Synthesis and characterization of multiarm star-branched polyisobutylenes: Effect of arm molecular weight

A series of star-branched polyisobutylenes with varying arm molecular weights was synthesized using the 2-chloro-2,4,4-trimethylpentane/TiCl₄/pyridine initiating system and divinylbenzene (DVB) as a core-forming comonomer (linking agent). The resulting star-branched polymers were characterized with regard to the weight-average number of arms per star molecule (N̄_w) and dilute solution viscosity behavior. As the molecular weight of the arm (M̄_{w, arm}) was increased, dramatically longer star-forming reaction times were needed to produce fully developed star polymers. It was calculated that N̄_w varied from 50 to 5 as the M̄_{w, arm} was increased from 13,000 to 54,000 g/mol. The radius of gyration, R_g, of the star polymers was observed to increase as M̄_{w, arm} was increased. The solution properties of the star polymers were evaluated in heptane using dilute solution viscometry. It was determined that the stars had a much higher [η] compared to the respective linear PIB arms, but a much lower [η] compared to a hypothetical linear analog of an equivalent molecular weight. The dependence of [η] on temperature for the stars and linear arms was very small over the temperature range 25 to 75°C, with only a very slight decrease with increasing temperature. [η]_star was also determined to increase with increasing M̄_{w, arm}, but decrease with increasing M̄_{w, star}. The branching coefficient, g′, calculated for the stars at 25°C, increased as N̄_w decreased and agre ed well with literature values for other star polymer systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3767–3778, 1997     

Polyisobutylene-containing block polymers by sequential monomer addition. IV. New triblock thermoplastic elastomers comprising high Tg styrenic glassy segments: Synthesis,characterization and physical properties

New linear triblock thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by two glassy endblocks of various styrenic polymers have been synthesized by living carbocationic polymerization by sequential monomer addition. First isobutylene (IB) was polymerized by a bifunctional tert-ether (dicumyl methyl ether) initiator in conjunction with TiCl₄ coinitiator in CH₃Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at ?80°C. After the living narrow molecular weight distribution PIB midblock ( = 1.1–1.2) has reached the desired molecular weight, the styrenic monomers together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to start the blocking of the glassy segments from the living ⊕PIB⊕ chain ends. While p-methylstyrene (pMeSt), p-t-butylstyrene (ptBuSt) and indene (In) gave essentially 100% blocking to the corresponding glassy endblocks, the blocking of 2,4,6-trimethylstyrene (TMeSt) and α-methylstyrene (αMeSt) were ineffective. Uncontrolled initiation by protic impurities was prevented by the use of DtBP. In the simultaneous presence of DtBP and the strong ED N,N-dimethylacetamide (DMA), TPEs with good mechanical properties (10–20 MPa tensile strength, 300–600% elongation) were prepared. The products exhibit a low and a high temperature T_g characteristic of phase separated rubbery and glassy domains. The service temperature of these new TPEs exceeds that of PSt–PIB–PSt triblock copolymers due to the higher T_gs (PpMeSt = 108, PptBuSt = 142 and PIn = 220–240°C) of the outer blocks. The T_g of the glassy blocks can be regulated by copolymerizing two styrene derivatives; a triblock copolymer with outer blocks of poly(pt-butylstyrene-co-indene) showed a single glassy transition T_g = +165°C, i.e., in between that of PptBuSt and PIn. Virgin TPEs have been repeatedly compression molded without deterioration of physical properties. The high melt flow index obtained with a TPE containing PptBuSt endblocks suggests superior processability relative to those with PSt end-blocks. The tensile strength retention at 60°C of the former TPE is far superior to that of a PSt–PIB–PSt triblock of similar composition.     

Characterization of Polymer Architectures by Multidetection Size Exclusion Chromatography

Summary: This paper discusses the analysis of star-branched and dendritic polyisobutylenes (PIBs) using branching parameters based on radii of gyration R_g,z and hydrodynamic radii R_h,z. R_g,z and R_h,z were measured by Size Exclusion Chromatography equipped with a Wyatt Technology Viscostar viscometer (VIS), a Wyatt Optilab DSP RI detector, a Wyatt DAWN EOS 18 angle Multiangle Light Scattering (MALS) detector and a Wyatt Quasi-elastic Light Scattering QELS detector. Branching parameters were calculated from these measurements and compared with those computed for these architectures.     

