Hydroxyl-terminated Polybutadienes Research Articles

Comparative study of structures and properties of HTPBs synthesized via three different polymerization methods

Hydroxyl-terminated polybutadienes (HTPBs) were obtained via free radical polymerization, living anionic polymerization, and ring-opening metathesis polymerization. Although the differently synthesized microstructures of HTPBs have a very similar molecular weight, we observed a significant difference in the molecular weight distribution, in the types of addition microstructures, and in the kinds of hydroxyl terminal groups. The HTPB prepared via living anionic polymerization is nearly monodisperse with a molecular weight distribution (Mw/Mn) value lower than 1.1, whereas the free radical and the ring-opening metathesis polymerization processes yielded HTPBs with an Mw/Mn value higher than 1.3. Furthermore, these three polymerization processes led to different percentages of 1,4-addition microstructures, and various types of hydroxyl terminal groups in the polymer backbone. The HTPB prepared via free radical polymerization contains 77.3% of 1,4-addition microstructures and three types of allyl hydroxyl groups, whereas the HTPB synthesized via the living anionic polymerization contains 90.7% of 1,4-addition microstructures and two types of aliphatic hydroxyl groups. The HTPB produced using the ring-opening metathesis polymerization only contains 1,4-addition microstructures (100%) and two types of allyl hydroxyl groups. Finally, the differences of HTPBs' hydroxyl values, thermal properties and viscosity have been further explored, suggesting that HTPBs have the similar glass-transition temperatures and decomposing temperatures, but different hydroxyl values and viscosities.

Methacrylate-based polymer blends containing oligomeric 1,2-polybutadienes

Partly miscible polymer blends with semi-IPNs structure built from polydimethacrylate networks and hydroxyl-terminated liquid polybutadienes with predominant 1,2-structure (LBH) were prepared by photopolymerization method. Photopolymerization kinetics of dimethacrylate–LBH mixtures were monitored by DSC technique under isothermal conditions. Kinetic curves and related parameters, like polymerization rate and degree of double bond conversion were determined as functions of dimethacrylate structure, LBH molecular mass, and its content in the mixture as well as polymerization temperature. The photopolymerization kinetics and activation energy for the polymerization rate were discussed taking into account the phase separation occurring during the curing reaction. The extent of phase separation (based on Tg’s measurements) depended on LBH content and dimethacrylate chemical structure. The effect of LBH content on hardness of polymer blends was also examined.

Vapor-Induced Response of HTPB/MWNTs-COOH PU Conductive Films Based on Hydrogen Bonding Interactions

Novel polyurethane (PU) conducting films consisting of hydroxyl-terminated polybutadienes (HTPB) and carboxyl functionalized multi-walled carbon nanotubes (MWNTs-COOH) were developed by a simple coupling approach based on hydrogen bonding interactions between MWNTs-COOH and PU moieties. The morphologies and structural characterization were conducted by means of FTIR, TEM and TGA etc; and the influence of the MWNTs-COOH loading and curing temperature on vapor response was investigated. The experimental results indicated that a micro-phase separation structure between soft and hard segments was formed, and MWNTs-COOH was tightly encapsulated by PU moieties and homogeneously dispersed in the PUs. The developed films displayed selective response to non-polar organic solvent vapor and good long-term stability.

Mechanical and thermal properties of polyurethane elastomers based on hydroxyl‐terminated polybutadienes and biopitch

AbstractBiopitch is a renewable source of polyol obtained from Eucalyptus tar distillation, which was studied as an active component of polyurethane (PU). The polymerization occurred in one step, with a mixture of biopitch and hydroxyl‐terminated polybutadiene polyols reacted with 4‐4′‐diphenyl methane diisocyanate in the presence of dibutyltin dilaurate. Solid‐state 13C‐NMR, IR spectroscopy, elemental analysis, and thermal analysis [thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)] were used to characterize the biopitch. The biopitch sample showed an aromatic and oxygenated structure with great thermal stability at high temperatures. Multiphasic PUs were synthesized and characterized by IR spectroscopy (attenuated total reflectance), elemental analysis, thermal analysis (TGA and DSC), mechanical assays (tensile strength, elongation at break, toughness, hardness, and resilience), and water absorption resistance (ASTM D 570‐81). In a comparative study of the synthesized elastomers, biopitch content increased tensile strength and hardness and decreased thermal stability, elongation at break, and water absorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 759–766, 2003

