Prepolymer Method Research Articles

Effect of the composition ratio of copolymerized poly(carbonate) glycol on the microphase‐separated structures and mechanical properties of polyurethane elastomers

AbstractRandomly copolymerized poly(carbonate) glycols were employed as starting materials for the synthesis of polyurethane elastomers (PUEs). The poly(carbonate) glycols had hexamethylene (C6) and tetramethylene (C4) units between carbonate groups in various composition ratios (C4/C6 = 0/100, 50/50, 70/30, and 90/10), and the number‐average molecular weights of these poly(carbonate) glycols were 1000 and 2000. The PUEs were synthesized with these poly(carbonate) glycols, 4,4′‐diphenylmethane diisocyanate, and 1,4‐butanediol by a prepolymer method. Differential scanning calorimetry measurements revealed that the difference between the glass‐transition temperature of the soft segment in the PUEs and the glass‐transition temperature of the original glycol polymer decreased and the melting point of the hard‐segment domain increased with an increasing C4 composition ratio. The microphase separation of the poly(carbonate) glycol‐based PUEs likely became stronger with an increasing C4 composition ratio. Young's modulus of these PUEs increased with an increasing C4 composition ratio. This was due to increases in the degree of microphase separation and stiffness of the soft segment with an increase in the C4 composition ratio. The molecular weight of poly(carbonate) glycol also influenced the microphase‐separated structure and mechanical properties of the PUEs. The addition of different methylene chain units to poly(carbonate) glycol was quite effective in controlling the microphase‐separated structure and mechanical properties of the PUEs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4448–4458, 2004

Influence of system variables on the morphological and dynamic mechanical behavior of polydimethylsiloxane based segmented polyurethane and polyurea copolymers: a comparative perspective

The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding.

Highly Softened Polyurethane Elastomer Synthesized with Novel 1,2-Bis(isocyanate)ethoxyethane

A novel diisocyanate, 1,2-bis(isocyanate)ethoxyethane (TEGDI), whose backbone is ether bonds was used for the preparation of polyurethane elastomers (PUEs). 1,6-Hexamethylene diisocyanate (HDI) was also used as a control. The PUEs were prepared with either TEGDI or HDI, poly(oxytetramethylene) glycol (PTMG), and curing agent by a prepolymer method. Differential scanning calorimetry, infrared spectroscopy, and wide-angle X-ray diffraction revealed that the phase separation of the network TEGDI-based PUEs was much weaker compared with that of the HDI ones. Highly softened TEGDI-based PUEs were successfully prepared on account of flexibility of TEGDI itself and weaker phase separation.

Optical and infrared imaging of growing polyolefin particles

AbstractA method was developed that observes polymer particles during a polymerization reaction using optical‐ and infrared imaging. The yielding images give good insight into catalyst‐specific properties as shape replication, distribution of activity, and the activation. The advantage of this method is the possibility to link behavior of individual particles to its own specific properties. The infrared method measures surface temperatures of growing particles. Such data are useful to feed mathematical models describing the growth of single particles. The temperature–time curves showed maximum temperature to be reached after some minutes; a simple model was used to describe this effect qualitatively. The maximum particle temperature rise was 20 K, but depended strongly on reaction rate and particle size. Temperature, prepolymerization method, catalyst recipe, and catalyst activation time were varied for a fourth‐generation Ziegler‐Natta catalyst in polymerization of propylene and ethylene.

Polymerization of liquid propylene with a fourth‐generation Ziegler–Natta catalyst: Influence of temperature, hydrogen, monomer concentration, and prepolymerization method on powder morphology

