Poly lithium initiator

Many random copolymers have found commercial use as elastomers and plastics. For example, SBR (62), poly(butadiene- (9-styrene) [9003-55-8] has become the largest volume synthetic mbber. It can be prepared ia emulsion by use of free-radical initiators, such as K2S20g or Fe /ROOH (eq. 18), or in solution by use of alkyl lithium initiators. Emulsion SBR copolymers are produced under trade names by such companies as American Synthetic Rubber (ASPC), Armtek, B. F. Goodrich (Ameripool), and Goodyear (PHoflex) solution SBR is manufactured by Firestone (Stereon). The total U.S. production of SBR in 1990 was 581,000 t (63). 

The preparations by anionic mechanism of A——A type block copolymers of styrene and butadiene can be carried out with the styrene being polymerized first. Use of alkyl lithium initiators in hydrocarbon solvents is usually a good choice, if one seeks to form the greatest amount of c/s-1,4 microstructure [346]. This is discussed in Chap. 4. It is more difficult, however, to form block copolymers from methyl methacrylate and styrene, because living methyl methacrylate polymers fail to initiate polymerizations of styrene [347]. The poly(methyl methacrylate) anions may not be sufficiently basic to initiate styrene polymerizations [345]. 

Subsequent work by D. Braun and collaborators dealt with the effect of solvent polarity and countercation on the tacticity of poly(methyl methacrylate) (PMMA) initiated with various organo alkali metal compounds. By using proton NMR analysis they concluded that polar solvents and alkyl lithium initiators favored syndiotactic configurate on( ) while non-polar solvents favored isotactic piacement( )." ... 

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

The difficulties encountered in the early studies of anionic polymerization of methyl methacrylate arose from the unfortunate choice of experimental conditions the use of hydrocarbon solvents and of lithium alkyl initiators. The latter are strong bases. Even at —60 °C they not only initiate the conventional vinyl poly-addition, but attack also the ester group of the monomer yielding a vinyl ketone1, a very reactive monomer, and alkoxide 23). Such a process is described by the scheme. 

The latter relations are relevant for polymerization of ortho-methoxystyrene initiated in toluene by BuLi, and investigated by Smets, Van Beylen and Geerts 69). Calculations based on the subsequently obtained results show that the fraction of the active non-associated lithium poly-ortho-methoxystyrene vary in this system from 15% at 18 10 3 M concentration of lithium to 60% as its concentration decreases to 0.5 10 3 M. The experimental data published in their paper are listed in Table 3, and presented graphically in Fig. 10. 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

The data in Figure 1 show no dramatic concentration dependence for the interaction of either tetrahydrofuran or 2,5-dimethyltetrahydrofuran with poly(styryl)lithium. The absence of distinct breaks within the range of R values from 0.2 to 2 can be regarded as evidence that the initial base coordination process (eq 1) is followed by successive coordination with other tetrahydrofuran molecules as shown in eq 2. 

Several workers (l. 2,3,4) have used H nmr to study the propagating chain end in the polymerization of 1,3-butadiene (1,3 BD) with a butyllithium initiator. They concluded that the poly(butadienyl) lithium chain end is virtually ICO percent 1,4 with no 1,2 structures, even though 1,2 units are incorporated in the chain. The lithium is bonded to the carbon, and there is no evidence of a T allyl type of delocalized bonding involving the Y carbon. However, the presence of vinyl in-chain units was taken as evidence for the presence of an undetectable amount of the 7 bonded chain ends in equilibrium with the bonded chain ends. Glaze and coworkers (3) further suggested that the stereochemical course of allyllithium reactions may depend on the aggregation of the reactive species. 

A glass substrate carrying an ITO film having a thickness of 150 nm was spin coated with 70 nm of poly(3,4)ethylenedioxythiophene/polystyrenesulfonic acid thin film and then dried at 200°C for 10 minutes. A 50-nm coating of a selected experimental agent was sprayed onto the initial film and dried. Lithium fluoride, calcium, and aluminum were then vapor-deposited at 0.4 nm, of 5 and 180nm, respectively. 

A Kjeldahl flask was charged with ,/V -dimethyl-1,6-diaminohexane (5.75 mmol) dissolved in 10 ml of THF and then treated with the dropwise addition of -butyl-lithium (5.75 mmol) while vigorously stirring. This solution was then treated with chlorotrimethylsilane (5.75 mmol) and stirred at ambient temperature for 30 minutes and then filtered off through a poly(tetrafluoroethylene) (PTFE) filter and 15 mL of the filtrate charged into a 150-ml glass bottle. This aliquot was then treated with tetramethylethylene diamine (4.23 mmol) and n-butyllithium (4.23 mmol) and used immediately as a polymerization initiator. 

Initial enthalpies for addition of small amounts of bases to dilute solutions (0.2 M) of polymeric organolithiums at low R values ([base]/[Li]) provide direct information on the strength of the base interactions as well as the steric requirements of the bases. Data for initial enthalpies of interaction for a variety of bases with poly(styryl)lithium in benzene are listed in Table 8 88,89>. It is especially significant to note that the basicity order observed for poly(styryl)lithium (TMEDA > diglyme > THE > 2,5-Me2THF > dioxane > TMEDP > Et3P > EtzO = Et3N) is very similar to the order for simple alkyllithiums (see Tables 6 and 7) TMEDA > THF >... 

The presence of residual initiator in the polymerization leading to the polystyrene whose distribution is shown in Fig. 8 b was verified as follows 108). At the completion of the polymerization, both THF and monomer were added to the system. The intensity of the absorption band of poly(slyryl)lithium (Xinax 334 nm) was found to increase to an extent which demonstrated that ca. 75% of the added t-butyllithium remained at the completion of the first polymerization. 

---