Burning‐rate enhancement of a high‐energy rocket composite solid propellant based on ferrocene‐grafted hydroxyl‐terminated polybutadiene binder

Four different samples of ferrocene‐grafted hydroxyl‐terminated polybutadiene (Fc‐HTPB), containing 0.20, 0.52, 0.90, and 1.50 wt % iron, were synthesized by the Friedel–Crafts alkylation of ferrocene with hydroxyl‐terminated polybutadiene (HTPB) in the presence of AlCl₃ as a (Lewis acid) catalyst. The effects of the reaction conditions on the extent of ferrocene substitution were investigated. The Fc‐HTPBs were characterized by IR, ultraviolet–visible, ¹H‐NMR, and ¹³C‐NMR spectra. The iron content and number of hydroxyl groups were estimated, and the properties, including thermal degradation, viscosity, and propellant burning rates (BRs), were also studied. The thermogravimetric data indicated two major weight loss stages around 395 and 500°C. These two weight losses were due to the depolymerization and decomposition of the cyclized product, respectively, with increasing temperature. The Fc‐HTPB was cured with toluene diisocyanate and isophorone diisocyanate separately with butanediol–trimethylolpropane crosslinker to study their mechanical properties. Better mechanical properties were obtained for the gumstock of Fc‐HTPB polyurethanes with higher NCO/OH ratios. The BRs of the ammonium perchlorate (AP)‐based propellant compositions having these Fc‐HTPBs (without dilution) as a binder were much higher (8.66 mm/s) than those achieved with the HTPB/AP propellant (5.4 mm/s). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure-property relationship of HTPB-based propellants. II. Formulation tailoring for better mechanical properties

There has been a constant endeavor to improve the mechanical properties of hydroxylterminated polybutadiene (HTPB) -based composite solid propellants. A systematic study has been conducted on different batches of HTPB resins with varying molecular weights and hydroxyl values. Propellant formulation experiments were conducted wherein the ratio of chain extender to crosslinker was systematically varied, with a view to achieve the maximum possible strain capability and moderately high tensile strength, keeping all other parameters constant. The influence of increasing hydroxyl content from trimethylolpropane at the expense of hydroxyl content from butanediol, on the mechanical properties of the finished propellant, has been depicted on 3-dimensional graphs. The isoproperty lines, plotted as a triangular chart with the percentage hydroxyl contents from the three constituents, can be used to arrive at the suitable formulation for a specified application depending upon the OH value of the resin. HTPB resins with high molecular weight, low functionality, and low hydroxyl value require higher levels of trifunctional curing agent and higher NCO / OH ratios to obtain outstanding mechanical properties, especially elastic properties, compared to low molecular weight, high functionality resins. The impact of hard and soft segment domain structure on the mechanical behavior of the cured systems is more pronounced in the low molecular weight resin formulations due to the higher hard segment content compared to those attainable in high molecular weight resin formulations. © 1993 John Wiley & Sons, Inc.     

阴离子端羟基聚丁二烯的表征及其固化物的力学性能

简述了以硅烷保护羟基的烷基锂为引发剂,环己烷为溶剂合成丁羟胶的聚合方法;通过IR、^1H—NMR和GPC等方法研究了阴离子端羟基聚丁二烯主链结构、分子质量分布、官能度及其分布;对其固化物力学性能进行了评价。研究结果表明,阴离子端羟基聚丁二烯的1,4-结构含量高达约90％、分子质量分布指数≤1．05、官能度接近2,其固化物具有优异的力学性能。     

Engineering plastics from lignin. XVII. Effect of molecular weight on polyurethane film properties

A series of five fractions with number average molecular weights (M?_n) between 1500 and 10,000 daltons were isolated from a Kraft hydroxypropyl lignin (HPL). From ¹H-NMR and UV analysis the chemical properties of the HPLs were found to vary slightly with molecular weight. The hydroxyl content decreased while the glass transition temperature (T_g) increased as the HPL molecular weight increased. The Fox-Flory equation adequately described the M?_n vs. T_g relationship. The HPL fractions were used as polyols for the preparation of solvent-cast polyurethane networks (PU) in film form. The T_g of the PUs increased from 40° to 120°C as the M?_n of the polyol rose from 1500 to 10,000 daltons. The molecular weight between crosslinks (M?_c) of the networks was determined by swelling. An observed decrease in M?_c with an increase in M?_n was related to the functionality of the system. The strength properties of films prepared from fractionated HPLs were superior to those prepared from nonfractionated HPLs.     

