Homopolymerization dienes

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). 

Geometric considerations would seem to dictate that 1,4- and 1,5-dicncs should not undergo cyclopolymerization readily. However, in the case of 1,4-dienes, a 5-hexenyl system is formed after one propagation step. Cyclization via 1,5-backbiling generates a second 5-hexenyl system. Homopolymerization of divinyl ether (22) is thought to involve such a bicyclization. The polymer contains a mixture of structures including that formed by the pathway shown in Scheme 4.18. 

Along with homopolymerization, copolymerization has also been studied within the framework of initiation by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (Bauld et al. 1998a). Generally, cation-radical cycloaddition occurs more efficiently when the reactive cation-radical is the ionized dienophile (Bauld 1989, 1992). In the cited work on copolymerization, the bis(diene) was chosen to be resistant against ionization by the initiator used. As to the dienophile functionality, propenyl rather than vinyl moieties were selected because terminal methyl groups sharply enhance the ionizability of the alkene functions. The polymerization shown in Scheme 7.18 was performed in dichloromethane at 0°C. 

The hnal copolymer was obtained in 90% yield it had a molecular weight of 10,800 and polydispersity index of 2.1. In this case, Diels-Alder copolymerization dominates over the cyclobntane homopolymerization. It means that Diels-Alder addition of the dienophile cation-radical to the diene is substantially faster than the competing addition of the dienophile cation-radical to the nen-tral dienophile. 

Monomer reactivity ratios and copolymer compositions in many anionic copolymerizations are altered by changes in the solvent or counterion. Table 6-12 shows data for styrene-isoprene copolymerization at 25°C by n-butyl lithium [Kelley and Tobolsky, 1959]. As in the case of cationic copolymerization, the effects of solvent and counterion cannot be considered independently of each other. For the tightly bound lithium counterion, there are large effects due to the solvent. In poor solvents the copolymer is rich in the less reactive (based on relative rates of homopolymerization) isoprene because isoprene is preferentially complexed by lithium ion. (The complexing of 1,3-dienes with lithium ion is discussed further in Sec. 8-6b). In good solvents preferential solvation by monomer is much less important and the inherent greater reactivity of styrene exerts itself. The quantitative effect of solvent on copolymer composition is less for the more loosely bound sodium counterion. 

The stereochemistry of the 1,3-diene units in copolymerization is expected to be the same as in homopolymerization of 1,3-dienes. This expectation has been verified in styrene-1,3-butadiene copolymerizations at polymerization temperatures of —33 to 100°C [Binder, 1954],... 

Lithium diethylamide has been shown to be an effective initiator for the homopolymerization of dienes and styrene llr2). It is also known that such a polymerization process is markedly affected by the presence of polar compounds, such as ethers and amines (2,3). However, there has been no report of the use of a lithium amide containing a built-in polar modifier as a diene polymerization initiator. This paper describes the preparation and use of such an initiator, lithium morpholinide. A comparison between polymerization with this initiator and lithium diethyl amide, with and without polar modifiers, is included. Furthermore, we have examined the effects of lithium-nitrogen initiators on the copolymerization of butadiene and styrene. 

Thus in these systems, there is an apparent "reversal of reactivity" of styrene and the diene, since for the homopolymerization situation styrene is a much more reactive monomer than either diene. 

It has been emphasized in the copolymerization of styrene with butadiene or isoprene in hydrocarbon media, that the diene is preferentially incorporated. (7,9,10) The rate of copolymerization is initially slow, being comparable to the homopolymerization of the diene. After the diene is consumed, the rate increases to that of the homopolymerization of styrene. Analogously our current investigation of the copolymerization of butadiene with isoprene shows similar behavior. However, the... 

Although the serious effects of crosslinking on the properties of commercial polymers have long been recognized, systematic study of the phenomenon has been somewhat neglected. It is true that Flory (4) outlined the basic kinetics of the crosslinking process for the homopolymerization of dienes which gave the proportion of crosslinks v as a function of the fraction conversion a as ... 

A parallel situation is encountered for the copolymerization of 1,3-butadiene with isoprene. McGrath et al. 251) have shown that in homopolymerizations, under equivalent conditions, isoprene exhibits a rate constant which is more than five times larger than that observed for butadiene. However, butadiene is favored in the copolymeriza-tion. The available reactivity ratios for various diene and styrenyl monomer pairs in hydrocarbon solvents are listed in Table 24. 

