Polyurethane tri‐block copolymers—Synthesis,mechanical, elastic,and rheological properties

A series of polyurethane tri‐block copolymers were synthesized by reacting a 4,4′‐methylenebis(phenyl isocyanate) (MDI)‐endcapped poly(tetramethylene oxide) (PTMO, M_n = 2,000 g/mol) with a monoamine‐diamide (6T6m) hard segment (HS). The concentration of the HS in the copolymer was varied between 9 and 33 wt % by changing the length of the soft mid‐block segment. The structure of the copolymers was analyzed by nuclear magnetic resonance, the amide crystallinity was investigated by Fourier transform infra‐red and the thermal properties were studied by differential scanning calorimetry. The mechanical and elastic properties of the tri‐block copolymer were subsequently explored by dynamic mechanical analysis, compression set and tensile experiments, and the melt rheological behavior was studied by a parallel plate method. The amide end groups displayed a high crystallinity and the modulus of the tri‐block copolymers was relatively high. The fracture strain increased strongly with the molecular weight and the copolymers demonstrated a ductile fracture behavior for molecular weights above 6000 g/mol. Good compression set values were obtained for the tri‐block copolymers despite their low molecular weight. In the molten state, the tri‐block polymers displayed a gelling effect at low frequencies, which was believed to be a result of a clustering of the end‐segments. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Melt rheological behavior of a triblock copolymer based on aramide end‐segments

Melt rheological behavior of a ABA triblock polymer made of poly(tetramethylene oxide) (PTMO) (M_n = 2,900 g mol^?1) soft segment and aramide hard segment was studied. The aramide end‐segments ( A ) were short and mono‐disperse in length. The mid‐segment ( B ) consisted of PTMO₂₉₀₀ extended with terephthalate units to a molecular weight of 9000 g mol^?1. The molecular weight of the triblock was 9700 g mol^?1. Rheological behavior of this material was studied by parallel‐plate and capillary method. The ABA triblock copolymer was compared with a B polymer (PTMO‐terephthalate) of a similar molecular weight. The low molecular weight B polymer had a Newtonian behavior. The low molecular weight triblock copolymer had at high frequencies a low complex viscosity. However, at low frequencies the triblock copolymer had a very high complex viscosity. Also the G″/G′ ratio decreased with decreasing frequency to values less then one and the G′ seemed to have at low frequencies a plateau value. The activation energy of the process increased in value with decreasing shear rate. All these results indicate that the triblock copolymer at low frequencies had a gel‐like behavior and this probably due to the clustering of the aramide segments. The aramide clusters are thought to be the (weak) network points of the gel. This network was also found to have a time dependant rheological response and thus a thixotropic behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The influence of composition ratio on the morphology of biomedical polyurethanes

Two series of thermoplastic polyurethane elastomers were synthesized from 4,4′‐methylenediphenyl diisocyanate (MDI), 1,4‐butanediol (BDO) chain extender, and each of poly(tetramethylene oxide) (PTMO) and poly(hexamethylene oxide) (PHMO) macrodiols. The PTMO and PHMO molecular weights were kept constant at 993 and 852 g/mol, respectively. In the PTMO‐based series, the composition ratio was varied between 48 and 58% (w/w) of macrodiol; 2 commercially available PTMO‐based polymers were also included. These were Pellethane 2363 80A® and its harder counterpart, Pellethane 2363 55D®. In the PHMO‐based series, the composition ratio was varied between 50 and 60% (w/w) of macrodiol. The materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). Mechanical performance was also assessed by tensile testing, stress hysteresis, and hardness testing. Altering the composition ratio had a similar effect on morphology and properties for both the PTMO and PHMO‐based series. An increase in hard segment content was associated with increased hard microdomain crystallinity, hardness, and stiffness. In both series, he beginning of hard microdomain interconnectivity was observed at a composition ratio of 52% soft segment. That is to say, for the processing and annealing conditions employed, macrodiol contents of 52% and below began to produce continuous, rather than discrete, hard microdomains. Pellethane 80A® was shown to have a discrete hard microdomain morphology, while Pellethane 55D® was shown to incorporate interconnecting hard microdomains. It is suggested that the superior biostability performance of Pellethane 55D relative to Pellethane 80A may be related to its interconnecting hard microdomain texture. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 937–952, 1999     

