Coupling and linking reactions of living polyisobutylene by allylsilanes

The reactions of living polyisobutylene (PIB⁺) with different allylsilanes, as potential linking and coupling agents, have been studied. Quantitative monoaddition of 2-Phenylallyltrimethylsilane to living PIB⁺ yielded macromonomer (I), however coupling was absent. Rapid and quantitative coupling has been observed with 1,3-bis[2-(3-trimethylsilyl)-propenyl]benzene (bTPB). Using 1-(2-propenyl)-3-[2-(3-trimethylsilyl)-propenyl]benzene (PTPB) star polymers with an average of four arms have been prepared with high efficiency. The study of this linking reaction revealed that star formation takes place in two well separated steps. In the first step a macromonomer is formed in situ by the rapid reaction of PIB⁺ with the allyltrimethylsilyl functionality. Subsequent reaction of this macromonomer with the remaining electrophilic PIB⁺ ends followed by interchain reactions results in the formation of star polymers. Received: 16 May 1999/Revised version: 1 September 1999/Accepted: 1 September 1999     

Living carbocationic polymerization

Mono- and bifunctionaltert-alcohols, i.e., cumyl alcohol (CumOH), 2,4,4-trimethyl-2-pentanol (TMPOH), 2,6-dihydroxy-2,4, 4, 6-tetramethylheptane (TMHDiOH), in conjunction with BCl₃ have been shown to be efficient initiating systems for the living polymerization of isobutylene (IB) in CH₃Cl or CH₂Cl₂ solvents in the –10° to –80°C range. The living nature of the polymerizations was demonstrated by linear M_n versus amount of polyisobutylene (PIB) formed (W_PIB) plots starting at the origin and corresponding horizontal number of PIB moles formed (N) versus W_PIB plots. Quenching with methanol producestert-chlorine terminated PIBs. Quantitative dehydrochlorination of the latter products yields exo-olefin (isopropylidene) end groups. These experiments demonstrate that living carbocationic polymerizations have in fact been conducted in these laboratories long ago (1) without having been recognized as such.     

Halogen-free polyisobutylene by in situ methylation of living polyisobutylene using dimethylzinc

Summary Halogen-free polyisobutylene (PIB) was synthesized by in situ methylation of living PIB using dimethylzinc. Quantitative methylation of living PIB was achieved within 60 min using a ratio of [(CH₃)₂Zn]/[TiCl₄]₀= 1 without any side reactions. Under similar conditions, living PIB capped with 1,1-diphenylethylene (PIB-DPE⁺) yielded close to 1:1 mixture of methoxy- and methyl-functionality. By using the ratio of [(CH₃)₂Zn]/[TiCl₄]₀≥ 3, however, quantitative methylation of PIB-DPE⁺ could be achieved in 120 min without any side reactions as confirmed by spectroscopic and chromatographic analyses. Received: 1 February 2000/Revised version: 23 April 2000/Accepted: 23 April 2000     

Facile synthesis of diphenylethylene end-functional polyisobutylene and its applications for the synthesis of block copolymers containing poly(methacrylate)s

The convenient synthesis of methoxy-free 1,1-diphenylethylene end-functionalized polyisobutylene (PIB-DPE) has been accomplished by capping living PIB with 1,4-bis(1-phenylethenyl)benzene, followed by hydride transfer reaction with tributylsilane. The proposed method eliminates the need for methylation of the capped living PIB in which large excess of dimethylzinc must be used, resulting in a large amount of inorganic salt contamination. The obtained PIB-DPE was quantitatively lithiated with 1.5-fold excess n-butyllithium in tetrahydrofuran (THF) at room temperature. The methine proton at the chain end remained intact during the lithiation procedure. The resulting macroanion efficiently initiated the polymerization of alkyl methacrylates. Poly(methyl methacrylate) (PMMA)-b-PIB-b-PMMA, poly(2-hydroxyethyl methacrylate) (PHEMA)-b-PIB-b-PHEMA and poly(tert-butyl methacrylate) (P^tBMA)-b-PIB-b-P^tBMA have been prepared with high blocking efficiency by the proposed methodology. Complete hydrolysis of P^tBMA-b-PIB-b-P^tBMA into poly(methacrylic acid) (PMAA)-b-PIB-b-PMAA was realized in THF/1,4-dioxane, as confirmed by FTIR, ¹H NMR, and DSC analyses.     

