Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Poly chain transfer constant

Table 10. Chain-Transfer Constants to Common Solvents for Poly(ethyl acrylate) ... Table 10. Chain-Transfer Constants to Common Solvents for Poly(ethyl acrylate) ...
The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... [Pg.167]

Chain transfer to solvent is an important factor in controlling the molecular weight of polymers prepared by this method. The chain-transfer constants for poly(methyl methacrylate) in various common solvents (C) and for various chain-transfer agents are Hsted in Table 10. [Pg.266]

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). [Pg.465]

Liquid trichloroethylene has been polymerized by irradiation with Co y-rays or 20-keV x-rays (9). Trichloroethylene has a chain-transfer constant of <1 when copolymerized with vinyl chloride (10) and is used extensively to control the molecular weight of poly(vinyl chloride) polymer. [Pg.23]

Nair et al. studied the kinetics of the polymerization of MMA at 60-95 °C using N,1SP-diethyl-NjW-di(hydroxyethyl)thiuram disulfide (30a) as the thermal in-iferter [142]. The dependence of the iniferter concentration on the polymerization rate was examined. The chain transfer constant of the propagating radical of MMA to 30a was determined to be 0.23-0.46 at 60-95 °C, resulting in the activation energy of 37.6 kj/mol for the chain transfer. Other derivatives 30b-30d were also prepared and used to derive telechelic polymers with the terminal phosphorus, amino, and other functional aromatic groups [143-145]. Thermal polymerization was also investigated with the end-functional poly(St) and poly(MMA) which were prepared using the iniferter 13 [146]. [Pg.92]

Problem 6.22 Vinyl acetate has a relatively high monomer chain transfer constant (2x10 at 60°C). What is the upper limit of molecular weight of poly(vinyl acetate) made by radical polymerization at 60°C ... [Pg.497]

Allyl alcohol, acting as a transfer agent, allows the terminal hydroxyl function to be obtained. The chain transfer constant of allyl alcohol was calculated to be about 2 x 10-2 towards poly(styryl radical). The authors used different monomers (Table 11) and always got functionalities close to 2, according to gel permeation chromatography (GPC) PS standards. Results in terms of conversion were excellent (above 70%). Oligomers were obtained with PDI around 1.8. [Pg.57]

The kinetics of chain transfer to ammonia has been investigated for potassium amide-initiated polymerization of styrene in liquid ammonia at —33.5 °C. The calculated chain transfer constant ( / ) was 2.34 x 10 " [109]. The chain transfer reaction of poly(styryl)lithium with toluene at 60 °C was investigated during the polymerization of styrene using " C-labeled toluene. The calculated chain transfer constant was 5 x 10 [41]. A much larger chain... [Pg.139]

In a study of chain-transfer constants of the monomeric vinyl acetate it was found that the formation of nonhydrolyzable branches is virtually negligible while hydrolyzable branches are formed at position 1 of Structure 1 by a terminal double-bond reaction rather than by a polymer-transfer reaction. The long nonhydrolyzable branches in poly(vinyl alcohol) are, presumably formed almost exclusively by a polymer transfer mechanism [35]. [Pg.219]

Of the common solvents, tert-butyl alcohol because of its very low chain-transfer constant, may be used to produce polymers of relatively high molecular weight. If we concede that single-point measurements of specific viscosity and inherent viscosity may be considered indications of the general trend of molecular weights, then the effect of various solvents on the molecular weights of the poly(vinyl acetate) produced may be seen in Table XV. [Pg.234]

As model compounds, we used isopropyl p-nitrobenzoate for poly(vinyl p-nitrobenzoate), p-nitrophenyl iaobutyrate for poly(p-nitrophenyl acrylate), p-nitrocumene for poly(p-nitrostyrene), and p-nitrophenyl isopropyl ether for poly(p-nitrophenyl vinyl ether). The structure and Hammett s a constants of these model compounds and the chain transfer constants of polystyrene radicals to these compounds are given in Table 5 (3). [Pg.48]

The chain transfer constant of polystyrene radicals to ethylene-vinyl p-nitrobenzoate copolymer was compared with those to poly(vinyl p-nitrobenzoate) and their model compound, isopropyl p-nitrobenzoate. As expected, the value of chain transfer constant to the copolymer is larger than that to poly(vinyl p-nitrobenzoate) and smaller than that to the model compound isopropyl p-nitrobenzoate obtained according to the method of Mayo et al. (7) (Table 8). [Pg.54]

Table 8. Chain Transfer Constants of Polystyrene Radicals to Poly(vinyl p-Nitrobenzoate), Ethylene-Vinyl p-Nitrobenzoate Copolymer and Isopropyl p-Nitrobenzoate... Table 8. Chain Transfer Constants of Polystyrene Radicals to Poly(vinyl p-Nitrobenzoate), Ethylene-Vinyl p-Nitrobenzoate Copolymer and Isopropyl p-Nitrobenzoate...
In this paper we will discuss evidence for the existence of CTC s of styrene and acrylonitrile and the resultant differences in the copolymer produced from them. We will also report the preparation of copolymers with block copolymer characteristics from poly(styrene-co-acrylonitrile) macroradicals prepared in tert-butyl alcohol. This solvent is a poor solvent for the macroradical and exhibits a very low chain transfer constant (28). The copolymers reported in this paper were prepared in the absence and presence of zinc chloride (ZnCU), and the effect of ZnClz on the reactivity of the macroradical will be discussed. [Pg.107]

The polymerization of vinyl acetate can be carried out in a wide variety of solvents in which both the monomer and polymer are soluble. Azo, peroxide, and hydroperoxide initiators as well as many other organic-soluble initiators can be used. Solvents with low chain-transfer constants, such as benzene, toluene, acetic acid, acetic anhydride, acetone, and cyclohexanone, are required to obtain reasonably high molecular weights. Solution techniques are especially convenient for the laboratory preparation of poly(vinyl esters) and are used in certain commercial applications in which the polymers are sold directly as solutions. [Pg.187]

VFc rmdergoes oxidation with peroxide initiators for which azoinitiators have been used almost exclusively. Unlike most vinyl monomers the molecular weight of poly(vinylferrocene) (PVFc) does not increase with the decrease of the initiator concentration. This is the consequence of an anomalously high chain-transfer constant [11]. [Pg.306]


See other pages where Poly chain transfer constant is mentioned: [Pg.316]    [Pg.167]    [Pg.87]    [Pg.316]    [Pg.214]    [Pg.167]    [Pg.316]    [Pg.499]    [Pg.50]    [Pg.167]    [Pg.499]    [Pg.218]    [Pg.7]    [Pg.133]    [Pg.48]    [Pg.97]    [Pg.158]    [Pg.559]    [Pg.8867]    [Pg.124]    [Pg.244]    [Pg.168]    [Pg.480]    [Pg.23]    [Pg.325]   


SEARCH



Chain constant

Chain transfer constants

Poly chain

© 2024 chempedia.info