Synthesis of triphenylsilyl- and triphenylmethyl-telechelic polyisobutylene: An approach to the synthesis of multi-ion telechelic ionomers

Triphenylsilyl- and triphenylmethyl-telechelic polyisobutylene (PIB) were prepared by lithiation of three-arm star PIBs carrying either olefinic or tert-alkyl chloride end groups, followed by reaction with triphenylsilyl chloride or triphenylcarbenium ion, respectively. Since the lithiated intermediate is a substituted allylic carbanion, the chain end also possesses a double bond which is located β-γ relative to the silyl or triphenylmethyl group. The phenyl groups were incorporated into the polymers to provide extra sites for sulfonation, in addition to the double bond, to enable the synthesis of multi-ion telechelic ionomers. ¹H- and ¹³C-NMR spectroscopy showed that triphenylsilylation and triphenylmethylation were essentially quantitative when applied under the prescribed conditions to either the model compound, 2,4,4-trimethyl-1-pentene, or to the telechelic PIBs. It was observed that exhaustive sulfonation of these materials using acetyl sulfate or chlorosulfonic acid yielded only about 50% sulfonation of the available sites. This suggests that sulfonation of closely adjacent, multiple sites within the same molecule fails due to deactivation of the remaining sites after one or perhaps two sulfonations. However, the triphenylsilyl- and triphenylmethyl-telechelic PIBs represent novel prepolymers which can perhaps be derivatized by some method other than sulfonation, and the general concept for producing telechelic ionomer precursors with multiple sulfonation sites may prove successful with other moieties containing spacer groups between sites. © 1993 John Wiley & Sons, Inc.     

Analysis of 1H-NMR spectra of various end-functionalized polyisobutylenes

¹H-NMR spectra of various telechelic (i.e., ～ CH₂C(CH₃)₂Cl, ～ CH₂C(CH₃)?CH₂, ～ CH?C(CH₃)₂, and ～ CH₂CH(CH₃)CH₂OH capped) polyisobutylenes (PIB) have been analyzed. The products were prepared by living carbocationic polymerization followed by end-group functionalization. Shielding and deshielding effects strongly influence the ¹H-NMR spectra of these products. Inductive effects (chlorine-ended PIBs), magnetically anisotropic end-groups (olefin groups and phenyl rings), allylic coupling (olefin end-groups), chirality (hydroxyl end-groups), and the interaction of these effects on the ¹H-NMR spectra are discussed. Numerous heretofore unidentified resonances have been assigned and better insight into the detailed structure of end-functionalized PIBs has been obtained. © 1994 John Wiley & Sons, Inc.     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

Effect of reaction conditions on synthesis and properties of multiarm star-branched polyisobutylenes

A series of multiarm star-branched polyisobutylenes was synthesized from narrow polydispersity arms with molecular weights ranging from 12,000 to 60,000 g/mol, via living carbocationic polymerization using the cumyl chloride/TiCl₄/pyridine initiating system and divinylbenzene (DVB) as core-forming comonomer. The effect on star development of arm molecular weight, temperature, solvent composition, and DVB concentration was studied. The rate of star formation and the weight-average number of arms per star polymer, N̄_w, were found to scale inversely with arm molecular weight; N̄_w = 60 was attained for 13,100 g/mol arms, but N̄_w = 2.5 for 60,000 g/mol arms. It was established that star formation was much faster at −80°C compared to 23°C, regardless of solvent composition. For hexane : methyl chloride (MeCl) solvent compositions containing from 40 to 60 vol % MeCl, star–star coupling was observed at −80°C, but not at 23°C, even after 312 h; for the most polar 40 : 60 hexane : MeCl composition, star–star coupling was so extensive at −80°C that gelation was observed after only 44 h. The rate of star formation was found to be substantially higher in 60 : 40 hexane : MeCl compared to 60 : 40 hexane : methylene chloride (MeCl₂). Some reactions containing MeCl were immediately warmed to 23°C after DVB addition, and the MeCl thus volatilized was replaced with either MeCl₂ or hexane for the duration of the star-forming reaction. Slightly higher rates were consistently observed when MeCl₂ was the replacement solvent. The strong influence of initial MeCl content on rate of star formation was found to persist throughout the star-forming reaction, even when the solvent was immediately converted to 100% hexane. The fraction of arms that remained unlinked into stars was found to be higher at the higher temperature and at lower solvent polarity. Regardless of solvent or temperature, the residual arm fraction was approximately the same at a given stage of star development as measured by the average number of arms per star. One star sample was produced with the UV-transparent 2-chloro-2,4,4-trimethylpentane initiator; analysis showed that the residual arm fraction had approximately the same UV absorbance as the star fraction, indicating efficient crossover to DVB and the potential for approximately quantitative arm incorporation given sufficient time. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 471–483, 1998     

