End-capped polymer chains and products thereof

This application claims the benefit of priority to U.S. provisional patent application No. 60/480,121 filed Jun. 20, 2003, which is incorporated herein by reference in its entirety.

The present invention relates processes for converting a carbocationically terminated polymer to an anionically terminated polymer, and to products formed using such processes.

Living polymerizations provide versatile synthetic routes for the preparation of a wide variety of well-defined polymer structures, such as end-functionalized polymers, star-shaped polymers and/or block copolymers. Because specific living polymerization methods (e.g., anionic and carbocationic living polymerizations) are each applicable only to a limited number of monomers, the combination of different living polymerization techniques should lead to new and unique combinations of blocks in block copolymers. Recent success in the synthesis of functionalized polyisobutylene (PIB) with quantitative functionality, and of block copolymers with high structural integrity, is based on the applications of non-homo-polymerizable monomers such as 1,1-diphenylethylene (DPE) in cationic polymerization. Bac, Y. C.; Faust, R. Macromolecules 1998, 31, 9379. These processes involve the intermediate capping reaction of living PIB with DPE or its derivatives. The resulting stable and fully ionized carbenium ions have been successfully employed for the quantitative end-functionalization of living PIB with soft nucleophiles such as silyl ketene acetals (see Fodor, Z.; Hadjikyriacou, S.; Li, D.; Faust, R. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1994, 35(2), 492-493) and the controlled initiation of the second monomers such as p-methyl styrene (see Fodor, Z. Faust., R. J Macromol. Sci., Pure Appl. Chem. 1994, A31 (12), 1985-2000) and isobutyl vinyl ether (see Hadjikyriacou, S. Faust., R. Macromolecules 1995, 28, 7893-7900).

Block copolymers of isobutylene (IB) and polar monomers, such as methacrylates, acrylamides, polyethers, or polyesters should combine the high environmental stability of elastomeric, non-polar PIB with the large variety of structures and properties of polar polymers. However, because PIB can only be effectively obtained by carbocationic polymerization, many attempts have been undertaken to transform living cationic PIB chain ends to radical (see Chen, X.; Ivan, B.; Kops, J.; Batsberg, W. Macromol. Rapid Commun. 1998, 19, 585) or anionic (see Kitayama, T.; Nishiura, T.; Hatada, K. Polym. Bull. 1991, 26, 513) ones.

Although many prior attempts were less successful, metalation of DPE end-capped PIB with Na/K alloy or cesium followed by anionic polymerization allowed for the synthesis of PIB-b-PtBMA diblock copolymers, PMMA-b-PIB-b-PMMA triblock copolymers, and (PMMA-b-PIB)₃ starblock copolymers. See Feldthusen, J.; Iván, B.; Müller, A. H. E. Macromolecules, 1997, 30, 6989; and Feldthusen, J.; Iván, B.; Müller, A. H. E. Macromolecules 1998, 31, 578-585. Metalation with alkali metals, however, is inconvenient and lithiation with alkyllithium (e.g., butyllithium) would be preferable. Unfortunately, lithiation of DPE end-capped PIB by alkyllithium does not proceed quantitatively.

Recently, Faust et al. showed that furan (Fu) functional polyisobutylene (PIB-Fu) can be obtained by the quantitative reaction of living PIB and 2-tributylstannyl furan. See Hadjikyriacou, S.; Faust, R. Macromolecules 1999, 32, 6393-6399. Using unsubstituted Fu, however, side reactions in which two living chain ends were coupled to a single Fu were not avoided. Once formed, PIB-Fu chain ends could be lithiated with n-BuLi, however, the polymerization of methacrylates using this macroinitiator was accompanied by side reactions. See Scheunemann, S. G., Diplomarbeit, Universität Mainz, 1999.

In place of PIB-Fu, the present inventors have discovered that it is also possible to use thiophene (T) functional PIB (PIB-T) in the metalation reaction. An advantage is that unsubstituted T may be used to prepare PIB-T while avoiding the above noted difficulties associated with Fu, since the reactivity of T is about one tenth that of Fu.

Iván et al. reported on attempts to use T as a coupling agent for living PIB, but under the conditions chosen (−80° C., methylcyclohexane/dichloromethane 60/40 v/v, [TiCl₄]/[initiator]/[T]=10/2/1) only 17% of coupling product was formed after 2 h and 36% after approx. 24 h when stirred at room temperature. See Iván, B.; De Jong, F.; WO 9909074 (1999), assigned to Infineum Holdings B.V., Netherlands.

According to one embodiment of the present invention, a method for converting a carbocationically terminated polymer to an anionically terminated polymer is provided. The method comprises: (a) providing a carbocationically terminated polymer; (b) reacting said carbocationically terminated polymer with a heterocyclic compound of the formula

where —X— is selected from —S-(thiophene), —O— (furan), —NH-(1H-pyrrole) or —NR—, where R is an alkyl or aryl, thereby providing an end-capped polymer; and (c) reacting said end-capped polymer with an organolithium compound to yield an anionically terminated polymer.

In the above scheme, at least 75 wt % of the carbocationically terminated polymer is preferably attached to the heterocyclic compound in a monofunctional (mono-substituted) fashion, more preferably, at least 90 wt %, at least 95 wt %, or even 99 wt % or more of the carbocationically terminated polymer.

In general, the molar ratio of the heterocyclic compound to the carbocationically terminated polymer in the reaction mixture is greater than 1:1, more preferably greater than 3:1, greater than 10:1, greater than 30:1 or even 100:1 or greater. The amount of carbocationically terminated polymer can typically be approximated by the amount of initiator that is supplied at the beginning of a cationic polymerization reaction scheme.

Examples of carbocationically terminated polymers include carbocationically terminated polymers of cationically polymerizable monomers, for instance, olefins such as isobutylene, 2-methylbutene, isoprene, and the like, vinyl aromatics such as styrene, alpha-methyl styrene, para-chlorostyrene, para-methylstyrene and the like, vinyl ethers such as methyl vinyl ether, isobutyl vinyl ether, butyl vinyl ether, N-vinyl carbazole, and the like.