Polymerization diene monomers Included

The M[ZnR4] and M[A1R4]2 ate complexes (M = Ca, Sr, Ba) polymerize vinyl and conjugated diene monomers including styrene, methylmethacrylate, acrylonitrile, vinyl-ketones, isoprene and butadiene . The bimetallic complexes produce polymers of differing microstructure to that formed by simple alkaline-earth metal initiators, so that the presence of Zn or A1 influences the stereochemistry of propagation. Thus, polybutadiene obtained in benzene from a Ba-Zn initiator contains more than 90% 1,4-bonds (trans-1,4 75-81 %) ... 

Significant improvement in controlled polymerizations of a variety monomers, including styrene, acrylates, acrylamide, acrylonitrile, 1,3-dienes, and maleic anhydride has been achieved when alkoxyamines have been used as initiators for living, free radical polymerization.(696c, 697) Alkoxyamines can be easily synthesized in situ by the double addition of free radicals, generated by thermal decomposition of an azo-initiator, such as 2,2 -azo-h/.s-/.so-butyronitrile (AIBN), to nitrones (Scheme 2.206). 

Diene polymers refer to polymers synthesized from monomers that contain two carbon-carbon double bonds (i.e., diene monomers). Butadiene and isoprene are typical diene monomers (see Scheme 19.1). Butadiene monomers can link to each other in three ways to produce ds-1,4-polybutadiene, trans-l,4-polybutadi-ene and 1,2-polybutadiene, while isoprene monomers can link to each other in four ways. These dienes are the fundamental monomers which are used to synthesize most synthetic rubbers. Typical diene polymers include polyisoprene, polybutadiene and polychloroprene. Diene-based polymers usually refer to diene polymers as well as to those copolymers of which at least one monomer is a diene. They include various copolymers of diene monomers with other monomers, such as poly(butadiene-styrene) and nitrile butadiene rubbers. Except for natural polyisoprene, which is derived from the sap of the rubber tree, Hevea brasiliensis, all other diene-based polymers are prepared synthetically by polymerization methods. 

Traditional Ziegler-Natta and metallocene initiators polymerize a variety of monomers, including ethylene and a-olefins such as propene, 1-butene, 4-methyl-1-pentene, vinylcyclo-hexane, and styrene. 1,1-Disubstituted alkenes such as isobutylene are polymerized by some metallocene initiators, but the reaction proceeds by a cationic polymerization [Baird, 2000]. Polymerizations of styrene, 1,2-disubstituted alkenes, and alkynes are discussed in this section polymerization of 1,3-dienes is discussed in Sec. 8-10. The polymerization of polar monomers is discussed in Sec. 8-12. 

In this section the occurrence of LCB in several other of the more important polymers during free-radical polymerization will be discussed branching due to irradiation or the use of multifunctional monomers (including dienes) will not be... 

TMPAH was used successfully for the homo-, co-, and block polymerizations of IP. In this case, due to the less reactive diene monomer, no additional free nitroxide was necessary to control the polymerization and both low and high molecular weight polymers (Mn=4500 to Mn=100,000) with narrow molecular weight distributions (Mw/Mn= 1.07-1.3) were synthesized [159]. Copolymers with various styrene and (meth)acrylate derivatives, including acrylic acid and HEMA, were obtained, with the content of isoprene varying from 10% to 90% in the comonomer feed. Block copolymers were also produced, starting from either ptBA or pSt macroinitiators however, the alternate order of blocks (i.e., starting from a pIP macroinitiator) was only achieved with St. Chain extension with tBA resulted in inefficient initiation [159], as had been found for pSt-pnBA block copolymers [71]. 

Cumyl potassium (pTf 43 based on toluene) [2] is a useful initiator for anionic polymerization of a variety of monomers, including styrenes, dienes, methacrylates, and epoxides. This carbanion is readily prepared from cumyl methyl ether as shown in Equation 7.9, and is generally used at low temperatures in polar solvents such as THE [63]. 

As mentioned extensively, PPE is not mainly used as such, but in polymeric blends and copolymers to faciUtate the fabrication. Some of these copolymers act also as impact modifiers for example, block copolymers built from styrene, ethylene, butylene, and propylene. Naturally, the impact can be improved by using high impact poly(styrene) (HIPS) instead of ordinary PS in blends. Other impact modifiers include rubbery materials, such as poly(octenylene), and ethylene propylene diene monomer rubber. 

More recently, ADMET was used to synthesize precision poly(ethylene-co-vinyl amine) with primary amine branches placed on every 9th, 15th, 19th, or 21st carbon along the PE backbone [81]. This was accomplished by synthesizing a symmetrical diene monomer that included a BOC-protected amine, which was thermally deprotected after polymerization. The thermal deprotection yielded a minimally soluble product, as did chemical approaches to deprotection, but the thermal approach resulted in less sample contamination. This insolubility hampered characterization efforts, but the final deprotected polymer was characterized by solid-state NMR, NMR, and TGA, all of which proved... 

A notable exception to the emphasis on free-radical polymerization studies was provided by Karl Ziegler and his co-workers who extended the study of the alkali metal polymerization of dienes to include metals other than sodium and various metal alkyls. Of particular interest were the results obtained with the simplest Group I alkali metal, lithium. It was found that when lithium metal was used as a polymerization initiator 1,4- structures predominated over 1,2-polymers. It was also found that polymerization in hydrocarbon solvents further favoured production 1,4- structures whilst polymerization in polar liquids such as ethers and amines often favoured the formation of 1,2- units. It was also found that reaction of lithium with monomer led to the production of an organo-lithium compound which made feasible homogeneous polymerization—a discovery which eventually led to commercial exploitation. 

Ae metal complexes have been involved in polymerization processes of C=C containing compounds to different extents and in different circumstances. In this chapter, C=C cOTitaining monomers include three main subclasses (a) ethylene and related a-olefins, (b) styrene and conjugated dienes, and (c) what is often referred to as poW olefins, namely acrylates and methacrylates. For these three classes of monomers, Ae compounds have shown valuable, sometimes unique, abilities either as discrete compounds or in binary or even more comphcated tertiary combinations with other main group or transition metal compounds. Another essential distinction to be highlighted is the actual role of the Ae compounds in these processes they may be, as simply anticipated, the real active polymerization species, but they may be also involved in binary or tertiary combinations, as a partner component , undergoing tiansmetallation reactions with another metallic species which is in charge of polymerizatiOTi. 

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