Diene-containing polymers

By designing the repeat unit into the parent diene (containing either an alkyl branch or functionality), only a single type of repeat unit is formed upon polymerization, giving pure polymer microstructures. To date, perfectly controlled ADMET ethylene copolymers have included ethylene-CO,34 ethylene-vinyl alcohol,35 ethylene-vinyl acetate,36 and ethylene-propylene.20 Figure 8.12... 

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

Poly(3HAMCL)s have also been produced from free fatty acid mixtures derived from industrial by-products which are potentially interesting low-cost renewable resources. Isolation and analysis of the polymer allowed the identification of 16 different saturated, mono-unsaturated and di-unsaturated monomers [46]. Except for the presence of diene-containing monomers and a large number of minor components, the composition of the fatty acid mixture derived PHA did not differ significantly from oleic acid derived PHAs. 

The rationale in using these particular dienes is that only the strained double bond of dicyclopentadiene and the terminal double bond of 1,4-hexadiene undergo polymerization with Ziegler catalysts. Consequently the polymer chains contain one double bond for each molecule of dicyclopentadiene or 1,4-hexadiene that is incorporated. These double bonds later can be converted to cross-links by vulcanization with sulfur (Sections 13-4 and 29-3). 

ADMET is a step growth polymerization in which all double bonds present can react in secondary metathesis events. However, olefin metathesis can be performed in a very selective manner by correct choice of the olefinic partner, and thus, the ADMET of a,co-dienes containing two different olefins (one of which has low homodimerization tendency) can lead to a head-to-tail ADMET polymerization. In this regard, terminal double bonds have been classified as Type I olefins (fast homodimerization) and acrylates as Type II (unlikely homodimerization), and it has been shown that CM reactions between Types I and II olefins take place with high CM selectivity [142], This has been applied in the ADMET of a monomer derived from 10-undecenol containing an acrylate and a terminal double bond (undec-10-en-l-yl acrylate) [143]. Thus, the ADMET of undec-10-en-l-yl acrylate in the presence of 0.5 mol% of C5 at 40°C provided a polymer with 97% of CM selectivity. The high selectivity of this reaction was used for the synthesis of block copolymers and star-shaped polymers using mono- and multifunctional acrylates as selective chain stoppers. 

The ADMET polymerization of sugar-based monomers is much less explored than the ROMP approach, and only a few examples have been reported to date. Bui and Hudlicky prepared a,oo-dienes derived from a biocatalytically synthesized diene diol, from which chiral polymers (up to 20 kDa) with D-c/uro-inositol units were prepared via ADMET in the presence of 1 mol% of C4 [169]. Furthermore, several ot,co-dienes containing D-mannitol, D-ribose, D-isomannide, and D-isosorbide have been synthesized by Enholm and Mondal [170]. Also in this study, C4 was used to catalyze the ADMET polymerizations at 1 mol% catalyst loading. As pointed out by the authors, the viscosity increased as the reactions progressed and vacuum had to be applied to efficiently remove the released ethylene. Unfortunately, the polymers obtained were not further analyzed. As already mentioned above, Fokou and Meier have also reported the ADMET polymerization of a fatty acid-/D-isosorbide-based a,co-diene [126]. Furthermore, Krausz et al. have synthesized plastic films with good mechanical properties by cross-linking fatty esters of cellulose in the presence of C3 [171-173]. 

Polymers of 1,3-dienes containing one residual double bond per repeat unit after polymerisation can contain sequences with different configurations (Fig. 2.2). 

When conjugated dienes polymerize by 1,4-enchainment, the polymer backbone contains a carbon-carbon double bond. The two carbon atoms in the double bond... 

Polymers that contain a double bond in their backbone (that cannot rotate) can exhibit structural isomerism. Such polymers have distinct structural isomers, such as cis, trans-, and vinyl-polybutadiene shown in Fig. 1.3. These isomers result from the different ways that dienes, such as butadiene, can polymerize and many synthetic polymers have mixtures of cis and trans structural isomers along their chains. A particular mixture reflects the probabilities of various ways that monomers add to the growing chain. 