Photochemical reduction of 1-methyl-3-carbamoyl-pyridinium by cyanoborohydride induced by outer-sphere charge transfer excitation

The NAD⁺ subunit 1-methyl-3-carbamoyl pyridinium cation (or 1-methyl nicotinamide cation, MNA⁺) forms an ion pair with BH₃CN⁻ which shows a new absorption (λ_max=453 nm) which is assigned to an outer-sphere charge transfer (OSCT) transition from BH₃CN⁻ to MNA⁺. At r.t. this ion pair is not stable and undergoes a hydride transfer from BH₃CN⁻ to MNA⁺ with the formation of MNAH. At −77°C this ion pair is persistent but the hydride transfer occurs as a photoreaction which is induced by OSCT excitation.     

Polyisobutylene model elastomers prepared using demonstrably complete end-linking reactions

Summary Cationic polymerizations with a trifunctional initiator-chain transfer agent were used to prepare three-arm polyisobutylene [C(CH₃)₂CH₂] (PIB) molecules with hydroxyl groups at all three chain ends. Extensive spectroscopic analyses confirmed the essentially perfect trifunctionality of the polymers, which were then end-linked using an aromatic diisocyanate to give trifunctional model networks. The PIB elastomers were found to have negligible sol fractions, which demonstrates that the end-linking reactions used to prepare them were essentially complete. They were studied, swollen, with regard to their equilibrium stressstrain isotherms in uniaxial extension at 25°C. As was found to be the case for trifunctional and tetrafunctional PIB networks prepared from the linear chains, the results were in satisfactory agreement with theory and yielded no evidence that inter-chain entanglements contribute to the modulus at elastic equilibriums.     

New polyisobutylene stars XI. Synthesis and characterization of allyl-telechelic octa-arm polyisobutylene stars

The synthesis and characterization of a novel star comprising eight allyl-terminated polyisobutylene (PIB) arms radiating from a calix[8]arene core is described. The synthesis was accomplished by a core-first method, by inducing the living polymerization of isobutylene (IB) by a suitably functionalized calix[8]arene initiator (1) in conjunction with BCl₃-TiCl₄ coinitiators, and terminating the growth of the living PIB^⊕ arms by allyltrimethylsilane. The relative concentrations of BCl₃ and TiCl₄ are critical for the synthesis of well-defined 8-arm stars. Characterization of the products (which included triple detector GPC studies and ¹H NMR spectroscopy) indicated quantitative allylation. A mechanism which summarizes the experimental observations is proposed. Received: 17 July 1997/Revised version: 11 September 1997/Accepted: 19 September 1997     

Polyisobutylene-containing block polymers by sequential monomer addition

Novel poly(acenaphtylene-b-isobutylene-b-acenaphtylene) (PAc-PIB-PAc) triblock copolymers exhibiting thermoplastic elastomer (TPE) properties have been prepared. The synthesis involved the addition of acenaphtylene (Ac) to living polyisobutylene dications (PIB) obtained by living isobutylene (IB) polymerization induced by the dicumyl methyl ether (DiCumOMe)/TiCl₄ initiating system at-80°C. The triblocks contain very short polyacenaphtylene (PAc) blocks (M_n9,000) and consequently yield very soft, low modulus TPEs. Efforts to develop conditions for the living carbocationic polymerization (LCPzn) of Ac have failed.For Part VIII of this subseries see J. P. Kennedy, S. Midha, B. Keszler: Macromolecules (in press)     

Viscometric Behavior of Solution of Polyisobutylene in Hexane and Cyclohexane Solvents: Viscosity-Molecular Weight Relationships

The behavior of three different high molecular weight polyisobutylenes (PIB) in solutions of hexane and cyclohexane at 30°C has been investigated by viscometry. Mark–Houwink relations have been examined, the polymer–solvent interaction is discussed in terms of the calculated Huggins constant, k; parameter a of the Mark–Houwink equation; and equivalent hydrodynamic volumes V _e. The molecular weights of the three sample of polyisobutylene are remarkably well fitted with the intrinsic viscosity data.     

