Macromonomer method

The macromonomer route assures uniform distribution of dendrons along the polymer backbone. Acrylates and styrenes with pendant dendrons proved to be well suited for polymerisation [57]. However, steric hindrance between monomers bearing higher-generation dendrons and the spatial requirements of the end of the chain cause problems The monomer reacts with the chain end only in the case of slight, if any, steric hindrance. Thus the method only provides access to dendronised linear polymers with relatively low molar masses 

To summarise, a common feature of all methods for the preparation of dendronised linear polymers is the change of shape of a formerly flexible filamentary molecule by attachment of dendrons to the backbone of the polymer. As the extent of dendronisation increases, the coil structure extends and acquires greater rigidity, until the polymer assumes a linear extended form with a stiffened backbone. Stiffening of the polymer molecules to this extent has hitherto only been accom- 

Extreme loading of the polymer with dendrons results in a cylindrical shape of the denpol polymer (Fig. 2.19) with polydisperse properties. It is thus possible to influence or even control the size of the coupled dendron and the density of its coverage on the polymer backbone through choice of the type of polymer (e.g. polyacrylate or polystyrene see Table 2.1). 

The dimensions of the dendritic cylinder depend on the one hand upon the degree of polymerisation, which determines the length, and on the other hand upon the generation of the dendron, which determines the diameter (about twice the size of the attached dendron). Conventional polymers have diameters in the Angstrom range, whereas the dendronised linear polymers described here have nanometre diameters. 

Such well-defined architectures could be useful for nanoscale applications in, for example, catalysis or as carrier materials for chemical transport. 

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An important polymer modification reaction is the grafting to or from a polymer backbone by some chemical method to produce a branched structure Q). The characterization of the products of these reactions is often somewhat less well defined than block copolymers (2) due to the complexity of the mixture of products formed. It is therefore useful to prepare and characterize more well defined branched systems as models for the less well defined copolymers. The macromonomer method (3 ) allows for the preparation of more well defined copolymers than previously available. 

Statistical, gradient, and block copolymers as well as other polymer architectures (graft, star, comb, hyperbranched) can be synthesized by NMP following the approaches described for ATRP (Secs. 3-15b-4, 3-15b-5) [Hawker et al., 2001]. Block copolymers can be synthesized via NMP using the one-pot sequential or isolated macromonomer methods. The order of addition of monomer is often important, such as styrene first for styrene-isoprene, acrylate first for acrylate-styrene and acrylate-isoprene [Benoit et al., 2000a,b Tang et al., 2003]. Different methods are available to produce block copolymers in which the two blocks are formed by different polymerization mechanisms ... 

The method adopted for the synthesis of these stars can be considered as a macromonomer method, since end-reactive vinyl groups were used for the linking of the PS arms. There is a possibility that the silyl vinyl anion formed after the addition of the living PS chains reacts with silyl vinyl groups this effect was minimized using short VS blocks and a large excess of PS anions. 

The macromonomer method was used by Fujimoto et al. for the preparation of (PS)(PDMS)(PtBuMA) stars [53], as described in Scheme 20. The lithium salt of the p-(dimethylhydroxy)silyl-a-phenyl styrene was synthesized and used as initiator for the polymerization of hexamethylcyclotrisiloxane (D3). Living PS chains were reacted with the end double bond of the macromonomer, followed by the anionic polymerization of the f-BuMA. 

The composition distribution of the graft copolymers obtained by the macromonomer method has been shown theoretically to be statistically broader than in the corresponding conventional linear copolymer, due to the high MW of the macromonomer branches [45, 46]. This has been experimentally confirmed by Teramachi et al. with PSt macromonomers, 23 or 24, copolymerized with MMA [47-49]. The chemical composition distribution was found to broad-... 

The macromonomer method (C) has also been adopted in cationic polymerization. For instance, amphiphilic graft polymers of vinyl ethers are synthesized by the cationic polymerization of a vinyl ether-capped macromonomer (26) with a block copolymer chain consisting of IBVE and AcOVE segments, followed by alkaline hydrolysis of the latter part into the HOVE units [165], This graft polymer also undergoes a host-guest interaction similar to those with amphiphilic star block copolymers [220]. 

Randomly branched comb-shaped polymers can be prepared by three general synthetic methods the grafting onto , the grafting from , and the grafting through or macromonomer method.88... 

