Hard segment connectivity in low molecular weight model ‘trisegment’ polyurethanes based on monols

Low molecular weight model trisegmented polyurethanes based on monofunctional polyols, or ‘monols’, with water-extended toluene diisocyanate (TDI) based hard segments (HS) are investigated. The formulations of the materials generated are similar to those of flexible polyurethane foams with the exceptions that the conventional polyol is substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight; and no surfactant is utilized. Plaques formed from these model systems are shown to be solid materials at ambient even at their relatively low molecular weights of 3000 g/mol and less. SAXS, DSC, and AFM are utilized to investigate the microphase separated morphologies of the samples generated. WAXS results show that the local packing of the HS is of a similar nature as that in actual flexible polyurethane foams. AFM phase images, for the first time, reveal the ability of the HS to self-assemble through bidentate hydrogen bonding and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system is well dominated by the two terminal liquid-like polyether segments.     

Polyurethane/olefinic ionomer blends. 1: Compatibility characterization

The compatibility behaviour of melt-mixed blends of a polyester-type polyurethane (PU) with the Zn²⁺ ionomer of poly(ethylene-co-methacrylic acid-co-isobutylacrylate) terpolymer (Ion., Zn²⁺) was investigated in the complete composition range. The techniques applied were tensile testing, dynamic mechanical analysis (d.m.a.), differential scanning calorimetry (d.s.c.), Fourier transform infrared (FTi.r.) spectroscopy and optical microscopy. Tensile properties were typical of a compatible system and d.m.a. results indicated a miscible blend. FTi.r. results failed to reveal the nature of the specific forces involved in bringing about compatibilization. Analysis of the thermal data obtained allowed the determination of a polymer–polymer interaction parameter which had a near zero value at the elevated temperatures where it was determined.     

Effects of unsaturation and different ring-opening methods on the properties of vegetable oil-based polyurethane coatings

A variety of vegetable oil-based, waterborne polyurethane dispersions have been successfully synthesized from different vegetable oil polyols exhibiting almost constant hydroxyl functionalities of 2.7 OH groups per molecule. The vegetable oil polyols, which have been prepared from vegetable oils with different fatty acid compositions (peanut, corn, soybean, and linseed oil), range in residual degree of unsaturation from 0.4 to 3.5 carbon–carbon double bonds per triglyceride molecule. The effects of residual unsaturation on the thermal and mechanical properties of the resulting polyurethane films have been investigated by dynamic mechanical analysis, differential scanning calorimetry, and thermal gravimetric analysis. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) has been used to accurately determine the molecular weight and mass distribution of the vegetable oil polyols. Higher residual unsaturation results in polyurethane films with increased break strength, Young's modulus, and toughness. This work has isolated the effect of unsaturation on vegetable oil-based polyurethane films, which has been neglected in previous studies. The effect of different oxirane ring opening methods (methanol, butanol, acetic acid, and hydrochloric acid) on the properties of the coatings has also been examined.     

Effects of soft-segment prepolymer functionality on structure-property relations in RIM copolyurethanes

Segmented copolyurethanes comprising 40-60% by weight of polyurethane hard segments (HS) and polyether soft-segment (SS) with different functionalities (SS-f_n), have been formed by reaction injection moulding (RIM). The HS were formed from 4,4′ diphenylmethane diisocyanate (MDI) reacted with ethane diol (ED). The three SS-prepolymers used were all hydroxyl-functionalised poly(oxypropylene-b-oxyethylene)s with different nominal functionalities (f_n) of 2, 3 and 4 but with a constant molar mass per functional group of ∼2000 g mol⁻¹. RIM materials were characterised using differential scanning calorimetry, dynamic mechanical thermal analysis, tensile stress-strain and single-edge notch fracture studies. Predictions using a statistical model of the RIM-copolymerisation showed that increasing SS-f_n lead to more rapid development of copolymer molar mass with isocyanate conversion. Experimentally, the RIM-PU exhibited a wide range of mechanical behaviour resulting from differences in molecular and morphological structures. Increasing SS-f_n produced materials with improved mould release behaviour and fracture resistance. However, increasing SS-f_n also reduced the degree of phase separation developed in the copolyurethanes, resulting in increased modulus-temperature dependence and poorer tensile properties.     

阻燃剂在聚氨酯树脂制品中的使用及发展趋势

首先介绍阻燃剂在聚氨酯塑料中国内外的使用情况,现国内、外主要阻燃剂生产企业概况及在火灾事故中显示阻燃剂的重要性,在使用过程中应严格遵守有关防火法规,以及今后PUR用阻燃剂的发展趋势,最终对我国今后生产阻燃剂提出一些看法。     

Adhesion Mechanisms of Polyurethanes to Glass Surfaces. III. Investigation of Possible Physico-Chemical Interactions at the Interphase

