Low Molecular Weight Polypropylene Glycol Research Articles

Highly crosslinked and uniform thermoset epoxy microspheres: Preparation and toughening study

A new type highly crosslinked and uniform thermoset epoxy microspheres (EMs) was prepared through the thermal curing between a trifunctional epoxy resin (TGPAP) and an aromatic amine hardener (DETDA), by precipitation polymerization in a low molecular weight polypropylene glycol (PPG-600) medium. The formation of EMs and the phase separation process were investigated in detail. The structure and thermal properties of EMs were characterized, and the result showed that EMs was active microspheres with hydroxyl and amino groups on its surface, and it had a high glass transition temperature Tg of 205 °C and high thermal stability. EMs was further used to toughen brittle epoxy resins. The effect of EMs on the curing behavior, mechanical and thermal properties of epoxy resins was studied. EMs accelerated the curing and the effect reached maximum till 5 wt% amount. Mechanical and thermal performance measurements exhibited that EMs not only significantly improved the toughness of epoxy matrix, but also increased the Tg. When 5 wt% EMs was introduced, the impact strength rose from 17.8 kJ m−2 to 42.4 kJ m−2 and Tg increased more than 10 °C. The excellent toughening performance of EMs was attributed to its high stiffness and active surface.

Thermo-mechanical properties and microstructural considerations of MDI isocyanate-based bituminous foams

Stable bituminous foams have been obtained by using a 35/50 penetration grade bitumen and a reactive prepolymer (MDI-PPG) synthesized by the reaction of polymeric 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polypropylene glycol (PPG). In a first step, MDI-PPG and bitumen were allowed to react for up to 7 days. Foams were then obtained by adding an excess of water. The results obtained point out important changes in the material colloidal structure, as a consequence of the reactions between the –NCO groups and bitumen most polar fractions. Modification led to bituminous foams with low density and improved in-service properties (higher elasticity and resistance to deformation at high in-service temperatures, reduced thermal susceptibility and better flexibility at low temperatures), demonstrating their adequacy to be used in building applications. Properties were enhanced by subjecting the material to longer periods of curing prior to promote foaming.

Improvement of the thermal properties of poly(3‐hydroxybutyrate) (PHB) by low molecular weight polypropylene glycol (LMWPPG) addition

AbstractIn this work, blends of poly(3‐hydroxybutyrate) (PHB) with 5, 10, 15, and 20 wt % low molecular weight poly(propylene glycol) (LMWPPG) have been prepared and characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) with attenuated total reflectance (ATR) accessory and simultaneous thermal analysis (TG/DTA). FTIR and thermal analyses suggested that the presence of LMWPPG led to a maximum crystallinity for the blend PHB/PPG (90/10) blend. The presence of LMWPPG also caused a significant increase of the PHB processability window, i.e., the difference of the melting and degradation temperature, of PHB from 105 to 134°C, which is extremely important for the industrial uses of PHB. This PHB stabilization effect is discussed in terms of an intermolecular interaction of the PHB carbonyl with LMWPPG methyl groups which probably hinders the classical radon β‐scission PHB intramolecular decomposition mechanism. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Bituminous polyurethane foams for building applications: Influence of bitumen hardness

Bitumen source is a key factor in the development of new bituminous products, such as dimensionally stable bituminous polyurethane foams, for building applications. With this aim, three neat bitumen samples, with very different chemical compositions and penetration grades, were modified with a reactive polymer, synthesized from the reaction of 4,4′-diphenylmethane diisocyanate with a low molecular weight polypropylene glycol (MDI–PPG). Firstly, modified bitumen were obtained by adding 10wt.% MDI–PPG to each bitumen. Then, bituminous foams were achieved by adding an excess of water. Water reacted with the remaining NCO groups, generating CO2, which was used as a chemical foaming agent. The reactions involved in this bitumen modification were followed by using different techniques, such as thin layer chromatography (TLC–FID), and Fourier transform infrared spectroscopy (FTIR). The rheological properties of foamed bitumen are greatly improved by addition of small quantities of MDI–PPG and the degree of enhancement is dependent on bitumen characteristics. Thus, despite bitumen composition, dimensionally stable bituminous foams can be successfully obtained, even from the softest base.

Magnetic fluids stabilized by polypropylene glycol

A series of samples of magnetic fluids stabilized with low-molecular weight polypropylene glycol (PPG) of different molecular masses were synthesized. The use of PPG allowed the maximum extension of the carrier fluid range to include ethyl- and butyl-acetate, ethanol, butanol, acetone, carbon tetrachloride, toluene, kerosene and PPG itself. Magnetic and rheological properties of the samples were investigated. Based on the results of investigation it has been concluded that magnetic nanoparticles are covered by a monolayer of surfactant molecules. At low temperatures the propanol-based sample preserves fluidity up to −115 °C. Measurement of critical temperatures of other base fluids showed that alcohols are the best carrier medium. Coagulation stability of the ethanol-based ferrocolloid with respect to water and kerosene was explored. It has been found that kerosene, whose fraction by weight exceeds 22.5%, does not mix with the colloid. This effect can be used to produce magneto-controllable extractors of ethyl alcohol. Under the action of water the colloid coagulates, which allows one to substitute the carrier fluid and to separate the colloid into fractions.