Adhesive behavior of polyurethane-based materials

The role of prepolymer on the interfacial strength of polyurethane-based assemblies is examined for two hydroxyl-terminated (telechelic) polybutadienes, R45M and R45HT. Although it is known that both prepolymers lead to very different adhesive behavior, the reasons that explain this are not understood. In this study, we show that two main effects have to be considered: the length of the free chains, which can diffuse across the interface during the formation of the joint and the relative reactivity of the various hydroxyl groups of the chains and chain extenders with the isocyanate. The R45M chains are more efficient connectors than the R45HT chains. Migration of chain extenders and isocyanate over large distances creates a thick interphase where physical crosslinks appear. This interphase is thicker for R45M-based polyurethane showing the role of the chain reactivity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 665–671, 2000

Pyrolysis Behavior of Hybrid-Rocket Solid Fuels Under Rapid Heating Conditions

An experimental investigation of the thermal pyrolysis behavior of several hybrid-rocket solid fuels under rapid heating conditions was conducted to determine pyrolysis laws and to identify and quantify the products of fuel pyrolysis. The study focused on four fuel formulations: pure hydroxyl-terminated polybutadienes (HTPB), 80% HTPB/20% Alex, 80% HTPB/20% Al, and the Joint Industrial Research and Development fuel formulation. A rapid conductive-heating technique was developed and employed to determine Arrhenius-type pyrolysis laws. All four fuels displayed two sets of Arrhenius parameters, depending on the range of surface temperature. For pure HTPB,Ea = 4:91 kcal/mol andA = 11.04mm/s above722K, whileEa = 13:35 kcal/mol andA = 3965mm/s below 722 K. These results agree well with those obtained previously using a lab-scale hybridmotor operating under realistic conditions. The gas chromatograph/mass spectrometer tests of the nonmetalized fuels, using a  ash-heating oven, indicated that the relative concentrations of the pyrolyzed species depended strongly on temperature. For pure HTPB seven major products were identiŽ ed, with 1,3-butadiene representing the dominantproduct at all temperatures tested, up to 1073 K. The measured mole fractions of the pyrolysis products and deduced pyrolysis laws of the fuels studied can be utilized in a comprehensive model simulation for combustion performance predictions.

Hydroxyl-terminated polybutadiene. I. A study of the polymerization of butadiene in the presence of hydrogen peroxide

The polymerization of butadiene in a solution of 1-butanol as a solvent and in the presence of hydrogen peroxide as an initiator was studied. The influence of four factors—polymerization temperature, concentration of the initiator, polymerization time, and stirring rate—on the yield, molecular weight characteristics, and the number-average functionality of the hydroxyl-terminated polybutadienes (HTPBs) were determined. Regression models which adequately fit the experimental data were obtained. On this basis, the optimum values of the most significant factors—polymerization temperature and concentration of the initiator for obtaining maximum yield of HTPB—were evaluated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2491–2496, 1997

Characterization of hydroxyl-terminated polybutadiene

The structures of hydroxyl terminated polybutadienes (HTPB) obtained by free radical polymerization of butadiene in ethanol medium initiated by thermal and photochemical hydrogen peroxide decomposition were studied. The incorporation of alcohol in the polymer chain ends was evidenced by 1 H and 13 C NMR spectroscopy.

Characterization of hydroxyl-terminated polybutadiene

A comparison between the molecular structure of conventional and low molecular weight hydroxyl terminated polybutadienes (HTPBs) is presented. The conventional HTPB samples were R45M, R45HT (Atochem), Liquiflex P and H (Petroflex, Brazil), and the low molecular weight ones were R20LM (Atochem) and two laboratory synthesized materials. The structural differences found were attributed to dissimilarities in fabrication processes for each type of HTPB. Some mechanistic pathways for the polymerization are suggested.