Ionene segmented block copolymers containing imidazolium cations: Structure-property relationships as a function of hard segment content

Imidazolium ionene segmented block copolymers were synthesized from 1,1′-(1,4-butanediyl)bis(imidazole) and 1,12-dibromododecane hard segments and 2000 g/mol PTMO dibromide soft segments. The polymeric structures were confirmed using ¹H NMR spectroscopy, and resonances associated with methylene spacers from 1,12-dibromododecane became more apparent as the hard segment content increased. TGA revealed thermal stabilities ≥250 °C for all imidazolium ionene segmented block copolymers. These ionene segmented block copolymers containing imidazolium cations showed evidence of microphase separation when the hard segment was 6-38 wt%. The thermal transitions found by DSC and DMA analysis found that the T_g and T_m of the PTMO segments were comparable to PTMO polymers, namely approximately −80 °C and 22 °C, respectively. In the absence of PTMO soft segments the T_g increased to 27 °C The crystallinity of the PTMO segments was further evidence of microphase separation and was particularly evident at 6, 9 and 20 wt% hard segment, as indicated in X-ray scattering. The periodicity of the microphase separation was well-defined at 20 and 38 wt% hard segment and found to be approximately 10.5 and 13.0 nm, respectively, for these ionenes wherein the PTMO soft segment is 2000 g/mol. Finally, the 38 and 100 wt% hard segment ionenes exhibited scattering from correlations within the hard segment on a length scale of approximately 2-2.3 nm. These new materials present structure on a variety of length scales and thereby provide various routes to controlling mechanical and transport properties.     

Polyurethanes with monodisperse rigid segments based on a diamine–diamide chain extender

Polyether(bisurethane‐bisurea‐bisamide)s (PEUUA) based on poly(tetramethylene oxide) (PTMO) were synthesized by chain extension of PTMO endcapped with a diisocyanate (DI), and a diamine–diamide extender. The prepolymers were PTMOs with molecular weights between 1270 and 2200 g mol^?1, either endcapped with 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (2,4‐TDI), or 1,6‐hexane diisocyante (HDI) and with a low content of free diisocyanate (<0.1 wt %). The diamine–diamide (6A6) extender was based on hexamethylene diamine (6) and adipic acid (A). In this way, segmented polyurethanes with monodisperse rigid segments (DI‐6A6‐DI) were obtained. The PEUUAs were characterized by DSC as well as temperature‐dependent FTIR and DMTA. The mechanical properties of the polymers were evaluated by compression set and tensile test measurements. The polyurethanes with monodisperse rigid segments displayed low glass transition temperatures, almost temperature‐independent rubbery plateaus and sharp melting temperatures. The crystallinities of the hard segments were 70–80% upon heating and 40–60% upon cooling. The rate of crystallization was moderately fast as the supercooling (T_m ? T_c) was in the order 36–54°C. The polyurethanes based on HDI had a much higher rubber modulus as compared to the MDI and 2,4‐TDI‐based polymers, because of a higher degree of crystallinity and/or a higher aspect ratio of the crystallites. The HDI residues are flexible and not sterically hindered and could therefore be more easily packed than MDI or 2,4‐TDI residues. Polyurethanes with monodisperse DI‐6A6‐DI hard segments have interesting properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tensile and elastic properties of triblock copolymer based on aramide end‐segments and polyether mid‐segments