Novel stable MDI isocyanate-based bituminous foams

Foam building materials are used in roofing and water proofing membranes, insulation, pipe covers, vapour barriers, crack suppressant membranes, and as installed flooring protection. In this study, new stable bituminous foams have been developed, in a two-step method, using a reactive polymer, synthesized from the reaction of 4,4′-diphenylmethane diisocyanate with a low molecular weight polypropylene glycol (MDI–PPG). Firstly, a modified bitumen was obtained by adding 10 wt.% MDI–PPG to bitumen, at 90 °C. In a second step, an excess of water was added, which reacted with the remaining –NCO groups and generating CO 2, which was used as a chemical foaming agent to produce stable bituminous foams. In general, polymer addition improves the bituminous foam rheological properties, mainly in the high in-service temperature region. In this range of temperature, the rheological properties are clearly affected by reaction time.

Novel bitumen/isocyanate-based reactive polymer formulations for the paving industry

Reactive modification is lately gaining acceptance as a successful way to give added value to bitumen, a crude oil refining by-product. In order to study the effect of both bitumen type and processing method, isocyanate-based reactive modification was carried out with four types of bitumen from different sources, by following two different procedures (“water-free” and “water-involved” processing). The polymer used (MDI–PPG) was synthesized from the reaction of 4,4′-diphenylmethane diisocyanate with a low molecular weight polypropylene glycol. The results obtained demonstrate that the addition of small quantities of this reactive polymer to bitumen endows the resulting modified binder with an improved performance at high in-service temperatures. Interestingly, two different modification pathways have been identified: the first one, which occurs during mixing, is the result of chemical reactions between -NCO groups of the reactive polymer with functional groups containing active hydrogen atoms (mainly, –OH), such as those typically present in the most polar bitumen fractions; the second one has been proved to be a consequence of series reactions involving water. Both pathways, but mainly the latter, lead to bituminous paving materials showing a more complex microstructure, with the consequent change in their rheological response. Finally, very different degrees of modification, depending on the colloidal features of the as-received bitumen, were observed.

Influence of Bitumen Colloidal Nature on the Design of Isocyanate-Based Bituminous Products with Enhanced Rheological Properties

This work deals with the influence that bitumen colloidal nature exerts on the rheological properties of bitumen samples modified by isocyanate-based reactive polymers. Shear rheology tests, modulated differential scanning calorimetry (MDSC), chemical characterization by TLC-FID, and AFM microstructural analysis were carried out on four different 150/200 penetration neat bitumen samples and the corresponding MDI-PPG (a low molecular weight polypropylene glycol functionalized with a polymeric 4,4′-diphenylmethane diisocyanate) modified binders. The results obtained demonstrate that the bitumen modification degree depends on bitumen reactivity and microstructure. Thus, the highest modification capability is obtained with neat bitumen samples that exhibit both a well-developed three-dimensional network and a high chemical reactivity with the isocyanate groups. The results obtained may be used to improve the performance of these materials, according to their final application.

Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids

Viscosities eta and their temperature T and volume V dependences are reported for seven molecular liquids and polymers. In combination with literature viscosity data for five other liquids, we show that the superpositioning of relaxation times for various glass-forming materials when expressed as a function of TV(gamma), where the exponent gamma is a material constant, can be extended to the viscosity. The latter is usually measured to higher temperatures than the corresponding relaxation times, demonstrating the validity of the thermodynamic scaling throughout the supercooled and higher T regimes. The value of gamma for a given liquid principally reflects the magnitude of the intermolecular forces (e.g., steepness of the repulsive potential); thus, we find decreasing gamma in going from van der Waals fluids to ionic liquids. For some strongly H-bonded materials, such as low molecular weight polypropylene glycol and water, the superpositioning fails, due to the nontrivial change of chemical structure (degree of H bonding) with thermodynamic conditions.

Interfacial tension between low molecular weight polymers from the static analysis of cylindrical drops and their break‐up dynamics

AbstractA spinning drop tensiometer was used to measure the interfacial tension between the coexisting phases of mixtures of low molecular weight polypropylene glycol, Mw = 1000, and polyethylene glycol, Mw = 300, 400, or 550. Two types of experiments gave concordant interfacial tensions. First, the static analysis of the equilibrium diameter of cylindrical drops according to Vonnegut and, second, Tomotika's dynamic analysis of Rayleigh instabilities caused by a sharp decrease of the angular speed. The end‐pinching process also lead to the break‐up of the drops and it was characterized by a rapid expansion of the hemispherical ends followed by a slower pinching step. The pinching rate increases as the final angular speed decreases while the growth rate of Rayleigh instabilities shows no definite trends in the range 118‐245 rad · s−1. It is shown that the end‐pinching of long cylindrical drops can be analyzed in terms of short fiber retraction to get the interfacial tension. © 1995 John Wiley & Sons, Inc.