TiCl4 Reaction Order in Living Isobutylene Polymerization at Low [TiCl4]:[Chain End] Ratios

Isobutylene (IB) polymerization kinetics at -80 degrees C were monitored in real time using midinfrared ATR-FTIR spectroscopy, with diamond-composite insertion probe and light conduit technology. Monomer concentration as a function of time was obtained by monitoring the absorbance at 887 cm(-1) associated with the = CH2 wag of IB. Polymerizations were initiated using 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (t-Bu-m-DCC) or 2-chloro-2,4,4-trimethylpentane (TMPC1) in conjunction with TiCl4 co-initiator, in hexane/methyl chloride or methylcyclohexane/methyl chloride (60:40 v/v) cosolvents. Either 2,4-dimethylpyridine (DMP) or 2,6-di-tert-butylpyridine (DTBP) was used as an electron donor (ED). Reaction conditions were [ED] = 2.00 x 10(-3) M, [IB](0) = 1.0 M, and [TMPC1] (or 2[t-Bu-m-DCC]) = 2.08 x 10(-2) M. Go-initiator concentrations were designed to be less than or equal to the growing chain end concentration and ranged from [TiCl4] = 7.20 x 10(-3) to 2.28 x 10(-2) M. Steady-state polymerization kinetics were found to be independent of the nature of initiator, slightly faster when conducted with the noncomplexing DTBP rather than DMP and slightly faster when methylcyclohexane rather than hexane was utilized as the hydrocarbon diluent. In all cases, polymerizations exhibited a second-order dependence on the effective TiCl4 concentration ([TiCl4](eff)). The latter was defined in terms of the nominal amount of TiCl4 added to the reactor minus the fraction calculated to be unavailable for co-initiation of the polymerization due to formation of a neutral complex with the ED and/or pyridinium salts as a result of proton scavenging. Second-order dependence on the effective TiCl4 concentration was attributed to the predominance in the propagation reaction of active carbocations associated with dimeric counteranions of the form Ti2Cl9-

Initiation Effects in the Living Cationic Polymerization of Isobutylene

Isobutylene (IB) polymerization kinetics were monitored in real time using mid-infrared ATR-FTIR spectroscopy, with diamond-composite insertion probe and light conduit technology. Monomer concentration as a function of time was obtained by monitoring the absorbance at 887 cm(-1) associated with the =CH2 wag of IB. The measured intensity of this band was found to decrease slightly with increasing temperature (0.42% per 1.0 degrees C). Polymerizations were initiated using the aromatic difunctional initiator 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (t-Bu-m-DCC) and a series of monofunctional aliphatic initiators: tert-butyl chloride (t-BuCl), 2-chloro-2,4,4-trimethylpentane (TMPCl), and 2-chloro-2,4,4,6,6-pentamethylheptane (TIBCl). The co-initiatior was TiCl4 and the Lewis base 2,4-dimethylpyridine (DMP) was used as an electron donor. Polymerizations were performed in methylcyclohexane/methyl chloride (60:40 v/v) cosolvents at temperatures ranging from -80 to -40 degrees C. Reaction conditions were consistently [DMP] = 2.00 x 10(-3) M and [IB](0) = 1.0 M. Initiator concentrations were [TIBCl] = [TMPCl] = [t-BuCl] = a[t-Bu-m-DCC] = 2.08 x 10(-2) M. Go-initiator concentrations ranged from [TiCl4] = 7.20 x 10-3 to 6.79 x 10-2 M. Inspection of the monomer concentration vs time data revealed a number of deviations from first,order decay, depending on initiator. It was observed that polymerizations initiated with t-Bu-m-DCC exhibited an initial regime of rapid monomer consumption (RMC), which is accompanied by a significant reaction exotherm. This phenomenon was attributed to a higher ionization equilibrium constant for the tert-benzylic chloride initiator relative to tert-alkyl chloride PIE chain ends. It was proposed that cations formed from the initiator undergo a number of propagation steps prior to the first ion-pair collapse and that this number yields an estimate of the number of IB units consumed per successful ionization during propagation. This number was observed to decrease with increasing temperature. It was also proposed that the RMC event may offer a means for the experimental determination of the absolute rate constant for IB propagation in TiCl4-co-initiated polymerizations. RMC behavior was completely absent with aliphatic initiators; initiation was extremely slow with t-BuCl and sluggish with TMPCl, relative to TIBCl

Real-Time Monitoring of Carbocationic Polymerization of Isobutylene Using In Situ FTIR-ATR Spectroscopy with Conduit and Diamond-Composite Sensor Technology

Isobutylene (IB) polymerization kinetics were monitored in real time using mid-infrared FTIR-ATR spectroscopy, with a diamond-composite insertion probe and light conduit technology. Polymerization was initiated using the 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (t-Bu-m-DCC)2,4-dimethylpyridine (DMP)/TiCl4 (1:2:20) system in hexane/methyl chloride (60:40 v/v) cosolvents at -80 degrees C, with [t-Bu-m-DCC] = 1.90 x 10(-3) M and [IB](o) = 1.0 M. Monomer concentration as a function of time was obtained by monitoring the absorbance at 887 cm(-1) associated with the =CH2 wag of IB. The calculated apparent first-order rate constant of 8.4 x 10(-4) s(-1) was within 3% of the value determined from traditional gravimetric methods (8.6 x 10(-4) s(-1)) withing the same range of conversion. Inspection of the first-order plot generated from the FTIR data revealed a number of deviations from linearity, which were attributed primarily to a transient rise and subsequent fall in reactor temperature caused by the initial large exotherm of polymerization. An artifact associated with the method of data analysis was also identified. These small differences in instantaneous rate were not detected by the gravimetric method due to insufficient accuracy and density of data points

Synthesis and Characterization of Carboxylic Acid-Terminated Polyisobutylenes

tert-Chloride-terminated polyisobutylenes (PIB) (1020 \u3c= M-n \u3c= 6700 g/mol) were dehydrochlorinated nonregiospecifically using basic alumina, or regiospecifically either via potassium tert-butoxide or in situ quenching of quasiliving PIB. Olefin-terminated PIBs were quantitatively ozonized at -78 degrees C using hexane/methylene chloride/methanol, 62/31/7 (v/v/v) cosolvents, and an ozone generator, employing pure oxygen as source gas. The primary ozonides were reduced using trimethyl phosphite to yield pure PIB methyl ketone from exo-olefin PIB, and a mixture of PIB methyl ketone and PIB aldehyde from mixed olefin-PIB. PIB methyl ketone was oxidized to carboxylate via the haloform reaction; titration revealed near-quantitative functionalization, but the reaction was slow. Tetrahalomethane oxidation was identified as a preferred alternative method, and was conducted using either CCl4 as the reaction solvent, THF as the solvent with CCl4 in reagent amounts, or hexane as the solvent with a phase-transfer catalyst and CCl4 in reagent amounts. The system using hexane, with tetra-n-butyl ammonium chloride as phase-transfer catalyst, showed complete conversion in similar to 4 h. PIB carboxylic acid was recovered by acidification and isolation. (C) 2008 Wiley Periodicals, Inc