ADMET bulk polymerization

Usually ADMET polymerizations are conducted in the bulk state (neat) to maximize the molar concentration of the olefin, and so the examples discussed in this chapter describe bulk polymerization conditions. 

The equilibrium of the ADMET polymerization is forced towards high polymer by running bulk polymerizations under vacuum to remove ethylene. Working under bulk conditions or in solution, ADMET polymer products have been isolated up to 80 kg mol using [Mo] on hydrocarbon monomers and up to 70 kg mol" using [Ru]" on peptide functionalized monomers [39,40]. 

Introduction of ADMET polymerization leads to the synthesis of perfect PE with absence of undesired SCB and SCBD. The polymer also known as ADMET PE is obtained via bulk polymerization of 1,9-decadiene in presence of first-generation Grubb s or Schrock s catalyst. The resulting polyoctenamer is exhaustively hydrogenated producing a completely saturated linear PE, as is shown in Figure 2. 

Another factor in step-growth polymerizations is cyclization versus linear polymerization.1516 Since ADMET is a step-growth polymerization, most reactions are carried out in the bulk using high concentrations of the reactant in order to suppress most cyclic formation. A small percentage of cyclic species is always present but is dependent upon thermodynamic factors, typical of any polycondensation reaction. 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Examples of such reactions are shown in Table 8.5. Divinyl ether is unreactive but diallyl ether, when treated in bulk with 8, gives an equilibrium mixture of 63% 2,5-dihydrofuran and 37% of its -trans, ring-opened polymer, albeit of low MW (Fig. 8.3). The analogous tungsten complex is not a good initiator for the ADMET polymerization of diallyl ether. 

ADMET of this monomer, 2-butene, was much less volatile than ethylene hence, polymerization of this monomer in bulk proved difficult Polymerization in a high-boiling solvent at reflux facilitated removal of the 2-butene, albeit with reduced molecular weights, which was attributed to a rapid catalyst death due to the elevated temperature. Despite their low molecular weights, these well-defined poly(3-hexylthiophene vinylenes) exhibited properties that were in agreement with other reported examples. 

The kinetics of the ADMET reaction is not amenable to study by many traditional means, as these polymerizations are mostly conducted in bulk. The most effective way to measure the kinetics of the polymerization is to monitor the volume of evolved ethylene. This technique has been used to probe the difference in activity between [Mo] 2 and [Ru]l for ADMET polymerization of 1,9-decadiene [37]. At 26 °C in bulk monomer, [Mo] 2 promotes ADMET polymerization of 1,9-decadiene at a rate approximately 24 times that of [Ru]l. Additionally, [Mo] 2 polymerizes 1,5-hexadiene 1.7 times faster than 1,9-decadiene, while [Ru]l only cyclodimerizes 1,5-hexadiene to 1,5-cyclooctadiene. Monomers with coordinating functionality, specifically ethers and sulfides, were also investigated. Predictably, these monomers did not undergo polymerization as rapidly as hydrocarbon monomers however, this difference was dramatically more pronounced with [Ru]l than with [Mo]2. In fact, the dialkenyl sulfide monomers that were studied completely shut down the polymerization with [Ru]l, whereas the catalytic activity of [Mo]2 was only slightly lowered. This reduction in polymerization rate is most likely due to coordination of the heteroatom to the vacant coordination site of [Ru] 1, following phosphine dissociation. This reversible coordination of heteroatoms to the ruthenium complex likely occurs both intramolecularly and intermolecularly. Conversely, the steric bulk of the ligands in [Mo] 2 makes it less likely to intramolecularly form a coordinate complex, despite molybdenum being far more electrophilic than ruthenium. 

While siloxanes are also amenable to ADMET polymerization, they display trends similar to silanes, in that the steric bulk near the reacting olefin prevents productive metathesis [107]. Specifically, l,l,3,3-tetramethyl-l,3-divinyl-disiloxane proved unreactive, while l,3-diallyl-l,l,3,3-tetramethyldisiloxane almost exclusively cyclized. Still, longer di- and tri-siloxane monomers have been shown to polymerize via ADMET. Ring-chain equilibria are well known for polysiloxanes, and some of these polymers degrade over time via intrachain siloxane exchange reactions to form cyclic oligomers [108]. 

A systematic study of the effect of molecular weight on the photovoltaic performance has also been performed on poly(3-hexadecylthienylene vinylene) synthesized by ADMET polymerization [164]. The molecular weights of the polymers ranged from 6.0x10 to 3.0 X lO gmoD, and were incorporated into bulk heterojunction solar cells with [6,6]-phenyl-Cg -butyric acid methyl... 

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