端羟基液体聚丁二烯橡胶微观结构及其力学性能

通过FT—IR,HNMR,CNMR,GPC等方法,对相同牌号HTPB样品A和B的主链微观结构、羟基类型、环氧基团、官能度分布和固化物力学性能进行了对比,2个样品的主链微观结构、羟基类型、环氧基团含量基本一致,而官能度分布存在较大差异,由结果可得,HTPB官能度分布对其力学性能影响较大,二官能度为84．2％的样品A具有较好的力学性能,二官能度为676％的样品B具有相对较差的力学性能。     

Functionality determination of hydroxyl–terminated butadiene prepolymers

Functionality of hydroxyl–terminated butadiene prepolymers (HTPB) was determined from gel point measurements as described by Strecker and French.² Commercial HTPB samples had functionalities ranging from 1.9 to 2.6, with most of the material close to 2.0. In order to calculate functionality from gel point measurements, the hydroxyl content of the HTPB must be known. A method was developed which gave reproducible results. Curing agents used in the gel studies were viscous liquid poly-functional isocyanates with functionalities of 2.00 and 2.50. An extensive study showed that no side reactions were occuring with the isocyanates at the temperatures employed. It is estimated that the precision of the method is ±0.80%. Functionality calculated by dividing molecular weight by equivalent weight results in lower values in all cases when compared to gel point measurements.     

Characterization of the network structure of hydroxyl terminated poly(butadiene) elastomers prepared by different reactive systems

Three types of hydroxyl terminated poly(butadiene) (HTPB) networks having different NCO/OH reactive group ratios were prepared using three different reactive systems (i.e., Desmodur N-100 pluriisocyanate, isophorone diisocyanate (IPDI)/trimethylol propane (TMP), and hexamethylene diisocyanate (HMDI)/TMP). Desmodur N-100 and TMP were used as polyfunctional reactants. The polymer–solvent interaction parameters (χ₁) for HTPB–tetrahydrofuran (THF) and HTPB–chloroform systems at 45°C were determined, using a vapor pressure osmometer (VPO), as 0.31 and 0.24, respectively. Equilibrium swelling values of the networks in THF and chloroform and the data obtained by osmometry were further used for the calculation of the mean number-average molecular weight between junction points (M _c) of HTPB networks through the Flory-Rehner equation. The M _c values of each network, which were calculated from the swelling data obtained in THF and chloroform using the corresponding χ₁ parameters for polymer–solvent systems, were found to be nearly the same. The changes in the mechanical, swelling, and the solubility properties of the networks prepared by three different reactive systems were followed. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1129–1135, 1998     

Synthesis and characterization of iron carbonyl‐modified hydroxyl‐terminated polybutadiene: A catalyst‐bound propellant binder for burn‐rate augmentation

Iron was coordinately linked to the hydroxyl‐terminated polybutadiene (HTPB) backbone using iron carbonyl via a ligand displacement reaction. The modified HTPB thus obtained was reddish brown in color and was characterized by GPC, FTIR, NMR, thermal, and propellant studies. No significant changes in the rheology, molecular weight, and molecular weight distribution were seen in the modified resin when the bonded Fe content was >0.8.0 wt %. However, the hydroxyl value of the resin decreased by 3–7 irrespective of the weight percent of the bonded Fe, and this was more likely due to the Fe‐catalyzed oxidation of the ? CH₂OH moiety, mostly to the ? CHO group. Apparently, this has not affected the cure characteristics of the binder, as demonstrated by the good mechanical properties of the gum stock and the propellant. The catalytic efficiency of the bonded Fe on the burn rate of the propellant was more efficient than was the free Fe added to the propellant. The aging characteristics of the resin for the bound iron content of ≤0.8 wt % was apparently good, as its viscosity and molecular weight did not undergo any drastic changes even after 18 months' storage under ambient conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2813–2823, 2003     

Swelling properties of cross-linked maxillofacial elastomers

Silicone specimens cross-linked with various amounts of cross-linking agent were studied in terms of mechanical and swelling behavior. The measured tensile modulus allowed calculation of the average molecular weight between cross-links (M?_c). Equilibrium swelling data were also used, in combination with the determined M?_c values, to obtain the interaction parameter χ of various silicone–solvent systems at 25°C. Part of this work was also the study of swelling of silicone samples with varying network density in selected solvents such as toluene, ethyl acetate, n-butanol, and methyl ethyl ketone. © 1993 John Wiley & Sons, Inc.     

