Molecular Weight Polyisobutylene Research Articles

The influence of some factors on the characteristics of metallized incendiary mixtures

In this article, the influence of some factors on the characteristics of metallized incendiary mixtures (pyrogels) was studied. The pyrogel-type contains benzene, polyisobutylene, magnesium, aluminum-magnesium alloy, sodium nitrate, and different additives. It is shown that the molecular weight of polyisobutylene, the amount of aluminum-magnesium alloy, the particle size of metal combustibles, and the amount and type of polyester threads have different effects on the heat of combustion, flash point, burning rate, flame height, and adhesion to the material surface. The optimal pyrogel contains 38-40% thickened benzene - PIB with molecular weight 175000-225000, 25-27% aluminum-magnesium alloy with particle size ≤ 160µm, 10-12% magnesium powder with particle size ≤ 180µm, 15% sodium nitrate, 8% phenol-formaldehyde resin and 1.5% (over 100%) 3D polyester threads.

Synthesis, characterization, and photopolymerization of (meth)acrylate‐functional polyisobutylene macromers produced by cleavage/alkylation of butyl rubber

AbstractLinear, multi‐functional polyisobutylene (PIB) macromers bearing pendent and terminal (meth)acrylate moieties were prepared via electrophilic cleavage/alkylation of butyl rubber in the presence of (3‐bromopropoxy)benzene, followed by displacement of the resulting bromide moieties with potassium (meth)acrylate. Number average functionality (Fn) ranged from 2.8–7.9; functional equivalent weights ranged from 2.3–4.7 kg/mol. For comparison, a three‐arm, end‐functional PIB triacrylate with equivalent weight of 3.3 kg/mol was also synthesized via living polymerization and end quenching with 4‐phenoxy‐1‐butyl acrylate. All polymers were photocured using Darocur 1173 photoinitiator, and curing kinetics were monitored by real time Fourier‐transform infrared spectroscopy. All systems reached ~100% conversion by 1,800 s, but the linear macromers displayed slower curing rates compared to the PIB triacrylate. The curing rate of linear macromers increased as molecular weight decreased. Cured networks were characterized using dynamic mechanical analysis and tensile testing. Tensile strength varied from 0.15–0.80 MPa. Young's modulus varied from 0.13–1.8 MPa. Strain at break for most networks ranged from 34–54%, but the network derived from the lowest molecular weight PIB reached 113% at failure. Percent extractables, measured using solvent extraction, was about 2% for linear macromers and about 4% for PIB triacrylate.

“D-optimal experimental design” analysis in preparing optimal polyisobutylene based pressure sensitive adhesives

The aim of this work was to model the mechanical properties of different blends of polyisobutylene (PIB) pressure sensitive adhesives (PSAs) with different molecular weights (36,000, 51,000, 75,000, 400,000, and 1,100,000). The mechanical properties of PSAs are usually described by tack, peel, and shear strength which are strongly depended on the bulk viscoelastic properties of the adhesive system. It is assumed that the blends of high and low molecular weight PIB could affect these properties. According to D-optimal design of Design Expert software, various blends of five different molecular weights of PIB have been selected for study in this investigation. Using manual regression analysis, the quadratic model generated for three responses (tack, peel, and shear) was found to be statistically significant (p < 0.05). It was found that tack increases with decreasing molecular weight. It was also found that the presence of B10 and B12 as low molecular weight polymers and B50 as a high molecular weight polymer in increasing peel strength was more dominant compared with B15 and B100. Furthermore, shear strength was found to increase with an increasing concentration of the low molecular weight PIB, B15. The results have shown that statistical analysis meets theoretical expectations and they suggest desired blends of polymer for different aims.

Self-healing polymer sealant for encapsulating flexible solar cells

Herein we demonstrate the utility of polyisobutylene (PIB) as a fully printable self-healing sealant for protecting organic photovoltaic devices from degradation under ambient conditions. These sealants can be applied on flexible substrates using drop casting, spin coating or blade coating. PIB-based crosslinked sealants show excellent device stability, especially the low molecular weight PIB.

Rubbery wound closure adhesives. I. design, synthesis, characterization, and testing of polyisobutylene-based cyanoacrylate homo- and co-networks

