Studies on Dilithium Initiators. 4. Effect of Structure Variations

Abstract

New double 1,l-diphenylethylene (DDPE) compounds with different substituent groups on 1,3-bis(l-phenylethenyl)benzene (PEB) and samples of l,3-bis[ 1-(methylphenyl)ethenyl]benzene (MPEB) with different methyl group positions on the phenyl rings were prepared. Included in the preparation was also a non-DDPE diolefinic compound in which the center phenyl ring of PEB was replaced by a saturated one. The behavior of isoprene polymerization initiated by the dilithium initiators obtained by the addition reaction of sec-butyllithium (8-BuLi) with these diolefinic compounds was studied. The slow propagation from the initial initiator-isoprene adduct observed for the initiators based on PEB and W E B was not affected by any of the structural variations. Structural variations, however, had an influence on the relative reaction rate of the two double bonds on the diolefinic compounds with s-BuLi. Replacement of the center phenyl ring with a saturated cyclohexane ring drastically reduced the double bond reaction rate with s-BuLi. IntroductionA family of dilithium initiators (DLI) prepared by the addition reaction of see-butyllithium (s-BuLi) with compounds containing two 1,l-diphenylethylene functional groups (DDPE; double 1,l-diphenylethylene compounds) have been rep0rted.l Unlike other DLI, they can be made in hydrocarbon solvents without the presence of any polar additives. The reaction was swift, and the DLI can be made nearly free of residual reactants and other byproducts. Among the members of the DLI reported, the ones derived from the DDPE compounds, l,&bis(lphenyletheny1)benzene (PEB) and l,&bis[l-methylpheny1)ethenyll benzene (MPEB) are most interesting because of their solubilities in hydrocarbon solvents.2 Useful high strength styrene-butadiene-tyrene and other butadiene triblock copolymers3f4 have been prepared from these DLI. However, styrene-isoprene-styrene (SIS) triblock copolymer made from them was weak and had a broad bimodal molecular weight distribution.The formation of the bimodal distribution in isoprene polymerization has been attributed to the inadvertent presence of monofunctional initiator (MFI) in the DLI systems and the slow propagation from the initial addition product of isoprene with the DLL5 The initiation by a MFI and the subsequent propagation were fast, and the polyisoprene derived from it became the high molecular weight peak of the bimodal distribution. The initiation of isoprene by a DLI, though not slow, led to a very slow propagation from the initial addition product of isoprene with the initiator. The main peak of lower molecular weight and broader molecular weight distribution was the polyisoprene from the DLI. Complete elimination of MFI from any DLI system was difficult. As low as 2-3% of MFI would cause the formation of bimodal distribution and a deterioration of SIS properties.This slow propagation of isoprene from the initial DLIisoprene adduct was believed to be caused by a strong intramolecular association of the adduct. Polar additives, particularly N,lV,N'"",N''-pentameth...

Anionic polymerization: High vacuum techniques

“…The major problem is that these initiators are usually highly associated in hydrocarbon solvents, leading to the formation of insoluble products, which are not reactive initiators. One of the most effective difunctional initiators, soluble in hydrocarbon media, is the one formed by the addition reaction of sec ‐BuLi with 1,3‐bis(1‐phenyl‐ethenyl)benzene 56–59 …”

Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons, mathematical simulations, and their experimental testing

“…They assumed that the cyclic associates are considerably less reactive than the intermolecular acyclic ones. The authors of the subsequent works [2][3][4][5], in which this phenomenon was investigated in more detail, accepted this explanation too. Madani and colleagues [6] attempted to calculate the fraction of the cyclic associates depending on the length of the "living" bifunctional macromolecules and described the obtained results based on these calculations.…”

“…Authors of the works mentioned above [1][2][3][4][5][6] is easy to show that the concentration of the "living" active sites in such gel is huge at the initial stage of polymerization, i.e. for the very short chains.…”

Synthesis and Evaluation of Multifunctional Anionic Initiators Based on n‐BuLi and Meta‐Diisopropenyl Benzene

“…According to Hofmans and Beylen, polar additives can prevent chain aggregation due to the higher solvation capacity of these solvents when interacting with the lithium cations. Typical polar additives are ethers and amines . However, the use of polar additives can also exert significant effects on the reaction between the diolefin and the n‐BuLi, leading to production of different initiators …”