Methyl acrylate telomers

For analysis, the crude ACT reaction mixtures were subjected to a standard telomer assay as follows [14, 15]. The tin products were removed by chromatography and treatment with KF. The resulting macrocyclic mixtures were then hydrolyzed under acidic conditions to yield the corresponding acrylic acid telomers. Hydrolysis of the desired n=4 macrocycle is shown in Scheme 8-9. Esterification of the reaction mixture with diazomethane gave the methyl acrylate telomers 26 that were then readily identified by gas chromatography/mass spectrometry. 

It should be noted that the ACT sequence and the standard telomer assay were employed to study oligoselectivity with this template and thus the products analyzed are the same methyl acrylate telomers identified in the previous studies. The ACT reaction of 40 under standard conditions with cyclohexyl iodide and allyltributyltin (2.5 /80V200 "), without the aid of a counter-ion, showed interesting results. The product histogram obtained with 40 after telomer assay is presented in Scheme 8-15. 

A simple template-free methyl acrylate telomerization was conducted using the cyclohexyl iodide/allyltributyltin system in order to identify retention times for the telomers 26 from the ACT reactions. Telomerization of methyl acrylate (900 mM) with 120 mM cyclohexyl iodide and 300 mM allyltributyltin gave 27% of the n=4 telomers. Scheme 8-10. Under the best GC conditions found, only four different n=4 telomers, out of a possible 16, were observed in this product mixture. This experiment gives a baseline value for telomer distribution obtained without the use of a template. It is clear that simple template-free telomerization is not useful for the preparation of an oligomer of a specific length. 

The feasibility and practicality of the ACT sequence in obtaining diastereomerically pure n=4 telomers were investigated using the optimum conditions determined for template 24. The possibility of isolation of the desired n=4 template from all of the other reaction products by the use of HPLC was explored. In a standard template-free stereorandom methyl acrylate telomerization, three peaks are observed for the = 3 telomers by normal-phase HPLC and three more broad peaks are separated for the =4 telomers. Each of these latter peaks represents a mixture of isomers as determined by GC analysis. 

Much literature precedent supports the assignment of tacticity in methyl acrylate polymers using NMR techniques [40,41]. In the H-NMR spectrum, the shift of the methylene protons is sensitive to dyad stereochemistry. For example, in an isotactic (meso) dyad 28, the methylene protons are chemically non-equivalent and appear as two separate sets of signals, whereas in a syndiotactic (racemic) dyad 29, the methylene protons are equivalent. The H-NMR spectrum of 27 showed multiplets at 1.89 and 1.5 ppm due to the two diastereotopic methylene protons of the isotactic dyad. The rest of the spectrum is consistent with the structure of the n=4 tetrad 27. A racemic dyad structure would have been expeeted to give resonances of intermediate shift to that of the two resonances observed for the telomer 27. This evidence strongly implies that 27 has the allisotactic configuration shown in Scheme 8-12. 

The kinetic analysis in the case of RITP of methyl acrylate at 70 °C showed the existence of an initialization period during which iodine is consumed to form short A-Mn-I telomers which can further act as reversible transfer agents (reversible chain... 

Photolysis of this polymer gives radicals on which side chains can be formed, giving graft polymerization 122, 123, 153). Similarly the polymerization of styrene (152) or vinyl acetate (157) in the presence of bromotrichloromethane gives telomers carrying terminal bromine atoms and trichloromethyl groups. By ultraviolet irradiation (3500 A) in the presence of methyl methacrylate the carbon-bromine links are broken and block copolymers are formed. The telomerization of acrylonitrile and acrylic acid with bromoform is based on the same technique the end groups of both polyacrylonitrile and polyacrylic acid were photolyzed in the presence of acrylamide and afforded polyacrylamide blocks linked to polyacrylonitrile or polyacrylic acid blocks (164, 165). 

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