Phase separation and phase inversion of polyurethane networks

Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol and different polyols with a M n of 2000 by a one‐shot, hand‐cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV‐visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695–701, 2007. © 2007 Society of Plastics Engineers.

Shape memory polyurethanes (SMPUs) were synthesized by 4,4′-diphenylmethane diisocyanate (MDI), hexane-1,6-diol (HD), polypropylene glycol (PPG), and recycled polyvinyl butyral (PVB). Dynamic mechanical analysis, differential scanning calorimetry and Fourier transformation infrared attenuated total reflection spectroscopy was used to characterize the poly (vinylbutyral-urethanes). Micro-phase domain separation of hard and soft segments and phase inversion were investigated. Increasing the hard segment content, i.e., average hard segment molecular weight, leads to an increase in the degree of micro-phase separation, hard domain order and crystallinity. The crystalline hard segment structures combined with the elastic nature of soft segment matrix provide enough physical and chemical crosslinks to have shape memory effect.

Various segmented polyurethanes with a hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), a poly(tetramethylene adipate) glycol with an Mn of 2000, and various combinations of aliphatic diols as chain extenders by a one‐shot, hand‐cast bulk polymerization method. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), ultraviolet‐visible spectrometry, differential scanning calorimetry (DSC), and X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC data indicate rather good miscibility between the soft segments and the hard segments that accounts for the good transparency. The incorporation of a small amount of a second chain extender into MDI and 1‐4‐butanediol‐based segmented polyurethanes decreases the crystallinity of the hard segment, thus enhancing the transparency. A segmented polyurethane derived from MDI and 1,6‐hexanediol exhibits better transparency due to its relatively lower crystallinity of the hard segment. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:33–40, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20086

Hard segment composition, morphology, tensile properties and biostability of linked-macrodiol based siloxane poly(urethane urea)

A series of polyether-based thermoplastic polyure thanes, varying in soft segment molecular weight and hard seg ment content was prepared and studied. Poly(oxypropylene- oxyethylene) diols of Mn of 1000, 2000, 3000, and 4000 were the soft segment polyols. The hard segment, 4,4'-diphenyl methane diisocyanate (MDI) extended with 1,4-butanediol (BDO), and also the soft segment content were varied from 20 to 80 weight percent. Physical-mechanical, thermal (DSC) and dynamic-mechanical property data are used to elucidate the mechanical and morphological behavior of these polymers. Two distinct phases are detected in most of the polymers. The Tg of the amorphous soft phase decreases with increasing polyether molecular weight and is relatively unaffected by soft segment content except at very low levels (≤ 30%). Hard segments appar ently separate into ordered structures which melt between 150 and 220°C. The melting points and the heats of fusion generally increase with hard segment content and soft segment Mn. Soft segment molecular weight also has a significant influence on the mechanical properties of the polymers. In general, the ambient flexural moduli and the dynamic moduli (E') increase with in creasing soft segment Mn and the modulus/temperature curve is flattened.

Melamine formaldehyde (MF) resin was synthesized by the reaction between melamine and formaldehyde under alkaline condition in tetrohydrofuran medium with 1:3 melamine to formaldehyde molar ratio. The synthesized resins were characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Curing and reaction mechanism was studied by thermal and spectroscopic analysis. Two exothermic peaks were observed in the DSC analysis indicating a two-step crosslinking reaction process was correlated to TGA analysis. FTIR studies at different temperatures explained the two-stage curing mechanism which is concurring with the DSC data. At a temperature range of 140–160 °C, reversible demethylolation is dominating to the crosslinking reaction. At temperature >160 °C, the crosslinking reaction dominates. On the basis of DSC and FTIR data, a possible crosslinking reaction route was derived and explained. The first stage of curing is the conversion of methylol groups to primary amine and the second stage is the crosslinking of methylol groups to the final product, methylene bridges. The thermal stability of the methylol groups, methylene bridges and the triazine ring, as well as the evaporation of effluents at different stages of curing, are also discussed based on combined TGA and DSC results. Curing studies and reaction mechanism of MF resin was studied by thermal and spectroscopic tools comparing DSC and FTIR studies explains the two-stage thermal curing mechanism. The first step of thermal curing at temperature range of 140–160 °C is the reverse reaction of methylol groups to melamine and second step occurring at temperature >160 °C is the crosslinking of methylol groups to the final product, methylene bridge. Hence, by the mutual agreement of DSC and FTIR studies, a possible reaction route was derived for the thermal curing process. The DSC–TGA thermogram supports the two-step process of the cure reaction by exhibiting two peaks in the same temperature region.

