Grafting, anionic Initiator

Anionic Polymerization. Anionic grafting polymerization initiated on the inorganic particles is also possible to give composite particles. The amino group incorporated into the surface of silica caused anionic polymerization of N-carboxy-a-amino acid anhydride to give poly(amino acid) grafting [Reaction (8)1 (21). 

In this paper graft copolymerization onto both polystyrene and styrene-butadiene block copolymer will be discussed. It will be shown that radical processes do not permit the addition of monomers onto polystyrene and that one must use anionic initiation in order... 

Anionic Graft Copolymerization onto Polystyrene. We have been able to initiate graft copolymerization onto polystyrene by the use of anionic initiators but even here the reaction does not proceed as one may expect. Once again one would likely think that the benzylic hydrogen is the most acidic and should be the one removed by a lithium reagent... 

Another kind of anionic initiation is being used by Asahi Chemical Industries Corporation (134) in their patent describing the grafting of methyl methacrylate, acrylamide, acrylic acid, and 2-methyl-5-vinyl-pyridine onto partially cyanoethylated and oximated cotton in presence of TiClg, VO or VC12 as effective agents. 

The production of aldehyde groups through periodate oxidation and subsequent formation of oxime groups is being used as a basis for an anionic initiation of grafting with titanium chloride as catalyst according to a process claimed by Asahi Chemical Industries Company (135). With this method styrene was grafted onto viscose rayon. Also bi- and tri-valent vanadium salts can be used as initiators. 

Baskaran and co-workers" performed anionic surface-initiated polymerization of styrene in the presence of anionic initiator-immobilized MWCNTs prepared by Diels-Alder cycloaddition of 1-benzocyclobutene-T-phenylethy-lene (BCB-PE) and CNTs at 235 °C. The PS-grafted CNTs were characterized by FTIR spectroscopy, NMR, TGA and TEM. The thickness of grafted PS layer approached 30 nm (Figure 5.18). 

The polymer carbanion can also be used as an anionic initiator for polymerizing a conventional organic monomer to generate a poly-phosphazene-co-organic polymer (Fig. 3.50). The polystyrene graft copolymer prepared as shown above is actually separated into the individual polystyrene and polyphosphazene phases. This is found by the detection of two separate Tg s at +100 °C and +37 °C. 

Scheme 1.6 Grafting polymerization of polymeric anionic initiators...

Fig. 5. Protocol for living anionic surface initiated polymerization (LASIP), with initiators attached to silica nanoparticles or clay (a) grafting of initiator and general polymerization scheme (b) nanoparticle grafting procedure. From Ref 36.

A lower graft molecular weight and more frequent grafting usually results from anionically initiated graft copolymerization. Zilkha et al. initiated graft polymerization of ethylene and propylene oxides with alkali metal oxides of starch. Their... 

Grafting from Initiation of graft polymerization of various monomers from radical, cationic and anionic initiating groups previously introduced onto nanop>article surfaces... 

The anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

Bamford, Eastmond and coworkers have employed metal complexpolymeric halide redox systems to initiate block and graft copolymerization. The polymeric halides can be synthesized by a variety of techniques, including radical polymerization,281 anionic polymerization (Scheme 7.28),"so... 

Anionic polymerization of pivalolactone with the polystyrene anion produced only homopolymer mixtures, but the polystyrene carboxylate anion was able to give a block copolymer336. The block efficiency depends on catalyst ratio and conversion because the initiation step is slow compared with propagation337. Tough and elastic films were obtained by graft copolymerization or block copolymerization of pivalolactone onto elastomers containing tetrabutylammonium carboxylate groups338,339. ... 

Kennedy and co-workers 2 117) used the changing effect of the initiation ability of the Lewis acids according to Eq. (17) and the termination tendency of the anion formed according to Eq. (18) in order to obtain telechelic polymers , block copolymers and graft copolymers in a controlled manner. Quantum chemical calculations provide the possibility to discuss structural influences which work on the equilibrium Eq. (19) and therefore on the stability of the two adjacent ions. 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

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