Synthesis and characterization of carboxylic acid‐terminated polyisobutylenes

tert-Chloride-terminated polyisobutylenes (PIB) (1020 ≤ M_n ≤ 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 °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 ∼ 4 h. PIB carboxylic acid was recovered by acidification and isolation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3229–3240, 2008     

Polyisobutylene Based Supramolecular Networks via Living Carbocationic Polymerization

Functionalized, styrene based monomers were investigated for copolymerization with isobutylene (IB) via living carbocationic polymerization. The achieved incorporation of polar moieties into the polymer backbone yielded supramolecular networks, which were analyzed and characterized via rheological measurements.     

Synthesis and characterization of novel dendritic (arborescent,hyperbranched) polyisobutylene–polystyrene block copolymers

The synthesis of novel arborescent (arb; randomly branched, “tree‐like,” and often called “hyperbranched”) block copolymers comprised of rubbery polyisobutylene (PIB) and glassy polystyrene (PSt) blocks (arb‐PIB‐b‐PSt) is described. The syntheses were accomplished by the use of arb‐PIB macroinitiators (prepared by the use of 4‐(2‐methoxyisopropyl) styrene inimer) in conjunction with titanium tetrachloride (TiCl₄). The effect of reaction conditions on blocking of St from arb‐PIB was investigated. Purified block copolymers were characterized by ¹H NMR spectroscopy and Size Exclusion Chromatography (SEC). arb‐PIB‐b‐PSt with 11.7–33.8 wt % PSt and M_n = 468,800–652,900 g/mol displayed thermoplastic elastomeric properties with 3.6–8.7 MPa tensile strength and 950–1830% elongation. Samples with 26.8–33.8 wt % PSt were further characterized by Atomic Force Microscopy (AFM), which showed phase‐separated mixed spherical/cylindrical/lamellar PSt phases irregularly distributed within the continuous PIB phase. Dynamic Mechanical Thermal Analysis (DMTA) and solvent swelling of arb‐PIB‐b‐PSt revealed unique characteristics, in comparison with a semicommercial PSt‐b‐PIB‐b‐PSt block copolymer. The number of aromatic branching points of the arb‐PIB macroinitiator, determined by selective destruction of the linking sites, agreed well with that calculated from equilibrium swelling data of arb‐PIB‐b‐PSt. This method for the quantitative determination of branching sites might be generally applicable for arborescent polymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1811–1826, 2005     

In Situ Quenching Methods Toward exo-Olefin-Terminated Polyisobutylene

exo-Olefin-terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N-hydro-2,5-disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure-based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N-Hydro-2,5-disubstitutedpyrroles were proposed to form the η⁵-2,5-disubstitutedpyrrolyltrichloro-titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo-olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di-tert-butylsulfide and diisopropyl ether.     