Novel rubbery wound closures containing various proportions and molecular weights of polyisobutylene (PIB) and poly(2-octyl cyanoacrylate) [P(OctCA)] for potential clinical use were designed, synthesized, characterized, and tested. Homo-networks were prepared by crosslinking 3-arm star-shaped PIBs fitted with terminal cyanoacrylate groups, [O(PIB-CA)3], and co-networks by copolymerizing O(PIB-CA)3 with OctCA using N-dimethyl-p-toluidine (DMT). Neat O(PIB-CA)3, and O(PIB-CA)3/OctCA blends, upon contact with initiator, polymerize within seconds to optically transparent strong rubbery co-networks, O(PIB-CA)3-co-P(OctCA). Homo- and co-network formation was demonstrated by sol/gel studies, and structures and properties were characterized by a battery of techniques. The Tg of P(OctCA) is 58 °C by DSC, and 75 °C by DMTA. Co-networks comprising 25% O(PIB-CA)3 (Mn = 2400 g/mol) and 75% P(OctCA) are stronger and more extensible than skin. Short and long term creep studies show co-networks exhibit high dimensional stability and <6% creep strain at high loading. When deposited on porcine skin co-networks yield hermetically-adhering clear rubbery coatings. Strips of porcine skin coated with co-networks could be stretched and twisted without compromising membrane integrity. The co-network is nontoxic to L-929 mouse fibroblasts. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1640–1651

Investigation of the migration behavior of polyisobutylene with various molecular weights in ethylene/α‐olefin copolymer blown stretch films for improved cling properties

AbstractHigh retention forces are the basic requirements on stretch films for agricultural or pallet wrapping of goods and significantly influenced by cling properties (autohesion) that are essential for a reliable load stability during transportation and storage. Low molecular weight polyisobutylene (PIB) has tacky properties and is immiscible with polyethylene. Blended with ethylene/α‐olefin copolymers in coextruded stretch films, PIB can migrate to the film surfaces and cause cling properties. Cling and adhesion forces were investigated using the mechanical cling test, atomic force, and scanning electron microscopy and infrared spectroscopy. The molecular weight of the PIB as well as density and crystallinity of the matrix material have strong influences on migration kinetics and therefore, on the cling forces. Cling forces increase with increasing aging time, having a maximum after 2 weeks of production. The following slight decrease of the cling force might be correlated with a beginning degradation process of the UV sensitive PIB. Polyisobutylene with higher molecular weight diffuses slower through a linear low density polyethylene (LLDPE) matrix than lower molecular weight PIB, but can cause higher cling forces on the film surfaces. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40239.

Synthesis of high molecular weight polyisobutylene via cationic polymerization at elevated temperatures

A novel simple but effective initiating system of H2O/AlCl3/veratrole (VE) has been developed to synthesize high molecular weight polyisobutylene (PIB) at elevated temperatures via cationic polymerization of isobutylene (IB) in solvent mixture of hexane/methylene dichloride (n-Hex/CH2Cl2 = 2/1, V/V). VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight (M w) of 1117000 and 370000 g/mol could be synthesized with H2O/AlCl3/VE initiating system at VE concentration of 5.4 mmol/L at −80 and −60 °C respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be −3.52 via FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree (E DP) could be determined to be around −23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L.

Strength Enhancement in Miscible Blends of Butyl Rubber and Polyisobutylene

The thermodynamic miscibility of polyisobutylene (PIB) with butyl rubber (IIR), a copolymer of isobutene and a few mole % isoprene, was established through observation of spontaneous interdiffusion of the polymers. Networks were prepared from their blend, in which only the IIR component was cross-linked (PIB cannot be cross-linked by sulfur vulcanization or any other method). The blends were significantly stronger (almost 3-fold higher tensile strength) and tougher than neat IIR networks, when compared at equal modulus. This improvement was greater for blends having higher molecular weight PIB. The results show that miscible blends with components having large disparities in their degree of cross-linking (infinite in the present case) circumvent the trade-off between stiffness and strength found for conventional elastomers. The operative mechanism is alleviation of local overstresses by configurational rearrangement of unattached, but entangled, chains. This mechanism is common to other approaches that improve the mechanical properties of networks, such as bimodal networks and hydrogel blends.

Investigation of structure–property relationships of polyisobutylene-based biomaterials: Morphology, thermal, quasi-static tensile and long-term dynamic fatigue behavior

This study examines the morphology, thermal, quasi-static and long-term dynamic creep properties of one linear and three arborescent polyisobutylene-based block copolymers (L_SIBS31, D_IBS16, D_IBS27 and D_IBS33). Silicone rubber, a common biopolymer, was considered as a benchmark material for comparison. A unique hysteretic testing methodology of Stepwise Increasing Load Test (SILT) and Single Load Test (SLT) was used in this study to evaluate the long-term dynamic fatigue performance of these materials. Our experimental findings revealed that the molecular weight of polyisobutylene (PIB) and polystyrene (PS) arms [MnPIB(arm) and MnPS(arm)], respectively had a profound influence on the nano-scaled phase separation, quasi-static tensile, thermal transition, and dynamic creep resistance behaviors of these PIB-based block copolymers. However, silicone rubber outperformed the PIB-based block copolymers in terms of dynamic creep properties due to its chemically crosslinked structure. This indicates a need for a material strategy to improve the dynamic fatigue and creep of this class of biopolymers to be considered as alternative to silicone rubber for biomedical devices.