AbstractLiquid propylene was polymerized in a 5‐L autoclave batch reactor using a commercially available TiCl4/MgCl2/Al(ethyl)3/DCPDMS Ziegler–Natta catalyst, with a phthalate ester as internal electron donor. The powders from these polymerizations were characterized using laser diffraction particle size distribution (PSD) analysis, scanning electron microscopy (SEM), and bulk density measurements. These characteristics were analyzed as a function of the process conditions, including hydrogen and monomer concentration, polymerization temperature, and the prepolymerization method. It was shown that polymerization temperature influences the powder morphology to a large extent. At low temperatures, high‐density particles were obtained, showing regular shaped particle surfaces and low porosities. With increasing temperature, the morphology gradually was transferred into a more open structure, with irregular surfaces and poor replication of the shape of the catalyst particle. When using a prepolymerization step at a relatively low temperature, the morphology obtained was determined by this prepolymerization step and was independent from conditions in main polymerization. The morphology obtained was the same as that observed after a full polymerization at temperature. Even when using a short polymerization at an increasing temperature, the morphology was strongly influenced by the initial conditions. The effect of variation in hydrogen concentration supported the conclusion that the initial polymerization rate determines the powder morphology. In the absence of hydrogen, high bulk densities, and regularly shaped particles were obtained, even at high temperatures. With increasing hydrogen concentration, the reaction rates increased rapidly, and with that changed the morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1421–1435, 2003

Kinetic Aspects of Chain Extension Reaction Using Water-Soluble Diamines in Aqueous Polyurethane Dispersion

ABSTRACT Chain extension reaction using water-soluble chain extenders was investigated with varying carbon number of the chain extenders (ethylene diamine, diaminobutane, and 1,6-hexane diamine) and their feed rates in the preparation of polyurethane dispersions using prepolymer method. The chain extension reaction between residual NCO groups from aliphatic diisocyanate (isophorone diisocyanate) and water-soluble diamines was observed by monitoring pH of the aqueous phase. A separate swelling experiment using these water-soluble diamines was conducted to investigate the locus of chain extension reaction and chain extension model based on the experimental results was suggested. Apparent reaction rate obtained by pulse-relaxation and the time-evolution average particle size were strongly dependent on the chain length of the diamines as well as feed rate of the chain extender. Moreover, the tensile strength and elongation of the thin films cast from these polyurethane dispersions were also influenced by the chain length.

Polymerization of liquid propylene with a 4th generation Ziegler–Natta catalyst—influence of temperature, hydrogen and monomer concentration and prepolymerization method on polymerization kinetics

In a batch-wise operated autoclave reactor, liquid propylene was polymerized using a 4th generation, TiCl 4/MgCl 2/phthalate ester–AlEt 3–R 2Si(OMe) 2, Ziegler–Natta catalyst system. By using a calorimetric principle it was possible to measure full reaction rate versus time curves for obtaining data on polymerization kinetics, under industrially relevant conditions. The influence of polymerization temperature, the hydrogen and monomer concentration, and the prepolymerization method on reaction kinetics were investigated. A new method for prepolymerization, the so-called non-isothermal prepolymerization, is described. In this short prepolymerization procedure featuring an increasing polymerization temperature the thermal runaway on particle scale was avoided. It was shown that this prepolymerization method can relatively easily be applied to an industrial process, with the introduction of a continuous plug flow reactor, giving a narrow residence time distribution, acceptable yield-in-prepolymerization and a method for monitoring catalyst activity. Using different methods for calculating the monomer concentration at the active site of the catalyst, the influence of polymerization temperature was determined. It was shown that at high polymerization temperatures, the reaction rate is barely influenced by polymerization temperature, when no prepolymerization is used. This is ascribed to thermal runaway on particle scale of a fraction of the catalyst particles. When a prepolymerization is used, this effect disappears and thermal runaway is avoided. When systematically reducing the monomer concentration ( C m,bulk ) in the bulk by replacing part of the liquid propylene by hexane, the reaction rate proved to be remarkably independent of the monomer concentration. With reducing C m,bulk , reaction rate decreased very slowly until C m, bulk =150 g/ l . When further decreasing C m,bulk , reaction rate dropped rapidly. The hydrogen concentration was varied over a wide range at 60°C and 70°C. For both temperatures it was shown that reaction rates increased rapidly with increasing hydrogen concentration at low hydrogen concentrations. At higher hydrogen amounts, this effect disappeared and a maximum reaction rate was found.