Direct functionalization of polyisobutylene by living initiation with α‐methylstyrene epoxide

This article describes the synthesis and characterization of polyisobutylene (PIB) carrying one primary hydroxyl head group and a tertiary chloride end group, [Ph? C(CH₃)(CH₂OH)–PIB–CH₂? C(CH₃)₂Cl] prepared with direct functionalization via initiation. The polymerization of isobutylene was initiated with the α‐methylstyrene epoxide/titanium tetrachloride system. Living conditions were obtained from ?75 to ?50 °C (198–223 K). Low molecular weight samples (number‐average molecular weight ～ 4000 g/mol) were prepared under suitable conditions and characterized by Fourier transform infrared and ¹H NMR spectroscopy. The presence of primary hydroxyl head groups in PIB was verified by both methods. Quantitative Fourier transform infrared with 2‐phenyl‐1‐propanol calibration and ¹H NMR performed on both the hydroxyl‐functionalized PIB and its reaction product with trimethylchlorosilane showed that each polymer chain carried one primary hydroxyl head group. The synthetic methodology presented here is an effective and simple route for the direct functionalization of PIB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1005–1015, 2002     

Precision synthesis and characterization of thymine‐functionalized polyisobutylene

A new two‐step synthesis of polyisobutylene (PIB) with precisely one thymine functionality per chain (PIB‐T) is reported. The primary hydroxyl‐functionalized PIB (PIB‐OH) precursor was prepared by direct functionalization via living carbocationic polymerization of isobutylene initiated by the α‐methylstyrene epoxide/TiCl₄ system. Matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS) of a low molecular weight PIB‐OH precursor demonstrated the effectiveness of direct functionalization by this method. A PIB‐acrylate precursor (PIB‐Ac) was obtained from such a PIB‐OH, and the PIB‐T was subsequently prepared by Michael addition of thymine across the acrylate double bond. MALDI‐ToF MS of the products verified that all polymer chains carried precisely one thymine group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3501–3506, 2010     

Living cationic polymerization of olefins. How did the discovery come about?

The tortuous road to living carbocationic polymerizations is chronicled. The impetus for this project was my conviction that, just as living anionic polymerizations have started with a critical insight, a similar breakthrough will also be possible with cations. Upon retrospect, the facts show a three-step progression to the objective: Discovery of 1) controlled initiation, 2) reversible termination (quasiliving systems), and 3) controlled chain transfer. But what good is the discovery of a process without demonstrating its usefulness in terms of desirable products? Thus, a section concerns unique microarchitectures obtainable only by this technique: functional liquids, telechelics, thermoplastic elastomers, etc. The marketing of some of these products has already started, and the fundamental exploration of the promises of this technique is in progress worldwide. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2285–2293, 1999     

Synthesis of asymmetric star-branched polymers consisting of three or four different segments in composition by means of living anionic polymerization with a new dual-functionalized 1,1-bis(3-chloromethylphenyl)ethylene

A series of four-armed A₂BC, AB₂C, and ABC₂ asymmetric star-branched polymers with a three-component system, the A, B, and C segments of which are polystyrene, polyisoprene, and poly(4-trimethylsilylstyrene), respectively, have been successfully synthesized with a methodology based on living anionic polymerization with dual-functionalized 1,1-bis(3-chloromethylphenyl)ethylene ( 1 ). These star-branched polymers have well-defined architectures and precisely controlled chain lengths, as confirmed by size exclusion chromatography, ¹H and ¹³C NMR, vapor pressure osmometry, and static light scattering analyses. A simple and convenient one-pot process for star-branched polymer synthesis is an additional advantage of this methodology. One problem to be solved is that the synthetic route is limited in some cases by the inherently low reactivity of polyisoprenyllithium toward the 1,1-diphenylethylene functionality of in-chain-functionalized polymers. A new four-armed ABCD star-branched polymer, the A, B, C, and D segments of which are polyisoprene, poly(4-methoxystyrene), polystyrene, and poly(4-trimethylsilylstyrene), could also be synthesized through the extension of the methodology using 1 to a four-component system. The successful results strongly demonstrate the synthetic versatility and potential of this methodology for a wide variety of well-defined asymmetric star-branched polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4535–4547, 2004     

Polyisobutylene-containing block polymers by sequential monomer addition. X. Synthesis of poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) thermoplastic elastomers

