Polyisobutylene model elastomers prepared using demonstrably complete end-linking reactions

Summary Linear polyisobutylene (PIB) molecules with either hydroxyl or isopropenyl groups at the chain ends were prepared using cationic polymerizations with bifunctional initiator-chain transfer agents. Extensive spectroscopic analyses confirmed the essentially perfect difunctionality of the two types of polymers. The former polymers were end-linked using an aromatic triisocyanate, and the latter by means of a tetrafunctional silane. The resulting trifunctional and tetrafunctional model PIB networks were found to have absolutely negligible sol fractions, which demonstrates that the end-linking reactions used to prepare them were essentially complete. The networks were studied with regard to their equilibrium stress-strain isotherms in uniaxial extension at 25 °C. The results thus obtained are in satisfactory agreement with theory and yield no evidence whatever for significant elastic contributions from inter-chain entanglements.     

Synthesis,characterization, and properties of novel polyisobutylene-based urethane model networks

This paper concerns the synthesis, characterization, and physical properties of novel polyisobutylene (PIB)-based urethane model networks prepared from diphenylmethane diisocyanate (MDI) and three-arm star PIBs capped with ? CH₂OH end groups (PIB(CH₂OH)₃). The PIB(CH₂OH)₃ starting materials were produced by the inifer method in the M?_n = 13,550–27,000 range. The best networks were obtained with NCO : OH = 1. Solvent extractions showed uncatalyzed network formation to be essentially complete and swelling studies indicated the expected architecture, i.e., M?_c = 2M?_n/3 and virtual absence of dangling chains. Stannous octoate was found to increase the rate of network formation in the absence of side reactions (i.e., allophanate formation), while other catalysts also accelerated undesirable reactions. The effect of molecular weight between crosslinks (M?_c) on network physical properties has been studied in the M?_c = 900–18,500 range. The tensile strength increases with decreasing M?_c up to a limiting value after which it sharply declines. Elongations at break decrease monotonously with decreasing M?_c. Low temperature tensile studies show higher tensile data at ?20°C, and, surprisingly, a retention of elongations at break. The T_g's decrease with increasing M?_c's until a plateau is reached at ?73°C. Hysteresis is fairly constant and permanent set is constant and low. The PIB-based urethane networks exhibit excellent hydrolytic stability, negligible moisture absorption, and outstanding heat-aging stability, far beyond what is expected for a polyurethane. Conceivably the thermal deblocking of the urethane group may be reversible (? NH? COO? CH₂? ? ? NCO + HOCH₂? ) because the isocyanate that arises in the highly hydrophobic PIB matrix recombines with the alcohol, and cannot react with moisture as in conventional urethane networks.     

Novel amphiphilic membranes of poly(N,N-dimethyl acrylamide) crosslinked with octa-methacrylate-telechelic polyisobutylene stars

Summary A series of novel amphiphilic networks were synthesized by free-radical mediated copolymerization/crosslinking of N,N-dimethyl acrylamide (DMAAm) with various molecular weight octa-methacrylate telechelic polyisobutylene stars (PIB(MA)₈) as crosslinking agents. The overall composition of the PDMAAm-l-PIB(MA)₈ networks were controlled by controlling the concentration of the starting materials. Crosslinking was essentially complete as indicated by negligible sol fractions in both methanol and n-hexane. Swelling ratios and swelling rates of various PDMAAm-l-PIB(MA)₈ in water and n-heptane were determined and contrasted with those of networks prepared with di- and tri-methacrylate-telechelic PIB croslinkers (PIB(MA)₂ and PIB(MA)₃). The mechanical properties of water-swollen tubules made of PDMAAm-l-PIB(MA)₈ were studied and compared with tubules made with PIB(MA)₂ and PIB(MA)₃. Received: 30 January 2002 / Revised version: 6 May 2002 / Accepted: 7 May 2002     

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.     

13C NMR characterization of unsaturated terminal structures in oligoisobutylenes

Summary ¹³C NMR analysis revealed the existence of additional unsaturated terminal structures in oligoisobutylene samples, in addition to the well-known-CH₂C(CH₃)=CH₂ and-CH=C(CH₃)₂. Structure with a double bond between two quaternary carbons was detected both in commercial Oppanol B3 and in a oligoisobutylene (PIB) sample prepared by polymerization in CH₂Cl₂ with a high concentration of monomer in the presence of BCl₃ at-20°C. In the latter sample, another type of the structure with a double bond between quaternary carbon and methine carbon (-CH=C(CH₃)-CH₂CH₃) was found in a large amount.     