Solvent-influenced mesostructures in polyurethane-based membranes of different transport parameters using SAXS synchrotron method

The state of solvent in a membrane and the membrane mesostructure are of prime importance for the understanding of membrane transport phenomena. In our last SAXS (small angle X-ray scattering) study we have given evidence that the model of permeation with the permeate phase transition level is not correct for the polyurethane membrane. Instead, inside the membrane, a structure of the system polymer-solvent is formed, which changes gradually from structure of dry polymer to the one saturated with solvent, depending on the depth in the permeating membrane [1]. This result confirmed the correctness of models of permeation, taking into account “anomalous diffusion.” The anomalous diffusion can be caused by some physical parameters such as entrapping effects due to geometric constraints on the pathway of the solvent molecules [2–5]. Also modelling of the diffusion process in heterogeneous media containing impermeable domains (liquid crystal type) was carried out using a random-walk simulation [6]. The domains acts as obstructions in the diffusional path and the solvent molecules diffuse through the amorphous polymer matrix via tortuous path around the domains. Segmented polyurethanes are regarded as multiblock copolymers of the (AB)n type, in which A and B are the hardand soft-segment repeat units respectively. Microphase separation in this type of materials, due to thermodynamic incompatibility between segments of both types and formation of impermeable hard-segment domains dispersed in the rubbery soft-segment matrix, was observed. The structure of the microphase was assumed to be lamellar [7]. So, the structure of these lamellar systems and its change upon a solvent action should have a real influence on the transport parameters. The aim of this work was to find a change caused by solvent in the structure of the previous lamellar system in membranes differing in transport parameters. The segmented polyurethanes studied in this work were prepared using a prepolymer method in DMF solution. In the case of PU-P-1, a prepolymer consisting of PTMO (hydroxy-terminated polytetramethylene oxide, M = 1000) and TDI (2,4-tolylene diisocyanate) was obtained, which was followed by a chain extension with PP (4,4′-diaminodiphenylmethane). PU-B-1 was obtained in a similar manner using PBD (hydroxyterminated polybutadiene with a similar molecular weight) as a macrodiol component. The details of the synthesis have been described previously [8]. The schematic representation of the molecular structure of the obtained polyurethanes is given in Fig. 1. They are denoted as PU-X-x , where X describes type of macrodiol used (P as PTMO, B as PBD), and x is a number of repeat units in the hard segment (Fig. 1). The overall compositions of the investigated PUs and their physicochemical characteristics are given in Table I. Films of the PUs were obtained by casting a 15% DMF solution of the polymer onto a glass plate and evaporating the solvent in an oven. The densities of the polyurethane films were measured by buoyancy in water. The molecular weights of the synthesized PUs and the polydispersity index were determined using gel-permeation chromatography (GPC). The measurements were carried out in DMF solutions at 80 ◦C with a Knauer apparatus based on polystyrene standards. Differential scanning calorimetry (DSC), used for the determination of the glass transition temperatures, was conducted with a Rheometric Scientific DSC plus apparatus at a heating rate 10◦/min. Sorption experiments were carried out at 25 ◦C by placing the PU samples in solvent. The liquid uptake was monitored gravimetrically by weighing the PU samples until equilibrium weight was attained. The sorption equilbrium values given in Table II were determined as the moles of liquid sorbed in 100 g of a dry sample.

Characterization of thermoplastic polyurethane adhesives with different hard/soft segment ratios containing rosin as an internal tackifier

Three thermoplastic polyurethanes (TPUs) containing different hard/soft (h/s) segment ratios (1.05-1.4) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′diisocyanate) and polyadipate of 1,4-butanediol (M w = 2440) were allowed to react to produce the prepolymer. To provide the polyurethanes with high immediate adhesion to different substrates, a rosin + 1,4-butanediol mixture (1 : 1 equivalent%) was used as chain extender (TPU-Rs). These TPU-Rs had two types of hard segments: (i) Urethane hard segments, produced by reaction of the isocyanate and the 1,4-butanediol, and (ii) Urethan-amide hard segments, produced by reaction of the isocyanate and the carboxylic acid functionality of the rosin. The TPUs and TPU-Rs were characterized using FTIR spectroscopy, gel permeation chromatography, differential scanning calorimetry, stress-controlled plate-plate rheology, stress-strain measurements, and Brookfield viscosity. The TPUs and TPU-Rs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC joints. The addition of rosin as an internal tackifier increased the average molecular weight, more markedly in the TPU-Rs containing higher hard/soft segment ratios, but the elastic and viscous moduli decreased. An increase in the hard/soft segment ratio of the TPU-Rs retarded the kinetics of crystallization (which was determined by the soft segment content in the polyurethane), and increased the immediate T-peel strength in PVC/polyurethane adhesive/PVC joints (which was determined by the urethan-amide hard segments). Furthermore, addition of rosin to the polyurethanes decreased the final adhesion, although always reasonably high peel strength values were obtained.

