Influence of the composition on the glass transition temperature of polyurethane and polyurethane acrylate networks

Linear polyurethane, linear segmented polyurethane, polyurethane networks, and polyurethane acrylate networks of various composition were synthesized. The variation of T_g with the type of macrodiol, its length, and the chemical composition of the polymer were studied in relation with the percentage of soft segments, the molar mass between crosslinks, and the concentration of urethane bonds. In this work, the networks were considered as composed of chain segments of various composition between point-like crosslinks. The chemical heterogeneities of the networks were not taken into account. For polyurethanes, it was shown that T_g values are essentially controlled by the amount of urethane bonds. For polyurethane acrylates, the T_g values are dependent on the amount of urethane bonds but also on the presence of crosslinks whose number is varying with the excess of diisocyanate of the first step three times faster for PUA compared with PU. No clear relation was observed between T_g and the molar mass between point-like crosslinks. Another approach considering the network heterogeneities is indispensable and will be used in a following work. © 1996 John Wiley & Sons, Inc.     

Interpenetrating polymer networks of polyurethane and graft vinyl ester resin–polyurethane formed with diphenylmethane diisocyanate

For enhancing the compatibility and/or the interpenetration of the simultaneous interpenetrating networks (SINs) composed of polyurethane (PU) formed with uretonimine modified 4,4′‐diphenylmethane diisocyanate and vinyl ester resin (VER), a series of graft VERs consisting of different lengths of side chains were synthesized and characterized. It was found that there exists some limited short‐range order due to the strong hydrogen bonding in the graft VER network composed of butanol side chains (BO‐g‐VER). The graft VER network composed of poly(oxypropylene) (PPO) side chains (M_n: 200, 200‐g‐VER) showed compatible system, while the VER network consisting of longer PPO grafts (M_n: 390, 390‐g‐VER) exhibited microphase separated morphology. Based upon the DSC and FTIR measurements as well as the SEM and TEM observation, the lengths of side chains existing in graft VER network have great effect on the morphologies of PU/graft VER SINs. For PU/BO‐g‐VER SINs, there has been some interpenetration between the two networks because of the miscibility between the BO‐g‐VER network and the hard segments existing in the PU network. For PU/200‐g‐VER SINs, the good compatibility and/or the interpenetration between the two phases was observed, since the long‐range ordered structure of hard segments in PU phase was greatly suppressed, resulting from the excellent miscibility between the urethane groups as well as the PPO side chains existing in the 200‐g‐VER network and those in the PU network, respectively. Thus, the strong reinforcement effect of these two graft networks on the PU network and the excellent mechanical properties of the SIN systems were observed. However, the PU/390‐g‐VER SINs showed the complicated morphologies because of existing microphase‐ separated morphology of 390‐g‐VER network in itself. In this case, the enhancement effect of such a graft VER network on the PU network is limited. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 136–144, 2000     

Chlorine degradation of polyether-based polyurethane

The tensile properties of polyether-based polyurethane (PU) filaments decrease with increasing chlorine concentrations as well as with treatment times. Fourier transform infrared (FTIR) results show the formation of quinoid, azo, and aldehyde groups in the chlorine-treated PU, and increased hydrogen bonding between the C O C in the soft segment and the N H in the hard segments. A breakdown mechanism involving chain cleavages along the ether linkages in the soft segments as well as at the urethane linkages of the hard–soft segment interfaces is proposed. Chlorine-treated PU showed increased solubility in tetrahydrofuran (THF). The molecular weight data of the THF-soluble portion of treated PU also support the proposed locations of chain scissions. The increased soft segment T_g and T_m with increasing chlorine concentrations are results of increased phase-mixing and hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3263–3273, 1997     

Preparation of high‐temperature polyurethane by alloying with reactive polyamide

A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4‐tolylenediisocyanate and then was end‐capped with phenol. Soluble PA was prepared by the reaction of 1‐(m‐aminophenyl)‐2‐(p‐aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass‐transition temperatures (T_g's), a lower T_g due to the PU component and a higher T_g due to the PA component, suggesting that the two polymer components were phase‐separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high‐temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497–3503, 2002     

Structure-property relationship of polyurethane ionomer

Polyurethane (PU) ionomers were prepared using various types of polyol (PTAd, PCL, PTMG, and PPG) and isocyanate (MDI, HDI, and IPDI), together with different extender (DMPA) contents, degree of neutralization, and number average molecular weight (M _n) of polyol. Modulus (E), strength (_b), and glass transition temperature (T _g) significantly increased with the increased amount of extender and extender neutralization. Among three of the iocyanate used, PU from MDI gave the highest modulus, strength, andT _g. With regard to theM _n of PTAd (600, 1000, 2000), PU from PTAd 600M _n gave the highest modulus, strength, andT _g, due probably to the highest hard segment content and phase mixing. On the other hand, PU from PTAd 2000M _n gave significantly improved strength over PTAd 1000M _n, and the highest elongation. The results were interpreted in terms of soft-segment crystallization, and soft-hard phase separation, which was concluded from the lowered softT _g.     

