Polymers have been reacted with various polyfunctional compounds capable of insertion reactions into C--H bonds. Such polyfunctional compounds having at least two functional groups capable of C--H insertion reactions are referred to herein as C--H insertion compounds. Those skilled in the art are familiar with such reactions and the functional groups associated therewith. For example, carbenes, as generated from diazo compounds, are disclosed in Tetrahedron, (1985), 41(8), pages 1509-1516, and nitrenes, as generated from azides, are disclosed in J. Org. Chem., (1977), 42(17), 2920-6, and J. Org. Chem., (1975), 40(7), 883-9. C--H insertion compounds include compounds such as alkyl and aryl azides (R--N3), acyl azides (R--C(O)N3), azidoformates (R--O--C(O)--N3), phosphoryl azides ((RO)2-(PO)--N3), phosphinic azides (R2-P(O)--N3), silyl azides (R3--Si-N3) and sulfonyl azides (R--SO2-N3).
Sulfonyl azides are reported to be useful for a variety of purposes including polymer crosslinking. U.S. Pat. Nos. 3,058,944; 3,336,268; and 3,530,108 disclose the reaction of certain poly(sulfonyl azide) compounds with isotactic polypropylene and other polyolefins by nitrene insertion into C--H bonds. More recently, sulfonyl azides have been found useful in modifying the rheology of certain polyolefins as disclosed in U.S. application Ser. Nos. 60/057,713 and 60/057,677, filed on Aug. 27, 1997; U.S. application Ser. Nos. 09/129,163, 09/129,161 and 09/129155 file on Aug. 5, 1998; U.S. application Ser. No. 09/140,603 fled on Aug. 26, 1998 and U.S. application Ser. No. 09/133,244 filed on Aug. 13, 1998; each of which is hereby incorporated herein by reference in its entirety. The result of reacting a sulfonyl azide with a polyolefin is the coupling of one polymer chain to another via a sulfonamide linkage. When polymer chains are thus coupled or linked, they are referred to as coupled or chain coupled polymers, and as rheology modified polymers.
As used herein, the term "rheology modified" refers to a change in the resistance of the molten polymer to flow. The resistance to flow is indicated by (1) the tensile stress growth coefficient and (2) the dynamic shear viscosity coefficient. The tensile stress growth coefficient is measured during start-up of uniaxial extensional flow as described by J. Meissner in Proc. XIIth International Congress on Rheology, Quebec, Canada, August 1996, pages 7-10 and by J. Meissner and J. Hostettler, Rheol. Acta, 33, 1-21 (1994). The dynamic shear viscosity coefficient is measured with small-amplitude sinusoidal shear flow experiments as described by R. Hingmann and B. L. Marczinke, J. Rheol. 38(3), 573-87, 1994.
Polymer compositions have also been rheology modified using nonselective chemistries involving free radicals generated by peroxides or high energy radiation. Although these techniques are useful for polyethylene, free radical generation at elevated temperatures tend to degrade the molecular weight of polymers such as polypropylene and polystyrene, due to the high rate of chain scission reactions along the polymer backbone.
Therefore, previous coupling technologies have been ineffective at high temperatures, e.g.&gt;250.degree. C., due to the formation of undesirable amounts of free radicals and/or decomposition. There remains a need for successful coupling of polymers which are typically processed at temperatures above 250.degree. C., without degradation or crosslinking of the polymer.