Effect of Solubility Parameter of Polymer‐Solvent Pair on Turbulent Drag Reduction

AbstractPolymer‐induced turbulent drag reduction by adding a minute amount of high‐molecular weight polyisobutylene (PIB) into two different organic solvents of n‐heptane and xylene was examined using a rotating disk system. The dependence of drag reduction (DR) efficiency on various factors such as polymer molecular weight, polymer concentration (C), and solvent quality was examined. Based on the linear relationship between C and C/DR for different molecular weights of PIB, a universal curve was able to characterize a particular polymer/solvent family, independent of the molecular weight of polymer.

The Effect of PIB Molecular Weight on the Cling Characteristics of Polyethylene-PIB Films for Stretch and Cling Film Applications

The effect of molecular weight on the migratory characteristics of polyisobutylene (PIB) additive from the bulk to the surface of a range of monolayer and multilayer extruded polyethylene films has been analyzed by FTIR-ATR and peel cling analysis. Migration rates are shown to be higher for lower molecular weight PIB additive, and cling strength increases as the PIB molecular weight increases.

Cationic grafting of olefins from PVC: The effect of reaction conditions

The cationic grafting of isobutylene, styrene, α-methylstyrene, and β-pinene from a poly(vinyl chloride) (PVC) backbone was investigated. Grafting-from was induced by Et2AlCl in 1,2-dichloroethane and methylene dichloride solutions from 20 to −70 °C. The effects of temperature and proton trap [2,6-di-tert-butylpyridine (DtBP)] on grafting-from efficiency (Geff), extent of grafting, branch length (molecular weight), and number of branches per PVC molecule were determined. Reducing the temperature invariably increased the Geff and the molecular weight of polyisobutylene, polystyrene, poly(α-methylstyrene), and poly(β-pinene) branches attached to PVC. The magnitude of the effects was different with the various olefins and depended on the reaction conditions. The effect of DtBP was examined in the 5 × 10−4–4 × 10−3 mol/L range. By increasing the DtBP concentration the Geff increased; however, the number-average molecular weight of the grafted branches decreased. The lengths of the grafted branches can be controlled, and Geff's close to 100% were obtained. The fact that the proton trap reduced the molecular weights of grafted branches suggests that besides proton scavenging, DtBP may also abstract protons from the growing carbenium ion site. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1675–1680, 2001

Universal drag reduction characteristics of polyisobutylene in a rotating disk apparatus

Turbulent drag reduction (DR) in a rotating disk apparatus was examined for a homologous series of polyisobutylene (PIB) with two different solvent systems to investigate the effect of solvent on universal DR characteristics. The concentration dependence of DR for these systems obeys an empirical universal DR equation. A linear correlation between polymer concentration (C) and C/DR for different molecular weights of PIB was also obtained. The intrinsic concentration was found to be an extremely useful quantity in normalizing the DR data for a homologous series of PIB. The characteristic value, K, was found to depend upon the solvent system.

Rod-Climbing characterization of kaolinite suspended polyisobutylene solutions

The rod-climbing constants of kaolinite-suspended polyisobutylene (PIB) solutions are investigated from rod-climbing experiments. For a low deformation rate, this particle suspended polymer solution can be regarded as a second-order fluid, and the rod-climbing constant for such fluids is correlated with the rheological properties of the particle-suspended polymer solutions. The rod-climbing constants for kaolinite suspended PIB solutions were found to decrease with temperature and increase with PIB concentration, molecular weight of PIB, solvent viscosity, and particle concentration. The rheological properties were measured using rotational rheometer, and the shear viscosity and the first normal stress difference of the kaolinite suspended PIB solution show the Boger-fluid characteristics.

Characterisation of spread monolayers of functionalised polyisobutylenes with various chain architectures

Nine polyisobutylene (PIB) samples, consisting of three chain architectures (linear and branched), each of three molecular weights, were each derivatised at one, two or three chain ends with a hydrophilic head group based on diethyl azodicarboxylate. The surface pressure–area isotherms for spread monolayers of these polymers at the air/water interface were determined using a Langmuir trough, and the thicknesses of the films determined by ellipsometry. The isotherms showed that the area per molecule increased, whereas the collapse pressure decreased, with increasing molecular weight. The area per molecule and collapse pressures both increased with functionality, suggesting that the PIBs adsorb with all of the head groups at the interface. This was confirmed by the ellipsometry data which showed that the film thickness decreased with increasing functionality for similar molecular weight PIBs. Compared to other head groups which have been used to functionalise PIB, the azo head group has a much weaker affinity for water, leading to higher collapse areas and lower collapse pressures.