Aluminum—tetradentate ligand catalyst system, in epoxide homopolymerization, 11, 601 Aluminum(I) tetrahedra, synthesis, 9, 262 Aluminum(III)-tin exchange, process, 9, 265 Aluminum-transition metal bonds, characteristics, 9, 264 Amavadine, for alkane carboxylations, 10, 234—235 Ambruticin S, via ring-closing diene metathesis, 11, 218 Amide-allenes, cyclizations, 10, 718 Amide ether complexes, with Zr(IV) and Hf(IV), 4, 783 Amide hybrid ligands, in organometallic synthesis, 1, 64 Amides... 

This review will feature the kinetics and mechanism of RLi-initiated, homo- and copolymerization of hydrocarbon diene and olefin monomers, with and without polar ligands. Hydrocarbon olefin homopolymerization in nonpolar media will not be discussed per se because simple olefins such as ethylene do not polymerize under such conditions, and such reactive, hydrocarbon a-olefins as styrene behave similarly to dienes in... 

As in the case of olefin or diene homopolymerization by RLi, copolymerization is particularly sensitive to solvent effects. Initial-charge (all monomers added together) copolymerization of butadiene and styrene tends to result in a tapered block copolymer (a block of butadiene with increasing levels of styrene, followed by a block of styrene) in hydrocarbon solvents and a random copolymer (a uniform distribution of butadiene and styrene) in polar media. 

Ferulic acid, a phenolic acid that can be found in rapeseed cake, has been used in the synthesis of monomers for ADMET homo- and copolymerization with fatty acid-based a,co-dienes [139]. Homopolymerizations were performed in the presence of several ruthenium-based olefin metathesis catalysts (1 mol% and 80°C), although only C5, the Zhan catalyst, and catalyst M5i of the company Umicore were able to produce oligomers with Tgs around 7°C. The comonomers were prepared by epoxidation of methyl oleate and erucate followed by simultaneous ring opening and transesterification with allyl alcohol. Best results for the copolymerizations were obtained with the erucic acid-derived monomer, reaching a crystalline polymer (Tm — 24.9°C) with molecular weight over 13 kDa. 

In addition to the polymerization of dienes the versatility of NdP-based catalysts is exceptional regarding the number of different non-diene monomers which can be polymerized with these catalysts. Acetylene is polymerized by the binary catalyst system NdP/AlEt3 [253,254]. Lactides are polymerized by the ternary system NdP/AlEt3/H20 [255,256]. NdP/TIBA systems are applied in the copolymerization of carbon dioxide and epichlorhy-drine [257] as well as for the block copolymerization of IP and epichloro-hydrin [258]. The ternary catalyst system NdP/MgBu2/TMEDA allows for the homopolymerization of polar monomers such as acrylonitrile [259] and methylmethacrylate [260]. The quaternary system NdP/MgBu2/AlEt3/HMPTA is used for the polymerization of styrene [261]. 

Beside the homopolymerization of BD Nd-based Ziegler/Natta catalyst systems are also applied for the homopolymerization of IP, the copolymerization of the dienes BD and IP, the homopolymerization and copolymerization of substituted dienes as well as for the copolymerization of BD with alkenes such as styrene, ethylene and other ethylene derivatives. 

From an industrial point of view the other aspects dealt with in this section are less exciting. Therefore, the homopolymerization of substituted dienes other than IP, the copolymerization of BD and styrene and the copolymerization of BD with ethylene and higher 1-alkenes are only briefly summarized. The Nd-catalyzed homo- and copolymerization of monomers with polar entities are not dealt with in this review. 

Another positive aspect of Nd catalysis is the high selectivity of Nd catalysts towards the polymerization of dienes. This feature is exploited in two ways. First, homopolymerization of BD in the presence of styrene as a solvent and second, selective homopolymerization of IP in the crude C5 cracking fraction. 

Binary neodymium alk(aryl)oxide/dialkylmagnesium diene polymerization catalysts were reported by J.-F. Carpentier and coworkers [181,192], The homopolymerization of butadiene, and copolymerization with styrene and... 

