30 research outputs found

    Liquid chromatography at critical conditions (LCCC): Capabilities and limitations for polymer analysis

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    This paper investigates liquid chromatography at critical condition (LCCC) for polymer analysis. Based on controversial claims on the separation of cyclic polymers from linear analogues in the literature, the efficiency of LCCC for separation and purity analysis is questioned. Polyisobutylene (PIB) and poly(3,6-dioxa-1,8-octanedithiols) (polyDODT) were used for the study. The structure of low molecular weight cyclic and linear polyDODT was demonstrated by MALDI-ToF. NMR did not show the presence of thiol end groups in higher molecular weight PIB-disulfide and polyDODT samples, so they were considered cyclic polymers. When a low molecular weight polyDODT oligomer with only traces of cycles, as demonstrated by MALDI-ToF, was mixed with an M_n = 27 K g/mol cyclic sample, LCCC did not detect the presence of linear oligomers at 6 wt%. Based on the data presented here, it can be concluded that the LCCC method is not capable of measuring <6 wt% linear contamination so earlier claims for cyclic polystyrene (PS) samples purified by LCCC having <3% linear contaminants are questioned

    Liquid chromatography at critical conditions (LCCC): Capabilities and limitations for polymer analysis

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    This paper investigates liquid chromatography at critical condition (LCCC) for polymer analysis. Based on controversial claims on the separation of cyclic polymers from linear analogues in the literature, the efficiency of LCCC for separation and purity analysis is questioned. Polyisobutylene (PIB) and poly(3,6-dioxa-1,8-octanedithiols) (polyDODT) were used for the study. The structure of low molecular weight cyclic and linear polyDODT was demonstrated by MALDI-ToF. NMR did not show the presence of thiol end groups in higher molecular weight PIB-disulfide and polyDODT samples, so they were considered cyclic polymers. When a low molecular weight polyDODT oligomer with only traces of cycles, as demonstrated by MALDI-ToF, was mixed with an M_n = 27 K g/mol cyclic sample, LCCC did not detect the presence of linear oligomers at 6 wt%. Based on the data presented here, it can be concluded that the LCCC method is not capable of measuring <6 wt% linear contamination so earlier claims for cyclic polystyrene (PS) samples purified by LCCC having <3% linear contaminants are questioned

    Kinetics of the Carbocationic Homopolymerization of Isobutylene with Reversible Chain Termination

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    The kinetics of isobutylene (IB) polymerization, initiated by 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCI4 initiator/coinitiator system in methyl chloride/methyl/cyclohexane solvent mixture at −90°C, was investigated. The existence of a dynamic equilibrium between dormant and active species was verified by obtaining ‘living’ conditions and 100% initiator efficiency using a large excess of initiator over coinitiator [TMPCI]0 \u3e\u3e [I]4. It was shown that the polymerization rate is first order in monomer and is directly proportional to [TiCI4]0 and [TMPCI]0. From polymerization rate data the overall polymerization rate constant k′p=kpK1 was calculated, where kp is the rate constant of propagation and K1 = k1/k−1 is the equilibrium constant for the dormant-active species equilibrium. The rate of TMPCI consumption was shown to be first order in [TMPCI]. While polymer concentration increased during the rather slow initiator consumption, the polymerization rate did not accelerate as the concentration of active species, determined by the dormant-active species equilibrium, remained constant. From initiator consumption data k1 and kp/k−1 values were estimated. The estimated rate constant values were used to simulate monomer and initiator conversion histories versus time. The simulated histories were in good agreement with measured data

    Carbocationic Polymerization

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    This article summarizes fundamental and general aspects of carbocationic polymerizations, with a historical overview and up-to-date references. Following general considerations, the basic elements of carbocationic polymerization, such as monomers, initiating systems, solvents, and temperature, are discussed. Special attention is given to carbocation stability and monomer nucleophilicity, and dynamic interactions. The section on the kinetics of carbocationic polymerization presents current understanding of the elementary reactions—initiation, propagation, termination, and transfer reactions, and copolymerization. Controlled (living) carbocationic polymerization is discussed in a separate section. Finally, industrial carbocationic polymerizations are reviewed

    Chain Carriers and Molecular Weight Distribution in Living Carbocationic Polymerizations

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    See Lin

    New High-throughput Approach to Measure Copolymerization Reactivity Ratios Using Real-time Ftir Monitoring

