANi and render it soluble in certain solvents such as decalin. The resulting solutions can be mixed with conventional polymers and used to prepare films and fibers. 

---