Construction of supramolecular structures from cyclodextrins, polymers

Cyclodextrins (CDs) have been found to form inclusion complexes with various polymers with high specificity to give stoichiometric compounds in crystalline states. In these complexes, polymer chains were threaded into cyclodextrins and recognized by the host. For example, α-cyclodextrin (α-CD) formed complexes with poly(ethylene glycol) (PEG) of molecular weight higher than 200, although β-CD did not form complexes with PEG of any molecular weight. However, β-CD formed complexes with poly(propylene glycol) (PPG) of various molecular weights with which α-CD did not form complexes. γ-CD formed complexes with poly(methyl vinyl ether) (PMVE), though α-, β-CD did not form complexes with PMVE. α-CD formed complexes with oligoethylene, but only γ-CD formed complexes with polyisobutylene of molecular weight over 500. The structures and properties of the complexes have been studied by spectroscopic methods. Polyrotaxanes in which many CDs are threaded on a single chain were prepared by capping the chain ends with bulky groups.

Universal Characteristics of Drag Reducing Polyisobutylene in Kerosene

A homologous series of oil-soluble polyisobutylene (PIB) in kerosene was investigated to study the drag reduction in a turbulent flow with a rotating disk apparatus (RDA). The drag reduction data were plotted to observe the universal characteristics of PIB-kerosene systems. Intrinsic concentration [C] was found to be extremely useful quantity in normalizing the drag reduction data for different molecular weights of PIB and concentrations similar to poly(ethylene oxide) (PEO) in water. An explanation of the drag reduction phenomenon by an individual molecule was obtained by the plot of intrinsic drag reduction vs. [C].

Preparation and Characterization of Inclusion Complexes of Polyisobutylene with Cyclodextrins

β-Cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) formed inclusion complexes with polyisobutylene (PIB) of various molecular weights to give stoichiometric compounds in crystalline states. α-Cyclodextrin (α-CD) did not form complexes with PIB of any molecular weight. The yields of the complexes with β-CD decreased with an increase in the molecular weight of PIB. In contrast, the yields of the complexes with γ-CD increased with an increase in the molecular weight and the complexes were obtained almost quantitatively with PIB of molecular weight 1350. The chain-length selectivity is reversed between β-CD and γ-CD. The inclusion complexes were isolated and found to be 3:1 (monomer unit:CD). The complexes were characterized by IR, 1H NMR, 13C NMR, 13C CP/MAS NMR, 13C PST/MAS NMR spectra, and X-ray (powder), thermal, and elemental analyses. The structures of the complexes are discussed.

Determination of optimized blending fractions for particle size distributions or molecular weight distributions involving various physical properties

AbstractIt has been shown in this study that the effects of particle size distribution or molecular weight distribution on selected physical properties can be related by a generalized blending approach that involves similar equations. The blending equations developed involve different z‐fractions where z = 3 for volume blending of spherical particles, or z = 2 for surface blending of spherical particles, or z = 1 for the weight blending of molecular weights. This new analysis approach addresses the magnitude of the ratios of particle size averages, Dx/Dy, or ratios of molecular weight averages, Mx/My, as well as the location of this maximum, the level of distribution information available for the starting materials, and the type of z‐fraction blending. To illustrate this approach suspension viscosity/concentration data was used to show how the Dx/Dy ratio could be introduced successfully to analyze latex volume blending where z = 3. In addition, the maximum steady‐state elastic compliance, Je, as a function of weighted blends (z = 1) of two different molecular weights of polyisobutylene was shown to fit the simple equation Je = 1.187 (M3/M2) (M4/M1) reasonably well. © 1995 John Wiley &amp; Sons, Inc.

Viscous properties of polymer‐thickened water‐in‐oil emulsions

AbstractThe viscous flow properties of polymer‐thickened water‐in‐oil emulsions were measured using a coaxial cylinder viscometer. The emulsions were prepared using deionized water and polyisobutylene in oil solutions. Three different molecular weight polyisobutylenes (Vistanex MML‐140, Vistanex MML‐100, and Vistanex MML‐80) were studied. The effects of polymer concentration and water (droplet) concentration on the flow properties were determined. The polymer concentration varied from 0 to 3.96% by weight based on the oil phase whereas the water concentration varied from 0 to 80% by volume (based on total emulsion volume). The polymer solutions behaved like non‐Newtonian Ellis model fluids. At low water concentrations, the flow curves for emulsions were similar to their suspending medium (polymer solution). At high values of water concentration, emulsions clearly exhibited a yield stress. The yield stress increased with both water and polymer concentrations. The shear stress/shear rate data for the emulsions possessing a yield stress were described adequately by a modified Herschel‐Bulkley model. A comparison was also made of the relative viscosities of emulsions having different polymer concentrations. The relative vis‐cosities for polymer‐thickened emulsions were found to be significantly lower than the corresponding values for emulsions without polymer. The correlation of relative viscosity/ concentration data is discussed. © 1993 John Wiley &amp; Sons, Inc.