The tensile and elastic behavior of triblock copolymers containing uniform aramide (TΦB) hard end‐segments (HS) and poly(tetramethylene oxide) (PTMO, M_n = 2900 g/mol) soft segments (SSs) was studied. The molecular weight of the copolymer was varied by changing the length of the soft mid‐segment; by extending the PTMO₂₉₀₀ with terephthalate units, the SS length was increased from 2900 g/mol to 21,000 g/mol and concurrently the aramide concentration decreased from 18 to 3 wt %. The mechanical properties were investigated by means of tensile testing, stress relaxation (SR) experiments, and cyclic tensile set (TS) tests. The E‐modulus was found to increase with increasing aramide content. The low molecular weight copolymers were brittle whereas the high molecular weight copolymers displayed large fracture strain values. The transition from brittle to ductile seemed to occur at a triblock copolymer molecular weight of 6600 g/mol. A strain‐induced crystallization was observed at strains above 250%, and both the fracture strain and stress were found to be highly dependant on the molecular weight of the copolymer. Cyclic tensile experiments showed that the materials had low TS values up to the strain hardening point. On the other hand, the SR data at 10% strain seemed to be little dependant on the molecular weight. The higher molecular weight copolymers did not display lower SR values than their low molecular weight counterparts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Monomer sequence length distributions of hard segments of linear segmented poly(urethane–urea)s 1: chromatographic study

An attempt was made to determine, by the chromatographic method, monomer sequence length distributions of the hard segments in segmented poly(urethane–urea)s (PURs) synthesised in a two-step process: (1) a prepolymer formation reaction of an excess of methylenebis(4-phenylisocyanate) (MDI) with poly(tetramethyleneoxide) (PTMO) and (2) a polymerisation reaction of the prepolymer containing unreacted MDI with ethylenediamine, giving PUR. The monomer sequence length of the hard segment was found to become longer and its distribution to broaden as the initial concentration ratio of MDI to PTMO increased. This result is attributable to an increase of the concentration ratio of the unreacted MDI to the prepolymer, leading to gelation of the polymer solution. By comparing the chromatographic results with the theoretical data calculated in the simple case of the equal reactivity of the reactants in the prepolymerisation and polymerisation reactions, respectively, the existence of unequal reactivities of the reactants in both reactions, is predicted.     

Polyether‐amide segmented copolymers based on ethylene terephthalamide units of uniform length

Segmented copolymers were synthesized using the crystallizable bisesterdiamide segment (N,N′‐bis(p‐carbomethoxybenzoyl)ethanediamine) T2T‐dimethyl (a one‐and‐a‐half repeating unit of nylon 2,T) and poly(tetramethyleneoxide) segments. Poly(tetramethyleneoxide) (PTMO) is amorphous and has a low T_g. The segment length was varied from 650 to 2800 g/mol by extending PTMO₆₅₀ using dimethyl isophthalate. The polymers were synthesized in the melt, and test samples were prepared by injection molding. The melting behavior, as well as the torsion modulus spectrum as a function of temperature, were studied using DSC and DMA, respectively. The T2T‐PTMO polymers were found to have sharp glass (T_g) and flow transitions (T_fl), and the modulus at the rubbery plateau appeared to be virtually temperature independent. The T_g value was found to be independent of the diamide concentration, thus indicating that the T2T segments were fully crystallized. The T_fl was found to decrease with increasing soft segment length; this was ascribed to a “solvent” effect of the amorphous phase of the crystalline T2T units. The difference between the melting and crystallization temperatures was found to be low, thus suggesting that on cooling, there is a high rate of crystallization. When ethanediol was added as a T2T segment extender, amide‐ester‐amide segments were introduced. These amide‐ester‐amide segments form a separate lamellar phase with a much higher melting temperature (>300°C). It was found that the crystallization rate of the T2T units was enhanced by the presence of the amide‐ester‐amide segments, indicating that upon cooling, the crystallized amide‐ester‐amide segments form the nucleation sites for the nonextended T2T segments. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1173–1180, 2001     

Effects of co‐hard segments on the microstructure and properties thermoplastic poly(ether ester) elastomers