Mechanism of catalysis by ferric acetylacetonate of the reaction between isocyanates and hydroxybutadiene oligomers

Kinetics of the reaction between 3-chlorophenylisocyanate and telechelic hydroxyl-terminated polybutadienes ( M=3000 to 7000), catalysed by ferric acetylacetonate has been studied by microcalorimetry. A mechanism is proposed for the catalytic action, which takes into account the role of π-bonded and self-associated hydroxyl groups. Stability constants have been determined for complexes of the catalyst with hydroxyl groups of the two types, and also the rate constants valid in the limiting stage of the catalysed reaction.

Effects of low molecular weight aliphatic diols on the polyurethane elastomers prepared from hydroxyl‐terminated polybutadienes

AbstractHydroxyl‐terminated polybutadienes were prepared by using azo initiators such as di(4‐hydroxybutyl)‐2,2′‐azobisisobutyrate and di(3‐hydroxybutyl)‐2,2′‐azobisisobutyrate, one of which contains primary and the other secondary hydroxyl groups. The effects of aliphatic diols and 2,4‐toluene diisocyanate (TDI) in the presence of dibutyltindilaurate (DBTDL) as catalyst, on crosslinking of primary and secondary hydroxyl groups, were studied. Polyurethane elastomers from these polymers are prepared by using different ratios of diols, 2,4‐toluene diisocyanate and catalyst. Physical properties such as hardness, tensile strength, 100% modulus, and elongation at break of these polymers were studied with a view to compare them with the physical properties of elastomers prepared from ARCO R‐45M.

Azo initiators for the preparation of hydroxyl‐terminated polybutadienes

AbstractAzo compounds such as di(4‐hydroxybutyl)‐2,2′‐azobisisobutyrate, di(3‐hydroxybutyl)‐2,2′‐azobisisobutyrate, di(2‐hydroxypropyl)‐2,2′‐azobisisobutyrate, and di(2‐hydroxyethyl)‐2,2′‐azobisisobutyrate were prepared and used as initiators for the preparation of hydroxyl‐terminated polybutadienes (HTPBs) of molecular weight (M̄n) ranging from 2000 to 7500 and functionality between 1.90 and 3.0. The polymers were prepared by free‐radical solution polymerization in dioxane and toluene. The polymers obtained were characterized for their molecular weight, hydroxyl number, functionality, and instrinsic viscosity.

Structural and mechanical properties of polybutadiene‐containing polyurethanes

AbstractA series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure‐property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment Tg at −74°C for the unsaturated polyurethanes and at −69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The low Tg, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90‐95 percent of the urethane N‐H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene‐containing polyurethanes the extent of H‐bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segment Tg and stress‐strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σb), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.

Functionality Distribution of Hydroxyl-Terminated Polybutadienes by Gel Permeation Chromatography. II. Measurements for Commercial Polymers

Abstract The study of molecular weight and functionality parameters of telechelic hydrocarbon-based prepolymers has received much attention in recent years owing to the influence that these parameters exert on the vulcanization and product properties. An excellent review of these systems has been presented by French. Previous work has been limited to the determination of the average functionality of the whole polymer or of fractions obtained by some appropriate fractionation procedure. Muenker and Law, for instance, used extensive column elution techniques for separating the various species and then determined the average functionality of the fractions. In the previous paper, we described a dual-detector gel permeation chromatography (GPC) method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distributions of hydroxyl-terminated polybutadienes. The method is based on the simultaneous use of a differential refractive index and ultraviolet GPC detectors to analyze the polymers before and after derivatization of the hydroxyl groups with phenyl isocyanate. In this paper, the method will be utilized to determine these parameters for several commercial hydroxyl-terminated polybutadiene prepolymers and to compare the data with existing literature values.