Surface free energies of polyurethanes made from toluene diisocyanate and 1, 4 butanediol-based hard segments and caprolactone polyol-based soft segments were calculated using additive functions. Good agreement was found between the calculated values based on additive functions and the calculated values based on contact angle measurements. The phase-separated polyurethanes were found to have a higher polar surface free energy component (γ^P). This was linked to the preferential segregation of butanediol/butanediol-derived moieties to the polyurethane surfaces due to phase separation. The adhesion values of these polyurethanes to soda-lime glass were correlated with their respective γ^P values and a linear relationship was found. It was also shown that the adhesion values of the low γ^P polyurethanes improved substantially when the glass surfaces were coated with a thin layer of butanediol prior to the bonding. The modulus of the interphase region rich in butanediol was evaluated. Although a modulus increase was found at the interface, this increase was found to play a secondary role in the adhesion. The chemical interactions at the polyurethane/glass interphase were investigated by pre-treating the glass surfaces with methyl-trimethoxysilane and trimethylchlorosilane prior to adhesion testing. The adhesion data showed no significant difference between the uncoated and the silane-treated glass substrates. Based on this experimental evidence, the possibility of any covalent or ionic bonding at the polyurethane/glass interphase was assumed negligible. It was determined that the mechanism of adhesion between the polyurethanes and the glass surface could be through the formation of an interphase region in which hydrogen bonding between the butanediol-rich interphase region and the hydroxylated glass surface plays a key role.     

The Properties of Reactive Hot Melt Polyurethane Adhesives: Effects of Molecular Weight and Reactive Organoclay

We studied the affect of molecular weight on the adhesion properties of reactive hot melt adhesive (RHA), which has polyurethane prepolymer as its major component. The RHAs that were prepared by the two-shot method and were of a higher average molecular weight showed improved initial bond strength development compared to that of RHAs prepared by the one shot method but with the same recipe. However, the viscosity of the RHA was increased by this method, which reduced the cross-linking in the cured RHA. This was confirmed by its deteriorated tensile properties and increased tan δ value. The reactive organoclay, Cloisite 30B, also improved the initial bond strength development and raised the viscosity of the RHA, thereby reducing cross-linking in the cured RHA.     

Synthesis of bis[(4-hydroxyethoxy)phenyl]sulfone containing urethane acrylates and their applications

UV-curing processes are used in industrial applications because of their advantages such as high speed applications and solvent-free formulations at ambient temperature. UV-curable sulfone containing polyurethane acrylates were synthesized from bis[(4-hydroxyethoxy)phenyl]sulfone (BHEPS), polyols, isophorone diisocyanate (IPDI) and 2-hydroxyethyl methacrylate (HEMA). The polyurethane acrylates characterized with ¹H NMR and FT-IR spectroscopies. The UV-cured coatings and films were formulated with polyurethane acrylates, reactive diluents such as dipropyleneglycol diacrylate (DPGDA), 1,6-hexanediol diacrylate (HDDA) and photoinitiator. The water wettability of the UV-cured films was investigated by measuring contact angle. Sulfone containing polyurethane acrylates increase mechanical properties such as pendulum hardness, pencil hardness, tensile strength, and e-modulus values. These mechanical properties and chemical-solvent resistance may have been strongly dependant on the sulfone content and crosslinking density.     

Carbon2Polymer: A CO2-based Route to Polyurethanes via Oxidative Carbonylation of TDA with Methyl Formate

The Carbon2Polymer project involves a multistep reaction sequence for the non-phosgene synthesis of the high-value polymer precursor toluene-2,4-diisocyanate (TDI) starting from carbon dioxide. The present study of the oxidative carbonylation revealed that for the intermediate toluene-2,4-dicarbamate (TDC) the productivity is highest with Pd@ZrO₂, followed by Pd@CeO₂. As one of the side products which are formed in parallel and consecutive reactions the methylene-bridged dimer “TDCCH2TDC” (5) has a promising potential for industrial application.     

Structure and molecular dynamics of hyperbranched polymeric systems with urethane and urea linkages

Two series of hyperbranched polymers (HP), polyurethanes and polyureas, with aromatic and aliphatic structures, are synthesized in one-pot method using commercially available monomers. The obtained HP samples were characterized by ¹H Nuclear Magnetic Resonance (NMR) spectroscopy, Gel Permeation Chromatography (GPC), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) measurements. Molecular dynamics in these systems were investigated by combining Thermally Stimulated Depolarization Currents (TSDC) and broadband Dielectric Relaxation Spectroscopy (DRS) techniques. High conductivity contribution in dielectric loss does not allow the study of the segmental α relaxation associated with the glass transition. In the glassy state two secondary relaxation mechanisms have been investigated, the γ and the β mechanism. The γ relaxation mechanism, at low temperatures/high frequencies, is attributed to motions of the end groups (-OH for polyurethanes and -NH₂ for polyureas), and has been found faster in the hyperbranched polyureas. In addition, our results reveal that γ relaxation mechanism in both series depends on the chemical structure, being faster for aliphatic structures. The β relaxation mechanism, at higher temperatures/lower frequencies, is attributed to the motions of branched ends with polar groups. Our study suggests that this mechanism may be a typical relaxation process for hyperbranched polyurethanes structures, not existed in the linear counterparts. All the systems exhibit dc conductivity at temperatures higher than T_g which shows Arrhenius-like temperature dependence and is characterized by rather high activation energies (in the order of 200 kJ/mol). At temperatures lower than T_g all the systems studied exhibit remarkably high charge mobility. In particular, aliphatic hyperbranched polyureas exhibit dc conductivity which has been found to be of VTF type concerning the temperature dependence. This result implies that the conduction mechanism is coupled with molecular motions in the glassy state of the polymer.