Synthesis of poly(styrene-co-isopropenyl acetate) -g-polyisobutylene graft copolymers via combination of radical polymerization with cationic polymerization

Random copolymers of poly(styrene-co-isopropenyl acetate) (SIPA) with an average number of 9 initiating sites per chain were synthesized by free radical copolymerization of styrene with a small amount of isopropenyl acetate using 2,2′-azo-bis-(isobutyronitrile) as an initiator at 70 °C. SIPA copolymer could be further used as macroinitiator for the grafting cationic polymerization of isobutylene (IB) from SIPA chain in CH₂Cl₂ at ?40 °C to produce graft copolymers of SIPA-g-PIB. The effect of SIPA concentration ([SIPA]), TiCl₄ concentration ([TiCl₄]) and IB concentration ([IB]) on initiation efficiency of macroinitiator, grafting efficiency of initiating sites, average length of PIB branches of the resulting graft copolymers were investigated. It can be found that almost all of the initiating sites of IPAc units on SIPA chains were active for the cationic polymerization of IB and both initiation efficiency and grafting efficiency were close to 100% at sufficient molar ratio of TiCl₄/IPAc. This synthetic route presents quantitative grafting efficiency and possibility to control length of PIB branches. The graft copolymers of SIPA-g-PIB with average 9-branched PIB chains having terminal functional tert-chlorine groups could be successfully obtained. The average molecular weight of PIB branches in SIPA-g-PIB graft copolymers could be mediated from 3900 to 47,300 g mol^?1 by changing the ratios of macroinitiator to monomer and concentration of TiCl₄.     

Creation of a functional polysiloxane layer on the surface of magnetic nanoparticles using the sol-gel method

The developed methods using tetraethoxysilane and trifunctional silanes were applied to obtain Fe₃O₄ magnetic particles that contain amino groups with compositions of ≡Si(CH₂)₃NH₂, ≡Si(CH₂)₃NH(CH₂)₂NH₂, and [≡Si(CH₂)₃]₂NH. The XRD data show that the nuclei of nanoparticles in the obtained materials preserve the structure of the primary carrier, namely, that of Fe₃O₄ magnetite. The thermograms show a high thermal stability of the applied surface layers, i.e., their destruction was found to start at temperature above 250°C. The DRIFT spectra indicate the formation of the silica bond framework in the surface layers of nanoparticles and also the existence of hydrogen bonds between amino groups and silanol groups with the participation of water molecules aided. All of the obtained materials exhibit magnetic properties and offer promising application in medicine.     

Living carbocationic polymerization

Summary The efficient synthesis of symmetrical telechelic polyisobutylenes carrying CH₂C(CH₃)₂Cl groups at either end of the molecule, , has been accomplished by rapid living polymerization using aromatic di-tert.-ether/BCl₃ initiator system in CH₃Cl at –70°. The living nature of the polymerization was demonstrated by linear M_n versus amount of PIB formed (W_PIB) plots starting at the origin. The effect of temperature and solvent composition (polar/nonpolar) on the polymer structure has been investigated. Undesirable indanyl end groups which form during polymerizations carried out at –30° and –50°C can be eliminated by decreasing the temperature to –70°C. The apparent activation energy differences have been determined in the –30 to –70°C range at different polar/nonpolar solvent compositions: E_a of decreases from 2.6 to 1.0 kcal/mole by decreasing the polarity of the medium from 100% CH₃Cl to a 60/40 v/v CH₃Cl/hexanes mixture.     

Isobutylene polymerization in the presence of t-BuCl/SnCl4

Summary The effect of tert-butyl chloride in the polymerizations of isobutylene carried out in the presence of SnCl₄ in dichloromethane at temperatures-20°C and-78°C was investigated. Synthesized polyisobutylene samples showed a bimodal molecular weight distribution (MWD) and it was found that the weight content of the lowermolecular weight (LMW) fraction increased with increasing t-BuCl concentration in the polymerization mixture. The effect of ageing of the initiation mixture t-BuCl/SnCl₄ in CH₂Cl₂ prepared in advance on MWD of the PIB samples was also studied. Ageing of the initiation system supports the formation of the LMW fraction and this oily PIB is the only product of the polymerization at-20°C, .     

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.     

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     

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     

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     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The unsaturated aliphatic dichlorides cis and trans Cl(CH₃)₂C-CH=CH-C(CH₃)₂Cl in conjunction with BCl₃ have been found to be excellent binifers and yield tert.-Cl capped polyisobutylenes PIB in CH₃Cl at –30°C. Intramolecular cyclization is absent and terminal chlorine functionality is F_n = 2.0±0.1. The normalized inifer constants have been determined: ^CItrans = 1.05, and ^CIcis = 3.8 and 1.05, respectively, for the first and second allylic chlorines in the cis isomer. The inequality of the chlorines have been analyzed. The cis and trans isomers have identical relative termination constants (k_t/k_p = 6×10^–3). The structure of the PIBs obtained has been analyzed by a variety of techniques. Model experiments with isobutylene/Cl-(CH₃)₂C-CH=CH-C(CH₃)₂Cl = 2/1 in the presence of BCl₃ gave the expected trans Cl(CH₃)₂CCH₂-(CH₃)₂C-CH=CH-C(CH₃)₂-CH₂C(CH₃)₂ -Cl. The end groups of polymers have been quantitated. The central position of the -CH=CH- residue in polymers has been demonstrated by molecular weight determinations i.e., the M_n of PIB has decreased by a factor of two after oxidative cleavage. The uniform distribution of -CH=CH-group across all polymeric species has also been established.     

