Role of chain symmetry and hydrogen bonding in segmented copolymers with monodisperse hard segments

Thermoplastic segmented polyurethane and polyurea copolymers whose monodisperse hard segments are based on only a single diisocyanate molecule are discussed. The solid-state structure-property behavior of these materials demonstrates that a proper selection of the level of symmetry and/or cohesiveness of the hard microdomains may allow elimination of the traditional requirement of chain extension to obtain melt processable segmented urethanes, and more specifically, urea copolymers with useful structural properties.     

Numerical analysis on reaction injection molding of polyurethane foam by using a finite volume method

Foam reaction injection molding (FRIM) is one of the most popular and useful processes for producing polyurethane foam with a complex geometry. A theoretical model which includes chemical reactions, foaming, and mold filling was developed to analyze FRIM. Energy balance equation was derived by considering polyurethane reaction, water-isocyanate reaction, and evaporation of physical blowing agents. Density and viscosity model was proposed for the bubble suspension, which was assumed to be a homogeneous phase. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out to predict flow field, flow front advancement, and density distribution during mold filling. Mold filling of a refrigerator cavity was investigated numerically. The density and thermal conductivity of the foam in the flow front was higher than those in the initially filled region.     

Reactive Energetic Plasticizers for Energetic Polyurethane Binders Prepared via Simultaneous Huisgen Azide‐Alkyne Cycloaddition and Polyurethane Reaction

Reactive energetic plasticizers (REPs) for use in glycidyl azido polymer (GAP) based polyurethane (PU) energetic binders were investigated. These REPs consisted of an activated terminal alkyne group that was expected to give rise to Huisgen azide‐alkyne 1,3‐dipolar cycloaddition within the specific pot life for a PU formulation to prevent the migration of plasticizers, and with a gem‐dinitro group as an energy resource. A quantitative miscibility investigation between the plasticizers and uncured GAP showed that REPs exhibited better miscibility than conventional energetic plasticizers. The plasticization effect of the REPs on the GAP prepolymer with respect to the reduction of the viscosity illustrated REPs can effectively reduce the viscosity of the GAP prepolymer from 6,015 cP to 150–240 cP at the processing temperature when 50 wt‐% of REP was added. A comparison of the click reactivity and activation energies (E_a) of REPs and GAP prepolymer elucidated that the reactivity of azide‐alkyne cycloaddition depended on the dipolarophilicity of REPs which could be controlled by adjusting the length of methylene spacer between electron‐withdrawing groups (EWG) and neighboring alkynes in REPs. Thermogravimetric analysis manifested REP/GAP‐based PU binders maintained the thermal stability of the control GAP‐based PU binder. The mechanical properties and impact insensitivity of the GAP‐based PU binders were also improved by the incorporation of REPs.     

Novel nucleophilic/basic and acidic organocatalysts for reaction between poorly reactive diisocyanate and diols

Original basic or acidic organic compounds derived from guanidine or phenyl phosphonic acid were specifically designed and tested as new catalysts for the bulk synthesis of polyurethane prepolymers from a precursor system with particularly low reactivity (secondary alcohol + aliphatic isocyanate at low temperature). Both families showed interesting catalytic activities at 60–80 °C, but must nevertheless be used in much higher amounts (1 mol%, i.e. between 0.15 and 0.50 wt%) than traditional metal-based catalysts. The efficiency of guanidine derivatives seems to be related to their nucleophilicity, whereas that of phosphonic acid derivatives depends on their acidity. However, the solubility of the considered species in the reactive medium also plays a major role. The water/alcohol selectivity of the catalysts, especially at room temperature, was then examined as an additional criterion. Guanidines are not selective and favor the reaction of isocyanate groups with water as much as that with alcohols. Phenyl phosphonic acid derivatives are more selective, and particularly pentafluorophenyl phosphonic acid displays a remarkable catalytic activity together with an acceptable selectivity and could represent an interesting and safer alternative to toxic tin and mercury derivatives for many industrial polyurethanes.     

Synthesis of a polydimethylsiloxane-block-hydroxyl grafted acrylate prepolymer copolymer to improve the adhesion between silicone rubber and polyurethane by induced surface reconstruction

A new class of hydroxyl-functionalized polydimethylsiloxane-block-hydroxyl graft acrylate prepolymer (PDMS-b-HGAP) copolymers was synthesized. The copolymers were characterized using Fourier transform infrared spectroscopy as well as ¹H and ¹³C nuclear magnetic resonance spectroscopy. The hydroxyl groups of the HGAP were reacted with the chlorine terminal in the PDMS to yield a triblock copolymer consisting of two segments of PDMS linked to a HGAP segment. The induced surface reconstruction of silicone rubber (SR)by blending polysiloxane reactants with bifunctional PDMS-b-HGAP copolymers and curing using mold materials having high critical surface tension such as polyethyleneterephthalate was attempted to improve the adhesion between chemically-inert SR and polyurethane (PU). Surface characterization using Foruier transform infrared-attenuated total reflectance indicated that the surface of the SR was enriched with HGAP. The increased content of surface HGAP was suggested to account for the improved adhesion between SR and PU.     

