Iodination termination

As will be described in Section 5.3, the living polypropylene can be terminated with iodine to give an iodine-bonded monodisperse polypropylene. The analysis of the iodine-terminated polypropylene gives us an information on the structure of the active vanadium-carbon bond because a vanadium is replaced by an iodine atom. The following structure (4) of end groups has been observed in the H NMR spectrum of iodine-terminated polypropylene 98). 

An iodine-terminated polypropylene has been prepared by the reaction of living polypropylene with iodine at — 78 °C l04>. The reaction was complete within a few minutes to yield an almost monodisperse polypropylene (lftw/Mn = 1.15). The elementary analysis of iodine-terminated polypropylene revealed that iodine reacted quantitatively with the vanadium-polymer bond to give a new iodine-polymer bond. 

The iodine-terminated monodisperse polypropylene was reacted with an excess amount of ethylene diamine at room temperature in THF solution, followed by wash-... 

Fig. 21a and b. H NMR spectra of a iodine-terminated propylene oligomer (Mn = 630) and b HC1-terminated propylene oligomer. Chemical shifts are in ppm down-field from TMS... 

Various types of well-defined block copolymers containing polypropylene segments have been synthesized by Doi et al. on the basis of three methods (i) sequential coordination polymerization of propylene and ethylene 83-m>, (ii) transformation of living polypropylene ends to radical or cationic ones which initiate the polymerization of polar monomers 104, u2i, and (iii) coupling reaction between iodine-terminated monodisperse polypropylene and living polystyrene anion 84). In particular, the well-defined block copolymers consisting of polypropylene blocks and polar monomer unit blocks are expected to exhibit new characteristic properties owing to the effect of microphase separation. 

Burgess et al.I14) found that the living cationic polymerization of THF was initiated with the mixture of isopropyl iodide and AgC104. Therefore, Doi et al.104) have conducted the block copolymerization of polypropylene with THF by using an iodine-terminated polypropylene (4) which was synthesized via the reaction of living polypropylene (3) with I2. Iodine-terminated polypropylene (Kln = 16,500, Klw/Sln = 1.15) was... 

Figure 26 shows a typical GPC elution curve of the ethanol insoluble polymers obtained at 0 °C, (b), together with the GPC curve of the original iodine-terminated polypropylene, (a). Curve b clearly shifted toward higher molecular weights relative to curve a, but retained a narrow molecular weight distribution (Mw/Mn = 1.14), indicative of the formation of a propylene-THF diblock copolymer. The 13C NMR spectrum of the block copolymer is shown in Fig. 27. 

Doi et al. 84) have synthesized a new type of diblock copolymer of propylene and styrene by the coupling reaction between the iodine-terminated polypropylene (4) and monofunctional living polystyrene anion (11) in toluene at 50 °C, as represented by Eq. (47). 

Polymerization of propylene with vanadium tris(acetylacetonate)-(C2H5)2Cl at low temperature proceeds in a living manner to give a syndiotactic polymer.153 A V-C bond of the living polypropylene end reacts quantitatively with iodine molecule to yield an iodine-polymer bond. The iodine-terminated polypropylenes of low molecular weight (Mn = 630 3200) were found by H and 13C NMR spectroscopy to have a secondary structure at the chain end.154... 

Now the reaction mechanism of iodine-terminated-copolymer with TAIC in the presence of peroxide was proposed, as shown in Figure 10. An initial radical formed by the decomposition of peroxide attacks the double bond of TAIC to form radical (II)[step(l), step(2)]. The radical (II) subtracts iodine from iodine-terminated-copolymer to form polymer radical [step(3)]. And then the polymer radical attacks the double... 

Fig. 10. Proposed reaction mechanism of iodine-terminated-copolymer with triallyl isocyanurate.

Very recently, Mn2(CO)io was, however, used as a photo-coinitiator for activated alkyl iodides (IDT) [101-103], or RAFT reagents [104] in controlled radical photo(co)polymerizations of VAc, acrylates, styrene, and alkenes, where Mn(CO)5 irreversibly activated iodine terminated chains [101], but the in situ generated Mn(CO)5-I [83] was not involved in the IDT. 

The living cationic polymerizations discussed above are invariably based on the nucleophilic iodide counteranion (activation of the carbon-iodine terminal bond Eq. 3). It is expected, however, that similar living processes are equally possible with other counteranions that can exert, as the iodide anion does, a suitably strong nucleophilic interaction with the growing carbocation. We have in fact found the phosphate anions to meet this requirement (10). Similarly to hydrogen iodide, monoacidic phosphate esters [H0P(0)R 2 R alkyl, alkoxyl, etc.] like diphenyl phosphate ( ) form a stable adduct 5) with a vinyl ether (Eq. 5). Zinc chloride or iodide then activates the phosphate bond in 5 by increasing its polarization (as in 6), and living cationic polymerization proceeds via an intermediate (7) where the carbocationic site is stabilized by a phosphate anion coupled with the zinc halide activator. 

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