Rudolf Faust

Living carbocationic polymerization of isobutylene with blocked bifunctional initiators in the presence of di-tert-butylpyridine as a proton trap

Abstract The polymerization of isobutylene (IB) has been studied using 5-tert-butyl-1,3-dicumyl-chloride, 5-tert-butyl-1,3-dicumyl-methyl ether, and 5-tert-butyl-1,3-dicumyl-acetate initiators in the absence and presence of 2,6-di-tert-butylpyridine (DTBP) as a proton trap. It is demonstrated that living polymerization can be achieved in the IB/initiator/TiCl4/methylchloride-n-hexane (40:60 v:v)/DTBP/-80°C system, and that polymers with close to a Poisson molecular weight distribution can be obtained in the presence of a proton trap in concentrations only slightly higher than the concentration of protic impurities in the system. The polymerization rate is a first-order function of the monomer concentration and is not affected by the excess amount of DTBP added, which indicates that the living nature of the polymerization is not due to carbocation stabilization.

Living carbocationic polymerization of styrene in the presence of proton trap

Abstract The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl4/MeCl:methylcyclohexane 40:60 v:v/−80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl4. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.

From Rouse dynamics to local relaxation: A neutron spin echo study on polyisobutylene melts

We investigated the single chain motions of monodisperse polyisobutylene chains in the melt by neutron spin echo spectroscopy. Thereby a wide range in momentum space over a large dynamic range was covered. Motional processes from the center of mass diffusion, the Rouse dynamics to the more local relaxation processes which limit the validity of the standard Rouse model, were elucidated. The observed dynamic structure factors were analyzed in terms of relevant theoretical approaches addressing the limiting factors of the Rouse model. We found that other than claimed in the literature effects of local chain stiffness—they were treated in terms of the all rotational states model and a bending force model—cannot account for the experimental observations. It appears that additional damping effects related to an internal viscosity of the chain have to be involved, in order to explain the experimental results.

Synthesis of Branched Polymers by Cationic Polymerization

The synthesis of branched polymers by cationic polymerization of vinyl monomers is reviewed. This includes star, graft, and hyperbranched (co)polymers. The description is essentially focused on the synthetic approach and characterization results are provided as a proof of the structure. When available, specific properties of the materials are also given.

Photoinduced Smart, Self-Healing Polymer Sealant for Photovoltaics

Polyisobutylene (PIB)-based polymer networks potentially useful as smart coatings for photovoltaic devices have been developed. Low molecular weight coumarin functional triarm star PIB was synthesized via a single step SN2 reaction of bromoallyl functional triarm star PIB with 4-methylumbelliferone or umbelliferone in the presence of sodium hydride. Quantitative end functionality was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. UVA (λmax = 365 nm) induced reversible photodimerization of the coumarin moieties resulted in cross-linked elastomeric films exhibiting self-healing behavior. The extent of photodimerization/photoscission was monitored by UV-vis spectroscopy. The low oxygen (1.9 × 10(-16) mol m m(-2) s(-1) Pa(-1)) and moisture (46 × 10(-16) mol m m(-2) s(-1) Pa(-1)) permeability of the cross-linked polymer films suggest excellent barrier properties of the cross-linked polymer films. The self-healing process was studied by atomic force microscopy (AFM). For this, mechanical cuts were introduced in the cross-linked PIB films through micromachining with an AFM tip and the rate of healing induced by UV, sunlight, or both was followed by taking AFM images of the film at different time intervals during the repair process.

Quasiliving Carbocationic Polymerization. II. The Discovery: The α-Methylstyrene System

Abstract A detailed analysis of elementary reactions of carbocationic polymerization culminated in the prediction and subsequent experimental demonstration of quasiliving polymerization. Quasiliving polymers are formed in a system provided that the process of chain termination and chain transfer to monomer are absent or reversible, i.e., the propagating ability of the chain end is maintained throughout the experiment, and the molecular weight increases in proportion to the cumulative amount of monomer added. The chain end can be active (carbocation) or dormant (reactivable polymeric olefin or cation source). Chain transfer is suppressed by keeping the monomer concentration low. Quasiliving polymerizations are maintained by continuous slow feeding of dilute monomer to a charge containing the initiating or propagating species (quasiliving polymerization technique). A comprehensive kinetic scheme has been developed that describes quasiliving polymerization in quantitative terms. Quasiliving polymerization wa...

