Additives monomers

Homogeneous GopolymeriZation. Nearly all acryhc fibers are made from acrylonitrile copolymers containing one or more additional monomers that modify the properties of the fiber. Thus copolymerization kinetics is a key technical area in the acryhc fiber industry. When carried out in a homogeneous solution, the copolymerization of acrylonitrile foUows the normal kinetic rate laws of copolymerization. Comprehensive treatments of this general subject have been pubhshed (35—39). The more specific subject of acrylonitrile copolymerization has been reviewed (40). The general subject of the reactivity of polymer radicals has been treated in depth (41). 

Emulsion Polymerization. Emulsion polymerization takes place in a soap micelle where a small amount of monomer dissolves in the micelle. The initiator is water-soluble. Polymerization takes place when the radical enters the monomer-swollen micelle (91,92). Additional monomer is supphed by diffusion through the water phase. Termination takes place in the growing micelle by the usual radical-radical interactions. A theory for tme emulsion polymerization postulates that the rate is proportional to the number of particles [N. N depends on the 0.6 power of the soap concentration [S] and the 0.4 power of initiator concentration [i] the average number of radicals per particle is 0.5 (93). 

Since all of the chains are intiated at about the same time and because growth continues until all of the styrene has been consumed, the chains will have similar lengths, i.e. there will be a narrow molecular weight distribution. In addition the chains will still have reactive ends. If, subsequently, additional monomer is fed to the reactor the chain growth will be renewed. If the additional monomer is of a different species to the styrene, e.g. butadiene, a binary diblock copolymer will be formed. 

While phenol is the most common monomer for novolac manufacture, it is far more common to see incorporation of other phenolic materials with novolacs than with resoles. Cresols, xylenols, resorcinol, catechols, bisphenols, and a variety of phenols with longer alkyl side chains are often used. While most resoles are made with a single phenolic monomer, two or more phenolic materials are often seen in novolac formulae. These additional monomers may be needed to impart special flow characteristics under heat, change a glass transition temperature, modify cure speed, or to adjust solubility in the application process among others. 

Reaction with additional monomers leads to the formation of larger rings (3, 4) and eventually to high molecular weight polymers, namely poly-... 

Kolbe radicals can be added to olefins that are present in the electrolyte. The primary adduct, a new radical, can further react by coupling with the Kolbe radical to an additive monomer I (Eq. 9, path a), it can dimerize to an additive dimer II (path b), it can be further oxidized to a cation, that reacts with a nucleophile to III (path c), or it can disproportionate (path d). 

To some degree the ratio of additive monomer to additive dimer can be infiuenced by the current density. High current densities favor the formation of additive monomers, low ones these of additive dimers (Table 8, Nos. 4, 5). This result can be rationalized according to Eq. 9 At high current densities, which corresponds to a high radical concentration in front of the electrode, the olefin can trap only part of the Kolbe radicals formed. This leads to a preferred coupling to the Kolbe dimer and a combination of the Kolbe radical with the primary adduct to the additive monomer. At low current densities the majority of the Kolbe radicals are scavenged by the olefin, which leads to a preferential formation of the additive dimer. 

No. Carboxylic acid Olefin Additive monomer (%-yield) Additive dimer (%-yield) Ref. 

However, the products can then react with additional monomers and with each other, so that polymers are generally produced, and the cyclic dienes are obtained only in low yield. The reaction between a cyclic and a linear alkene can give an ring-opened diene... 

Vinyl copolymers contain mers from two or more vinyl monomers. Most common are random copolymers that are formed when the monomers polymerize simultaneously. They can be made by most polymerization mechanisms. Block copolymers are formed by reacting one monomer to completion and then replacing it with a different monomer that continues to add to the same polymer chain. The polymerization of a diblock copolymer stops at this point. Triblock and multiblock polymers continue the polymerization with additional monomer depletion and replenishment steps. The polymer chain must retain its ability to grow throughout the process. This is possible for a few polymerization mechanisms that give living polymers. 

Step growth polymerization can also yield highly crosslinked polymer systems via a prepolymer process. In this process, we create a prepolymer through a step growth reaction mechanism on two of the sites of a trifunctional monomer. The third site, which is chemically different, can then react with another monomer that is added to the liquid prepolymer to create the crosslinked species. We often use heat to initiate the second reaction. We can use this method to directly create finished items by injecting a mixture of the liquid prepolymer and additional monomer into a mold where they polymerize to create the desired, final shape. Cultured marble countertops and some automotive body panels are created in this manner. 

