Functional polyisobutylenes via electrophilic cleavage/alkylation

Abstract

Lewis-acid catalyzed degradation of poly(isobutylene-co-isoprene) (butyl rubber) in the presence of an alkoxybenzene compound was studied as a new route toward low molecular weight multifunctional polyisobutylenes. Simultaneous cleavage and functionalization of butyl rubber was conducted at 270 8C and 240 8C under TiCl 4 or AlCl 3 catalysis in 60/40 hexane/methylene chloride cosolvents in the presence of (3-bromopropoxy)benzene (BPB) for various times up to 24 h. The butyl rubber (EXXON TM Butyl 365) possessed M n 5 1.91 3 10 5 g/mol, PDI 5 1.66 (GPC/MALLS), and 2.30 mol % isoprene units (nearly exclusively trans21,4). At 270 8C with TiCl 4 , molecular weight was reduced to various values within the range 7 to 11 3 10 3 g/mol depending on conditions; lower BPB concentration produced lower molecular weight. However, the ratio of isobutylene repeat units to BPB units (IB/Q) remained constant at about 43:1, which is approximately the same as the ratio of isobutylene to isoprene repeat units (IB/IP) in the starting butyl rubber (42.5:1). At 240 8C with TiCl 4 , molecular weight was reduced to about 5 3 10 3 g/mol, and IB/Q was reduced below IB/IP, indicating nearly a difunctional telechelic structure. AlCl 3 was a more active catalyst and produced results similar to TiCl 4 at 240 8C, even when used at seven times lower concentration.

Polyisobutylene containing covalently bound antioxidant moieties

“…A wide range of EW Q s and average functionalities (F n ) can be obtained by varying temperature, reaction time, F IP of the butyl rubber starting material, identity/concentration of the Lewis acid, quencher (i.e., Friedel–Crafts substrate) concentration, and butyl rubber concentration. Recently, our laboratory reported the cleavage/alkylation reaction of butyl rubber (F IP = 0.0230) using (3‐bromopropoxy)benzene . The latter is a versatile quencher that yields primary‐bromide functional groups along the PIB backbone for easy synthetic modification .…”

“…Characterization via GPC/MALLS indicated that Butyl 068 had a number average molecular weight () of 3.37 × 10 5 g/mol and a dispersity (Ð) of 1.29. 1 H NMR analysis showed that the mole fraction of isoprene (IP) comonomer units in the copolymer, F IP , was equal to 0.0108, and that the average IB homopolymer sequence length, n IB = IB units/IP units (assuming isolated IP units) was 91.6 . From the latter value, the isoprene equivalent weight, EW IP , was calculated to be 5.21 × 10 3 g/mol .…”

“…1 H NMR analysis showed that the mole fraction of isoprene (IP) comonomer units in the copolymer, F IP , was equal to 0.0108, and that the average IB homopolymer sequence length, n IB = IB units/IP units (assuming isolated IP units) was 91.6 . From the latter value, the isoprene equivalent weight, EW IP , was calculated to be 5.21 × 10 3 g/mol . Commercial control samples (Oppanol) were donated by BASF, Ludwigshafen, Germany; characterization via GPC/MALLS indicated that Oppanol B14 SFN had = 64,500 g/mol and Ð = 1.60, while Oppanol B15 SFN possessed = 74,100 g/mol and Ð = 1.53.…”

“…The following is a representative procedure adapted from Campbell et al . Butyl 068 (6.01 g, 1.15 mmol IP units) was dissolved in a mixture of 90 mL n ‐hexane and 60 mL dichloromethane, within a 250 mL round‐bottom flask equipped with a magnetic stir bar.…”

“…Additionally, the solubility characteristics of the modified polymer should be sufficiently similar to the unmodified polymer, such that the two can be used interchangeably in formulations. Recently, we reported a method for producing multifunctional PIBs via acid‐catalyzed cleavage/alkylation reactions of PIB‐based copolymers in the presence of an activated Friedel–Crafts substrate or “quencher” molecule, specifically an alkoxybenzene . The resulting PIB‐based copolymers were linear and possessed multiple alkoxyphenyl moieties pendant to the polymer backbone, as well as covalently bound to the polymer chain ends.…”