DeSimone, J. M., A. M. Hellstern, E. J. Siochi, S. D. Smith, T. C. Ward, P. M. Gallagher, V. J. Krukonis, and J. E. McGrath. 1990. Homogeneous and multiphase poly(methyl methacrylate) graft copolymers via the macromonomer method. Makro-mol. Chem., Macromol. Symp. 32 21. 

The method most used for the preparation of graft copolymers is the macromonomer method [42-46]. A macromonomer is an oligomeric or polymeric chain bearing polymerizable end groups. Copolymerization with another monomer provides graft copolymers. The macromonomers can be monofunctional or difunctional depending on whether they have one or two end groups which can be polymerized. 

Quemener D, Heroguez V, Gnanou Y (2006) Design of PEO-based ruthenium carbene for aqueous metathesis polymerization. Synthesis by the macromonomer method and application in the miniemulsion metathesis polymerization of norbornene. J Polym Sci Part A Polym Chem 44 2784-2793... 

The reaction scheme of the synthesis of a graft copolymer by macromonomer method is illustrated in Scheme 1. 

Scheme 1. Synthesis of Graft Copolymer by Macromonomer Method...

Graft copolymers of PMMA with poly(3-hydroxybutyrate) (PHB) segments as long side chains were prepared by the macromonomer method. PHB macromonomers were prepared from the esterification of oligomers with HEMA at their carboxylic acid end. Esterification products displayed low poly-dispersity indices ( 1.2) and a functionality over 83%, with a molecular weight measured by NMR of 2020 g mol". Using... 

An example of the macromonomer method is the preparation of graft copolymers of PEO by the free radical polymerization of vinyl acetate in the presence of PEO. The growing vinyl acetate radical would abstract a hydrogen atom from the PEO chain, creating a radical at this site. The newly created radical would then polymerize vinyl acetate to form a branch on the chain. The rather randomly occurring chain transfer reaction would form a graft copolymer of PEO and poly(vinyl acetate). 

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... 

Three general methods have been developed for the synthesis of randomly branched graft copolymers (1) the grafting onto , (2) the grafting from , and (3) the macromonomer method (or grafting through method) (8) (Fig. 2). 

The most commonly used method for the synthesis of graft copolymers is the macromonomer method. Macromonomers are oligomeric or polymeric chains bearing a polymerizable end group. Macromonomers having two polymerizable end groups have also been reported (8). Copolymerization of preformed macromonomers with another monomer yields graft copolymers. 

Segmented terpolymers of poly(alkyl methacrylate)-g-poly(D-lactide)/poly(dimethylsiloxane) (PLA/PDMS) were prepared by combination of a grafting through technique (macromonomer method) and controlled/living radical polymerization such as atom transfer radical polymerization (ATRP) or reversible addition-fragmentation chain transfer polymerization. In a single-step approach, the low molecular weight methacrylate monomer (methyl methacrylate... 

Using a variation of this dendritic macromonomer method, Percec et al. [185,186] synthesized a variety of dendritic 7-oxanorbornene macromonomers and polymerized them with ROMP catalysts [186] as shown in Figure 28, as well as with free radical or anionic catalysts. 

The macromonomer method is probably the most promising development at present concerning the synthesis of well-defined graft copolymers. The developments in this field up to 1999 have been reviewed by Ito and Kawaguchi [181]. Any macromonomer having a head group that is copolymerizable with styrene can be utilized for this purpose. 

Matyjaszewski, K., et al. (1998). Hydrogels by atom transfer radical polymerization. I. poly(N-vinylpyrrolidinone-g-styrene) via the macromonomer method. J. Polym. Sci., Part A Polym. Chem., 36(5) 823-830. 

Shinoda, H., Miller, P. J., and Matyjaszewski, K. (2001). Improving the structural control of graft copol5miers by combining ATRP with the macromonomer method. Macromolecules, 54(10) 3186-3194. 

Macromonomer method Macromonomers are conveniently used for the graft copolymer synthesis. A macromonomer of PEG chain having an oxazoline polymerizable group was prepared and used for a graft copolymer synthesis (Scheme 23). ... 

Macromonomer method was used for the synthesis of comb and graft polymers and their LCST behavior was examined, where a hydrophilic oligoEtOZO was utilized as side chains and a hydrophobic methacrylate as backbone... 

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