Polymerization butadienes

In spite of the assortment of things discussed in this chapter, there are also a variety of topics that could be included but which are not owing to space limitations. We do not discuss copolymers formed by the step-growth mechanism, for example, or the use of Ziegler-Natta catalysts to regulate geometrical isomerism in, say, butadiene polymerization. Some other important omissions are noted in passing in the body of the chapter. 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

Isoprene can be polymerized using free radical initiators, but a random polymer is obtained. As with butadiene, polymerization of isoprene can produce a mixture of isomers. However, because the isoprene molecule is asymmetrical, the addition can occur in 1,2-, 1,4- and 3,4- positions. Six tactic forms are possible from both 1,2- and 3,4- addition and two geometrical isomers from 1,4- addition (cis and trans) ... 

MOORE ET AL. Antontc Butadiene Polymerization from (16) and (18) one can obtain... 

Thus it becomes unlikely that 7 can exist long enough to allow extensive dimerization or oligomerization of butadiene. It has also been speculated (7, 9) that the presence of coordinated chlorides on the Rh complex prevents the occurrence of butadiene polymerization reaction. 

Figure 1.25 Minimum-energy diastereoisomeric monomer free intermediates for butadiene polymerization catalyzed by titanium complexes presenting Cp group as ancillary ligand. Chiralities of coordination of allyl groups (assumed to be si) and back-biting double bonds (si or re) are indicated, in order to easily visualize possible stereoregularity (iso or syndio) of model chains. In fact, like and unlike chiralities would possibly lead to isotactic and syndiotactic enchainments, respectively.

Nickel 2,6,10-dodecatrien -1,12-diyl, as catalyst for butadiene polymerization, 23 303 Nickel formate as nickel catalyst, 32 226-229 Nickel hydride... 

Supported Ziegler-type neodymium surface species (54, see below) have been prepared by mixing molecular components composed of [Nd(naph)3] (derived from naphthenonic acids) and alkyl aluminium reagents such as Al2Et3Cl3, Al( Bu)3 and/or Al( Bu)2H at 50-60°C with silica (source QiLu Petrochemicals Co., China) [158-160]. Although the immobihzed neodymium species are iU-defined, the materials display interesting properties in butadiene polymerization (Section 12.4.1.2). 

The situation is exactly analogous to the polymerization of monosubstituted alkenes the various polymer structures would be those in Fig. 8-1 with R = — CH=CH2. With chloroprene and isoprene, the possibilities are enlarged since the two double bonds are substituted differently. Polymerizations through the 1,2- and 3,4-double bonds do not yield the same product as they would in 1,3-butadiene polymerization. There are, therefore, a total of six structures possible—corresponding to isotactic, syndiotactic, and atactic structures for both 1,2- and... 

An unstable analogue of prostaglandin, PGE, formulated in a poly butadiene polymeric matrix, was placed in a SFE cell and extracted with C02/formic acid (95 5) at 15°C Extraction was continued for 60 min and then the extract was collected in hexane/ethanol (2 1) at 0"C. The advantages of the SFE method were that the solvent effected simultaneous cleavage of the polymer-prostaglandin bond without instability problems and with improved mass transfer enabling good recovery from the polymer matrix. 

Figure 8 illustrates a comparison between measured and computed rates of butadiene polymerization in an rf plasma sustained at 13.56 MHz. A perfect fit is achieved by adjusting the rate coefficients appearing in the model to the following values ... 

For the conditions shown in Fig. 8, it was estimated that the electron density was 8x 10 cm" . This means that kj = 2.5 x 10" cm /s, a value in good agreement with measured rate coefficients for dissociation of small molecules by electron impact . The gas phase propagation rate coefficient kp was also found to be in very good agreement with values determined for conventional butadiene polymerization. The agreement of the adjusted parameter values with those measured independently lends further support to the validity of the proposed model of plasma polymerization. 

Polymerization of butadiene with lithium morpholinide, an initiator with a built-in microstructure modifier, has been carried out in hexane. In general, the vinyl content of the polymers prepared with this initiator is dependent on the initiator concentrations and on the polymerization temperatures. This dependence is identical to that observed in a THF-modified lithium diethylamide polymerization initiator system. A comparison of these initiator systems for polymerization of butadiene is presented. In addition, a study of the effect of metal alkoxides on the vinyl content of lithium morpholinide initiated butadiene polymerization is included. 

The effect of the addition of alkali metal b-butoxides on the lithium morpholinide-initiated heterogeneous butadiene polymerization was also studied at 30°C in hexane. The data in Table III show that the 1,2 content of the polybutadiene is sensitive to the type of alkali metal used. For example, by changing metal alkoxides from Li to Na to K, the 1,2 content of polybutadiene changes from 46.0% to 58.2% to 55.4%, respectively, at an initiator concentration of about 10 mmoles. However, the 1,2 content of the polybutadienes is unaffected by the metal alkoxide concentration (1,2 content, 42-46% for LiOtBu, 55-58% for NaOtBu, 53-55% for KOtBu) when the alkoxide/ morpholinide ratio is greater than 1 1. 

Lithium Diethylamide. This compound has been used as an initiator for the polymerization of diene by Vinogrador and Basayeva (1). In order to compare this initiator with lithium morpholinide (a lithium-nitrogen initiator with a built-in polar modifier), we have prepared lithium diethylamide according to the procedure described by vinogrador and Basayeva (1) and utilized it as an initiator for THF-modified butadiene polymerizations. 

EFFECT OF METAL T-BUTOXIDE ON LITHIUM MORPHOLINIDE INITIATED BUTADIENE POLYMERIZATION AT 30°C IN HEXANE ... 

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