Diene copolymerization

In diene copolymerization, also, the monomer sequence can be regulated by the choice of catalyst and polymerization conditions. 

Sulfur dioxide does not homopolymerize, but on reaction with olefins it yields copolymers.Terminal olefins react more readily than those with an internal double bond. The presence of various substituents affects the rate of polymerization. Conjugated dienes copolymerize with sulfur dioxide to give linear polymers containing residual double bonds. 

Tapered Block Copolymers. The alkyllithium-initiated copolymerizations of styrene with dienes, especially isoprene and butadiene, have been extensively investigated and illustrate the important aspects of anionic copolymerization. As shown in Table 15, monomer reactivity ratios for dienes copolymerizing with styrene in hydrocarbon solution range from approximately 8 to 17, while the corresponding monomer reactivity ratios for styrene vary from 0.04 to 0.25. Thus, butadiene and isoprene are preferentially incorporated into the copolymer initially. This type of copolymer composition is described as either a tapered block copolymer or a graded block copolymer. The monomer sequence distribution can be described by the structures below ... 

Olefin/nonconjugated diene copolymerizations can be an attractive alternative synthetic method to olefin/cycloolefin copolymerization, because homo- and copolymerizations of cycloolefins typically show low productivity. Bergemann et al. studied ethylene/l,5-HD copolymerization with the MAO-activated catalyst 11 (Figure 19.2) under a high ethylene pressure of 1500 bar. According to... 

To test the importance of vinyl bond content and copolymerization ability in LCB formation, we carried out a diene copolymerization series with two catalysts having very different comonomer responses, low inherent vinyl bond formation tendency, and very facile hydrogen reactivity. Concentration was kept high to avoid inherent LCB formation in the series. 1,7-Octadiene served as the diene comonomer. Polymerization results are summarized in Table 5. 

MA cyclic olefin copolymerizations, 350 MA-cyclodiene copolymerizations, 357, 361 MA-cyclohexene oxide reaction, 483 MA Diels-Alder reactions, 126, 135, 139 MA-diene copolymerizations, 346 MA-2,3-dihydrofuran copolymerization, 324 MA-p-dioxene copolymerization, 321, 386 MA-dodecyl vinyl ether copolymerization, 386 MA ene reactions, 166, 167 MA-epoxy resin reactions, 507-510 MA-ethylene copolymerization, 337 MA grafting on polybutadiene, 470 MA-indene copolymerization, 378 MA-isopropenyl dioxane copolymerizations, 331 MA-p-isopropyl-a-methylstyrene copolymerization, 372... 

Copolymerization can be carried out with styrene, acetonitrile, vinyl chloride, methyl acrylate, vinylpyridines, 2-vinylfurans, and so forth. The addition of 2-substituted thiazoles to different dienes or mixtures of dienes with other vinyl compounds often increases the rate of polymeriza tion and improves the tensile strength and the rate of cure of the final polymers. This allows vulcanization at lower temperature, or with reduced amounts of accelerators and vulcanizing agents. 

AlkyUithium compounds are primarily used as initiators for polymerizations of styrenes and dienes (52). These initiators are too reactive for alkyl methacrylates and vinylpyridines. / -ButyUithium [109-72-8] is used commercially to initiate anionic homopolymerization and copolymerization of butadiene, isoprene, and styrene with linear and branched stmctures. Because of the high degree of association (hexameric), -butyIUthium-initiated polymerizations are often effected at elevated temperatures (>50° C) to increase the rate of initiation relative to propagation and thus to obtain polymers with narrower molecular weight distributions (53). Hydrocarbon solutions of this initiator are quite stable at room temperature for extended periods of time the rate of decomposition per month is 0.06% at 20°C (39). 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Sodium is a catalyst for many polymerizations the two most familiar are the polymerization of 1,2-butadiene (the Buna process) and the copolymerization of styrene—butadiene mixtures (the modified GRS process). The alfin catalysts, made from sodium, give extremely rapid or unusual polymerizations of some dienes and of styrene (qv) (133—137) (see Butadiene Elastomers, synthetic Styrene plastics). 

However, no studies have been carried out until recently on the synthesis of AN copolymers containing only a small quantity of monomeric diene units which may have fibre forming properties. It is only in the last few years that several reports have appeared on the copolymerization of AN with butadiene in DMF28 and on the use of AN-butadiene copolymers to obtain fibres29. ... 

It is a characteristic feature of this copolymerization, as in general of binary systems in which one of the monomers is a diene, that with the progress of the reaction a secondary crosslinking process becomes possible. 

Ebdon and coworkers22 "232 have reported telechelic synthesis by a process that involves copolymerizing butadiene or acetylene derivatives to form polymers with internal unsaturation. Ozonolysis of these polymers yields di-end functional polymers. The a,o>dicarboxy1ic acid telechelic was prepared from poly(S-s tot-B) (Scheme 7.19). Precautions were necessary to stop degradation of the PS chains during ozonolysis. 28 The presence of pendant carboxylic acid groups, formed by ozonolysis of 1,2-diene units, was not reported. 

Another example of the flexibility of ADMET is the demonstration of successful polymerization of o /v-telechelic diene carbosilane macromonomers.45 The synthesis of macromonomer 30 is achieved using catalyst 23 and copolymerized with a rigid small-molecule diene, 4,4/-di-trans-l-propenylbiphenyl (Fig. 8.17). 

Figure 8.17 Copolymerization of telechelic oligomer 30 with a rigid aromatic diene.

The copolymerization of styrene and the dienes in hydrocarbons was first investigated by Korotkov 43) who reported an unexpected phenomenon. The polymeriza-... 

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

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