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Polymerization chain stoppers

Chain stoppers are unifunctional molecules of the form AX or BX, where the X moiety is nonreactive. They are used to stop the polymerization at a desired point or to stabilize the polymer chains by endcapping. [Pg.467]

Another method of achieving the desired molecular weight is by addition of a small amount of a monofunctional monomer, a monomer with only one functional group. Acetic acid or lauric acid, for example, are often used to achieve molecular weight stabilization of polyamides. The monofunctional monomer, often referred to as a chain stopper, controls and limits the polymerization of bifunctional monomers because the growing polymer yields chain ends devoid of functional groups and therefore incapable of further reaction. Thus, the use of benzoic acid in the polyamide synthesis yields a polyamide (XI) with phenyl end groups that are unreactive toward polymerization. [Pg.75]

Scheme 17 ATMET polymerization of high-oleic sunflower oil in the presence of methyl acrylate as chain stopper [115]... Scheme 17 ATMET polymerization of high-oleic sunflower oil in the presence of methyl acrylate as chain stopper [115]...
ADMET is a step growth polymerization in which all double bonds present can react in secondary metathesis events. However, olefin metathesis can be performed in a very selective manner by correct choice of the olefinic partner, and thus, the ADMET of a,co-dienes containing two different olefins (one of which has low homodimerization tendency) can lead to a head-to-tail ADMET polymerization. In this regard, terminal double bonds have been classified as Type I olefins (fast homodimerization) and acrylates as Type II (unlikely homodimerization), and it has been shown that CM reactions between Types I and II olefins take place with high CM selectivity [142], This has been applied in the ADMET of a monomer derived from 10-undecenol containing an acrylate and a terminal double bond (undec-10-en-l-yl acrylate) [143]. Thus, the ADMET of undec-10-en-l-yl acrylate in the presence of 0.5 mol% of C5 at 40°C provided a polymer with 97% of CM selectivity. The high selectivity of this reaction was used for the synthesis of block copolymers and star-shaped polymers using mono- and multifunctional acrylates as selective chain stoppers. [Pg.32]

Kilkson (35) solved this case using Z-transforms and obtained the moments of the distribution for a number of cases, including the use of chain stoppers. Such chain stoppers, monofunctional compounds which prevent further polymerization, limit the molecular weight and the extreme spreading of the MWD that otherwise arises, making it approach the Flory distribution (DN = 2) at high conversions. [Pg.35]

There are several ways in which block copolymers can be made. The three main methods are (1) sequential addition of monomers, (2) the preparation of a functionalized polymer followed by the use of the functionalized polymer as a macroinitiator or chain-stopper for initiation or termination of polymerization of the second monomer, and (3) use of a multiple-headed initiator. The purity of the block copolymers produced in these processes is dependent upon the livingness (lack of side reactions that lead to termination) of the chemistry used to make them. If the integrity of the chain-ends is maintained throughout the polymerization because all possible termination mechanisms are absent or eliminated, then pure block copolymers can be produced. If, however, impurities get into the process or if there are side reactions that lead to chain termination, the resulting block copolymers are contaminated with some homopolymer. Depending upon the application, some contamination of homopolymer in the block copolymer may be acceptable. [Pg.150]

ALKOXYAMINES AS CHAIN-STOPPERS IN STEP-GROWTH POLYMERIZATION... [Pg.155]

The molecular weights of polymers made using step-growth polymerization are typically controlled by the addition of a chain-stopper to the process. The chain-stopper to monomer ratio determines the final molecular weight of the polymer. If functionalized chain-stoppers are used, functionalized polymers are produced. If macro chain-stoppers are used, triblock copolymers are formed during the step-growth polymerization. [Pg.155]

Thus, practically, a concentrated solution of purified D4 in CH2C12 solvent is polymerized by CF3S03H. Traces of water should carefully be removed. The ratio [D4.]o/[CF3S03H]o yields the required polymerization degree. The polymer is precipitated in CH3OH and the solvent is removed from the oily or solid polymer under vacuum. Monofunctional chain-stoppers (like hexamethyldisoloxane) can also be used to control the polymer Mn. [Pg.217]

A series of well characterized a,w-hydrogen difunctional polydimethylsiloxane oligomers were prepared as shown in equation 6 by the cationic ring opening polymerization of 2,2,4,4,6,6,8,8-octamethylcyclotetrasiloxane (D4) in the presence of tetramethyldisiloxane as a chain stopper (10). [Pg.403]

Fokou, P.A. and Meier, M.A.R. (2008) AcycUc triene metathesis polymerization with chain-stoppers molecular weight control in the synthesis of branched polymers. Macromolecular Rapid Communications, 29(19), 1620-1625. [Pg.134]

Post-polymerization functionalization has also been applied to the synthesis of terpyridine-modified polymers [ 126]. In a recent approach, Schubert and colleagues employed this method to prepare poly(pentafluorostyrene) with terpyridines in the side chains [127]. First, poly(pentafluorostyrene) with a narrow polydispersity index of just 1.08 was synthesized by nitroxide-mediated polymerization. In a second step, this polymer was converted with amine-functionalized terpyridine under microwave heating, selectively substituting the para-fluorines. Addition of iron(II) sulfate to a solution of the terpyridine-functionalized polymer in a mixture of chloroform and methanol leads to gelation at a polymer concentration of 33 g In another work, Schubert and coworkers prepared metal-cross-Iinked polymer networks from linear and tri-arm PEG precursors, both functionalized with terpyridine at their OH-termini [128]. Quantitative functionalization of these precursors was achieved by conversion of the hydroxy-functionalized PEG derivatives with 4-chloro-2,2 6, 2"-terpyridine under basic conditions. However, quantitative cross-linking with iron(II) chloride was not observed in methanol solutions, neither at room temperature nor at elevated temperature, but only a small quantity of cross-linked material precipitated from the solution. This observation was attributed to a strong tendency of the tri-arm PEG to form intramolecular complexes, acting as a chain stopper rather than as a cross-linker. [Pg.14]

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... [Pg.53]

Uses Modifier for alkyd and epoxy resins alkyd resin chain stopper stabilizer for PVC polymerization regulator for polyesters additive in cutting oils corrosion inhibitor Manuf./Dlstrib. Alfa Aesar http //www.alfa.com] Howard Hall NOF http //www.nof.co.jp... [Pg.606]

Alkane sulfonates are applied in a widespread manner in emulsion polymerization. They are used as processing aids, in particular in the emulsion polymerization of vinyl chloride, vinyl acetate, styrene and acrylonitrile. Because they possess no double bonds, alkane sulfonates do not act as radical chain stoppers. Well-known lattices derived from emulsion polymerization are poly(vinyl chloride), ethylene-vinylacetate copolymers, polyacrylates, and butadiene and chloroprene rubbers. Alkane sulfonates also offer good stabilizing effects in lattices against coagulation by fillers. [Pg.285]


See other pages where Polymerization chain stoppers is mentioned: [Pg.283]    [Pg.175]    [Pg.504]    [Pg.322]    [Pg.61]    [Pg.3]    [Pg.562]    [Pg.79]    [Pg.97]    [Pg.283]    [Pg.1336]    [Pg.206]    [Pg.504]    [Pg.27]    [Pg.28]    [Pg.29]    [Pg.680]    [Pg.142]    [Pg.66]    [Pg.247]    [Pg.316]    [Pg.262]    [Pg.901]    [Pg.509]    [Pg.1357]    [Pg.1358]    [Pg.4951]    [Pg.288]   
See also in sourсe #XX -- [ Pg.55 ]




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Stoppering

Stoppers

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