A thermoplastic poly(ether ester) elastomer (TPEE) is composed of polyester hard segments and polyether soft segments. Polyester and polyether segments are often homopolymer segments. This work aims at incorporating poly(butylene phthalate (PBP) as co‐hard segments in the hard segments of poly(butylene terephthalate) (PBT)‐b‐poly(tetramethylene oxide) (PTMO) thermoplastic elastomer, and investigating structures and properties of the resulting materials, denoted as (PBT‐co‐PBP)‐b‐PTMO. (PBT‐co‐PBP)‐b‐PTMO was synthesized from dimethyl terephthalate (DMT), dimethyl phthalate (DMP), PTMO (M_n = 1000 g/mol), and 1,4‐butanediol (BDO). The crystallinity of (PBT‐co‐PBP)‐b‐PTMO first decreased and then increased with increasing PBP content from 5% to 10% due to a decrease in the average sequence length of the PBT hard segments. Its elongation at break was increased by 200–350%. When the mass fractions of PBT and PBP were 42% and 8%, respectively, the (PBT‐co‐PBP)‐b‐PTMO showed the best performance in terms of permanent deformation, strength, and hardness whose values were 30%, 25 MPa, and 37 D, respectively. All the synthesized copolymers had good thermal stability with a decomposition temperature of 400°C or so. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43337.     

Segmented blockcopolymers with uniform amide segments

Segmented blockcopolymers based on poly(tetramethylene oxide) (PTMO) soft segments and uniform crystallisable tetra-amide segments (TxTxT) are made via polycondensation. The PTMO soft segments, with a molecular weight of 1000 g/mol, are extended with terephthalic groups to a molecular weight of 6000 g/mol. The crystallisable segment is uniform of length and is based on a tetra-amide with terephthalamide groups. The length of the aliphatic diamine (x) in the tetra-amide segment is varied from x=2 to 8. The thermal properties of the blockcopolymers were studied with dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Due to the use of uniform TxTxT segments a fast and almost complete crystallization of the hard segments is obtained. The melting temperature of the blockpolymers increases with decreasing diamine length and the well-known odd-even effect is observed. The elastic behavior of the blockcopolymer was studied by compression set. All the blockcopolymers had a low compression set and were highly elastic.     

Syntheses and characterization of novel biostable polyisobutylene based thermoplastic polyurethanes

The synthesis of polyisobutylene (PIB) based thermoplastic polyurethanes (TPU) with enhanced mechanical properties have been accomplished using poly(tetramethylene oxide) (PTMO) as a compatibilizer. PIB TPUs with Shore 60-100 A hardness were prepared by employing PIB diols (hydroxyallyl telechelic PIBs) for the soft segment and 4,4′-methylenebis(phenylisocyanate) (MDI) and 1,4-butanediol (BDO) for the hard segment. The TPUs exhibited number average molecular weight (M_n) in the range of 83,000-110,000 g/mol with polydispersity indices (PDIs) = 1.8-3.1. These TPUs, however, were inferior compared to commercial TPUs such as Pellethane™ (Dow Chemical Co.) as they exhibited low tensile strength (6-15 MPa) and/or ultimate elongation (30-400%). Processing of the harder compositions was also difficult and some could not be compression molded into flat sheets for testing. Differential Scanning Calorimetry (DSC) showed the presence of high melting (≥200 °C) crystalline hard segments suggesting longer - MDI-BDO - sequences than expected based on the stoichiometry. Easily processable TPUs with excellent mechanical properties (tensile strength up to 40 MPa, ultimate elongation up to 740%) were obtained by incorporating PTMO in the soft segment. Examination of PIB-PTMO TPUs with varying hard: soft compositions (20:80, 35:65 and 40:60 wt:wt) and Shore hardness (60 A, 80 A and 95 A) indicated that substituting 10-30 wt% of PIB diol with PTMO diol is sufficient to reach mechanical properties similar to Pellethanes.     