Action of hydrocarbon and ester plasticizer in urethane elastomer for sealing purposes

AbstractA comparison of the effects of two types of modifiers, anthracene oil (hydrocarbon) and dioctyl phthalate (ester), on physical and mechanical properties of urethane elastomers prepared from polyetherols (propylene oxide derivatives of various functionalities and MW) and TDI was performed. The aim of the study was to assess their suitability as binders in permanently elastic urethane sealants for use in construction. The urethane elastomers under investigation were synthesized by a prepolymer method. The modifiers, added to the reactive mixture before curing, were found to be fully compatible with the urethane elastomers and did not interfere with the curing process. The usable range of application for both modifiers was found to be up to 40 phr. Over this range the modified urethane elastomers are viscoelastic liquids. The hydrocarbon modifier does enhance the hydrophobic properties of urethane elastomer, at a lower degree of crosslinking. It was found that modified urethane elastomers may be good binders for sealants, although their long‐term sealing properties must be confirmed under field conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 523–529, 2001

Effects of monomers on the properties of palm-oil-based radiation curable pressure sensitive adhesives (PSA) — a prepolymer method

Various low glass transition temperature ( T g) acrylate and methacrylate monomers were mixed with epoxidised palm oil acrylate (EPOLA) with the ratio of 50/50 prior to curing with electron beam (EB) irradiation. Methacrylate monomers such as dicyclopentenyloxyethyl methacrylate (DCPOEMA) and isobornyl methacrylate (ISBMA), although displaying relatively high adhesive properties were finally excluded from being further utilised as monomers for PSA because of a very slow curing speed. Literally, it is suggested that poorer adhesive performances of the cured films made from 50/50 : EPOLA/monomer mixture as compared to that of 100% monomer was attributed to the lack of compatibility between EPOLA and the particular monomers. Further compatibility investigations were continued using formulations prepared via the prepolymer route cured by ultraviolet (UV) irradiation and the results showed that several monoacrylate monomers with polar and non-polar groups exhibited high curing speed as well as good compatibility with EPOLA as shown by their cured film properties such as surface tackiness, peel adhesion and creep resistance. It is also suggested that these monomers were acting as surfactants for EPOLA which consequently enhance their compatibility upon mixing.

Chemical cross-talk in flow-type integrated enzyme sensors

In flow-type integrated enzyme sensors, hydrogen peroxide produced at an upstream electrode is transported to downstream electrodes, and causes non-specific responses which are called as “chemical cross talks (CCTs)”. In this study, the relationship between CCTs and enzyme immobilization methods, namely an electrochemical pyrrole polymerization, a gelatin–glutaraldehyde crosslinking, and a photocrosslinkable prepolymer (PVA-SbQ) method, was investigated. The flow rate dependency and the substrate concentration dependency of CCTs were dependent on the enzyme immobilization methods. Therefore, the effects of the membrane permeability and enzyme density of bioselective layers on upstream and downstream electrodes, on CCT were investigated by using a gelatin–glutaraldehyde crosslinking method as an enzyme immobilization method. The CCTs correspond to the membrane permeability and enzyme density of a bioselective layer on an upstream electrode. Based on these results, an elimination method for CCT was proposed.

Influence of the synthesis conditions on the properties of thermoplastic polyurethane elastomers

Thermoplastic polyurethane elastomers (TPUs) of constant composition were prepared by using the prepolymer method and by changing the reaction conditions (prepolymerization and chain-extension time) to study the influence of these conditions on the final TPU properties. The TPUs were characterized by gel permeation chromatography, differential scanning calorimetry, strain–stress measurements, and contact-angle measurements. To test the adhesion properties of the TPUs, poly(vinyl chloride) strips were bonded to each other by using TPU solutions and the T-peel strength of the adhesive joints was measured. It was found that provided a threshold is crossed, the prepolymerization time markedly influences the final properties of the TPUs (viscosity of solutions, molecular weight, mechanical and adhesive behavior), whereas the chain extension time does not. Therefore, it is possible to prepare TPUs with specific properties by playing with the prepolymerization conditions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1590–1595, 2000