Propagation steps lead to the incorporation of additional monomers to the polymer at the growing end of the chain. We make the assumption that the rate of addition is constant, regardless of the chain length, because the reaction itself is the same. This is the same assumption we made for the overall polymerization process in step growth polymerization. The reaction can be represented as shown in Eq. 4.10. 

Photostabilizers, regardless of their mechanism of action, have been added as low molecular weight materials at some point in processing. Subsequently, these stabilizers are often lost in further processing due to their volatility or else later migrate to the surface and evaporate. One method which avoids this modifies the polymer to include the quencher as an additional monomer in the polymerization. This paper will describe some recent efforts in our laboratory to pursue this latter approach in the stabilization of poly(ethylene terephthalate). 

Random copolymerization of one or more additional monomers into the backbone of PET is a traditional approach to reducing crystallinity slightly (to increase dye uptake in textile fibers) or even to render the copolymer completely amorphous under normal processing and use conditions (to compete with polycarbonate, cellulose propionate and acrylics in clear, injection molded or extruded objects). 

If anions R are oxidized in the presence of olefins, additive dimers (24) and substituted monomers (26) are obtained (Scheme 5, Table 8, and Ref. [94]). The products can be rationalized by the following pathway the radical R obtained by a le-oxidation from the anion R adds to the alkene to give the primary adduct (25), which dimerizes to afford the additive dimer (24) with regiospeciflc head-to-head connection of the two olefins, or couples with R to form the additive monomer (26). If the substituent Y in the olefin can stabilize a carbenium ion, (25) is oxidized to the cation (27), which reacts intra- or inter-molecularly with nucleophiles to give (28) or (29). 

Upon electrolysis of trifluoroacetate in MeCN-H20-(Pt) in an undivided cell in the presence of an electron, deficient olefins additive dimers and additive monomers are obtained. The selectivity can be controlled by current density, temperature, and the substitution pattern of the olefin [117]. 

Fig. 1.9 Terrestrial humic acid model (a) tetramer open form and (b) trimer trapping an additional monomer (Schulten, 2001)...

Applying the heUx coil theory to computational studies of the mPE backbone suggests that above a critical chain length of seven or eight repeat units the backbone can adopt a helical structure. The attachment of additional monomer units would further stabihze the helical structure and increase the cooperativity of the folding reaction [23]. 

In batch reactions, where the yield is high and no additional monomer is added, at the end of the reaction the average content of each monomer imit in the total copolymer formed will necessarily be directly related to the initial ratio of the two monomers. Thus, the copolymer content will vary depending on when the particular chains are formed but the final overall product will have an average of units in it reflective of the initial monomer concentrations. 

There is usually little or no difference in reactivity between free ions and ion pairs, similar to the situation in the polymerization of carbon-carbon double bond monomers [Penczek, 2000]. Covalent species are present in many systems as detected by NMR and other methods, but whether they are reactive or dormant is not always clear. When propagation by covalent species occurs, it is not covalent-to-covalent propagation in which monomer is inserted into a covalent bond to produce a new covalent propagating species containing an additional monomer unit [Penczek et al., 1995]. Covalent propagation is a two-step process. Monomer adds to the covalent species to form an ionic species (Eq. 7-22a), which collapses to (is in... 

Katz described the homogeneous nucleation of a supersaturated vapour using J(i), the net rate at which clusters of size i grow to size i + 1 [63]. In this kinetic equation, J(i) is the difference between the rate at which clusters of size i add an additional monomer, and the rate at which clusters of size i + 1... 

The living anionic ends can be functionalized by adding such agents as ethylene oxide, carbon dioxide, and methacryloyl chloride [33]. The resulting new polymer is capable of being copolymerized with additional monomers. This process can lead to the formation of various graft copolymers [29-32]. 

If this composition, M0, is allowed to polymerize to a low conversion as a seed particle, a polymer of composition, Pt, is formed. If an additional monomer is now added gradually at the same rate as the polymer is formed, a monomer composition, Mo, is maintained and only a polymer of composition, Pt, is formed. 

The indicated procedure for the production of a copolymer of predetermined final composition is to initiate a small amount of seed composition, M0, followed by the gradual addition of the monomers of the final composition, Pt. If the total charge of the addition monomer, P greatly exceeds the composition of M0 and the polymerization is stopped before all of the available monomer has been used up, the final product will consist substantially of composition Pt. 

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