Mechanistic Role of Lewis Bases and Other Additives in Quasiliving Carbocationic Polymerization of Isobutylene

Abstract

Isobutylene was initiated using 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene/TiCl4 in 60/ 40 hexane/methyl chloride: [IB]0 ) 1.0 M, [TiCl4] ) 0.12 or 0.24 M, [t-Bu-m-DCC] ) 0.0119 M, T ) -(40-80) °C. Most polymerizations contained a Lewis base or other additive, i.e., 2,4-dimethylpyridine, 2,6-di-tert-butylpyridine, tetra-n-butylammonium chloride, and/or pyridine hydrochloride. Polymerizations containing an additive yielded theoretical molecular weights, narrow polydispersity index, and apparent absence of irreversible chain termination (linear kinetic plots, ATR-FTIR spectroscopic data) and chain transfer, with two exceptions: coupled product was obtained at -40 °C, and protic initiation occurred with n-Bu4NCl alone. Polymerizations without an additive produced bimodal molecular weight distributions; however, essentially all chains were initiated from t-Bu-m-DCC. With an additive, Eact for propagation was -(5.3-5.5) kcal/mol. Removal of additives increased polymerization rate moderately at -80 °C but dramatically at -60 and -40 °C; this yielded higher Eact compared to that of systems containing additives. These results indicated that both paired and unpaired (free) ions are propagating species in absence of additives, with free ions less important at lower temperatures; free ion concentration and lifetime suggested the presence of adventitious common ions and chain transfer between free ions and tert-chloride-terminated PIB chains. The primary role of additives is suppression of free ions through in situ production, via the scavenging of protic impurities, of common ions.

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization

“…Molecular weights and polydispersities (PDIs) of polymers were determined using a SEC system consisting of a Waters Alliance 2690 Separations Module, an on-line multiangle laser light scattering (MALLS) detector (MiniDAWNe, Wyatt Technology Inc.) and an interferometric refractometer (Optilab DSPe, Wyatt Technology Inc.), as previously described [11]. Freshly distilled THF served as the mobile phase and was delivered at a flow rate of 1.0 ml/ min.…”

“…A ReactIR 1000 reaction analysis system (light conduit type) (ASI Applied Systems, Millersville, MD), equipped with a DiComp (diamond composite) insertion probe, a general-purpose type PR-11 platinum resistance thermometer, and CN76000 series temperature controller (Omega Engineering, Stamford, CT), was used to collect spectra of the polymerization components and monitor reactor temperature in real time as previously described [11]. The light conduit and probe were contained within a glove box (MBraun Labmaster 130), equipped with a hexane/heptane cold bath.…”

“…Quasiliving carbocationic polymerization (QCP) is applicable to monomers such as isobutylene (IB) and styrene and yields, among other interesting structures, poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) triblock copolymers [10][11][12] with predictable molecular weights, narrow MWDs, and well-defined block junctions. The synthetic utility of QCP is limited by the relatively narrow range of monomers to which it can be applied.…”

Isobutene–isoprene copolymerization initiated by [Cp∗MMe2][(n-C18H37E)B(C6F5)3] (M=Ti, Hf; E=O, S) and related compounds

“…The analogous Cp * HfMe 3 /B(C 6 F 5 ) 3 initiator system was also assessed, with and without co-initiators, and the results (experiments [13][14][15][16][17][18][19][20] show that it is almost as effective as the titanium system. For the most part, conversion are high in polar solvents although molecular eights are relatively low.…”

“…Although the chemistry of the propagation and chain transfer steps is extremely complex [10][11][12][13], it seems generally agreed [10,11,14] that rates of chain transfer are strongly affected by the nature of the counteranion and can be minimized by utilizing anions which are very weakly nucleophilic. Pi et al [14] by carrying out proton-induced polymerization of IB in the presence of the weakly nucleophilic anion [B(C 6 F 5 ) 4 ] À , thereby obtaining PIB of unusually high molecular weight.…”