Shape memory effect of poly(L‐lactide)‐ based polyurethanes with different hard segments

A series of biodegradable polylactide‐based polyurethanes (PLAUs) were synthesized using PLA diol (M_n = 3200) as soft segment, 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) as hard segment, and 1,4‐butanediol as chain extender. The structures and properties of these PLAUs were studied using infrared spectroscopy, differential scanning calorimetry, tensile testing, and thermomechanical analysis. Among them, the MDI‐based PLAU has the highest T_g, maximum tensile strength, and restoration force, the TDI‐based PLAU has the lowest T_g, and the IPDI‐based PLAU has the highest tensile modulus and elongation at break. They are all amorphous. The shape recovery of the three PLAUs is almost complete in a tensile elongation of 150% or a twofold compression. They can keep their temporary shape easily at room temperature (20 °C). More importantly, they can deform and recover at a temperature below their T_g values. Therefore, by selecting the appropriate hard segment and adjusting the ratio of hard to soft segments, they can meet different practical demands for shape memory medical devices. Copyright © 2007 Society of Chemical Industry     

Comparison of properties of segmented copolyetheresteramides containing uniform aramid segments with commercial segmented copolymers

The thermal (using differential scanning calorimetry), dynamic mechanical (using a dynamic mechanical analyzer), and mechanical properties of segmented copolyetheresteramides with aramid units of uniform length (TΦT) and poly(tetramethylene oxide) (PTMO) segments were compared to those of commercial segmented copolyetheresters (PBT–PTMO) and thermoplastic polyurethanes. The hard segments in TΦT‐containing polymers were found to crystallize almost completely, unlike the hard segments of Arnitel and Desmopan. Consequently, the glass‐transition temperature of TΦT‐containing polymers is lower and the melting temperature higher than those of Arnitel and Desmopan. Furthermore, the rubbery plateau of the TΦT‐containing polymers is temperature independent, making the service temperature range wider. In TΦT‐containing polymers a lower concentration of hard segment is needed to obtain dimensionally stable polymers with a high melting temperature. No melt phasing occurs during polymerization and therefore long PTMO segments can be used, producing very soft and elastic materials. The polymers crystallize faster than do commercial materials. The elasticity of the TΦT‐containing polymers is comparable to the elasticity of Desmopan and better than that of Arnitel. TΦT–(PTMO₁₀₀₀/DMT) copolymers are transparent and the solvent resistance is high. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1372–1381, 2001     

Influence of polydispersity of crystallizable segments on the properties of segmented block copolymers

Poly(ether‐ester‐amide)s (PEEAs) based on poly(tetramethylene oxide) and tetra‐amide segments were synthesized by a solution/melt polymerization. The tetra‐amide segments (T6A6T) were based on adipic acid (A), terephthalic acid (T), and hexamethylene diamine (6), and were synthesized prior to the polymerization. Monodisperse tetra‐amide segments, i.e. T6A6T, as well as polydisperse segments, consisting of a mixture of uniform segments of diamide (T6T), tetra‐amide (T6A6T), and hexa‐amide (T6A6A6T), were utilized in the preparation of the PEEAs. In this way, a polydispersity index ranging from 1.0 to 1.09 could be obtained. In addition, a random copolymer, synthesized by a one‐pot polymerization, was also studied and the copolymer had a polydispersity of 1.2. The low polydispersity of the one‐pot synthesis amide segments was mainly due to the uneven reactivity of the terephthalic ester groups. The properties of copolymers were studied by DSC, FTIR, DMTA, compression set, and tensile set measurements. When the polydispersity of the amide segments was increased, the copolymers displayed a slower crystallization, a lower final crystallinity, a broader melting transition, a decreased storage modulus at room temperature, as well as a decreased yield strength and inferior elastic properties. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Mixed macrodiol‐based siloxane polyurethanes: Effect of the comacrodiol structure on properties and morphology

