Protonation high-molecular-weight structure

VI. Kinetics of Protonation of High-Molecular-Weight Structures. 66... 

VI. KINETICS OF PROTONATION OF HIGH-MOLECULAR-WEIGHT STRUCTURE... 

Nuclear magnetic resonance has frequently been employed for general studies and for the structural studies of petroleum constituents (Bouquet and BaiUeul, 1982 Hasan et al., 1989). In fact, proton magnetic resonance (PMR) studies (along with infrared spectroscopic studies) were perhaps the first studies of the modem era that allowed stmctmal inferences to be made about the polynuclear aromatic systems that occm in the high-molecular-weight constituents of petroleum. 

In this laboratory the conversion of methanol (refs. 12-16) and the partial oxidation of methane (ref. 17) have been studied on heteropoly oxometalates, particularly those with Keggin structure. These are ionic solids with high molecular weight, cagelike anions and cations which may be chosen from a wide variety of possibilities, ranging from the proton to charged organic species. 

The structure of cationic polymers of spiro [2.n] alkanes is too hindered to allow the formation of high-molecular-weight polymer. The termination step occurs rapidly, probably by rearrangement, loss of a proton, and formation of a double bond, the existence of which is confirmed by a vinyl hydrogen NMR signal at about 8 =5.2 ppm. 

High molecular weight samples of the polyformal were kindly supplied by General Electric. The structure of the repeat unit is shown in Figure 1 as well as the structure of a partially deuter-ated form which was synthesized (9) to reduce proton crossrelaxation. A 10 weight percent solution of the polymer in deu-terated tetrachloroethane was prepared in an NMR tube, subjected to five freeze, pump, thaw cycles and sealed. 

Reaction of a mixture of BPA, potassium hydroxide pellets, Aliquat 336 (0.1 mole per mole of BPA) in refluxing methylene chloride for 15 hr gave, after methanol precipitation, a high molecular weight polyformal (, In] = 0.59 dl/g in 70% isolated yield. Proton and NMR spectra confirmed the structure of j6. Interestingly, because of the apparent kinetics of this reaction, kb ka (equation 6), methylene chloride can actually be used as the solvent and reactant in this condensation polymerization reaction. 

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