In vivo and in vitro characterization of poly(styrene-b-isobutylene-b-styrene) copolymer stent coatings for biostability, vascular compatibility and mechanical integrity

The TAXUS Express 2 Paclitaxel Eluting Coronary Stent System employs a coating consisting of the thermoplastic elastomer, poly(styrene-b-isobutylene-b-styrene; SIBS), selected for its drug-eluting characteristics, vascular compatibility, mechanical properties, and biostability. This study was conducted to evaluate the impact of different SIBS (17-51 mole % styrene) compositions on mechanical properties, chemical stability, and vascular compatibility. Mechanical property (stress-strain measurements) and stability studies were conducted on polymer films with five different styrene contents (17, 24, 32, 39, and 51 mole %). The ultimate tensile strength did not change significantly with composition, but the elongation at break decreased with increased styrene content. A pulsatile fatigue test further confirmed the mechanical stability of SIBS up to 39 mole % styrene. The vascular compatibility of five different SIBS compositions was assessed using SIBS-only coated stents, in the coronary and carotid arteries in a porcine model study. The stability of the vessel wall, rate/degree of endothelialization, inflammation, and thrombus at timepoints from 30 to 180 days were evaluated. The results confirm vascular compatibility over the range of 17-51 mole % styrene.

Living carbocationic polymerization. XXXVIII, On the nature of the active species in isobutylene and vinyl ether polymerization

Abstract The nature of the species that gives rise to living carbocationic polymerization (LP+Pzn) of isobutylene (IB) coinitiated by Friedel-Crafts acids (FCA) in the presence of electron pair donors (ED) has been investigated. It is proposed that the key species responsible for mediating LC+Pzn of IB are FCA·ED complexes, formed by Lewis acid-Lewis base interaction, where FCA = BCl3 TiCl4, and ED = ethyl acetate, tetrahydrofuran, etc. Free EDs are inhibitors of IB polymerization. These findings are in sharp contrast to those of LC+Pzn of vinyl ethers coinitiated by EtAlCl2 in which excess (i.e., free) EDs are required for the living polymerizations to occur. Comparison of IB polymerizations induced by the 2-chloro-2,4,4-trimethylpentane/BCl3 and 2-acetyl-2,4,4-trimethylpentane/BCl3 systems shows that these reactions do not proceed by the same intermediate (i.e., by tert-chlorides) and that the mechanisms of BC13- and TiC14-coinitiated living polymerizations are different. Experiments with the proton tra...

Long term in vitro biostability of segmented polyisobutylene-based thermoplastic polyurethanes

Long term in vitro biostability of thermoplastic polyurethanes (TPUs) containing mixed polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) soft segment was studied under accelerated conditions in 20% H(2)O(2) solution containing 0.1M CoCl(2) at 50 °C to predict resistance to metal ion oxidative degradation (MIO) in vivo. The PIB-based TPUs showed significant oxidative stability as compared to the commercial controls Pellethane 2363-55D and 2363-80A. After 12 weeks in vitro the PIB-PTMO TPUs with 10-20% PTMO in the soft segment showed 6-10% weight loss whereas the Pellethane TPUs degraded completely in about 9 weeks. Attenuated total reflectance Fourier transform infrared spectroscopy confirmed the degradation of Pellethane samples via MIO by the loss of the ∼1110 cm(-1) aliphatic C-O-C stretching peak height attributed to chain scission, and the appearance of a new peak at ∼1174 cm(-1) attributed to crosslinking. No such changes were apparent in the spectra of the PIB-based TPUs. The PIB-based TPUs exhibited 10-30% drop in tensile strength compared to 100% for the Pellethane TPUs after 12 weeks. The molecular weight of the PIB-based TPUs decreased slightly (10-15%) at 12 weeks. The Pellethane TPUs showed a dramatic decrease in M(n) and an increase in low molecular weight degradation product. Scanning electron microscopy (SEM) showed severe cracking in the Pellethane samples after 2 weeks, whereas the PIB-based TPUs exhibited a continuous surface morphology. The weight loss, tensile, and SEM data correlate well with each other and indicate excellent biostability of these materials.

Synthesis and Characterization of Novel Silicon‐Functional Polyisobutylenes and Their Applications: Polyisobutylene Brushes on Silicate Substrates via Living Cationic Polymerization

Abstract A series of novel chlorosilyl functional initiators have been prepared and applied for the first time in the living cationic polymerization of isobutylene (IB). Well‐defined polyisobutylenes (PIBs) carrying mono‐, di‐, and tri‐chlorosilyl head‐group, and a tert‐chloro end‐group were synthesized using newly designed silyl‐functional initiators in conjunction with TiCl4 in Hex:MeCl (60:40, v:v) at −80°C. End‐group analysis by 1H NMR spectroscopy verified the product structure and the survival of the Si‒Cl head‐groups during the polymerization. The chlorosilyl functional initiators and chlorosilyl functional PIBs have been employed for the synthesis of PIB brushes on planar silicate substrates by the “grafting from” and “grafting to” techniques. The products were characterized by x‐ray photoelectron spectra (XPS), atomic force microscopic (AFM), and ellipsometry. The “grafting from” approach yielded surface‐bound polymer brushes with more uniform surface and higher grafting density compared to the “grafting to” technique. The film thickness of PIB brushes formed by “grafting from” increased linearly with increasing molecular weight of PIB. In contrast, PIB brushes produced by “grafting to” gave constant thickness independent of the molecular weight of PIB.