Functionality Distribution of Hydroxyl-Terminated Polybutadienes by Gel Permeation Chromatography. I. Method and Calibration Procedure

Abstract In recent years, considerable attention has been focused on the structural characterization of functionally terminated hydrocarbon prepolymers used in propellant binders and other applications. The molecular weight averages and molecular weight distributions of hydroxyl-and carboxyl-terminated poly butadienes have been determined by gel permeation chromatography (GPC). The functionality distribution of these prepolymers has also been previously studied by column fractionation and a procedure combining GPC and column fractionation of the polymer by stepwise elution from silica gel. The carboxyl or hydroxyl equivalent weights of the fractions were determined by infrared or near-infrared spectroscopy. The fractionation procedure is quite laborious, and multiple peaks were observed in the elution profile, making it difficult to decide how the fractions were to be grouped for subsequent analysis. Previously, a technique for determining the distribution of unsaturation in copolymers containing a small number of double bonds as a function of GPC elution volume was developed. The technique utilized a GPC equipped with uv photometer and differential refractometer detectors to determine the ratio of the weight fraction of olefinic bonds to the weight fraction of polymer by GPC analysis of the polymer after derivatization of the double bonds with 2,4-dinitrobenzenesulfenyl chloride. It was suggested that the technique should be applicable for the determination of the distribution of other functional groups with the choice of suitable reagents for derivatization. The purpose of this investigation was to attempt to extend our previous study to simultaneously determine the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl-terminated polybutadienes by a GPC technique.

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. I. The method and calibration procedure

A method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl-terminated polybutadienes using GPC has been developed. The method is based on the preparation of a UV absorbing derivative of the hydroxyl group and GPC analysis using dual differential refractive index and UV detectors. In order to determine the hydroxyl equivalent weight, quantitative derivatization of the hydroxyl group is required. If the equivalent weight can be determined by an independent method, the derivatization reaction can be less than quantitative if sufficient UV absorptivity can be obtained. The procedure used for calibrating the GPC columns and UV detector are presented. Equations for calculating number- and weight-average functionalities from GPC data were also developed. The number-average functionality is independent of the functionality distribution, but the weight-average functionality is dependent upon the distribution of functionality. The ratio of the weight-average to number-average functionality is indicative of how the functionality is skewed as a function of molecular weight.

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. II. Measurements for commercial polymers

Abstract The study of molecular weight and functionality parameters of telechelic hydrocarbon-based prepolymers has received much attention in recent years owing to the influence that these parameters exert on the vulcanization and product properties. An excellent review of these systems has been presented by French. Previous work has been limited to the determination of the average functionality of the whole polymer or of fractions obtained by some appropriate fractionation procedure. Muenker and Law, for instance, used extensive column elution techniques for separating the various species and then determined the average functionality of the fractions. In the previous paper, we described a dual-detector gel permeation chromatography (GPC) method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distributions of hydroxyl-terminated polybutadienes. The method is based on the simultaneous use of ...

Telechelic diene prepolymers. IX. Re‐examination of the functionality of hydroxyl‐terminated polybutadienes

Telechelic diene prepolymers. IX. Re‐examination of the functionality of hydroxyl‐terminated polybutadienes

Polyurethane based on hydroxyl‐terminated polybutadienes

AbstractButadiene has been found to homopolymerise and copolymerise with other reactive vinyl monomers to yield unique liquid polymers which are terminated with reactive allylic hydroxyl groups. Through the use of an isocyanate cure reaction they offer a route to liquid castable general purpose elastomers, capable of reinforcement with various fillers and extension with a wide variety of low cost process oils.

Urethane Elastomers Based on Hydroxyl Terminated Polybutadienes

This article describes the preparation and properties of urethane elastomers based on hydroxyl-terminated polybutadienes. The liquid nature of these polybutadiene systems allows easy reaction with isocyanates even at ambient temperatures. Properties of elastomers produced can be easily improved by either chemical modification of the polymer backbone of the polybutadiene or the addition of solid reinforcing fillers, such as carbon black or clay. This article further describes the preparation of stable prepolymers of poly butadiene which can then be reacted with various diol or diamine chain extenders. Conceptually, the elastomers resulting from this technology would combine the properties of rubbers in having the ability to be oil extended or filler reinforced as well as having the high performance of cast urethane systems.