Copolymerization addition

Polymer Composition. Ethylene—acrylic elastomer terpolymers ate manufactured by the addition copolymerization of ethylene [74-85-1] and methyl acrylate [96-33-3] in the presence of a small amount of an alkenoic acid to provide sites for cross-linking with diamines (4). 

SBR is produced by addition copolymerization of styrene and butadiene monomers in either emulsion or solution process. The styrene/butadiene ratio controls the glass transition temperature (To) of the copolymer and thus its stiffness. T ... 

Strongly electrophilic or nucleophilic monomers will polymerize exclusively by anionic or cationic mechanisms. However, monomers that are neither strongly electrophilic nor nucleophilic generally polymerize by ionic and free radical processes. The contrast between anionic, cationic, and free radical methods of addition copolymerization is clearly illustrated by the results of copolymerization utilizing the three modes of initiation (Figure 7.1). Such results illustrate the variations of reactivities and copolymer composition that are possible from employing the different initiation modes. The free radical tie-line resides near the middle since free radical polymerizations are less dependent on the electronic nature of the comonomers relative to the ionic modes of chain propagation. 

Copolymerizations of nonpolar monomers with polar monomers such as methyl methacrylate and acrylonitrile are especially comphcated. The effects of solvent and counterion may be unimportant compared to the side reactions characteristic of anionic polymerization of polar monomers (Sec. 5-3b-4). In addition, copolymerization is often hindered by the very low tendency of one of the cross-propagation reactions. For example, polystyryl anions easily add methyl methacrylate but there is little tendency for poly(methyl methacrylate) anions to add styrene. Many reports of styrene-methyl methacrylate (and similar comonomer pairs) copolymerizations are not copolymerizations in the sense discussed in this chapter. 

Grafting can also be obtained by addition copolymerization of vinyl monomers with unsaturated polymers. The unsaturation may be located either in the side groups or in the backbone. 

By polymerizing in a second step ethyl acrylate or styrene in the presence of this unsaturated polymer, graft copolymers were obtained by addition copolymerization. In the same way a soluble first step copolymer was prepared from styrene and ethylidene dimethacryiate, to which methyl methacrylate was grafted by addition copolymerization (198). 

When unsaturatcd polymers have hydrogen or halogen atoms in a-position to the double bonds, they are especially sensitive to chain transfer by a free radical attack. Therefore in these cases, the graft copolymerization may involve a combination of two initiation processes which occur simultaneously and compete with each other, one by chain transfer, the other by addition copolymerization. The relative importance of both processes is again dependent on the nature of the polymerizing monomer and of the backbone polymer involved in the reaction. 

J. Grenci and D. B. Todd, Effect of Conversion on Chain Addition Copolymerizations Performed in a Backmixed Drag Flow Extruder Reactor, Int. Polym. Process., 15, 147-156 (2000). 

Commercial products based on copolymers of ethylene and TEE are made by free radical-initiated addition copolymerization.69 Small amounts (1 to 10 mol%) of modifying comonomers are added to eliminate a rapid embrittlement of the product at exposure to elevated temperatures. Examples of the modifying comonomers are perfluorobutyl ethylene, hexafluoropropylene, perfluorovinyl ether, and hexafluoro-isobutylene.70 ETFE copolymers are basically alternating copolymers,70 and in the molecular formula, they are isomeric with polyvinylidene fluoride (PVDF) with a head-to-head, tail-to-tail structure. However, in many important physical properties, the modified ETFE copolymers are superior to PVDF with the exception of the latter s remarkable piezoelectric and pyroelectric characteristics. 

T he theory and experimental practice of addition copolymerization have been well understood for many years (I). In the simplest... 

In a similar manner, sensitizer can diffuse into the alcohol-preswollen cellulose and either directly abstract hydrogen atoms (Equations 1 and 4) or rupture bonds as shown in Equation 5 to form additional copolymerization sites. 

Although Eqs. (1) and (2) eannot generally be applied to chain reactions, the latter has been extended to the speeial ease of chain polymerizations of symmetrieal divinyl eompounds by Stockmayer [2], He applied Flory s procedure to a mixture of polyfiinetional components with a generalized distribution of funetionality and obtained an expression, Eq. (3), for predicting the gel point in addition copolymerizations of monovinyl and divinyl monomers, in which it was assumed that the structure of both monomers is so closely related that all double bonds present have the same reaetivity and moreover, cyclization is ruled out. 

Rubbers, or elastomers, stretch readily to elongate by a factor of 10 before breaking. Natural rubber, obtained from the sap of certain trees, can be hardened and toughened by addition of sulfur in the vulcanization process. Synthetic rubber is produced by addition copolymerization of butadiene and styrene. 

There are three different mechanisms by which the cyclic olefin norbornene can be polymerized to reasonably high molecular weights ring-opening metathesis polymerization (or ROMP), vinyl addition copolymerization with acyclic olefins such as ethylene, and vinyl addition homopolymerization (see Fig. 4.2). Carbocationic and free-radical initiated polymerizations are ignored since they yield only low molecular weight oligomers [8]. 