Influence of the chain extender of a segmented polyurethane on the properties of polyurethane-modified asphalt blends

The influence of vinyl ester/styrene network structure on thermal and mechanical properties was investigated. The crosslink density of the resins was altered by changing the molecular weight of the vinyl ester oligomer and by varying the amount of styrene used during the crosslinking reaction leading to variations in both the physical network structure and the chemical composition of the polymeric networks. The glass transition temperatures of the network polymers were found to increase systematically with increasing crosslink density without the additional influence of the chemical composition as determined from both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The breadth of the glass transition regions increased with crosslink density for the DSC data, but the breadth assessed from the DMA data did not vary significantly for the network materials. A secondary relaxation was observed for the materials using DMA, and this relaxation did not appear to be significantly affected by changes in either the crosslink density or the composition of the network. Cooperativity studies involving time–temperature scaling of dynamic mechanical data in the glass formation temperature region were also conducted. The degree of segmental cooperativity at Tg appeared to be primarily influenced by the chemical composition of the networks. These issues dealing with the structure of the networks provided insight into the associated fracture properties in the glassy state (ambient temperature). Specifically, an empirically based linear correlation was found between the fracture toughness of the networks and the cooperative domain size at the glass transition temperature normalized by the crosslink density. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 917–927, 2001

Microstructure and properties of polyurethanes derived from castor oil

The effects of primary amine catalyzed thio-acrylate Michael reaction on the kinetics, mechanical and physical properties of thio-acrylate networks

ABSTRACTThis work applies different thermal analysis methods to polymer based materials degradation, studying the degradation process itself and evaluating the degree of material damage as a consequence of chemical degradation by thermal or radiation effects. On the one hand, thermal degradation in varied atmospheres is investigated by means of thermogravimetric analysis (TGA) in dynamic experiments. The authors find that the evolution of the sample mass follows a mixture of logistics models, and these can fit an overall TGA curve. The fitting parameters have important physical meaning related to the kinetics of the different processes involved and to the relative amount of each component in the sample. The method itself entails separating overlapping processes. Other improvements made by the authors are related to reducing the noise and smoothing the TGA and differential scanning calorimetry (DSC) data, particularly when estimating TGA derivatives through logistic regression.Analyzing many materials by means of TGA results in more or less complex traces that do not allow a simple parametric fit like the one described above. Although it reproduces asymptoticity at the beginning and end of the reaction, there are times when many processes overlap, resulting in a complex trace that would need a high number of logistic components to be adequately fitted. However, it is possible to use a local polynomial regression model instead. This is also applicable to DSC traces, whose shapes are totally different from those found in TGA. The authors propose a model based on a nonparametric estimation, where the fit's suitability very much depends on the bandwidth selection, especially where derivatives are concerned. The proposed model gives a satisfactory fitting. It smoothes noise and always provides reliable values, different from those obtained by other methods strongly dependent on user choice.On the other hand, to evaluate the degree of damage by thermal analysis methods, dynamic mechanical analysis (DMA) is applied to polyamides. The glass transition temperature is measured before and after exposure to varying doses of proton radiation, emulating the space environment. Other examples show how exposure over long periods at moderately elevated temperatures results in reduction of some mechanical properties. Additionally, the effect of different nanofillers on styrene-isoprene-styrene block copolymers is evaluated by DMA. A shift in the glass transition temperature seems to be dependent on nanofiller content. The degradation of some materials suitable for space applications, such as polyethylene and polyamide, are also briefly reviewed.

Synthesis and characterization of biodegradable acrylated polyurethane based on poly(ε-caprolactone) and 1,6-hexamethylene diisocyanate

Effect of soft segment length on the thermal behaviors of fluorinated polyurethanes

Structure–property relationships of segmented block copolyetheramides based on nylon 6 and polyoxypropylene (POP) were investigated as a function of the compositions and block lengths of the hard and soft segments by using differential scanning calorimetry, dynamic mechanical analysis, FT‐IR spectroscopy, wide angle x‐ray diffractometry (WAXD), and tensile testing. The nylon 6–D4 copolymers with the shortest soft segment exhibited the two‐phase structure of a crystalline nylon 6 phase and an amorphous phase composed of the hard and soft segments. Also they showed the tensile properties characteristic of a plasticized thermoplastic. On the other hand, the nylon 6–D20 and nylon 6–D40 copolymers exhibited the three‐phase structure of a crystalline nylon 6 phase, an amorphous nylon 6‐rich phase, and an amorphous POP‐rich phase. The nylon 6–D20 copolymers had better elastic properties with the increase of soft segment content; however, the nylon 6–D40 copolymers with the longest soft segment showed a substantial reduction of the elongation at break due to lack of the crosslinking density. © 1995 John Wiley & Sons, Inc.

Effect of intersegmental interactions on the morphology of segmented polyurethanes with mixed soft segments: A coarse-grained simulation study