Two series of polyurethanes were prepared to investigate the effect of comacrodiol structure on properties and morphology of polyurethanes based on the siloxane macrodiol, α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS). All polyurethanes contained a 40 wt % hard segment derived from 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol (BDO), and were prepared by a two‐step, uncatalyzed bulk polymerization. The soft segments were based on an 80/20 mixture of PDMS (MW 967) and a comacrodiol (MW 700), selected from a series of polyethers and polycarbonates. The polyether series included poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO), poly(hexamethylene oxide), and poly(decamethylene oxide) (PDMO), whereas the polycarbonate series included poly (hexamethylene carbonate) diol (PHCD), poly [bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (PSCD), and poly [hexamethylene‐co‐bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (COPD). Polyurethanes were characterized by size exclusion chromatography, tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The results clearly demonstrated that the structure of the comacrodiol influenced the properties and morphology of siloxane‐based polyurethanes. All comacrodiols, except PEO, improved the UTS of the polyurethane; PHMO and PTMO were the best polyether comacrodiols, while PSCD was the best polycarbonate comacrodiol. Incorporation of the comacrodiol made polyurethanes more elastomeric with low modulus, but the effect was less significant with polycarbonate comacrodiols. DSC and DMTA results strongly supported that the major morphological change associated with incorporation of a comacrodiol was the significant increase in the interfacial regions, largely through the compatibilization with the hard segment. The extent of compatibilization varied with the comacrodiol structure; hydrophilic polyethers such as PEO were the most compatible, and consequently, had poor mechanical strength. Among the polyethers, PHMO was the best, having an appropriate level of compatibility with the hard segment for substantial improvement in mechanical properties. Siloxy carbonate comacrodiol PSCD was the best among the polycarbonates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1071–1082, 2000     

Domain and segment orientation behavior of PBS–PTMG segmented block copolymers

Segment and domain orientation behaviors of a series of poly(butylene succinate) (PBS) –poly(tetramethylene glycol) (PTMG) segmented block copolymers containing different amounts of hard segment were studied with synchrotron small‐angle X‐ray scattering (SAXS) and infrared dichroic methods. Copolymers used in this work consist of PBS as a hard segment, and poly(tetramethylene oxide) (PTMO) of molecular weight 2000g/mol as a soft segment. As hard‐segment content increased, phase‐separated morphology changed from a phase of continuous soft matrix containing isolated hard domain to one of continuous hard matrix. Upon stretching, domains responded differently depending on their initial orientation. Based on SAXS results, two major domain deformation modes, that is, lamellar separation and shear compression, were suggested. The orientation behavior of the hard and soft segments was examined with infrared dichroic method. Upon drawing, the orientation function of the crystalline hard segment decreased at low‐draw ratios. It was interpreted in terms of rotation of long axis of hard domain along the stretching direction. The lowest value of the orientation function of PBS30 was approximately −0.5, that is, theoretical minimum. This result seems to indicate that for PBS30 containing about 30% hard segment, rotation of hard domain occurs without appreciable interdomain interaction, which is consistent with the morphological model suggested on the basis of SAXS results. Plastic deformation of the hard domain due to domain breakup was found to occur at low‐draw ratios for the sample containing higher hard‐segment content. Domain mechanical stability was tested by drawing a sample up to three different maximum draw ratios. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 699–709, 2000     

High molecular weight thermoplastic polyether ester elastomer by reactive extrusion

A reactive branched thermoplastic polyether‐ester elastomer (TPEE) precursor was synthesized by the esterification reaction of dimethyl terephthalate (DMT) with poly(tetramethylene etherglycol) (PTMEG), 1,4‐butadiene, and glycerol as a soft segment, hard segment, and a branching agent, respectively. The high molecular weight TPEE was further synthesized with the prepared branched TPEE precursor, poly(butylene terephthalate) (PBT) and modified methylene diisocyanate (m‐MDI, 0.5–2.0 wt%) by the reactive extrusion method. Their chemical structures were determined by Fourier Transform Infra Red (FTIR) and Proton‐Nuclear Magnetic Resonance (¹H NMR). Thermal characteristics and rheological properties of TPEE were measured by Differential Scanning Calorimetry (DSC) and rheometer as a function of m‐MDI content. The intrinsic viscosity (IV) and melt index ratio (MIR) of TPEE increased as the content of m‐MDI increased up to 1.5 wt% and remained constant thereafter. The variation of the MIR was consistent with that of the IV. The storage modulus and viscosity did not vary with the measurement time up to 1.0 wt% of m‐MDI at the first extrusion, which indicates that the m‐MDI reacted fully. However, the viscosity and storage modulus increased with increasing measurement time at m‐MDI contents over 1.5 wt%. POLYM. ENG. SCI., 2009. © 2009 Societyof Plastics Engineers     

