Dilithium Anionic Initiators Based on Double 1,1-Diphenylethylene Compounds

Abstract

Triblock copolymers containing a polydiene as the center block are important thermoplastic elastomers. Commercially they are made by anionic polymerization using butyllithium initiators.' To assure the optimum polydiene microstructure for good elastomeric properties, pure hydrocarbon solvents are used in all phases of the polymerization. Many monomers requiring polar solvents or additives for polymerization cannot be conveniently used in such processes. This restriction is removed if a dilithium initiator is used to polymerize first the center polydiene block. For example, Fetters and Morton2 prepared poly(oc-methylstyrene-isoprene-oc-methylstyrene), also, Morton and Mikesell" prepared poly(ethy1ene sulfidediene-ethylene sulfide) by such a route. The initiator used by them was 1,4-dilithio-1,1,4,4-tetraphenylbutane which was prepared by the reaction of 1,l-diphenylethylene with lithium dispersion in a hydrocarbon solvent containing 15% anisole. The amount of anisole present was shown to give no ill effect on the microstructure of the polydiene block. Other known dilithium initiators are formed by the reaction of metallic lithium with an aromatic hydrocarbon4 or by the addition reaction of sec-butyllithium with di~inylbenzene~ or diisopropenylbenzene6 in hydrocarbon solvents. The last preparative route appears to be the simplest. More recently Foss, Jacobson, and Sharkeyi prepared an initiator by reacting sec -butyllithium with m-diisopropenylbenzene in cyclohexane containing a small amount of triethylamine as an additive.It has been r e p~r t e d~.~ that butyllithium adds readily to 1,l-diphenylethylene (1,l-DPE) in hydrocarbon solvents. The product can initiate isoprene and butadiene to form copolymers with 1,l-DPE but because of the bulkiness of the phenyl groups 1,l-DPE does not homopolymerize. It appears then the addition of butyllithium to compounds containing two 1,l-diphenylethylene groups should produce useful dilithium initiators. We have prepared four such double 1,l-DPE compounds:

Trifunctional organolithium initiator for living anionic polymerization in hydrocarbon solvents in the absence of polar additives

“…The advantages of a built-in ether group have also been described in the work of Sanderson et al 33 The concept of intramolecular ether moieties in a multifunctional initiator was first presented by Tung et al 11 Several difunctional initiators based on DPE types have been extensively studied in many chemical variations in anionic polymerization. It will also assist in avoiding extended pi-conjugation of the resulting carbanion and possibly to reduce inter/intra molecular cross-association.…”

“…11,16,33 The previously reported trifunctional DPE precursor by Quirk et al, formed aggregates upon stoichiometric amount of sec-BuLi addition and required the use of a polar additive for polymerization to simultaneously initiate at all three sites. The chemistry and functionality of the diphenylethylene compound, and the chemical advantages of a built-in ether group, were taken into consideration during its design.…”

“…5 Attempts to synthesize multifunctional initiators via direct multilithiation, using multifunctional alkyl halides, have been limited due to eliminations caused by lithium-halogen exchange and intermolecular coupling reactions. 9,10 Highly studied difunctional organolithium initiators in non-polar solvents based on double DPE groups have been thoroughly studied by Tung,11,12 Quirk,13,14 Hocker, 15 and Szwarc. 8 However, alkyllithium compounds and their state of aggregation have complicated the synthesis of di-and trifunctional organolithium initiators in non-polar media.…”

Ionic Polymerization

“…In principle, block copolymers are accessible by sequential addition of monomers to either monofunctional or bifunctional [128,129] initiators (see Scheme 7.4, where the route from a monofunctional initiator to a three-block copolymer is shown as an example). The amount of undesired byproducts -homopolymers or di-block copolymers -depends on the reactivity ratios relative to propagation given in the scheme.…”

Hydroxytelechelic hydrocarbon copolymers with high aging resistance for elastomeric materials

“…The ease of the HTPB preparation by radical polymerization is balanced by the lack of regiospecificity as well as end group specificity. Living anionic polymerization therefore offers a potential solution22–24 but remains limited due to still some percents of 1,2 units, costly purity cares, and a necessary termination with an oxirane. Ring Opening Metathesis Polymerization (ROMP) of cyclic olefins of various sizes gives opportunity to get rid of vinylic units25, 26 and to decrease the number of backbone unsaturations.…”