A novel method for preparing bimodal elastomeric networks

Summary Hydroxyl-terminated chains of poly(dimethylsiloxane) (PDMS) were end linked with a trifunctional silane containing 3-aminopropyl groups. CuCl₂ or CoCl₂ added to the networks forms complexes with the amino groups on the cross links, thus introducing additional chains that are very short. The resulting PDMS networks are in this sense bimodal, and were found to have increased values of the ultimate strength.     

Amphiphilic networks. XI. Mechanical properties and morphology

The bulk properties of two types of amphiphilic networks, poly(2-hydroxyethyl methacrylate)-l-polyisobutylene (PHEMA-l-PIB, H-network) and poly(N,N-dimethylacrylamide)-l-polyisobutylene (PDMAAm-l-PIB, A-network), have been investigated. Tensile strengths decreased considerably by swelling, and the decrease was more severe by swelling in water than in n-heptane. Elongations increased by swelling in water; however, the change was not consistent upon swelling in n-heptane. The hardness of dry networks decreased with increasing PIB content, while for wet networks it was similar to dry networks containing 85 wt % PIB. Small-angle X-ray scattering showed that average interdomain spacings decreased with increasing PIB content. According to dynamic mechanical thermal analysis (DMTA) the glass transition temperatures (T_g) of the respective hydrophobic and hydrophilic components shift toward each other with increasing PIB content. A “liquid-liquid transition” (T_ll) above the T_g of the hydrophilic component was apparent by DMTA, but could not be found by differential scanning calorimetry (DSC). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 901–910, 1997     

Preparation and characterization of new anhydrous, conducting membranes based on composites of ionic liquid trifluoroacetic propylamine and polymers of sulfonated poly (ether ether) ketone or polyvinylidenefluoride

A novel ionic liquid of trifluoroacetic propylamine, i.e., [CH₃CH₂CH₂NH₃⁺] [CF₃COO⁻] (TFAPA), was synthesized from trifluoroacetic acid and propylamine. The ionic liquid of TFAPA was used to prepare anhydrous, conducting membranes based on polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF). The ionic conductivity and mechanical strength of the composite membranes were investigated at elevated temperatures and under anhydrous conditions. Conductivity of 0.030 S/cm was achieved with TFAPA at 180 °C, and of 0.019 S/cm with a membrane containing 70% (wt) TFAPA in SPEEK with a sulfonation degree of 86% at 160 °C. Increasing either ionic liquid content or temperature reduced the mechanical strength of the composite membrane. Efforts were made to improve the strength of TFAPA/SPEEK composite membranes by cross-linking the SPEEK, which led to some strength enhancement at 110 °C and 130 °C.     

The synthesis of chlorine-terminated telechelic polyisobutylene

In synthesizing chlorine-terminated telechelic polyisobutylene (PIB) with a p-DCCCp-dichlorocumene/BCl₃/CH₂Cl₂ system, it is found that cycloalkylation occurs parallel with propagation. The factors leading to cycloalkylation were investigated in detail, to clarify its origin, to define its effects upon the molecular parameters of the polymer produced and to find ways to suppress it. It is found that cycloalkylation drastically influences MW, MWD and functionality of the polymer produced. High temperature, high medium polarity, low monomer concentration and the order of addition of BCl₃ and p-DCC are the main factors favoring cycloalkylation.     

A new iodine-free initiating system for the living polymerization of isobutyl vinyl ether

Summary A new iodine-free initiating system, MeCH(Oi-Bu)Cl/n-Bu₄NTiCl₅, was found to induce the living carbocationic polymerization (LCPzn) of isobutyl vinyl ether (IBuVE) at-20 °C in CH₂Cl₂. Using this system, poly(isobutyl vinyl ether) (PIBuVE) with the theoretical molecular weights (up toca. 45,000) calculated from the initiator/monomer input and narrow molecular weight distribution (M_w/M_n < 1.1) can be readily obtained. The polymerization is first order in the monomer. The coinitiating function ofn-Bu₄NTiCl₅ may be due to a salt effect or to its Lewis acid character. An attempt for the synthesis of the polyisobutylene (PIB)-PIBuVE block copolymer has failed most likely becausen-Bu₄NTiCl₅ is unable to activate the C(CH₃)₂-Cl bond of the PIB termini.