Synthesis,Characterization and Properties of Nitropolybutadiene as Energetic Plasticizer for NHTPB Binder

The nitration of low molecular weight polybutadiene (PB) by a convenient and inexpensive procedure was investigated. To retain the unique physico‐chemical properties of the plasticizer, it was nitrated to an extent of 10 % double bonds. The product nitropolybutadiene (NPB) was characterized by FT‐IR and ¹H NMR spectroscopy as well as GPC, DSC, and TGA methods. The kinetic parameters for the decomposition of NPB from room temperature to 400 °C were obtained from non‐isothermal DSC. The changes in glass transition temperature (T _g) and inert uncured binder systems were used for determination of its efficiency as plasticizer. NPB was used in cured and unfilled nitro‐hydroxyl terminated polybutadiene (NHTPB) binder. Isothermal thermogravimetric analysis (Iso‐TGA) was employed to determine the migration rate in cured and unfilled HTPB binder systems compared to the dioctyladiphate (DOA) plasticizer. It was found that the exudation of the NPB plasticizer is slower than that of the DOA plasticizer. Thus, the NHTPB/NPB binder system (binder/plasticizer) presents more convenient mechanical properties than HTPB/DOA and is a promising new energetic binder system for polymer bonded explosives.     

Chain-extended polyurethanes—Synthesis and characterization

Thermoset polyurethane (PU) elastomers were prepared using hydroxyl-terminated polybutadiene (HTPB), toluene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI). The effects of various diamines and diols on the mechanical and thermal properties of polyurethanes are discussed. The average molecular weight between crosslinks (M?/_c) was determined by swelling studies. The properties imparted by the extenders are explained on the basis of the groups present in the diamines and the number of methylene carbons in the diols.     

Structure and viscoelastic properties of epoxy resins prepared from four-nuclei novolacs

The relation between the structure and the viscoelastic properties of seven kinds of epoxy resins was studied. Seven tetraglycidylethers were synthesized from four-nuclei novolacs in which the positions of methylene linkage or number of kind of substituents were different. These epoxy compounds were cured with diaminodiphenylmethane as a hardener. From the viscoelastic properties of the fully cured resins with the hardener, characteristic properties such as glass transition temperature (T_g), average molecular weight between crosslinking points (M̄_c), and front factor (ϕ) were obtained. It was concluded that higher linearity in the main chain of epoxy resins gave a cured resin with a higher T_g, a smaller M̄_c, and a larger ϕ.     

不同增溶剂体系合成端羟基聚丁二烯液体橡胶的性能及应用

研究了分别由工业乙醇／水和工业丙醇／水作增溶剂的聚合体系制备的端羟基聚丁二烯液体橡胶（ＨＴＰＢ）的相对分子质量及其分布、粘度、羟值及官能度等物理性能,结果表明２种体系的差别较大。应用结果表明,工业乙醇／水体系的ＨＴＰＢ的工艺及力学性能优于后者。对工业乙醇／水体系ＨＴＰＢ在固体推进剂、水轮机及电子灌封等领域的应用进行了简述。     

Synthesis of poly(propylene-glycol-diacrylates) and properties of the photocured networks