Novel block ionomers. III. Mechanical and rheological properties

Select rheological (dynamic viscoelastic) and mechanical properties of novel block cationomers and anionomers and their blends have been investigated. The block ionomers were linear di‐ and triblocks, and symmetric three‐arm stars comprising hydrophobic polyisobutylene (PIB) blocks attached to ionized poly(methacrylic acid) (PMAA^?X⁺, where X⁺ = Na⁺, Zn²⁺) and poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA⁺I^?) blocks. The specific structures investigated were the well‐defined diblocks PIB‐b‐PMAA^? and PIB‐b‐PDMAEMA⁺ and their blends, the triblocks PMAA^?‐b‐PIB‐b‐PMAA^? and PDMAEMA⁺‐b‐PIB‐b‐PDMAEMA⁺ and their blends, and the three‐arm star anionomer Φ(PIB‐b‐PMAA^?)₃. For comparison, the properties of the precursor PIBs and unionized blocks have also been studied. Hydrogen bonding between the carboxyl groups of the PMAA blocks in PIB‐b‐PMAA diblocks leads to inverse micelles. Neutralization of the PMAA by Zn(AcO)₂ and quaternization of the PDMAEMA segments by CH₃I in the triblock copolymers and star copolymers yielded ionic domains, which self‐assemble and produce physical networks held together by coulumbic interaction. The physical/chemical characteristics of the domains control the viscoelastic behavior and mechanical properties of these block ionomers. The mechanical properties of the various block ionomers were significantly enhanced relative to the precursors, and they were thermally stable below the transition temperature. Further, the thermomechanical properties of these novel materials were satisfactory even above 200°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1516–1525, 2003     

Synthesis and characterization of novel well-defined stars consisting of eight polyisobutylene arms emanating from an octa(dimethylsiloxy)octasilsesquioxane core

The synthesis and characterization of novel stars, octa(polyisobutylenedimethylsiloxy)octasilesquioxane (T₈ ^DPIB), consisting of eight polyisobutylene arms emanating from an octa(dimethylsiloxy)octasilsesquioxane (T₈ ^D) core are described. The synthesis involves: 1) The synthesis of allyl-terminated polyisobutylene (PIB^█01█) prearms, 2) The synthesis of octa(hydrodimethylsiloxy)octasilsesquioxane (T₈ ^DH) precore and 3) Star formation by hydrosilation of PIB^█01█ with T₈ ^DH. Conditions for the precision synthesis and characterization of well-defined octa-arm stars are described. Received: 13 September 1996/Accepted: 14 October 1996     

Synthesis and characterization of star‐branched polyisobutylene with SIpS triblock copolymer core

Well‐defined polystyrene‐b‐polyisoprene‐b‐polystyrene (SIpS) triblock copolymers with different microstructures were synthesized by living anionic polymerization. The synthesis of star‐branched polyisobutylene (PIB) was accomplished by the cationic polymerization in 2‐chloro‐2,4,4‐trimethylpentane/titanium tetrachloride/SIpS triblock copolymer/2,6‐di‐tert‐butylpyridine initiating system. The double bonds in SIpS triblock copolymer were activated as starting points for isobutylene polymerization. The formation of star‐branched architecture was demonstrated by size‐exclusion chromatography with quadruple detection: refractive index, multiangle laser light scattering, viscometric, and ultraviolet detectors. SIpS triblock copolymer with high 3,4‐PIp content is more reactive than that with high 1,4‐PIp content in cationic initiating stage. The yields of star‐branched PIB were remarkably dependent on the reaction time of TMP⁺ with SIpS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

In situ polymerization,thermal, damping,and mechanical properties of multiwalled carbon nanotubes/polyisobutylene‐based polyurethane nanocomposites