Synthesis and characterization of poly(urethane‐benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane‐benzoxazine) films as novel polyurethane ( PU )/phenolic resin composites were prepared by blending a benzoxazine monomer ( Ba ) and PU prepolymer that was synthesized from 2,4‐tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring‐opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane‐benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (T_g ) from viscoelastic measurements, indicating no phase separation in poly(urethane‐benzoxazine) due to in situ polymerization. The T_g increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane‐benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N‐dimethyl formamide, and N‐methyl‐2‐pyrrolidinone that easily dissolve PU s. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba . © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4165–4176, 2000     

Effect of the diisocyanate on the structure and properties of polyurethane acrylate prepolymers

In this study, we investigated the role of diisocyanate on the properties of polyurethane acrylate (PUA) prepolymers based on polypropylene oxide (M̄_n = 2000 g · mol⁻¹). The diisocyanates studied were isophorone diisocyanate, 4‐4′dicyclohexylmethane diisocyanate, and toluene diisocyanate (pure 2,4‐TDI, pure 2,6‐TDI, and a TDI mixture, TDI_tech). The molecular structure of the diisocyanate had a major role on the course of the polycondensation and, more precisely, on the sequence length distribution of the final prepolymer. Moreover, the structural organization of the prepolymer also strongly depended on the nature of the diisocyanate. Two types of behaviors were particularly emphasized. On the one hand, the PUA synthesized from 2,4‐TDI displayed an enhanced intermixing between soft polyether segments and hard urethane groups, as revealed by the analysis of hydrogen bonding in Fourier transform infrared. Consecutively, the glass transition shifted to higher temperatures for these polymers. On the other hand, strong hard–hard inter‐urethane associations were observed in 2,6‐TDI‐based prepolymers; these led to microphase segregation between polyether chains and urethane groups, as revealed by optical microscopy. This inhomogeneous structure was thought to be responsible for the unusual rheological behavior of these PUA prepolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2750–2768, 2000     

Basic structure–property behavior of polyurethane cationomers

Polyurethane (PU) cationomers were synthesized from polytetramethylene adipate glycol (PTAd), isophorone diisocyanate (IPDI), and N-methyl diethanolamine (MDEA) according to a prepolymer mixing process. Basic structure-property behavior of the emulsion (obtained by adding water to the ionomer solution) and emulsion cast film was studied with regard to the molecular weight (M_n) of PTAd, MDEA content, degree of neutralization, and extender functionality. Particle size decreased asymptotically with increasing M_n of PTAd due to the increased chain flexibility, and with the degree of neutralization due to the increased hydrophilicity of the PU. Emulsion viscosity generally showed the opposite tendency with particle size dependence. The major transition temperature, corresponding to the glass transition (T_g) of phase mixed PU or hard segment-rich phase of the PU monotonically increased with MDEA content, degree of neutralization, and with increasing extender functionality. However, with increasing M_n of PTAd, T_g first decreased (M_n = 1000) and then increased (M_n = 1500, 2000), due respectively to the increased hard fraction of phase mixed PU, and soft segment crystallization. Tensile strength increased and elongation at break decreased with MDEA content, degree of neutralization, and extender functionality. © 1994 John Wiley & Sons, Inc.     

Novel method for the preparation of poly(urethane–imide)s and their properties

A polymer blend consisting of polyimide (PI) and polyurethane (PU) was prepared by means of a novel approach. PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI) and then end-capped with phenol. Poly(amide acid) was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). A series of oligo(amide acid)s were also prepared by controlling the molar ratio of PMDA and ODA. The PU prepolymer and poly(amide acid) or oligo(amide acid) solution were blended at room temperature in various weight ratios. The cast films were obtained from the blend solution and treated at various temperatures. With the increase of polyurethane component, the films changed from plastic to brittle and then to elastic. The poly(urethane–imide) elastomers showed excellent mechanical properties and moderate thermal stability. The elongation of films with elasticity was more than 300%. The elongation set after the breaking of films was small. From the dynamic mechanical analysis, all the samples showed a glass transition temperature (T_g) at ca. −15°C, corresponding to T_g of the urethane component, suggesting that phase separation occurred between the two polymer components, irrespective of polyimide content. TGA and DSC studies indicated that the thermal degradation of poly(urethane–imide) was in the temperature range 250–270°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3745–3753, 1997     

