Chain-end functionalized polypropylene

Z. Wang, T.C. Chung, Synthesis on chain-end functionalized polypropylene and its applications in exfoliated PP/clay nanocomposite. Polymer Materials Science and Engineering 93 (2005) 573. 

Chain-end functionalized polypropylene has a very attractive polymer structure that possesses an unperturbed polymer chain with desirable physical properties (such as high melting temperature, crystallinity, good mechanical properties, etc.) almost the same as those of pure polypropylene. Nevertheless, the terminal reactive group at the polymer chain end has good mobility to diffuse to the surface and can provide a useful reactive site for many applications, such as adhesion to substrates, reactive blending, and the formation of block copolymers. 

There are six different types of end-functionalized polypropylenes that can be formed using metallocene catalysts (Figure 14). Chain termination by /3-hydrogen elimination forms vinylidene end groups, while /3-methyl elimination forms allyl chain ends. Polypropylene with isobutenyl groups has been proposed to come from allylic activation, and /3-hydrogen elimination after a 2,1-regioerror produces cis-... 

Lin W, Dong JY, Chung TC (2008) Synthesis of chain end functional isotactic polypropylene by the combination of metallocene catalyst and Borane chain transfer agent. Macnnnolecules 41 8452... 

The reactions of the living polypropylene end with various additives are summarized in Fig. 23. Some terminally functionalized polypropylenes with monodisperse chain length have been used for the synthesis of well-defined block copolymers, which will be described in next Section. 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

A miktoarm star copolymer carrying one PS arm and two polypropylene oxide) arms126 was prepared by the method given in Scheme 56. Living PS chains were end-capped with one unit of DPE, to reduce the reactivity of the chain end, followed by the addition of epichlorohydrin to produce the epoxide functionalized polymer. It was shown by SEC analysis and chemical titration that the epoxide content of the final product was 95 wt %. The desired functionalized... 

Shiono, T. Kurosawa, H. Ishida, O. Soga, K. Synthesis of polypropylenes functionalized with secondary amino groups at the chain ends. Macromolecules 1993, 26, 2085-2089. 

In this way, the functionalization of one component in immiscible polymer blends has attracted great interest in terms of the compatibilization.For example, Lambla and his coworkers reported a series of works on the in situ compatibilization of immiscible polymer blends by one-step reactive extm-sion. ° They described the chemical reactions related to compatibiUzing polymer blends, especially for the PBT/polypropylene (PP) blend system. They stressed that the monomers used for functionalizing PP, such as acrylic acid (ACID), MAH, GMA, and oxazoline, are potentially reactive towards the carboxylic acid and/or hydroxyl groups at the chain ends of the PBT and are melt grafted onto the PP by free-radical reactions. 

Stereosequence has an enormous influence on a polymer s physical and mechanic properties. For example, isotactic and syndiotactic polypropylene (PP) can be crystallized, while atactic PP fails to crystallize. PP made by radical polymerization usually has methyl groups arranged with random stereochemistry along the polymer backbone, that is, atactic PP. Catalysts can limit the incoming monomers to a specific orientation, so that they add to the polymer chain end only if they face in the correct direction. If the catalyst functions with the methyl group consistently on one side, isotactic PP is formed. These molecules coil into a helical shape and line... 

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