Macroinitiators graft copolymers

Many block and graft copolymer syntheses involving transformation reactions have been described. These involve preparation of polymeric species by a mechanism that leaves a terminal functionality that allows polymerization to be continued by another mechanism. Such processes are discussed in Section 7.6.2 for cases where one of the steps involves conventional radical polymerization. In this section, we consider cases where at least one of the steps involves living radical polymerization. Numerous examples of converting a preformed end-functional polymer to a macroinitiator for NMP or ATRP or a macro-RAFT agent have been reported.554 The overall process, when it involves RAFT polymerization, is shown in Scheme 9.60. 

Fig. 3. Comparison of SEC traces for poly(MMA-co-HEMA) starting macroinitiator curve a) and poly(MMA-g -CL) final graft copolymer curve b). For synthetic conditions, see Scheme 21...

To synthesize graft copolymers by ATRP, the initiation site for living radical polymerization can be incorporated into the polymer chain. In general, copolymerization of olefins with functional monomers can be adopted for syntheses of PO macroinitiators. 

PE graft copolymers were synthesized from PE-OH by Inoue et al. using ATRP techniques, adopting similar techniques as mentioned above [74]. PE-g-PMMA and Polyclhylcnc-gra/f-poly( -bulyl acrylate) (PE-g-PnBA) were prepared through the combination of metallocene-catalyzed ethylene/10-undecen-l-ol copolymerization and conversion of the copolymer into P E-g-Br, as a macroinitiator, for ATRP. Well-defined graft copolymers, PE-g-PMMA and PE-g-PnBA, were confirmed by analyses of the detached side chains. Resulting PE-g-PMMA worked well as a compatibilizer. 

All products were soluble in water, indicating the formation of the graft copolymer and the absence of ungrafted macroinitiator. Dialysis of the product also revealed the absence of low MW (<6000 g mol-1) homo poly(2-methyl-2-oxazoline). Due to the amphiphilic nature of the graft copolymer, aggregation in water as well as in chloroform was shown by NMR spectroscopy, solution vis-... 

Other useful modifications include acetylation, hydroxyethylation, hydro-xypropylation, cationic starches, succinate, and substituted succinate derivatives of starch. In starch-grafted copolymers, free radicals are initiated on the starch that then act as macroinitiators for the acryl or vinyl monomers. These products are used in firefighting fluids, electrolyte solutions for alkaline batteries, wound dressing, and so on. 

Pan et al. prepared a macroinitiator by chloromethylation of a commercially available AB block copolymer of poly (styrene-fe-ethylene-co-propylene) (SEP) and used it as a macroinitiator for the ATRP of ethyl methacrylate (EM A) [302]. The kinetic plot showed little evidence of termination during the reaction and the molecular weight of the graft copolymer increased linearly with the monomer conversion, resulting in a final Mn=73,200 and Mw/Mn=1.22. The weight ra-... 

Inorganic macroinitiators can also be used for graft copolymerizations. Pendant vinyl functional pDMS was subjected to hydrosilation with 2-(4-chlorometh-ylphenyl)ethyldimethylsilane to prepare a multifunctional ATRP macroinitiator by Matyjaszewski et al. [233,234]. The ATRP of St was carried out using a pDMS macroinitiator with Mn=6600 and Mw/Mn=1.76 to yield a graft copolymer with Mn=14,800 and Mw/Mn=2.10. The increased polydispersity was attributed to the variation in the number of initiating sites on the pDMS backbone. NMR analysis showed that less than 5% of the total number of benzyl chloride moieties were left unreacted and that the weight ratio of pSt/pDMS was 1.18 [234]. 

The field of densely grafted copolymers has received considerable attention in recent years. The materials (also called bottle-brush copolymers) contain a grafted chain at each repeat unit of the polymer backbone. As a result, the macromolecules adopt a more elongated conformation. Examples of brush copolymers have been provided within the context of ATRP [307-309]. Synthesis of the macroinitiator was achieved through one of two approaches. One method used conventional radical polymerization of 2-(2-bromopropionyloxy)ethyl acrylate in the presence of CBr4 to produce a macroinitiator with Mn=27,300, and a high polydispersity of Mw/Mn=2.3 (Scheme 46A) The alternative involved the ATRP of 2-trimethylsilyloxyethyl methacrylate followed by esterification of the protected alcohol with 2-bromopropionyl bromide. While synthetically more challenging, the latter method provided a macroinitiator of well-defined structure... 

Modification of Enzymatic Blocks to Form Macroinitiators 316 Enzymatic Synthesis of Graft Copolymers 319 Summary and Outlook 320 References 320... 

In the area of novel materials CMU protected (co)polymers prepared by ATRP except with CCI4 initiator and telechelic polymers prepared by CRP with MW > 20,000 (49) copolymers with a tme gradient segment (30) polar ABA block copolymers, (30) and well defined graft copolymers and segmented copolymers with one or more CRP blocks where the macroinitiator had been prepared by another polymerization process. (36) In addition, the use of tethered initiators allowed synthesis of hybrid core/shell copolymers. Pending applications disclose other novel polymeric materials. 

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