Since the fo s-cyclopentadienyl compoimds I—IV may also function as di-dienes, Dieles-Alder copolymerization reactions with di-dienophiles lead to high molecular weight polymers. In the Diels-Alder copolymerization reactions of these di-dienes, it is not necessary that a 1 1 ratio of monomers be included in the reaction mixture. The di-dienes will also homopolymerize and may serve in the capacity as di-diene, a di-dieno-phile and a dienophilic diene. A copolymer of a, a -fo s-cyclopentadienyl- -xylene and 4-phenylene-i>ts-maleimide has been reported in which... 

Copolymerization of styrene with diolefins provides further support that monomer coordinates with the cationic site prior to addition. Korotkov (218) showed that in homopolymerizations styrene is more reactive than butadiene, but in copolymerization the butadiene reacted first at its homopolymerization rate and when it was exhausted the styrene reacted at its homopolymerization rate. This interesting result has been duplicated by Kuntz (245) and analogous results have been obtained by Spirin and coworkers (237) for the styrene-isoprene system. Presumably, the diene complexes more strongly than styrene with the lithium and excludes styrene from the site. That the complex occurs at a cationic site, rather than at the anion or the metal-carbon bond, is indicated by the fact that dienes form more stable complexes than styrene with Lewis acids (246). It should be emphasized that selective monomer coordination is not the only factor influencing reactivities in copolymerizations. Of greatest importance are the relative reactivities of the different polymer anions. The more resonance-stabilized anion is more readily formed and is less reactive for polymerizing the co-monomer. 

Similarly, whereas the Diels-Alder reaction is accelerated at elevated temperatures, under polymerization conditions, the reaction of isoprene and maleic anhydride is extremely exothermic, and the relative amounts of adduct and copolymer are temperature dependent. It has been reported (81) that the rate of copolymerization is very fast compared with the rate of homopolymerization of the diene or the dienophile, and the energy of activation is approximately 5 kcal./mole. Although the rate of copolymerization increases at elevated temperatures, the simultaneous adduct formation which also occurs more readily at elevated temperatures limits the maximum rate to lower temperatures. 

Besides the performance of metallocene catalysts in the homopolymerization of ethylene also their ability for copolymerization under high pressure was proofed. As comonomers a number of 1-olefins and dienes were used. In Figure 5 the change of the productivity with the concentration of the comonomer in the feed is shown for the copolymerization of ethylene with... 

Vinylsilane monomers do not homopolymerize owing to steric inhibition within a required catalytic intermediate, yet will specifically copolymerize with an unhindered diene, resulting in isolated units of the vinylsilane within the copolymer. AUyhc silanes, however, show no resistance to homometathesis and yield novel high molecular weight, unsaturated polycarbosilanes with low glass transition temperatures and good thermal stability. 

While the majority of SBC products possess discrete styrene and diene blocks, some discussion of the copolymerization of styrene and diene monomers is warranted. While the rate of homopolymerization of styrene in hydrocarbon solvents is known to be substantially faster that of butadiene, when a mixture of butadiene and styrene is polymerized the butadiene is consumed first [21]. Once the cross-propagation rates were determined (k and in Figure 21.1) the cause of this counterintuitive result became apparent [22]. The rate of addition of butadiene to a growing polystyryllithium chain (ksd) was found to be fairly fast, faster in fact than the rate of addition of another styrene monomer. On the other hand, the rate of addition of styrene to a growing polybutadienyllithium chain (k s) was found to be rather slow, comparable to the rate of butadiene homopolymerization. Thus, until the concentration of butadiene becomes low, whenever a chain adds styrene it is converted back to a butadienyllithium chain before it can add more styrene. Similar results were found for the copolymerization of styrene and isoprene. Monomer reactivity ratios have been measured under a variety of conditions [23]. Values for rs are typically <0.2, while values for dienes (rd) typically range from 7 to 15. Since... 

These methods suggested in the present form by Caunt83) rely on inhibition (retardation) effects of strong catalyst poisons on polymerization. Typical poisons potentially usable for this purpose are carbon oxides, carbonyl sulfide, carbon disulfide, acetylenes and dienes. All these substances exhibit a strong unsaturation they have either two double bonds or one triple bond. Most of the works devoted to application of the poisons to determination of active centers 10,63 83 102 1O7) confirm a complicated nature of their interaction with the catalytic systems. To determine the active centers correctly, it is necessary to recognize and — as much as practicable — suppress side processes, such as physical adsorption and chemisorption on non-propagative species, interaction with a cocatalyst, oligomerization and homopolymerization of the poison and its copolymerization with the main chain monomer. 

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