The addition copolymerization of norbornene-type monomers with a-olefins [21] forms the basis of EPDM (ethylene propylene diene monomer) technology. Incorporation of smaU amounts of DCPD or ethylidene norbornene (ENB) in olefinic vinyl addition polymers provides latent crosslink sites in EPDM elastomers. It is weU known in the hterature that incorporation of higher amounts of rigid, bulky multicychc olefins results in materials with higher TgS [22]. In fact, more recent work has concentrated on increasing the Tg of norbornene-type monomer/a-olefin copolymers [23]. The use of late transition metal catalysts to prepare such copolymers is reviewed in Section 4.3. 

These materials can be considered linear copolymers of ethylene and propylene or precisely methyl-branched polyethylene. In addition, copolymerizations of the methyl-containing monomers with 1,9-decadierie yield polymers with lower propylene content [50]. These materials are of great interest to the polyolefin community, especially in the physical understanding of the effects of branching on physical properties. Polyethylenes with a variety of main chain functionality have also been synthesized and analyzed [51-54]. 

As an option, the polymer can then be fed to a fluidized bed gas-phase reactor, operated in series vith the MZCR, where additional copolymerization can take place to yield high-impact copolymer PP. This gas-phase reactor may be bypassed when homopolymer or random copolymers are produced. In this reactor, the elastomeric phase (ethylene/propylene rubber) is generated within the porous homopolymer matrix that resulted from the first reaction stage. The pores, developed inside the polymer particle in the MZCR upstream, allow the rubber phase to develop without the formation of agglomerates resulting from the sticky nature of the rubber. 

Unsaturated rubber polymers are especially important grafting vehicles. Consider, for example, the polymerization of styrene in the presence of l,4-poly(l,3-butadiene). A method consists of dissolving the polybutadiene rubber (about 5 to 10%) in monomeric styrene containing benzoyl peroxide initiator and applying heat. Polymer radicals, formed by (a) chain transfer between the propagating radical and polymer or (b) addition (copolymerization) of the propagating radical to the -double bonds of the polymer. 

Most unsaturated substances such as alkenes, alkynes, aldehydes, acrylonitrile, epoxides, isocyanates, etc., can be converted into polymeric materials of some sort—either very high polymers, or low-molecular-weight polymers, or oligomers such as linear or cyclic dimers, trimers, etc. In addition, copolymerization of several components, e.g., styrene-butadiene-dicyclo-pentadiene, is very important in the synthesis of rubbers. Not all such polymerizations, of course, require transition-metal catalysts and we consider here only a few examples that do. The most important is Ziegler-Natta polymerization of ethylene and propene. 

Scheme 7.37 Vinyl addition copolymerization of various norbornene derivatives using [Pd(CH3CN)4](BF4)2 in nitromethane at room temperature, using a procedure adapted from Risse and co-workers. ...

FIGURE 4.12 Curing of unsaturated polyesters, (a) Species in polyester resin ready for laminating, (b) Structures present in cured polyester resin. Cross-linking takes place via an addition copolymerization reaction. The value of n 2-3 on average in general-purpose resins. (After Brydson, J. A. 1982. Plastics Materials. Butterworth Scientific, London, UK.)... 

Orion is a highly polymeric fiber resulting from the catalyzed addition copolymerization of acrylonitrile with about 10% vinylpyridine, C7H7N. The vinylpyridine unit is incorporated into the polymer to enable dyes to be adsorbed more readily by the fiber. Normally the copolymer is dissolved in a solvent such as N,N-dimethylacetamide, from which it can be spun into threads. It can also be wet spun from concentrated salt solutions. 

Also, an alternating free-radical addition copolymerization of cyclohexene and formic acid, perhaps via charge transfer, donor-acceptor complexes, yields polyesters ... 

First comes the unsaturated polyester resin itself. From Chapters 12 and 15 we should have a clear idea of what is meant by a polyester resin and, in particular, a saturated polyester resin. Although a drying-oil alkyd is, in a sense, an unsaturated polyester resin, the term has come to be applied solely to polyester resins based on components which introduce unsaturation directly into the polyester backbone. This unsaturation must be capable of direct addition copolymerization with vinyl monomers. To give a linear polymer, any of the dibasic acids or dihydric alcohols mentioned in Chapters 12 and 15 may be used, but the resin should include some unsaturated components. These are usually, though not necessarily, acids, e.g. ... 

The main advantage of copolymerization is in the enormous variability of polymer properties. An almost unlimited number of different polymeric products can be achieved by varying the type and relative amounts of the different employed monomer units [50,51]. New and advanced properties can be obtained in respect to solu-bihty, permeability, greater affinity for dyes, or good oil resistance [52]. In addition, copolymerization can be used for producing three-dimensionaUy crosslinked polymers, as e.g., poly(styrene-cri-divinylbenzene). 

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