Dicarboxylates, dibutyltin

A number of recent studies have been concerned with the effects of commercial heat stabilizers on the photodegradation of PVC. During irradiation at room temperature under air with 253.7-nm light, several dialkyltin dicarboxylates were found to increase the rates of the photooxidation and cross-linking of the polymer (62). However, at 0°C under air in a sunshine weatherometer, photooxidation was shown to be retarded by certain dibutyltin dicarboxylates (63). The latter result was also obtained in experiments involving the use of dibutyltin maleate with irradiation in the (280-400)-nm wavelength region at 38°C under air (50,51,64, 5,66). 

We conclude that the reaction between dibutyltin dicarboxylates and dibutyltin dichloride near 30 °C is an equilibrium reaction (II) the chemical shifts observed are averages of the components present in the reaction. Since the process occurs rapidly even at —50°C, it must be a very facile one. These results are supported by the observations of Mitchell (17). 

The first synthetic route explored to produce cydic polymers made use of ring-chain equilibrium. This approach involves the natural equilibrium that occurs between linear and cydic polymers during condensation polymerizations although, inevitably, this yields linear byproducts and broad polydispersities. As a result, precipitation or preparative gel-permeation chromatography (GPC) was required to obtain cyclic polymers of sufficient purity for further study. This approach is amenable to a broad range of polymerization chemistries, induding the preparation of cyclic polyesters [7,8], polyethers [9], poly(dibutyltin dicarboxylates) [10,11], and poly(siloxanes) [12-15]. 

Dibasic acid monomers, 59 Dibasic acid poly esterifications, 17 Dibromo derivatives, 82 Dibutyltin dilaurate (DBTDL), 232 Dicarboxylic acid monomers, volatilization of, 72... 

Figure 4.4.14 Dibutyltin di(carboranecarboxylate), dicarboranetin (2,6-pyridine dicarboxyl ate) and di-carboranetin di(5-oxopyrrolidine-2-carboxylate)...

The existence of a ligand exchange reaction between dialkyltin dimercaptides and dicarboxylates (typical poly(vinyl chloride) stabilizers) and dialkyltin dichlorides is demonstrated by 1H and 13C NMR. Dibenzyl- and dibutyltin dimercaptides undergo the reaction instantaneously and quantitatively at 25° C to yield dialkylchlorotin mercaptides. Dialkyltin dicarboxylates and dimethyltin dimercaptides appear to participate in an equilibrium exchange reaction with dialkyltin dichlorides in which the individual components are not identifiable by NMR at 25°C. These results are discussed as they pertain to poly(vinyl chloride) stabilization. 

Two of the products from l,T-dicarboxylic ferrocene formed fibers (7). The fibers from dibutyltin dichloride were light brown in color with the product containing only about 5% fiber mass. Again, the fibers had some short spikes coming off a central fiber (Figure 18.6). Fiber lengths were about 200 mm with a diameter of about 8 mm for an aspect ratio of about 25. The product from dimethyltin dichloride... 

Figure 18.6 Product from dibutyltin dichloride and 1,1 -dicarboxylic ferrocene...

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