The influence of ageing of epoxy coatings on adhesion of polyurethane topcoats and protective properties of coating systems

The dependence of adhesion and protective properties of coating systems on surface properties of epoxy intermediate coatings, aged and non-aged before an application of polyurethane topcoats, were examined. The intermediate coatings were aged 500 h in UV chamber. The surface free energy and polar groups were estimated after ageing. After applying polyurethane topcoats on aged and non-aged epoxy coatings, resistance to salt spray and thermal shocks were tested as well as internal stresses were measured before and after corrosion tests.The results showed that adhesion in coating systems with polyurethane topcoats applied on aged epoxy coatings depends strongly on the degradation degree of epoxy intermediate coatings and the value of generated internal stresses. Coatings with good adhesion retention in corrosion environments have good protective properties even when temporary blistering has occurred.     

Effect of annealing on the properties of waterborne polyurethane adhesive containing urethane-based thickener

Different amounts of hydrophobically modified ethoxylated urethane-based thickener (HEUR) were added to improve the rheology of waterborne polyurethane adhesives. The thickened solid adhesive films were thermally annealed and characterised by IR spectroscopy, plate–plate rheology, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Hydrogen bonds played a key role in the thickening mechanism of polyurethane dispersions containing urethane-based thickener, along with ionic adsorption and micelles formation between hydrophobic groups. The adhesion properties were measured from T-peel test of leather/polyurethane adhesive/vulcanised styrene-butadiene rubber joints. Optimal results were obtained when water in the waterborne polyurethane adhesive (just before joint formation) was removed under open air, while forced air drying impeded the complete removal of water. On the other hand, the thermal annealing did not greatly affect the rheological and thermal properties of the thickened polyurethanes.     

Preparation and characterization of blend membranes of polyurethane and superfine chitosan powder

A novel kind of asymmetric blend membranes with superfine chitosan powder (SCP) and biomedical polyurethane was prepared by immersion precipitation phase inversion method. Effects of different SCP content on the morphology and properties of the blend membranes were investigated. The result showed that SCP content had little influence on the cross-section structure of the blend membranes, and the cross-section presented a cellular structure. WAXD results revealed that the aggregated structure of SCP remained. With an increment of SCP content, the pore diameter and porosities of blend membranes increased firstly, and then decreased. While, the water absorption rate and water vapor transmission rate were improved remarkably with increasing SCP content. The mechanical testing results indicated that with an increment of SCP ratio, mechanical properties presented a descending trend, whereas all blend membranes exhibited the good elasticity.     

汽车车灯用湿气固化聚氨酯热熔胶

用多元醇、二苯基甲烷4,4-二异氰酸酯（MDI）合成了车灯用湿固化聚氨酯热熔胶粘剂。研究了胶粘剂的粘度、粘度稳定性和初粘力等性能。结果表明：当高结晶性聚酯和热塑性聚酯用量在10%和15%时,胶粘剂剥离强度达到980N/25mm,耐热性达到180℃,基本上满足了汽车灯具密封与装配的要求。     

硬段结构对分子链含亲水基团的聚氨酯形状记忆性能的影响

采用自乳化法,用聚酯二元醇、二苯基甲烷二异氰酸酯(MDI)或异佛尔酮二异氰酸酯(IPDI)、二羟甲基丙酸(DMPA)、乙二胺(EDA)、三羟甲基丙烷(TMP)等单体合成了分子链含亲水基团的聚氨酯.用FTIR对聚氨酯进行了结构表征,并测试了胶膜力学性能和形状记忆性能.主要探讨了硬段结构与质量分数,回复温度和多次拉伸-回复对聚氨酯形状回复率的影响.结果表明,聚氨酯分子链内引入苯环或化学交联结构,可以改善材料的力学性能和形状记忆性能;聚氨酯的硬段质量分数有一最佳值,达到此值形状回复率最大;不同硬段结构的聚氨酯达到最大形变回复率的临界硬段质量分数不同,硬段的结构越稳定,其在形状记忆聚氨酯中的质量分数越低.多次拉伸-回复可以提高形状记忆性能.