Influence of structure-property relationship on the optical,thermal and mechanical properties of castor oil based transparent polyurethane for catheter applications

Castor oil based transparent polyurethane elastomers were synthesized, which can be used as an advanced catheter material. The effect of NCO: OH ratio on the structural, optical, thermal and physicomechanical properties of polyurethanes (PU) has been studied. The optical properties of the PU was analysed by studying its percentage transmittance and haze. The results showed a high transparency of 90.7% for the PU with a NCO: OH ratio of 0.9:1. Differential scanning calorimetry (DSC) analysis revealed an increase in the glass transition temperature (T_g) of PU with increasing hard segment content whereas thermogravimetric analysis (TGA) shows an increase in the initial decomposition temperature of PU from 262 to 268°C upon increasing the NCO: OH ratio from 0.9 to 1.5. A similar trend of increment in the tensile properties of PU has been observed as a consequence of increasing the molar ratio of NCO: OH. In vitro cytotoxicity analysis of PU was studied using human embryonic kidney (HEK293) cell line that revealed the nontoxic character of PU.     

Thermal properties of lignin-and molasses-based polyurethane foams

Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T _g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T _d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T _g and T _d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm⁻¹ K⁻¹ depending on mixing ratio of lignin and molasses.     

Use of blowing catalysts for integral skin polyurethane applications in a controlled molecular architectural environment: Synthesis and impact on ultimate physical properties

Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (T_g) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher T_g values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002     

Effects of organophilic montmorillonite on hydrogen bonding, free volume and glass transition temperature of epoxy resin/polyurethane interpenetrating polymer networks

Epoxy resin nanocomposites containing organophilic montmorillonite (oM) and polyurethane were prepared by adding oM to interpenetrating polymer networks (IPNs) of epoxy resin and polyurethane (EP/PU). The dispersion degree of oM in EP/PU matrix was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectrometry (FT-IR) showed that strong interactions existed between oM and EP/PU matrix, and oM had some effect on hydrogen bonding of these EP/PU IPNs nanocomposites. Positron annihilation spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were used to investigate the effect of oM and PU contents on free volume and glass transition temperature (T_g) of these nanocomposites. The PALS and DSC results clearly showed that the presence of oM led to a decrease in the total fractional free volume, which was consistent with increasing T_g upon addition of oM, ascribed to increasing hydrogen bonding in interfacial regions of oM and EP/PU matrix and enhancing the miscibility between EP phase and PU phase. In addition, with increasing PU content, the total fractional free volume increased, corresponding to decreasing T_g.     

Synthesis and electrical,rheological and thermal characterization of conductive polyurethane

This work studies the electrical, rheological, and thermal characteristics for polyurethane (PU) capped with tetraaniline as a new material, tetraaniline-containing poly(urethane–urea) (TAPU). The conductivities can be increased from less than 10⁻¹⁰ S/cm for pure PU to 10⁻⁴ S/cm for TAPU, independently of the length of the soft segment in the TAPU backbone chain. The tensile strength and modulus are increased when PU is copolymerized with tetraaniline. The viscoelastic creep can be effectively simulated using a Burgers model. Additionally, TAPU has higher viscosity, higher retardation time, and lower compliance J ₁ than regular PU. Restated, TAPU exhibits less elastic but superior permanent deformation than PU because tetraaniline functions as a chain holder. The thermogravimetric analytic (TGA) results reveal that TAPU has lower T _d, smaller T _mw1 and T _mw2, and higher char yield because the dehydration of the urea-containing polymer produces a thin layer from a nitrogen compound on the polymer’s surface, which insulates the underlying polymer from heat and oxygen.     

Incorporation of polydimethylsiloxane into polyurethanes and characterization of copolymers