Despite the development of strong, durable, and cost efficient polyisobutylene‐based polyurethane (PIB‐based PU) materials has yet to be achieved. The well dispersion and maximum interfacial interaction between the nanofiller and the PIB‐based PU at low loading have been scarcely studied. Here, the preparation of PIB‐based PU nanocomposites with Multiwalled carbon nanotubes (MWCNTs) using a simple in situ polymerization method is reported. The thermogravimetric analysis tests show that MWCNTs significantly improved the thermal stability of MWCNTs/PIB‐based PU nanocomposites. Compare to the pure PIB‐based PU the onset temperature of degradation for the nanocomposite was about 20°C higher at 0.7 wt% MWCNTs loading. Efficient load transfer is found between the nanofiller MWCNTs and PIB‐based PU and the mechanical properties of the MWCNTs/PIB‐based PU nanocomposite with well dispersion are improved. A 63% improvement of Young's modulus and slightly increased of tensile strength are achieved by addition of only 0.7 wt% of MWCNTs. The experimentally determined Young's modulus is in well agreement with the theoretical simulation. It is worth noting that the PIB‐based PU and MWCNTs/PIB‐based PU nanocomposites exhibit excellent damping properties (tan δ > 0.3) from −45°C to 8°C. POLYM. COMPOS., 36:198–203, 2015. © 2014 Society of Plastics Engineers     

Hyperbranched Acrylate Copolymer via Initiator‐Fragment Incorporation Radical Copolymerization of Divinylbenzene and Ethyl Acrylate: Synthesis,Characterization, Hydrolysis,Dye‐Solubilization,Ag Particle‐Stabilization,and Porous Film Formation

Summary: Soluble hyperbranched acrylate copolymers were prepared by the copolymerization of divinylbenzene (0.10 mol · L^?1) and ethyl acrylate (0.50 mol · L^?1) using dimethyl 2,2′‐azoisobutyrate of high concentrations (0.30–0.50 mol · L^?1) as initiator at 70 and 80 °C in benzene. The copolymer formed at 80 °C for 1 h showed the weight‐average molecular weight of 2.5 × 10⁵, the small radius of gyration of 10 nm, the low second virial coefficient of 5.7 × l0^?7 mL · g^?2 as shown by the MALLS measurements at 25 °C in tetrahydrofuran, and also the very low intrinsic viscosity of 0.10 dL · g^?1 at 30 °C in benzene. The hyperbranched copolymer exhibited an upper critical solution temperature (35 °C on cooling) in an acetone‐water (60:11 v/v). The copolymer showed an ability to encapsulate and transfer Rhodamine 6G as a dye probe and could stabilize Ag nanoparticles. The porous film was prepared by simply casting an acetone solution of the hyperbranched copolymer on a cover glass. The copolymer molecules radially arranged on the surface layer of the spherical pores as observed by the polarized optical microscope. The hyperbranched acrylate copolymer was hydrolyzed by KOH to yield poly(carboxylic acid).

Optical microscope image (crossed polarizers) of a porous film from copolymer solution in acetone.     

Scale-up precision synthesis of octa-arm polyisobutylene stars

Summary This paper concerns the scale-up precision synthesis of octa-arm polyisobutylene (PIB) stars. Specifically, we have optimized to the 100–200 g scale the preparation of star polymers consisting of eight PIB arms radiating from a calix[8]arene core. The synthesis strategy involved the use of a calix[8]arene fitted with eight p-C(CH₃)₂OCH₃ groups as the initiator in conjunction with mixed BCl₃/TiCl₄ coinitiators in hexanes/methyl chloride solvent systems at − 80 °C. Various possible side-reactions have been identified and means for their suppression/elimination were developed. Received: 29 December 1999/Revised version: 22 May 2000/Accepted: 22 May 2000     

Living carbocationic polymerization

Summary Three-arm star telechelic liquid polyisobutylenes PIB carrying exactly three -CH₂C(CH₃)₂Cl end groups have been synthesized by living carbocationic polymerization using C₆H₃(C(CH₃)₂OCH₃)₃/BCl₃ complexes in CH₃Cl and CH₂Cl₂ diluents in the 0° to –30°C range. The living nature of the polymerizations was demonstrated by linear M_n versus W_PIB (g PIB) formed plots starting at the origin and horizontal N (moles of PIB) versus W_PIB plots. Initiating efficiency (I_eff) was close to 100% and M_n was determined by the [monomer]/[initiator] ratio. Polymerizations guenched by methanol yield tert.-chlorine end groups which have been quantitatively converted to isopropylidene (-CH₂C(CH₃)=CH₂) termini.     

