Pseudo-living polymerizations

The peroxide 179 dissociates in the presence of a monomer giving rise to alkoxyl (CO-) and borinate (BO-) radicals, but the latter are believed to be too stable to initiate polymerization. It should be mentioned that the molecular weight continuously increases throughout the process implying the pseudo-living mechanism for chain growth. After the completion of the process borane residue is completely oxidized into diol <2004MM6260>. Thus, the 8-boraindane molecule not only initiates the polymerization, but also is a precursor to two functionalities in the polymer chain. 

An essential feature of a strictly living polymerization is the absence of transfer reactions [652]. This requirement was found to be valid for the polymerization of IP catalyzed by NdCl3 TBP/TIBA in hexane. The lack of chain termination reactions, the second requirement for a living polymerization [652], was confirmed by the application of a mathematical model to the experimental data [279]. Bruzzone et al. realized that transfer reactions occur in the polymerization of BD. In spite of this observation the pseudo-living character of the polymerization was assigned to the superposition of chain growth and chain transfer both of which exhibit a different dependence on monomer conversion [87]. 

Modern polymerization techniques, such as sequential iodine transfer polymerization of fluoroalkenes [11,12], lead to novel thermoplastic elastomers (TPEs). These triblock copolymers can be produced in a process, which can be emulsion, suspension, microemulsion, or solution polymerization [13], Using pseudo-living technology or branching and pseudo-living technology, A-B-A phase separated copolymers with soft (amorphous) and hard (crystalline) domains can be produced. The hard domains can be composed from the following ... 

Block copolymers have also been produced by the addition of vinyl monomers to occluded or long lived macroradicals. These "pseudo" living macroradicals are produced when vinyl monomers are polymerized in poor solvents (16-18) or in viscous medium (19). 

Sanda, F., Fueki, T., Endo, T., 1999. Cationic ring-opening polymerization of an exomethylene group carrying cyclic carbonate. Pseudo-living polymerization of 5-methylene-l,3-dioxan-2-one by the assistance of the exomethylene group. Macromolecules 32, 4220—4224. 

On the other hand, a living (33) or pseudo living (25) nature of Ln-catalyzed polymerization was proposed to account for the proportional increase of molecular weight with conversion and proved by the formation of block copolymers when the reacting butadiene was substituted with isoprene. Moreover, a Nd-polybutadiene quenched with CO was found to contain functional end groups, even if their amount was not measured (31). The presence of Ln-CH -CH -Ln species, in analogy with Li chemistry, was also indicated in the reaction of 4f metals (Y, Sm) with ethylene (3). 

C-H Bond activation, with lanthanides Ethylene polymerization, with lanthanides Zeigler-Natta catalyst, lanthanide Diene polymerization, with lanthanides Olefin polymerization, with lanthanides Butadiene polymerization, with lanthanides Isoprene polymerization, with lanthanides Anionic propagation, at lanthanides Living polymers, at lanthanides Pseudo-living polymers, at lanthanides Reaction orders, diene polymerization Active sites, diene polymerization... 

Fischer, A., Brembilla, A., and Lochon, P. (1999). Nitroxide-mediated radical polymerization of 4-vinylpyridine study of the pseudo-living character of the reaction and influence of temperature and nitroxide concentration. Macromolecules, 52(19) 6069 072. 

This concept was further extended to totally eliminate the use of iodonium salts as the component of the photoinitiating system [KAH 09]. The cationic polymerization of vinyl ethers was initiated upon irradiation at A = 350 nm with vinyl halides in the presence of zinc iodide. A mechanism involving the formation of an adduct between the monomer and the products yielded from the photoinduced homolysis of the vinyl halide followed by electron transfer is proposed. In the subsequent step, the terminal carbon-halide bond in this adduct is activated by the coordinating effect of zinc iodide. This polymerization exhibited some characteristics of pseudo-living cationic polymerization. 

An inverse manner of copolymerization was proposed by Watanabe et First, they polymerized TMC using 4-(chlor-omethyl)benzyl alcohol (CBA) as an initiator and DBU as an organocatalyst. The benzyl chloride group was involved in the incorporation of dithiocarbamate for pseudo-living radical polymerization of vinyl monomers. The authors applied N-isopropylacrylamide, acrylamide glycolic acid, and 2-hydroxyethyl methacrylate as vinyl monomers for the second step of copolymerization (Scheme 93). The resulting block... 

Scheme 93 Preparation of polycarbonates with dithiocarbamate groups for pseudo-living radical polymerization of vinyl monomers.

With VLO and CLO, the polymerization has been shown to proceed via a pseudo-living character (proved by the linear dependence of the degree of polymerization on the degree of conversion) and has been explained by the tmusual balance between growth center formation, chain propagation, and side reactions. It has been calculated that less than 15% of the originally introduced lactone was responsible for the growth center formation. 

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. 

Many of the aforementioned characteristics of CRP are in common with those of previously developed (pseudo)living ionic polymerization techniques. However, it is the relative ease with which CRP can be employed to achieve these characteristics that has led to the continued success and growth of the field. Indeed, because most of the methods described in the chapters that follow can be conducted under relatively non-stringent conditions in a variety of solvents and at a wide range of temperatures, the barrier to entry to the field is minimal. Precision polymer synthesis is now possible in laboratories without access to expensive experimental equipment or extensive expertise. 

Both, E-caprolactone (CLO) and 8-valerolactone (VLO) behave similarly at 150°C (0-5 mol%), the polymerization has a pseudo-living character and shows the zero-order kinetics that is explained by an equilibrium between the formation and consumption of the growth centers, and by side reactions [38]. The activation energy of the process is similar to that of classical activated polymerizations, and ranges at about 80 kJ moT . 

---