Polymerization anionically initiated

Generally speaking, a monomer with electron-releasing groups will be more rapidly polymerized by cationic initiators. Anionic initiators polymerize olefins with electron-withdrawing groups more rapidly. A more sensitive test of the nature of the reaction is the behavior of a mixture of two such monomers in copolymerization in which they compete for the intermediate. This will be discussed in more detail in Chapter XII on polar versus radical mechanisms. 

The amide anion initiates polymerization via a similar reaction sequence by addition of L to monomer. Propagation follows in a like manner ... 

MW = 1034), biphenyl tetramer hexaol (MW = 782), /3-0-4 tetramer hep-taacetate (C55H66O22, MW = 1078) and /J-O-4 tetramer heptaol (MW = 784). The Igepal (GAF Corp., sold through Aldrich) standards F.W. = 749 and 1982 were also examined. Two synthetic polymers prepared by anion-initiated polymerizations of a quinonemethide according to the procedure of Chum et al. (20) were treated as intermediate MW lignin model polymers. 

Recently, efforts have been made to produce calibration standards of higher molecular weight that are chemically similar to lignins, by step-wise syntheses (12), anion-initiated polymerization of quinonemethides (13), and preparative HPSEC of acetylated lignins (14). Knowledge of the molecular weights of these materials is either built into the method of preparation or determined by absolute methods such as sedimentation equilibrium measurements. 

Continuous solution Anionic Pure styrene monomer Much recycled solvent Anionic initiators Polymerize to completion Low residual monomer High polymerization rate Good for spec, copolymer Sensitivity to impurities Initiator cost Color of product Cannot produce HIPS Not proven for high-volume GP... 

Anionically Initiated Polymerization. The disadvantages of radical polymerization of cyanoprene result from the operating conditions (temperatures) too many side reactions, chain-terminating reactions, and consecutive reactions occur. Because of this and the dimerization tendency of cyanoprene, catalysts had to be found that could fulfill two contradictory requirements. They should be so reactive that it would be possible to work at temperatures that exclude dimerizations as com-... 

Attempts to polymerize I by free radical or anion initiated polymerization techniques were unsuccessful. Attempts to prepare copolymers of I with S02 (10) led only to complex mixtures of low molecular weight products, in contrast to the claims of a patent (20). It proved possible to polymerize I with TiCli,/(iBu) 3AI catalysts at 25° when Ti/Al ratios of 2.7 were employed (21) but substantial portions (25-75%) of the product were crosslinked and the soluble portions contained approximately one double bond for every two monomer units. It seems that the double bonds in I react independently during such polymerizations. 

Polymer made by anionically initiated polymerization with MW, chain-end and chain-sequence control with defect-free chains... 

Figure 1.11 A typical anionically initiated polymerization of a vinyl monomer.

The 500 MHz proton NMR spectra recorded with a superconducting magnet (11.7 T) for two samples of poly (methyl methacrylate) (PMMA) as 10% solutions in chlor-obenzene-ds at 100 °C are presented in Fig. 20.7 [3]. A free radical initiator was used in the polymerization of the syn-diotactic sample (s-PMMA) in (a), while the isotactic sample (i-PMMA) in (b) was obtained with an anionic initiator [4]. It is apparent from the methylene proton portions of both spectra that free radical and anionic initiated polymerization of methyl methacrylate results in PMMA samples with very different microstructures. 

Only a few papers have been published regarding the polymerization of ot,p-unsaturated ketones begun with cationic initiators. This reflects the fact that stabilization of the active center by the conjugative effect of the carbonyl group is not as simple as in anionic-initiated polymerization. Coleman [369] and Schildknecht [370] describe the homopolymerization of some perfluoralkyl propenyl ketones with boron trifluoride at -80° C in bulk and in solution. However, the resulting products have not been characterized adequately. 

Diacrylate Michael Adducts. The synthesis of difiinctional NVF Michael adducts from diacrylates works only under particular conditions. Most successful alkoxide catalysts for the monofunctional derivatives gave slow reaction rates and low conversions. Stronger bases such as butyl lithium did enhance the reaction rate, however, BuLi inevitably promoted anionic initiated polymerization as well and resulted in gel formation. It was found that sodium hydride gave the best overall result, giving good reaction rates and conversions to gel free diftmctional products (Scheme 5). 

It has been demonstrated that it is possible to extend the anionically initiated polymerization of phosphoranimines to monomers bearing alkoxyalkoxy groups. These polymerization reactions obey first order kinetics in monomer and partial to t order l etics in inidator, depending upon the initiating system and solvent An anionic intmnediate has be n proposed to account for the kinetic data. Additionally, random and block copolymers have been synthesized between these monomers and tris(2,2,2-trifluoroethyl-N-trimethylsilylphosphoranimine). It is possible to control Ae mechanical and thermal properties of these materials by adjusting the monomer feed ratios and therefore the repeating unit ratios of the resulting polymers or by use of simultaneous or sequential polymerization techniques. 

---