Some polymers containing macrocycles in the backbone have been prepared by a cyclopolymerization process. This is a new method for preparing polymers with macrocycles containing oxygen and sulfur atoms in the backbone. An open chain a,o>-diene containing the heteroatoms in the chain was polymerized as shown below (Yokota, 1989). This process has not been used... 

A diene contains two double bonds and during polymerisation only one of them opens, which leads to the formation of polymers of three distinctly different kinds. The three forms for polybutadiene, obtained from butadiene, H2C=CH—CH=CH2, are shown in fig. 4.6. The vinyl 1,2 form, for which the double bond is in the side group X, can have any of the types of tacticity discussed above. The two 1,4 types, for which the double bond is in the chain backbone, illustrate a form of configurational isomerism. Rotation around a double bond is not possible, so these two forms are distinct. In the cis form the two bonds that join the unit shown to the rest of the chain are on the same side of a line passing through the doubly bonded carbon atoms of the unit, whereas for the trans form they are on the opposite side of that line. 

The use of highly reactive carbanions in polymer synthesis has proven to be an interesting subject. The work which has been described here indicates some of the potential for novel polymeric materials. Examination of the polymers prepared in this work hints at some of the endless possibilities for the preparation of similar materials. There are many other dicarbanions which can be used in analogous syntheses. One molecule which would be interesting to examine is the dicarbanion of 2,3-dimethyl-1,3-butadiene which would result in a silicon containing polymer that contains a backbone diene unit. Another area of interest which has emerged from this work is the preparation of polymers which contain other inorganic atoms in the polymer backbone such as tin. We believe materials such as these would have some very unique properties. 

Chemically, NR is a polymer of 2-methyl-1,3-butadiene, also known as iso-prene (Figure 9.2). Isoprene is a conjugated diene containing double bonds at alternate positions. 

The synthesis of ADMET polymers that contain a polymetallane segment was studied in the search for the basic rules that govern the compatibility between polymetallanes and hydrocarbon structures. Oligostannadienes with at least one Sn-Sn bond were set as synthetic goals, and after exploring a series of preparative routes, the one-pot procedure shown in Scheme 3 led us to a mixture of dienes containing mainly (although not exclusively) distannane units [25]. 

In the search for new materials, the idea of block copolymers emerged. Block copolymers are materials produced by the careful control of the synthesis a polymer and contain regular sequences of more than one type of monomer. In 1965, Shell brought to the market a number of polystyrene-fc/ock-polybuta-diene- /uck-polystyrene and polystyrene-fe/ock-polyisoprene-fc/ock-polystyrene... 

A series of methyl-substituted polymers, with varying numbers of methylene units between the terminal olefin and the branch point [58], demonstrated that, when there are at least two methylene units separating the olefin and branch point, there is little effect on the catalysis of the reaction. A series of poly(l,4-alkylenephenylene)s have also been prepared by ADMET with Schrock s molybdenum, Grubbs first-generation, and classical catalysts [59]. This series demonstrated that hydrocarbon dienes containing aromatic groups are readily polymerizable by ADMET, even when there is only one methylene unit between the olefin and the aromatic group. 

Monomers with multiple ether functionalities have also been polymerized via ADMET [76, 77]. Acetal-containing dienes have undergone ADMET polymerization with Grubbs [Ru] 1 catalyst to yield the polymer in quantitative yield [78,53]. Additionally, dienes containing primary, secondary, and tertiary alcohols have been shown to be amenable to ADMET polymerization (Figure 13.7) [79]. 

A series of polycarbonates has been synthesized via ADMET with Schrock s molybdenum catalyst [90]. A diene containing a bisphenol-A unit was polymerized to a polymer with an of 1.5 x lO gmol and a PDI of 1.9 (Figure 13.11). 

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