Novel copolymers of polyurethane (PU) were prepared by direct transurethanetion reaction of a commercial PU with polydimethylsiloxanes (PDMS, MW 1000, 5000, and 10,000) containing hydroxyl end-groups. Transurethanetions with different mass ratios of hydrophobic PDMS to hydrophilic PU chains (PDMS1000–PU: 43:57, 67:33, 71:29, and 80:20; PDMS5000–PU: 37:63, and 51:49; PDMS10000–PU: 51:49) were carried out in solution at 65 and 100 °C. In catalyzed reactions, dibutyltin dilaurate (SnC₃₂H₆₄O₄) was used to promote bond breaking in the PU chain and accelerate the reaction between hydroxyl end-groups of PDMS and regenerated isocyanates of PU. The chemical structures of the prepared copolymers were comprehensively characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopies. According to elemental analysis, the content of PDMS varied between 3 wt.% and 16 wt.%, and results obtained from the ¹H NMR spectroscopy were in good agreement with the results of elemental analysis. Increased length of the hydrophobic chain increased the content of PDMS in the copolymer. The GPC results showed that molar masses of the PUPDMS copolymers were lower than the molar mass of the starting PU. The glass transitions (T_g) of the copolymers were shifted to lower temperature as compared with T_g of the starting polyurethane. ATR FTIR spectroscopy showed the surface of the copolymer films to be enriched with siloxane groups and, according to electron microscopy, it was textured with microspheres. The static contact angles for copolymer films measured with deionized water ranged from 94° to 117°. The different structural, thermal and surface properties of the PUPDMS copolymers as compared with PU indicated that transurethanetion had taken place.     

Synthesis and radical polymerization of acrylate and methacrylate bearing an isocyanurate core with adamantyl bisurethane moieties

In this article, we report the synthesis of acrylate and methacrylate bearing an isocyanurate core with two adamantyl urethane moieties and their radical homo- and copolymerization with n-butyl methacrylate (BMA). The synthesized polyacrylate exhibits higher 5% weight loss and glass transition temperatures (T_d5 and T_g) than those of the comparative polyacrylate, synthesized from the isocyanurate-based acrylate with two hexyl urethane moieties, suggesting that the rigid adamantane core incorporated in the side chains of polymer largely contributes to increase in thermal stability of polymer. Similarly, the obtained copolymers show higher T_g values than that of homopolymer derived from BMA, leading to the synthesized monomers are useful as a comonomer to enhance thermal property of polymer.     

Effects of methyl sidegroup on the extent of hydrogen bonding and modulus of polyurethane elastomers

The effects of methyl sidegroup on the properties of polyurethane elastomers, mainly hydrogen bonding and elastic properties, were studied. Polyurethanes of almost equal crosslinking density and urethane group concentration, but with different side methyl groups, were prepared by a prepolymer method. The extent of hydrogen bonding was determined by an infrared technique. The density and Young's modulus are decreased by the introduction of methyl sidegroup, swelling ratio and T_g are increased, but the extent of hydrogen bonding is not affected.     

Thermal properties of polyurethanes derived from molasses before and after biodegradation

Polyurethane (PU) foams derived from molasses were placed in soil for various periods from 3 to 12 months. Thermal properties of PU's before and after biodegradation were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). Glass transition of PU's after 3 month's degradation was separated into two stages indicating that molecular chains of the original and decomposed portions move independently. Based on variation of glass transition temperature (T_g), heat capacity difference at T_g (δC_p), thermal degradation temperature and mass loss, the degradation mechanism of PU was established.     

The glass transition temperature of nonstoichiometric epoxy–amine networks

Glass transition temperatures (T_g) of nonstoichiometric epoxy-amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of T_g can be made using an empirical equation reported by L. E. Nielsen together with the experimental T_g value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variations of T_g with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD), the effect of elastic chains on the T_g value is much less significant.     

Formation, structure, thermal and dynamic mechanical behavior of polyurethane networks based on a diethanolamine derivative with mesogenic group

Dynamic mechanical, differential scanning calorimetry and X-ray scattering behavior of ordered polyurethane systems, based on a diol with rigid (mesogenic) group in side chain (D), 2(4)-methyl-1,3-phenylene diisocyanate (DI) and two triols (T)--stiff trimethylolpropane (TMP) or flexible poly(oxypropylene)triol (PPT), was investigated during crosslinking and on the networks. The networks were prepared at various stoichiometric initial molar ratios of the reactive groups, [OH]_T/[NCO]_DI/[OH]_D ranging from 1/2/1 to 1/20/19. From our measurements it follows that: (a) Power-law parameters, which are characteristic of the structure at the gel point (the gel strength S and the relaxation exponent n), are dependent on the initial ratio of the reactants. With increasing content of mesogenic diol in the system (increasing length of elastically active network chains, EANCs), the gel strength S increases and the relaxation exponent n decreases; higher S and lower n are found for stiffer TMP networks in comparison with more flexible PPT ones. (b) Introduction of crosslinks reduces the flexibility of the network chains in fully cured samples and inhibits conformational rearrangements required for ordering. A more complex thermal behavior was found for networks based on TMP in comparison with those based on PPT. (c) Strong physical interactions between the mesogens promote cyclization in the course of crosslinking; the fraction of bonds lost in intramolecular cycles is ∼15% for fully cured networks.