Polymer terminal

This expression is plotted in Fig. 6.7 for several large values of p. Although it shows a number distribution of polymers terminated by combination, the distribution looks quite different from Fig. 5.5, which describes the number distribution for termination by disproportionation. In the latter Nj,/N decreases monotonically with increasing n. With combination, however, the curves go through a maximum which reflects the fact that the combination of two very small or two very large radicals is a less probable event than a more random combination. 

Telechelic Ionomers. Low molecular weight polymers terminated by acid groups have been treated with metal bases to give ionomers in which the cations can be considered as connecting links in the backbones (67—71). The viscoelastic behavior of concentrated solutions has been linked to the neutralizing cation. 

Addition polymerization is employed primarily with substituted or unsuhstituted olefins and conjugated diolefins. Addition polymerization initiators are free radicals, anions, cations, and coordination compounds. In addition polymerization, a chain grows simply hy adding monomer molecules to a propagating chain. The first step is to add a free radical, a cationic or an anionic initiator (I ) to the monomer. For example, in ethylene polymerization (with a special catalyst), the chain grows hy attaching the ethylene units one after another until the polymer terminates. This type of addition produces a linear polymer ... 

The compounds formed continue condensation as long as the species present have different endings. The polymer terminates by having one of the monomers in excess. This produces a polymer with similar endings. For example, a polyester formed with excess diol could be represented ... 

Terminal-functionalized polymers such as macromonomers and telechelics are very important as prepolymer for construction of functional materials. Single-step functionalization of polymer terminal was achieved via lipase catalysis. Alcohols could initiate the ring-opening polymerizahon of lactones by lipase catalyst. The lipase CA-catalyzed polymerizahon of DDL in the presence of 2-hydroxyethyl methacrylate gave the methacryl-type polyester macromonomer, in which 2-hydroxyethyl methacrylate acted as initiator to introduce the methacryloyl group quanhtatively at the polymer terminal ( inihator method ).This methodology was expanded to the synthesis of oo-alkenyl- and alkynyl-type macromonomers by using 5-hexen-l-ol and 5-hexyn-l-ol as initiator, respechvely. 

Structural control of polymer terminal has been extensively studied since terminal-functionalized polymers, typically macromonomers and telechelics, are often used as prepolymers for synthesis of functional polymers. Various methodologies for synthesis of these polymers have been developed however, most of them required elaborate and time-consuming procedures. By selecting... 

End-functional polymers were also synthesized by lipase-catalyzed polymerization of DDL in the presence of vinyl esters [103,104]. The vinyl ester acted as terminator ( terminator method ). In using vinyl methacrylate (12.5 mol % or 15 mol % based on DDL) and lipase PF as terminator and catalyst, respectively, the quantitative introduction of methacryloyl group at the polymer terminal was achieved to give the methacryl-type macromonomer (Fig. 12). By the addition of divinyl sebacate, the telechelic polyester having a carboxylic acid group at both ends was obtained. 

Recently, Mecking et al. reported the synthesis of inverse micelles based on a hy-perbranched polyglycerol polymer. Terminal -OH groups were modified with palmi-toyl chloride and gave a polymeric catalyst soluble in organic solvents with hydrophilic core to immobilize water-soluble guest molecules such as PdCl2 or Pd(OAc)2. 

Telechelic polymers, containing one or more end groups with the capacity to react with other molecules, are useful for synthesizing block and other copolymers [Fontanille, 1989 Hsieh and Quirk, 1996 Nuyken and Pask, 1989 Pantazis et al., 2003 Patil et al., 1998 Quirk et al., 1989, 1996 Rempp et al., 1988]. Living anionic polymers can be terminated with a variety of electrophilic reagents to yield telechelic polymers. For example, reaction with carbon dioxide, ethylene oxide, and allyl bromide yield polymers terminated with carboxyl, hydroxyl, and allyl groups, respectively. Functionalization with hydroxyl or carboxyl groups can also be achieved by reaction with a lactone or anhydride, respectively. Polymers with amine end... 

The IR spectrum of the polymer shows a carbonyl absorption at 1720 cm characteristic of an ester group, indicating the incorporation of the axial acetoxy group of 18 into the polymer terminal. Thus, the polymerization is considered to start by insertion of the monomer into the central manganese atom-axial acetoxy group bond, and proceed via a manganese-alkoxide as the growing species. 

This is seen in Fig. 3. These results were accounted for by Yamagishi and myself(25) in the terms of the previous treatment. Denoting again by u and v the concentration of the monomeric living polymers terminated by styryl or para-methyl styryl unit, respectively, and by C the concentration of all the polymers, we find 0... 

Special interest has been devoted to the reaction of oxygen on carbanionic sites.- It has been established that triplet oxygen acts as an electron acceptor, and that the reaction may yield either terminal hydroperoxy or alcohol functions. Depending on the reaction conditions, the latter group which originates from a disproportionation process between a hydro-peroxidate and a carbanlon may be observed. By choosing proper conditions one can get polymers terminated quantitatively with hydroperoxide groups. The latter can be used in a later step as a radical initiator to prepare new block copolymers. 

Figure 6. Molecular weight distribution of polymer terminally coupled with polyhalide coupling agents (2%).

Allen et al. ( 2) measured a first-order decrease of the maximum of the UV spectrum of -Na in toluene/THF mixtures at +18°C. The same was found by L6hr (63) for PMMA-Cs in THF. The first-order decrease can be explained by intramolecular polymer termination. However, the rate constants measured are too low to explain the termination during polymerization. 

For over 300 years, the quinoline family of drugs, and chloroquine in particular, has been used as the primary treatment for malaria. Recent studies have demonstrated that this drug inhibits the aggregation of free heme into hemozoin, allowing levels of monomeric heme to rise until cell lysis occurs. Although the determined structure of hemozoin makes the polymer termination scheme proposed by Sullivan et al. unlikely, hemozoin drug heme interactions appear critical in the inhibition mechanism. Thus, researchers have identified the characteristics of... 

To examine the question whether such a stochastic process can be imbedded in a measure preserving flow we proceed as follows Let us number the possible states of the polymer according to the triad in which the polymer terminates ... 

Under the conditions used for the syntheses of these compounds, as well as the expected hydroxy-terminated polymers, which predominate due to the excess of the diol reactant, polymers terminated with acid or acid amide groups are also formed from the nitrile groups of AIBN. 

From the hydroxylated polymer (PV—OH) one obtains at first a polymer terminated by an oxychloroformyl group (PV—O—CO—Cl) by addition of phosgene, and, at last, a polymer terminated by a primary amine function (PV—NH2) by addition of a primary diamine21,22. ... 

Chain transfer is the most common chain terminating reaction in cationic polymerization and can include transfer to monomer, solvent, and polymer. Termination by combination with the counterion can also occur in some systems. In some cases, cationic polymerization may be used to prepare stereoregular polymers. Although the exact mechanism is unclear, it is known that stereoregularity varies with initiator and solvent.18 Lower temperatures also tend to favor more stereoregular polymers. 

By means of the latter relations, kinetic schemes can be completely solved, mean degrees of polymerization can be derived, as well as the polydispersity coefficients of polymers terminated by disproportionation (= Sf +1 V p) and of macroradicals or inactive macroradicals after transfer (= S + 1 /S l). For the number, weight, and z average, k = 0, 1, and 2, respectively. 

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