Preparatory to triblock synthesis experiments, the cationic polymerization of α-methylstyrene (αMeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl₄ initiating system in the presence of triethylamine (Et₃N) as electron donor (ED) and CH₃Cl/n-hexane mixed solvent in the ?80 to ?40°C range. Conversions are influenced by temperature, [TiCl₄], [Et₃N], and [αMeSt]. The polymerization of αMeSt is living at ?80°C: Both termination and chain transfer to monomer are frozen out, however, initiation is slow relative to propagation. Highly syndiotactic (>94%) Pα Mest was obtained. At?60deg;C initiator efficiency is ca. 100%, but termination becomes evident. Et₃N may act both as Ed and as proton scavenger. Novel poly(α-methystyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMeSt) triblocks have been synthesized by adding αMeSt to biliving polyisobutylene carbocations (⊕PIB⊕) in the ?80 to ?40°C range. The effects of temperature, solvent polarity, and [Et₃N] on the block copolymerization have been investigated. At ?80°C, the rate of crossover from ⊕PIB⊕ to αMeSt is lower than that of propagation of PαMeSt⊕, so that the triblock is contaminated by PIB and PIB-b-PαMeSt. At ?60°C, crossover occurs preferentially. The rate of propagation relative to that of crossover is also reduced by lowering the solvent polarity and increasing the [Et₃N]. High crossover efficiency and blocking efficiency can be obtained under optimum blocking conditions. The triblocks are novel thermoplastic elastomers (TPEs). © 1994 John Wiley & Sons, Inc.     

Multiarm-star polyisobutylenes by living carbocationic polymerization

This article describes the synthesis of high molecular weight multiarm-star branched polyisobutylenes by living polymerization, using multifunctional initiators, and their initial characterization. First, macrointiators carrying tert-hydroxy function-alities were synthesized by the radical copolymerization of 4-(1-hydroxy-1-methylethyl)-styrene with styrene. This copolymerization system was found to be ideal with r₁ ≡ r₂ ≡ 1. Selected macroinitiators with average functionalities of 8–73 were then used to synthesize the star-branched polyisobutylenes. Polymers with molecular weights up to M̄_n = 400,000 were obtained within 30–60-min reaction times, while under similar conditions the monofunctional 2-chloro-2,4,4-trimethylpentane initiator yielded M̄_n ≈ 10,000 in 20 min. This can be viewed as an indirect proof that simultaneous multiple initiation took place with the macroinitiators. Under controlled conditions a branchedpolyisobutylene with M̄_n = 375,000 and MWD = 1.2, and theoretically calculated 23 arms, with no detectable side products was obtained under living conditions in 60 min; the molecular weight of this polymer increased linearly with time. The branched structure of the polymers were demonstrated by SEC-LLS analysis and core destruction of selected samples. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 85–92, 1998     

Polyisobutylene‐based biomaterials

This article highlights the biomaterial‐related research of the Macromolecular Engineering Research Centre (MERC). The MERC group concentrated on polyisobutylene (PIB)‐based biomaterials. In this article, first the unique properties of PIB are discussed, followed by a review of PIB‐based potential biomaterials. MERC's systematic research program aimed to develop novel PIB‐based biomaterials is then highlighted, including surface modification and biocompatibility studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3091–3109, 2004     

Ziegler catalytic systems in cationic polymerization

The ternary catalytic system AlBuⁱ ₃-TiCl₄-CCl₄ initiates the cationic polymerization of isobutylene in toluene at room temperature, whereas the binary combinations of these components do not induce isobutylene polymerization. At low CCl₄ concentrations, the polymerization rates decrease sharply with time, and the quantitative yield of the polymer is achieved at an excess of CCl₄ with respect to the titanium and aluminum components. The molecular weights of the polymers range within 1300–4000, and the index of polydispersity, as a rule, does not exceed 2.7. The influence of the conditions of component mixing (order of addition, duration of exposure prior to addition of the third component) on the yield and molecular weight of the polymerization product was found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 711–714, April, 1999.