Influence of the prepolymerization on the properties of thermoplastic polyurethane elastomers. Part II. Relationship between the prepolymer and polyurethane properties

The synthesis of thermoplastic polyurethane elastomers (TPUs) is generally carried out using the prepolymer method. To study the influence that the properties of the prepolymer may have in the final TPUs, four TPUs were prepared by using different NCO/OH ratios. The prepolymers and the macroglycol used in their synthesis were characterized in the first part of this article. TPUs were characterized by using gel permeation chromatography, strain–stress measurements, differential scanning calorimetry, and contact-angle measurements. To test their adhesion properties, the T-peel strength of PVC/TPU/PVC adhesive joints was determined. It was found that the properties of the prepolymers determine the properties of the TPUs when the amount of hard segments (related to the soft-segments size) is small. In contrast, when the amount of hard segments (related to the soft-segments size) is high, it is the chain extension step that determines the TPUs structure and properties. On the other hand, it was observed that a high amount of ever hard or soft segments gives TPUs with similar properties. This behavior is explained by the structure of the prepolymer (related to the degree of polymerization) and the TPUs. Finally, it was found that the adhesive properties of the finished TPUs are comparable to those of blocked prepolymers prepared with low NCO/OH ratio. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1602–1607, 2000

Synthesis and characterization of new thermoplastic polyurethane adhesives containing rosin resin as an internal tackifier

Three thermoplastic polyurethane elastomers (TPUs) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′-diisocyanate) and the polyadipate of 1,4-butanediol (Mw = 2400) were reacted to produce a prepolymer containing unreacted isocyanate groups; chain extenders were different mixtures of 1,4-butanediol and a rosin resin (0-50%). The specific feature of this procedure was the introduction of a rosin resin as an internal tackifier to provide higher immediate adhesion to the TPUs. The new TPUs were characterized using gel permeation chromatography, wideangle X-ray diffraction, differential scanning calorimetry, stress-controlled rheology, and stress-strain measurements. The TPUs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC and leather/polyurethane adhesive/PVC joints. The addition of rosin resin as an internal tackifier contributed to the production of two types of hard segments, which affected the properties of the TPUs. Therefore, rosin resin as an internal tackifier produced an increase in the average molecular weight, an increase in the viscosity, and improved the rheological properties. The glass transtition temperature decreased if the TPUs contained rosin resin, due to a greater degree of incompatibility between the hard and soft segments. Consequently, slower kinetics of crystallization was obtained in the TPUs containing rosin resin. Depending on the amount of rosin resin in the TPU, different structures and properties were obtained. On the other hand, the immediate T-peel strength in all joints was improved if the TPU contained rosin resin.

Thermal stability of polyurethane elastomers before and after UV irradiation

In this work, we investigated the thermal degradation behavior of segmented polyurethane (PUR) elastomers before and after UV irradiation. The thermal degradation of PUR elastomers was studied over the temperature range of 25–600°C in an atmosphere of nitrogen using thermal gravimetric analysis (TGA). Four series of PUR elastomers derived from poly(oxytetramethylene)glycol (PTMO) of 1000 and 2000 molecular weight and poly(caprolactone glycol) (PCL) of 1250 molecular weight, 4,4′-diphenylmethane diisocyanate (MDI), and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) and 1,4-butanediol as an chain extender were synthesized by the prepolymer method. The derivative thermogravimetric (DTG) peaks observed in the experiments indicated that PUR elastomers degraded through two steps. We attributed the first step to degradation of the hard segment. The second degradation step could be ascribed to degradation of the soft segment. We found that the PUR elastomers based on poly(ester polyol) and aromatic diisocyanate exhibit better thermal stability than that of PUR elastomers based on the poly(ether polyol) soft segment in both steps of degradation. The thermal degradation is more prevalent in PUR elastomers based on cycloaliphatic diisocyanate. The higher values of the temperature of initial decomposition (Ti) indicate a higher thermal stability of UV-exposed elastomers on the beginning of degradation. This may be due to the formation of a crosslinking structure in the presence of UV irradiation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 864–873, 2001

