Homo-polymerization

Methyl-2-furaldehyde gave a similar overall behaviour, but a penultimate effect was observed in its copolymerization with isopropenylbenzene whereby two molecules of the aldehyde could add together if the penultimate unit in the growing chain was from the olefin. This was borne out by the copolymers composition and spectra. The values of the reactivity ratios showed this interesting behaviour rx = 1.0 0.1, r2 = 0.0 0.1. An apparent paradox occurred the aldehyde, which could not homo-polymerize, had equal probability of homo- and copolymerization and the olefin, which homopolymerized readily, could only alternate. The structure arising from this situation was close to a regular sequence of the type ... 

The optical and electrochemical properties of porphyrins make these chromophores useful building blocks for the synthesis of electro- and photoactive polymers. Two types of linear polymers have been constructed using the self-assembly approach homo-polymeric assemblies and hetero- or shish kebab polymers. 

The Dow corporation has recently developed constrained geometry addition polymerization catalysts (CGCT), typically Me2Si(C5Me4)(NBut)MCl2 (M = Ti, Zr, Hf) (141) activated with MAO. The homo-polymerization of a-olefins by CGCT afford atactic or somewhat syndiotactic (polypropylene rr 69%) polymers. The metal center of the catalyst opens the coordination sphere and enables the co-polymerization of ethylene to take place, not only with common monomers such as propylene, butene, hexene, and octene, but also with sterically hindered a-olefins such as styrene and 4-vinylcyclohexene [202]. 

The resulting complexes can be effectively employed as single component catalysts to homopolymerize ethylene or copolymerize ethylene with acrylates [50, 51] and a variety of other polar monomers including vinyl ethers, [51,52] vinyl fluoride [53], iV-vinyl-2-pyrrolidinone, and AMsopropylacrylamide [54], In fact, the resulting catalysts are so robust that they can be used as single component catalysts in aqueous emulsion homo-polymerization of ethylene and copolymerization of ethylene with norbomenes and acylates [55]. 

The action pattern and the specificity of enzymes acting on homo-polymeric substrates are determined by the nature of the active center.134-137 Hence, it may be assumed that the active centers of enzymes exhibiting the aforementioned action-patterns are different. 

Co-polymerizations and homo-polymerizations of monomers such as dienes or 4-methylene dioxolan, in which two or more types of ion may propagate simultaneously, are further examples of enieidic polymerizations. These dienes, of course, also provide examples of eniedic radical and anionic polymerizations. Indeed the idea of dieidic polymerization has been suggested by several authors in relation to anionic polymerizations it arose from the aggregation in solution of the lithium alkyls [135], and similar phenomena. 

The copolymerization between two different monomers can be described using only four reactions, two homo-polymerizations and two cross-polymerization additions. Through appropriate arrangements, equations that allow copolymer composition to be determined from the monomer feed ratio are developed. 

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

H5C6-CH = CH-F Polymerization Homo polymerization Homopolymerization Polymerization... 

Table 2 summarizes the experimental results [17], which includes two sets of comparative experiments (runs 2-5 and 6-9) and a control homo-polymerization (run 1). 

THF copolymerizes readily with other cyclic ethers such as oxides and oxetanes. The comonomers used include ethylene oxide (67), propylene oxide (99,100), epichlorohydrin (ECH) (101,102), phenyl glycidyl ether (102), 3.3-bis(chloromethyl) oxetane (BCMO) (25, 98, 101, 103) and 3-methyl-3-chloromethyl oxetane (103). Just as in THF homo-polymerization, a large variety of catalysts have veen used. In many cases the kinetics of copolymerization have been studied. Table 22 summarizes the monomer reactivity ratios, rx (THF), and r2 (comonomer) which have... 

It has been found (Table 24) that in hydrocarbon solvents, the diene polymerizes preferentially in diene-styrene systems, initially to the near exclusion of the styrene even though the latter monomer exhibits the faster rate of homo-polymerization. When the diene supply nears depletion, styrene begins to become incorporated into... 