A series of poly(propylene-glycol-diacrylates) (PPGDA) having molecular weights (MW) in the range 300–3,000 and an acrylic functionality near to two were synthesized by acrylation of the corresponding hydroxy-terminated oligomers with acrylic acid in the presence of p-toluensulphonic acid as a catalyst. The M¯_n of the acrylated products was found slightly lower than that of the starting oligomers, indicating the occurrence of an acidic degradation reaction which does not influence the acrylic functionality. The acrylated oligomers were ultraviolet (UV) cured until a complete double bond disappearance was obtained: only in the presence of tripropylene-glycol-diacrylate (TPGDA) were small amounts of residual unsaturations revealed. Rubbery materials were usually obtained, with the exception of TPGDA. The properties of the cured PPGDA were investigated by means of differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical thermal analysis. The T_g values were found to decrease by increasing the MW of the used oligomers, that is, by increasing the length of the chain between the two acrylic double bonds. A good agreement with the Nielsen equation was found. Moreover, the equilibrium swelling values in water were measured; the obtained values were interpreted in terms of the solubility parameters of the oligomers and of the crosslinking density of the networks. Finally, some mixtures of PPGDA oligomers with a typical epoxy-acrylate resin were UV cured; their properties confirm the high flexibilizing effect of the PPGDA oligomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:491–497, 1997     

Structural differences exhibited by networks prepared by chemical or photochemical reactions II — Thermoelastic properties

Thermoelastic properties and swelling measurements were used to characterise networks obtained either by peroxide curing or by photocrosslinking. In agreement with previous studies, it was shown, on the one hand that the measured value of the average molecular weight of a network strand (M _c) depends on its method of determination and that the ratio M _cT/M _cv2m is a characteristic of each crosslinking process, on the other hand photo-crosslinked materials exhibit a more homogeneous distribution of the crosslink points than do peroxide cured samples. Important parameters such as f_e/f, the energetic contribution to the equilibrium retractive force, and d In < r²> ₀/dT, the temperature coefficient of the unperturbed dimension of the macromolecular chain, were determined.     

Zur unverträglichkeit von polymergemischen. 1. Lichtstreuungsmessungen am system polystyrol/polymethylmethacrylat/benzol

A polystyrene (PS) with M?_w = 9,7 · 10⁴ was investigated by means of light scattering in the isorefractive polymer/solvens-mixture polymethylmethacrylate (PMMA)/benzene. It was found, that the second osmotic virial coefficient A₂ of PS was strongly dependent on the average viscosimetric molecular weight M?_v and on the concentration of PMMA, but scarcely on the temperature in the range of 20°C to 60°C. The θ-Point, where A₂ is zero, was independent of the temperature within experimental error. By defining the PMMA concentration at the θ-Point as c_θ, and by reducing the measured PMMA concentration c to c/c_θ, an unequivocal relation was obtained between A₂ and c/c_θ, which is independent of molecular weight and molecular weight distribution of PMMA. PS shows a high second virial coefficient in dimer and trimer MMA as well as in non-hydrogenated and hydrogenated MMA. The investigated PS constitutes a θ-System in PMMA of a degree of polymerisation of P?_w, ～ 17without the use of benzene.     

Melt fracture of polystyrene

The results of an experimental study of melt fracture using polystyrene samples of narrow and broad molecular weight distribution are presented. The weight average molecular weight (M?_w) ranged from 9.72 × 10⁴ to 1.80 × 10⁶ and the distribution breadth M?_w/M?_η from 1.06 to 9.21. The critical shear stress varies linearly with 1/M?_w, increases slightly with temperature and is independent of the distribution of molecular weights. This type of behavior is satisfactorily explained in terms of Graessley's entanglement theory.     

Structural differences exhibited by networks prepared by chemical or photochemical reactions. I stress-strain properties

Stress-strain properties and swelling measurements were used to characterise networks obtained either by peroxide curing or by photocrosslinking. It was shown that the value of the average molecular weight of a network strand (M _c) is dependent on its methods of determination (m _cf from modulus, M _cv2m from swelling ratios) and that the value of the ratio M _cp/M_cv2m is a characteristic of each crosslinking process. Moreover, the results have shown that the homogeneity of distribution of the crosslinks is dependent on the crosslinking process used.     

The determination of molecular weights of polymers from critical concentrations of ternary systems polymer-polymer-solvent

The dependence of the critical concentration of the ternary system polymer-polymer-solvent on the molecular weight can be expressed by the relation where c_c is the critical concentration, M? the appropriate average of the molecular weight of both polymers; A and c_c∞ are constants for the given system. The possibility of determining the molecular weight of one of the polymers from the value c_c and the molecular weight of the known polymer with the aid of equation (1) is discussed.     

Star oligomers for low VOC polyurethane coatings

Conclusion  Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.