Quasiliving polymerization

Living" carbocationic polymerizations are most difficult to achieve mainly because of chain transfer to monomer and termination processes both of which frequently occur in carbocationic polymerizations. It has recently been demonstrated (JL) that "quasiliving" polymerization of a-methylstyrene (aMeSt) can be achieved by slow and continuous monomer addition and that the number-average molecular weight (Mn) of PaMeSt increases linearly with the weight of added monomer. A theory for quasiliving polymerizations has been developed (2). 

Applying the slow and continuous monomer-addition (quasiliving) technique, we polymerized IBVE and MVE with the -DCC/ AgSbFg initiating system and defined optimum reaction conditions for the quasiliving polymerization of these monomers. Subsequent block polymerization starting poly(IBVE) quasiliving dications led to novel triblock polymers poly(aMeSt-b-IBVE-b-aMeSt) and poly-(MVE-b-IBVE-b-MVE). 

Quasiliving Polymerization of IBVE in CHzClz at -70° and -90°C. IBVE was polymerized by introducing the monomer slowly and continuously into a premixed -DCC/AgSbF6 charge in CH2Cl2 at -70 or -90°C. In all experiments polymer yields at any time... 

These results demonstrate that quasiliving polymerization of IBVE can be achieved by the use of CH2CI2 solvent at -70 or -90°C. This novel quasiliving technique leads to poly(IBVE) s with controlled (and high) molecular weights and narrow MWD. 

These trends indicate increasing interference of chain transfer at higher temperatures, i.e., these conditions are not suitable for quasiliving polymerizations. 

Effect of Solvent Polarity. Quasiliving polymerization of IBVE was also attempted in a nonpolar solvent, n-heptane, ap -50 and -70°C. Figure 5 gives results obtained at -70°C. The Mn versus Wj ve plots obtained at this temperature are strongly curved. Importantly, the N values were less than unity at the beginning of the reactions and they increased beyond unity with increasing WibVE Evidently initiation is slow in nonpolar media due to incomplete ionization of the initiator (i.e., N >1). 

At -50°C Mn s remained unchanged (Mn % 3 x 10, [p-DCC]Q = 0.50 mM) with increasing Wjgyg and Mw/Mn % 2.0. The polymerization is no longer quasiliving but follows a conventional chain-transfer-dominated course. Nonpolar media are evidently unsuitable for quasiliving polymerization of isobutyl vinyl ethers. 

Quasiliving Polymerization of Methyl Vinyl Ether. Similarly to IBVE polymerization, MVE was polymerized with premixed p-DCC/AgSbF initiating systems in CH2CI2 solvent at -70°C by slow and continuous monomer addition. Polymer yields were vL00% at every reaction time. ... 

Optimum Conditions for Quasiliving Polymerization. Table I summarizes H -W relationships obtained under a variety of conditions. nThI corresponding table for MVE is almost identical. The observed relationships are classified into three categories ... 

Linear M versus W plots passing through the origin, indicating quasiliving polymerizations 2) (X) M independent of... 

Inspection of Table I shows that optimum conditions for quasiliving polymerization of IBVE (and MVE) prevail in polar... 

Blocking aMeSt or MVE from Quasiliving Poly(IBVE) Dication. An important application of quasiliving polymerizations may be for the synthesis of block copolymers. Efforts have been made to prepare novel block polymers starting from quasiliving poly(IBVE) dication by the addition of aMeSt and/or MVE as the second monomer. Eq. 3 outlines the principle of the blocking experiments ... 

In the early 1980s, Kennedy and his co-workers reported quasiliving polymerizations, which are phenomenologically akin to living polymerizations [57]. These processes involved slow and continuous monomer addition to a stirred initiator solution kept at a relatively low temperature. The monomers used therein included a-methylstyrene, isobutene, styrene, and alkyl vinyl ethers. In most cases, the number-average molecular weights steadily increased with the weight of the added monomer and the formed polymers had relatively narrow MWDs. 

Irreversible termination is in principle absent in carbocationic polymerization coinitiated by perhalogenated Friedel-Crafts acids MtX . Reversible termination, however, exists in both impurity-induced or purposely-induced processes [43, 46, 47], Indeed, because of the recognition that irreversible termination does not occur in MtX -coinitiated carbocationic polymerizations, we have developed the concept of quasiliving polymerizations the focal point of which is reversible termination [1], The fundamentals of reversible termination and its consequences have been treated recently in great detail [18, 48, 49], and the reader is referred to these sources for further discussion on this subject. 

Alkoxybenzene compounds have been utilized as endquenching reagents in the quasiliving polymerization of IB. A variety of functionalized alkoxybenzene compounds have been utilized to prepare functionalized polymers including alkyl halides, amines, azides, and isocyanates as shown in Scheme 39. 

Quartarstruktur quartile stat Quartil, Viertelswert quartz glass Quarzglas quartz microbalance (QMB) Quarz-Mikrowaage (QMW) quartz thermometer Quarzthermometer quasiliving polymerization quasilebende Polymerisation quench polym abschrecken... 

Zhang, Y.,Tajima, K., Hirota, K., and Hashimoto, K. (2(K)8) Synthesis of all-conjugated diblock copolymers by quasiliving polymerization and observation of their microphase separation. Journal of the American Chemical Society, 130,7812-7813. 

It turned out that in many cases one uses the term of living polymerization for processes that only partially fell within the definition given by Szwarc. Therefore, introduce the concept of the pseudo-living or quasiliving polymerization. These concepts apply when the termination and transfer of chain rate constants are equal to zero and the condition ki>kw is not satisfied, or the propagation reaction is reversible, or a reversible chain transfer to polymer takes place. 

Polymerization by slow and con tinuous addition of monomers to an initiator solution ( quasiliving polymerization) ... 

Kennedy and Kelen proposed definitions of classical living and quasiliving polymerizations The classical living polymerization is a polymerization reaction... 

Quasiliving polymerization can also proceed with vinyl ethers as monomers ... 

Quite recently an interesting mathematical treatment has been reported for (quasiliving) polymerization involving reversible spontaneous chain transfer... 

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