Chain-growth copolymerization

In the copolymerization chain-growth reaction, we shall concentrate only on the propagation step in which a monomer adds to an active site at the end of a macromolecular species and the active site is transferred to the new terminal unit created by this addition. 

Chain-Growth Copolymerization Chain growth copolymerization can be described by Equation 16.9. Here we have ignored chain initiation and termination, since they... 

Chain-growth copolymerization. This topic is considered in Chap. 7. 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Table I summarizes the conditions used for network synthesis. The amount of TMSEMA was determined by the amount of HEMA required for a desired composition. The AIBN concentrations were kept low to insure adequate chain growth during the copolymerization (that is network formation). The obtained networks were transparent, homogeneous, tough, flexible materials demonstrating the utility of the approach. Desilylation of the networks was carried out by the use of...

The insertion of unsaturated molecules into metal-carbon bonds is a critically important step in many transition-metal catalyzed organic transformations. The difference in insertion propensity of carbon-carbon and carbon-nitrogen multiple bonds can be attributed to the coordination characteristics of the respective molecules. The difficulty in achieving a to it isomerization may be the reason for the paucity of imine insertions. The synthesis of amides by the insertion of imines into palladium(II)-acyl bonds is the first direct observation of the insertion of imines into bonds between transition metals and carbon (see Scheme 7). The alternating copolymerization of imines with carbon monoxide (in which the insertion of the imine into palladium-acyl bonds would be the key step in the chain growth sequence), if successful, should constitute a new procedure for the synthesis of polypeptides (see Scheme 7).348... 

We can create crosslinks during chain growth polymerization by copolymerizing dienes with vinyl monomers. When the two vinyl functions of the diene are incorporated into separate chains, a crosslink is formed. This process is shown in Fig. 2.18. When we use a low concentration of dienes, we produce a long chain branched polymer, while high concentrations of dienes create a highly crosslinked polymer network... 

The most industrially significant polymerizations involving the cationic chain growth mechanism are the various polymerizations and copolymerizations of isobutylene. In fact, about 500 million pounds of butyl rubber, a copolymer of isobutylene with small amounts of isoprene, are produced annually in the United States via cationic polymerization [126]. The necessity of using toxic chlorinated hydrocarbon solvents such as dichloromethane or methyl chloride as well as the need to conduct these polymerizations at very low temperatures constitute two major drawbacks to the current industrial method for polymerizing isobutylene which may be solved through the use of C02 as the continuous phase. 

Block copolymer synthesis from living polymerization is typically carried out in batch or semi-batch processes. In the simplest case, one monomer is added, and polymerization is carried out to complete conversion, then the process is repeated with a second monomer. In batch copolymerizations, simultaneous polymerization of two or more monomers is often complicated by the different reactivities of the two monomers. This preferential monomer consumption can create a composition drift during chain growth and therefore a tapered copolymer composition. 

Nearly all synthetic polymers are synthesized by the polymerization or copolymerization of different "monomers." The chain growth process may involve the addition chain reactions of unsaturated small molecules, condensation reactions, or ringopening chain-coupling processes. In conventional polymer chemistry, the synthesis of a new polymer requires the use of a new monomer. This approach is often unsatisfactory for Inorganic systems, where relatively few monomers or cyclic oligomers can be Induced to polymerize, at least under conditions that have been studied to date. The main exception to this rule is the condensation-type growth that occurs with inorganic dl-hydroxy acids. 

The attack of monomeric cation-radical of aniline on oligomeric amine cation-radical leads to chain growth. The chain growth can also proceed as copolymerization of two oligomeric species (Scheme 4.33). 

The chain growth mechanism for the free radical copolymerization of CO with C2H4 either through added initiators or induced by y-rays has been the subject of a number of papers 7 10). The possible propagation steps in the copolymerization... 

Direct evidence for a mechanism involving a single mode of chain growth as depicted in Scheme 1 came from our studies on the copolymerization reaction in alcoholic solvents35). The mechanism, as outlined in Scheme 1, involves the formation of Pd-acyl species as intermediates at every other step in the propagation sequence. Since the formation of esters through the reaction of transition metal-acyls with alcohols is well-precedented, it should be possible to intercept the propagation sequence if the polymerization was carried out in the presence of alcohols, Eq. (13). 

Indeed, the formation of esters of the type RO—(COCE CE ),—H was observed when the solvent for the copolymerization reaction was ROH (R=CH3, C2H5). The polyketoesters corresponding to n = 1-5 could be seperated and quantified, and gave well-behaved Schulz-Flory plots indicating the validity of the mechanism involving a single mode of stepwise chain growth as shown in Scheme 1. 

Because the purity of the monomers used affects the molecular weight of the polyester 39), we can assume that proton donors whether added to the monomer mixture or formed during copolymerization, participate in termination or transfer reactions. Termination of chain growth may occur by reaction of the growing chain end with proton donors according to Eqs. (77) and (78). 

Radical chain-growth copolymerization with aceto-acetoxy ethyl methacrylate AAEM... 

Comparison of the Two Reactions Step-Growth Polymerization in More Detail Making PET in the Melt Interfacial Poly condensation Chain-Growth Polymerization in More Detail Free Radical Chain Polymerization Going One Step Better Emulsion Polymerization Copolymerization Ionic Chain Polymerization It Lives ... 

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