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    This paper presents a novel high-throughput approach to measure copolymerization reactivity ratios from a single experiment using high-speed real-time Fourier transform infrared (FTIR) monitoring of the isobutylene/isoprene (IB/IP) system initiated by 2-chloro-2,4,4-trimethyl-pentane (TMPCl)/TiCl4 in hexane/methyl chloride (Hx/MeCl) 60:40 v/v solvent at −80 °C. Traditional polymer analysis is severely limited in this system, which is riddled by side reactions. The reactivity ratios calculated by linear (Mayo-Lewis and Kelen-Tüdös) methods and by a nonlinear least square (NLLS) method (van Herk algorithm) showed good agreement with r1 =1.32 and r2 = 0.74 calculated using Mayr\u27s nucleophilicity scale. Combination of the Kelen-Tüdös and NLLS methods yielded r1 = 1.17 ± 0.01 and r2 = 0.99 ± 0.02. These values agree well with those reported by Thaler et al. but disagree with most reported data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4084–4100, 200

    Synthesis and Characterization of Arborescent (Hyperbranched) Polyisobutylenes from the 4-(1, 2-oxirane-isopropyl) Styrene Inimer

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    The synthesis of the novel inimer (initiator-monomer) 4-(1,2-oxirane-isopropyl)styrene EPOIM and the copolymerization of this inimer with isobutylene (IB) to form arborescent polyisobutylene (PIB) is described. Polymerizations were accomplished by use of TiCl4coinitiator and the effect of reaction conditions was investigated. Size exclusion chromatography (SEC) was used demonstrate EPOIM incorporation across the whole molecular weight distribution. The average number of branch points (B) per chain measured by use of selective link destruction increased with increasing EPOIM/IB ratio and decreased with [TiCl4]. Large scale polymerizations were carried out based on results from small scale polymerizations. Architecture analysis carried out through use of branching parameters based on the radii of gyration Rg and hydrodynamic radii Rh measured by multidetector SEC corroborated the proposed arborescent architecture. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5847–5856, 200

    Controlled/living Carbocationic Copolymerization of Isobutylene with Alloocimene

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    The first example of a living carbocationic polymerization in emulsion is presented. Isobutylene was copolymerized with alloocimene, a tri-terpene. AFM, TEM, and DSC analysis demonstrated a phase separated nanostructure. NMR and TGA revealed the presence of a diblock structure in the material that displayed thermoplastic elastomeric properties with 6 MPa tensile strength and 1000% strain at break. Triblocks were also prepared by sequential monomer addition, yielding 12 MPa tensile strength with 640% strain at break

    Living Carbocationic Polymerization Xiv: Living Polymerization of Isobutylene with Ester.Ticl4 Complexes

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    The living polymerization of isobutylene (IB) has been induced by cumyl acetate·TiCl4 and cumyl propionate·TiCl4 complexes in CH2Cl2/n-C6H14 and CH3Cl/n-C6 H14 mixtures under conventional laboratory conditions at −40°C. The living nature of the polymerization was demonstrated by linear M̄n versus Wp (g PIB formed) plots starting at the origin. DPn obeys [IB]/[cumyl acetate·TiCl4] and molecular weight distributions (MWD) are very narrow, M̄w/M̄n = 1.05–1.13. PIBs having M̄n \u3e40000 have been prepared. The effects of the nature of the solvent, solvent composition, nature of the ester, ester/TiCl4 ratio and concentrations on rates, M̄ns and MWDs have been investigated. The living polymerization is faster by the cumyl acetate-TiCl4 than by the cumyl propionate·TiCl4 complex. The rate of living polymerizations is negligible at CuAc/TiCl4 = 1 and increases significantly in the presence of stoichiometric excess of TiCl4 over the ester. Undesirable initiation due to protogenic impurities can be suppressed by employing relatively nonpolar (hexane-rich) media, by increasing the ester/TiCl4, ratio, or by the addition of a non-initiating ester (ethyl acetate); however, the rates decrease as a consequence of these measures. Polymerizations induced by mixtures of cumyl acetate·TiCl4/cumyl propionate·TiCl4 complexes yield monomodal narrow MWDs indicating rapid ester exchange at the growing site which in turn suggests ionic active species. The kinetic findings are explained by a mechanistic scheme that rests on two propositions: Propagation involves activated (most probably ionized) polymer-ester·Lewis acid complexes, and free (uncomplexed) Lewis acid causes irreversible destruction of living propagation
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