Using living conditions with the state-of-the-art in catalyst technologies, crystal-amorphous polyolefin hybrids can be synthesized by successive polymerization, for instance, homo-polymerization and co-polymerization, of olefin monomers. By this methodology, block copolymers of polymer hybrids can be obtained. 

Addition Homo-Polymerization (Free-Radical Homo-Polymerization)... 

The polymerization described so far is homo-polymerization based on single monomers. Some polymers used in pharmaceutical applications are copolymers. They have properties that each homo-polymer does not exhibit. For example, the copolymer of hydroxyethyl methacrylate and methyl methacrylate is synthesized in order to obtain a polymer exhibiting a hydrophilic/hydrophobic balance. A variety of copolymers (alternating, block, random) can be formed from two different monomers. Special processes produce alternating and block copolymers, while random copolymers are produced by free-radical copolymerization of two monomers. The polymerization steps, such as initiation, propagation, and termination, are the same as in free-radical homo-polymerization. Copolymerization kinetics are depicted as follows ... 

Le rapport de rjjij, est certainement trfes different pour des homo-polymeres de masse moleculaire, M, elevee. En effet, on sait que la viscosite de cisaillement de ces corps varie selon la relation = f[T) M3>4, ou f(T) ne depend que de T (Fox et al., 1956). D autre part, comme la temperature de transition vitreuse des polym res lineaires est pratique-ment independante de M, si la chaine comporte plus d une centaine d uni-tes monom res (Fox et Flory, 1950 Beevers et White, 1960), il... 

Tsonis and Farona found Re(CO)sCl/EtAlCl2 active at 110°C for homo-polymerization of cyclic compounds containing 5-, 6-, 7-, and 8-membered rings to low-molecular-weight totally saturated materials (ring systems preserved). The initial active form of the catalyst is [(CO)4Re=CHEt ], the same as for the metathesis of internal and terminal olefins." ... 

Homopolymers have been briefly discussed above. Polymers of a few components represent a second loosely defined class of thermal polyamino acids. Although individual neutral amino acids do not homo-polymerize when heated (glycine excepted), they copolymerize with certain non-neutral amino acids. Lysine, aspartic acid, or glutamic acid have commonly been used for cocondensation (7). Glutamic acid, which alone forms pyroglutamic acid on heating and does not homopolymerize, is copolymerized with many neutral amino acids 13). Combinations of... 

The intercalation of polymer or prepolymer from the solution is described via minimum free energy principle. The driving force of polymer intercalation is the entropy from the solvent desorption. Several researchers investigated the thermodynamics properties of PCN with homo polymeric systems in a confined geometry. However, Lim et al. investigated ternary systems, and explained that the intercalation distance of poly-(methyl methacrylate) (PMMA)/organic-modified clay (OMMT) nanocomposite is larger than that for the... 

It has been reported previously that bls-trlfluoromethane-sulfonyl methane ("dlsulfone ) and its derivatives are good epoxy homo-polymerization catalysts (11,12). Calorimetric studies have shown that l,l,3,3-tetrakl8(trlfluoro methanesulfonyl) propane ("tetra-sulfone") is probably the only effective catalyst for homopolymerization of an aliphatic epoxide, e.g. butene oxide, in a non-polar solvent at room temperature (Figure 2). The other dlsulfone catalyst along with Bronsted acids are poor catalysts. 

Consider first three "homo-polymeric" enzymes, all shown to involve allosteric effects malate dehydrogenase, 3-phosphoglycerate dehydrogenase, and glutamate dehydrogenase. Malate dehydrogenase (Fig. 9.8), a dimer, has a single interface (29) 3-phospho-... 

IH.10. Charge-Transfer Initiators and Simultaneous Anionic and Cationic Homo-Polymerizations... 

The idea of two simultaneous homo-polymerizations was explored by Szwarc and his co-workers252. Pac and Plesch253 reported initiation of cationic polymerization of vinyl carbazole (VC) by tetranitromethane in nitrobenzene. They postulated the formation of a charge-transfer complex,... 

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