Multi-arm star polyisobutylenes

Summary The first synthesis of a multi-arm radial-star polyisobutylene (*-PIB) is described. The synthesis occurred by the addition of excess divinylbenzene (DVB) linking reagent to a living polyisobutylene (PIB) charge i.e., by the arm first method under specific conditions. The radial structure of the *-PIB was proven by determining the molecular weight of a sample by light scattering, then selectively destroying the aromatic polydivinylbenzene (PDVB) core, and finally determining the molecular weight of the surviving alphatic PIB arms. The synthesis strategy, kinetic observations during synthesis, and procedures leading to a representative *-PIB are described. This product whose g/mole with , contained 90.3 mole% (78 wt.%) PIB arms and 9.7 mole% (22 wt.%) aromatic core; thus the number of PIB arms emanating from the core was (number average number of arms)=56 or (weight average number of arms)=110.     

PMMA-block-polyisobutylene-block-PMMA prepared with α,ω-dilithiated polyisobutylene and its characterization

Summary A triblock copolymer of PMMA and polyisobutylene(PIB), PMMA-block-PIB-block-PMMA, was prepared by anionic polymerization of methyl methacrylate initiated with , -dilithiated poly(isobutylene) diisobutylate in tetrahydrofuran at -60°C. The molecular weight distribution of the block copolymer was close to that of the starting PIB. The stereoregularity of PMMA block was predominantly syndiotactic. Proton spin-lattice relaxation time and solution viscosity of the block copolymer in acetone, which is non-solvent for PIB, indicate that the block copolymer forms rigid spherical particles. Stereocomplex formation with isotactic PMMA was also studied.     

Living carbocationic polymerization

Summary The living synthesis of ,-di-tert.-chloropolyisobutylene ( ^t -Cl-telechelic PIB) has been accomplished by the use of the sterically hindered bifunctional initiator 1,3-di-(2-methoxy-2-propyl)-5-tert.-butylbenzene (tBu-m-DiCuOMe) in conjunction with BC1₃ coinitiator in CH₃Cl or CH₂Cl₂ diluents at –30°C and –10°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of PIB formed) plots starting at the origin and horizontal N (number of PIB moles) versus W_PIB plots. The molecular weight distributions are narrow (¯M_W/¯M_n < 2.0) and tend to decrease with increasing molecular weights. Number average end functionalities have been quantitated and found to be ¯F_n = 2.0±0.1.     

Properties of thin films of isotactic polypropylene blended with polyisobutylene and ethylene-propylene-diene terpolymer rubbers

An experimental study was carried out to investigate the kinetic, morphological and thermodynamic properties of thin films of isotactic polypropylene (iPP) blended with several elastomers such as ethylene-propylene-diene terpolymer (EPDM) and three samples of polyisobutylene (PIB) with different molecular masses. The addition of the rubber to iPP causes drastic modifications in the morphology, nucleation density, spherulite growth rate and thermal behaviour of iPP. Such modifications depend strongly on the chemical and molecular mass of the added elastomer and on the composition of the blend. All the elastomers studied seem to act as nucleating agents for the iPP spherulites. The addition of PIB to iPP results in a reduction of the spherulite growth rate G, whereas the addition of EPDM does not seem to have a great influence. For the iPP/PIB_HM iPP/PIB_MM and iPP/EPDM blends a depression of the equilibrium melting temperature T_m, with respect to that of pure iPP, is observed. This depression is increased for the blend containing 20% rubber. This effect is probably related to phenomena of partial miscibility in the melt and to the coexistence of processes such as molecular fractionation and preferential dissolution of the more defective molecules.