Tri-block copolymers with mono-disperse crystallizable diamide segments: Synthesis, analysis and rheological properties

Tri-block copolymers with polyether mid-segments and mono-disperse amide end segments were synthesized, analyzed and some properties studied. The end segment was an aromatic diamide (diaramide, TΦB). The polyether mid-segment was a difunctional poly(tetramethylene oxide) (PTMO, 1000 and 2900 g/mol). In order to increase the soft segment (SS) length, PTMOs were extended with terephthalic groups. The length of the mid-soft segment was varied from 1000 to 20,000 and thereby the concentration of the hard end segment changed from 22 to 3 wt.%. The molecular weight of the tri-block copolymers was determined by NMR and inherent viscosity measurements. The crystallinity of the hard segment was studied by IR and DSC measurements. Temperature modulated IR was carried out to explore the change in crystallinity with temperature. The morphology was investigated by AFM analysis and the thermo-mechanical properties by DMA, whereas the melt rheological behaviour was analyzed by a plate–plate method. The results of the tri-block copolymer were compared with those of a similar multi-block copolymer. The glass transition of the soft phase was low and the melting temperature of the diamide end blocks was high. The crystallinity of the hard end segments in the tri-block was found to be very high (>95%) and remained high until melting. The AFM picture showed crystalline ribbons with a high aspect ratio. Also the modulus at room temperature was relatively high, particularly at low contents of hard end segment. The melt rheological behaviour of a low molecular weight tri-block copolymer revealed a low melt viscosity at high shear rates, and a high viscosity at low shear rates. Moreover, a gelling of the melt was observed with decreasing frequency and this was probably due to agglomeration of the end segments.     

Properties and phase separation of reaction injection molded and solution polymerized polyureas as a function of hard block content

A series of amine terminated polypropylene oxide based thermoplastic polyureas with hard segment contents of 30%, 50%, and 70 percent were synthesized via solution polymerization and reaction injection molding (RIM). Amine terminated polypropylene oxide (PPO-NH₂) of M_n = 2000 was used as the soft segment and 4,4′-diphenylme-thanediisocyanate (MDI) extended with diethyltoluenediamine (DETDA) as the hard segment. These polyureas are linear, amorphous, and phase separated. Polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), small angle X-ray scattering (SAXS), and tensile testing. RIM polyureas had significantly lower molecular weights than solution polymerized polyureas, but their mechanical properties did not suffer, RIM polyureas have poorer phase separation than solution polyureas as evidenced by DSC, DMS, and SAXS, especially at high hard segment levels. SAXS shows phase separation levels of up to 100 percent for low hard segment polyureas and down to 10 percent for high hard segment RIM polyurea. DSC found no evidence of a hard segment glass transition, and the evidence from DMS was inconclusive. In addition to polymer characterization, demolding behavior was studied. The 30 percent hard segment was always tough and elastomeric, while the 70 percent hard segment was always very brittle. The 50 percent hard segment showed the greatest variation in properties, ranging from very brittle to very though as mold temperature and in-mold time were increased. Demold brittleness is explained by the presence of low molecular weight DETDA/MDI oligomers on demolding, which continue to react on aging.     

Morphology of crystalline polyurethane hard segment domains and spherulites

Chemical staining of the unsaturated hard segment portion of a segmented polyurethane based on poly(propylene oxide)/4,4′-diphenyl methane-diisocyanate/butenediol (PPO/MDI/BEDO) permitted observation of the hard segment domains by electron microscopy. The hard segment phase forms (para)-crystalline domains which are fibrillar in nature. The fibrils are arranged radially into spherulite structures. The concentration of the hard segment is greatest at the centre of the largest spherulites suggesting the preferential agglomeration of molecules with the longest hard segment sequences at the beginning of the phase separation process from solution.