Polymerization living-type

This finding is a significant improvement over aqueous ROMP systems using aqueous ROMP catalysts. The propagating species in these reactions is stable. The synthesis of water-soluble block copolymers can be achieved via sequential monomer addition. The polymerization is not of living type in the absence of acid. In addition to eliminating hydroxide ions, which would cause catalyst decomposition, the catalyst activity is also enhanced by the protonation of the phosphine ligands. Remarkably, the acids do not react with the ruthenium alkylidene bond. 

Narrow distribution in the backbone length as well as in the chemical composition or the branch frequency may be expected from a living-type copolymerization between a macromonomer and a comonomer provided the reactivity ratios are close to unity. This appears to have been accomplished to some extent with anionic copolymerizations with MMA of methacrylate-ended PMMA, 29, and poly(dimethylsiloxane) macromonomers, 30, which were prepared by living GTP and anionic polymerization, respectively [50,51]. Recent application [8] of nitroxide (TEMPO)-mediated living free radical process to copolymerizations of styrene with some macromonomers such as PE-acrylate, la, PEO-methacr-ylate, 27b, polylactide-methacrylate, 28, and poly(e-caprolactone)-methacrylate, 31, may be a promising approach to this end. 

Coordination Polymerization of 1,3-Dienes Single-Site (or Metallocene) Catalysts Living Radical Polymerizations Other Types of Polymerizations, Polymers Ring-Opening Polymerization... 

We possess more information on systems containing polar monomers. Organolithium and organomagnesium compounds initiate the polymerization of a number of monomers with an electron-withdrawing substituent. These polymerizations are rarely of the living type. The initiator usually reacts not only with the double bond of the monomer, but also with the polar substituent (both on the monomer and the polymer) yielding inactive products. 

The deciding factor which aroused increased interest in block copolymer production was the discovery of living anionic polymerization. New types of materials could be prepared by stepwise polymerization of several monomers. 

Most of the known cationic photoinitiators produce acid species in an irreversible reaction, and once formed these species continue to promote the polymerization reaction even after the end of irradiation. This behavior is of living type and is in contrast to the radical photoinitiated... 

Oxazoline polymerization has a living type character and therefore a great variety of block and graft polymers can also be produced. 

In THF the polymerization is second order at +25 °C and first order at -104°C. At —75°C in DMF and -104°C in THF there is a linear relationship between degree of conversion and molecular weight. Thus, it seems that larger activation energies are associated with transfer and termination than with initiation or propagation. At low enough temperatures the polymerization can be described as an ideal living type. 

Over the past few years there has been a tremendous interest in living radical polymerizations. One type of living radical polymerization is stable free radical polymerization, SFRP, where a stable free radical such as TEMPO (2,2,6,6-tetramethylpiperidinoxyl) is used to reversibly cap the growing polymer chain (L2). SFRP has the advantage over conventional radical polymerization in that the polymers prepared are living and can be used for further polymerization to make blocks or other complex architectures. The polymers prepared by the SFRP process have a narrower molecular weight distribution compared to polymers prepared by conventional radical polymerization in the case of block copolymers this may be a desirable attribute. This article focuses on the use of the SFRP process to prepare random copolymers. 

Experimental evidence suggests that these polymerizations involve living type polymers which allow one to control the molecular weight and to form block copolymers. 

Polymerization plays a key role in chemical microencapsulation. The basic mechanism of this method is to put a polymer wall (can be multilayer) through polymerization on a core material, which is in a form of small liquid droplets, solid particles, or even gas bubbles or to embed the core material in a polymer matrix through polymerization. Interfacial polymerization is one of the most important methods that have been extensively developed and industrialized for microencapsulation. According to Thies and Salaun, interfacial polymerization includes live types of processes represented by the methods of emulsion polymerization, suspension polymerization, dispersion polymerization, interfacial polycondensation/polyaddition, and in situ polymerization. This chapter is only focnsed on interfacial polycondensation and polyaddition in a narrow sense of interfacial polymerization. 

The polymerization rate depends upon the concentration of the amine and the monomer. The degree of polymerization is often, but not always, equal to the ratio of the monomer to the amine. ft means that the reaction may be similar to, but not identical to, a living-type polymerization. In addition, the molecular weight distribution curve may be broadened or bimodal. This may be due to some chemical termination reactions. These can be intramolecular reactions of the terminal amine group with some functional group in the side chain and lead to formation of hydantoic acid end groups. It may also be due to physical termination from precipitation of the product. 

Describe living metathesis polymerization. What types of catalysts are useful in such polymeriz ations ... 

The polymerization methods leading to linear diblock, triblock or segmented block copolymers are based on two general reaction schemes. In a first one, a or a, oj active sites are generated on a polymer chain poly A which then initiate the polymerization of a second monomer B. Such a polymerization can be of free radical, anionic or cationic type and preferably of living type which proceed without termination and transfer reactions. The concept of this synthesis is given in Figure 7.2. 

The characteristics of the organolithium-initiated polymerization of the dienes was clearly established by Morton and co-workers. It was demonstrated that the polymerizations are of the living type, which take place without a chain termination reaction in the absence of impurities.The implications of this behaviour in preparing polymers of controlled structure are well recognized today. 

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