Macromonomer technique

PS-fr-PBd) star-block copolymers were synthesized by the macromonomer technique in combination with anionic polymerization and ROMP [ 158], following the procedure outlined in Scheme 83. The macromonomers were prepared with two different methods. In the first the living diblock copolymer was reacted with ethylene oxide to reduce the nucleophihcity of the living end followed by termination with 5-carbonyl chloride bicycle (2.2.1) hept-2-ene, while in the second method the functional initiator 5-lithiomethyl bicycle... 

The present article is intended to discuss the state-of-the-art of the design and characterization of the branched polymers obtained by the macromonomer technique, with particular stress on the characterization and the properties of the brush polymers obtained by the homopolymerization of macromonomer. The synthetic aspects of the macromonomer technique, including preparation of various kinds of macromonomers, have been recently reviewed by one of the authors [1]. Therefore, we intend here to outline briefly the macromonomer technique and describe only the very recent important developments in syntheses. Preparation and characterization of the polymeric microspheres by use of macromonomers as reactive (copolymerizable) emulsifiers or dispersants will be described in some detail to represent one of their unique applications. 

Fig. 1 a—f. Various branched architectures obtained by the macromonomer technique a,b comb-like c,d star-like e brush f flower-like, a c, and e are poly(macromonomers) obtained by homopolymerization, while b, d, and f are graft copolymers obtained by copolymerization... 

The variety of branched architectures that can be constructed by the macromonomer technique is even larger. Copolymerization involving different kinds of macromonomers may afford a branched copolymer with multiple kinds of branches. Macromonomer main chain itself can be a block or a random copolymer. Furthermore, a macromonomer with an already branched or dendritic structure may polymerize or copolymerize to a hyper-branched structure. A block copolymer with a polymerizable function just on the block junction may homopolymerize to a double comb or double-haired star polymer. 

Needless to say, the best established architecture which can be designed by the macromonomer technique has been that of graft copolymers. With this technique we now have easy access to a variety of multiphased or microphase-separated copolymer systems. This expanded their applications into a wide area including polymer alloys, surface modification, membranes, coatings, etc. [5]. 

To summarize, macromonomers in polymerization and copolymerization are only fairly well understood compared to the conventional monomers. Effects, such as conformational, morphological, or due to incompatibility caused by the macromonomer chains, remain to be further investigated. As a result, the macromonomer technique is expected to lead to other unique applications including construction of novel branched architectures. 

Fi9 5 Schematic picture of a microsphere obtained in emulsion and dispersion copolymerization using macromonomer technique. The grafted chains are exaggerated in size... 

Fig. 8. Schematic representation of the possible conformations of adsorbed (co)polymers prepared using macromonomer technique a brush adsorption of graft copolymer b terminally-attached adsorption c the mushroom-brush transition for strongly overlapping chains proposed by de Gennes [130] and Alexander [155]...

Characterization of the poly(macromonomers) prepared by homopolymerization has proved that they provide a useful probe for discussing the structural characteristics of the star and brush polymers. Graft copolymers have been and will be a most important area of application of the macromonomer technique since a variety of multi-phased and microphase-separated systems can easily be designed just by an appropriate combination of a macromonomer and a conventional monomer. In general, however, characterization of their absolute MW, branch/backbone composition as well as their distributions remain to be studied in more detail. 

Amphiphilic macromonomers work effectively as reactive (copolymerizable) emulsifiers and dispersants for heterogeneous polymerizations. They are successfully applied to the design of the polymeric microspheres of submicron to micron size. Introduction of additional functions, such as environment-sensitivity, will be a matter of interest in the potential application of the macromonomer technique. 

Using of Terminal Silanolate Function for Building More Complex Macromolecular Structures by Macroinitiator and Macromonomer Techniques or by Sequential Copolymerization... 

The reaction scheme for graft copolyelectrolyte synthesis by free radical copolymerization according to the macromonomer technique is shown in Scheme 15. Besides the aspect of how to control the constitution of the graft copolyelectrolyte, suitable characterization techniques for unequivocal proof of the attained copolymer structure will also be elucidated. The synthesis, characterization and properties of the inversely structured poly(acrylic acid)-g-polystyrene graft copolymers it are covered in another article in this volume [178]. 

Scheme 15 Reaction scheme for the synthesis of poly( acrylic acid-graft-styrene) copolymers (PAA-g-PS) according the macromonomer technique...

A macromonomer technique was employed by Ishizu and Kuwahara to prepare miktoarm star copolymers of the (PS) (PI)m type.128 PS and PI macromonomers were prepared by coupling the living chains with />chloromethylstyrene. The PS and PI macromonomers (vinyl end-capped chains) were copolymerized anionically in benzene using n-BuLi as initiator. The products are comb-shaped copolymers, but they behave as miktoarm stars of the type A Bm. The reaction sequence is given in Scheme 58. 

DeSimone. J. M., A. M. Hellstern, T. C. Ward, J. E. McGrath, S. D. Smith, P. M. Gallagher, V. J. Krukonis, J. Stejskal, D. Strakova, and P. Kratochvil. 1988b. Elucidation of the chemical composition distribution of graft copolymers prepared by the macromonomer technique. Paper presented at the ACS Meeting, Los Angeles, CA, November. 

Synthesis, characterization, and chemical composition distribution investigations of graft copolymers prepared by the macromonomer technique. In Contemporary topics in polymer science, vol. 6 Multiphase macromolecular systems, ed. B. M. Culbertson. New York Plenum Press. 

Attempts to prepare star-block copolymers via the macromonomer technique have also appeared in the Hterature [26-28]. The method involves the preparation of diblock arms and subsequent end functionalization with p-chloromethyl-... 

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