Deterioration of novel polyesterurethane elastomers in outdoor exposure

Poly(esterurethane)-elastomers based on novel polyester glycols with methyl side groups were exposed outdoors for 2 years. The polyester glycols used are poly(β-methyl-δ-valerolactone)glycol (PMVL), poly(3-methyl pentamethylene adipate) glycol (PMPA), poly(nonamethylene-co-2-methyl octamethylene carbonate) glycol (PNOC). A mixture of PNOC and poly(dimethyl siloxane)glycol (PNOC/PDMS) was also used. Polyurethane network elastomers, were prepared from these polymer glycols, 4,4′-diphenylmethane diisocyanate, and a mixture of 1,4-butanediol with trimethylol propane by a prepolymer method. The deterioration behavior of the PUEs was measured by means of polarizing microscopy, DSC, tensile testing, dynamic viscometry, and ESR. The novel polyester-based PUEs have better weatherability than poly(oxytetramethylene) glycol (PTMG)-based PUE. The mechanisms of deterioration are discussed. ©

Mechanical properties and hydrolytic stability of polyesterurethane elastomers with alkyl side groups

Polyester-based polyurethane elastomers with alkyl side groups were prepared from poly(adipate) glycols which involved 2,4-diethyl-pentamethylenediol or 3-methyl-pentamethylene diol as a novel glycol component and 1,5-pentamethylenediol. Segmented and allophanate-crosslinked polyurethane elastomers were prepared from these polymer glycols, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol by a prepolymer method. Mechanical properties, dynamic viscoelastic properties, glass transition temperature ( T g), and thermal hydrolytic stability were measured. The properties of the polyurethane elastomers with alkyl side groups have good mechanical properties comparable to those of general purpose polyester urethanes. Novel polyester polyurethane elastomers with alkyl side groups had improved hydrothermal stability due to steric hindrance from hydrolysis of ester groups.

Hydrolytic and thermal stability of novel polyurethane elastomers

AbstractNovel Polyester glycols with alkyl side groups were used for the improvement of thermal stability and hydrolytic stability of polyester urethane elastomers. The novel polyester glycols used are poly( β ‐methyl‐ δ ‐valerolactone)glycol (PMVL), poly(3‐methyl pentamethylene adipate) glycol (PMPA), poly(nonamethylene‐co‐2‐methyl octamcthylene carbonate) gycol (PNCO). A mixture of PNCO and poly(dimethyl siloxane)gycol (PNCO/PDMS) was also used. Polyurethane network elastomers were prepared from 4,4′‐diphenylmethane diisocyanate (or 2,4‐tolylene diisocyanate), and a mixture of 1,4‐butane diol and trimethylol propane by a prepolymer method. Mechanical properties, Tg, thermal stability, and hydrolytic stability were measured. Morphology were also measured by means of polarizing microscopy, dynamic viscoelastometer, and ESR. The properties of novel polyurethane elastomers have good mechanical properties comparable to those of the general purpose polyester urethanes, and better thermal and hydrolytic stability than PTMG‐based polyurethane. These polyurethane elastomers were exposed in out door during 2 year in Nagasaki, JAPAN. The novel polyurethane clastomers held alomost constant values for gel fraction, swelling ratio, relative modulus during 12 months, while poly(oxytetramethylene oxide)‐based polyurethane as a control decreased the these values. Relationship of degradation behaviors with chemical structure and morphology were discussed.

Monomer sequence length distributions of hard segments of linear segmented poly(urethane–urea)s 2: computer simulation by the Monte Carlo method

AbstractAn attempt was made to calculate, by the Monte Carlo method, monomer sequence length distributions of the hard segment (MSLDH) within a linear segmented poly(urethane–urea) (PUR) synthesised by the prepolymer method in which an isocyanate‐terminated prepolymer. A…A, an unreacted monomer diisocyanate, BB, and a diamine as chain extender, XY, are reacted to form PUR. MSLDH is governed by the molar ratio of [A…A]/[BB] and is dramatically affected when three kinds of unequal reactivity associated with the reactants are significant simultaneously; the induced asymmetry, the penultimate effect of an NCO group, and the induced asymmetry of an amino group. By applying the above simulation technique, the unequal reactivities are estimated in both the prepolymerisation and polymerisation reactions based on methylenebis(4‐phenylisocyanate), MDI, poly(tetramethyleneoxide), PTMO, and ethylenediamine, EDA. In addition, the effect of the one‐shot method instead of the prepolymer method on MSLDH is also examined.