ROMP macromonomers

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... 

Short PS macromonmers (DP = 4 or 9) polymerized completely under ROMP conditions. Macromonomers with DP = 14 to 46 invariably led to incomplete polymerization, suggesting that the dense polymacromonomer imposes steric limitations on the polymerization. Heroguez et al. studied the ROMP of polyethylene oxide) macromonomers [111, 112], The macromonomers are prepared from a norbornene derivative according to the following sequence ... 

Living ROMP of a macromonomer with MW = 2600 yields star-like polymers with 10 to 100 arms on average possessing a somewhat broad MW distribution (i.e., 1.2—1.4). 

Macromonomers containing a norbornene group have been polymerized by ROMP (Sec. 7-8) to form graft copolymers [Breunig et al., 1995 Heroguez et al., 1997]. 

Initially, the polymerization of macromonomers was achieved by free radical polymerization reactions, which allowed only a limited control of the final properties. With the advent of ROMP and new free radical polymerization techniques, such as atom transfer radical polymerization (ATRP) the control of final properties became more facile (16). ATRP and ROMP techniques can be combined for the synthesis of macroinitiators (17). 

Monomers in this category fall into three groups (i) those with small substituents, giving polymers which may be thermoplastic466 (ii) those with substituents of intermediate size and of such a character that the polymers can have liquid-crystalline or other interesting properties and (iii) macromonomers in which a polymer is terminated by a norbornenyl group and which can be used to make graft copolymers by ROMP. Except where stated the monomers are endo/exo mixtures. 

Norbornenyl-ended macromonomers from poly(ethylene oxide) (PEO), 15, as well as from PEO-b-PSt or PSt-b-PEO block copolymers, 16a, 16b, have been prepared by the initiation or termination method of living anionic polymerization [22, 23]. The ROMP of 16 afforded various types of controlled, core-shell... 

Gnanou and coworkers [15,22,23] prepared several types of regular star- and comb-shaped polymers by living, ROMP of co-norbornenyl macromonomers, 8, 15 and 16. Some of them were characterized by means of the universal calibration in SEC to discuss the chain density, radius of gyration, and shrinking factor [63]. 

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

The grafting-through methodology has certain drawbacks, related to the limited side chain size (length and shape), the MWD of the main chain, and the narrow concentration window of macromonomers. The ROMP of norbomenyl-terminated represents a promising approach, because it provides a better control of the main chain growth process. In addition, the repeating unit in the main chain has five C-C bonds, which can accommodate more spacious side chains. 

The (co)polymerization of macromonomers based on PS and/or PEO by ring-opening metathesis polymerization (ROMP) [34] offers the advantage of a quantitative process, to yield star-like polymers that are free from any macromonomeric precursors. 

It is well known that the macromonomer method represents a privileged way to get access to highly compact polymers. In a recent addition to this field, we demonstrated that macromonomers can be polymerized under truly living conditions via ROMP. Provided the macromonomers are end-fitted with a norbornene unsaturation, polymacromonomer samples of controlled size and varying compactness can be synthesized using well-defined molybdenum Schrock complexes as initiator. Depending... 

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