Polyurethane Networks from Fatty-Acid-Based Aromatic Triols:  Synthesis and Characterization

Abstract

Novel biobased aromatic triols (1,3,5-(9-hydroxynonyl)benzene and 1,3,5-(8-hydroxyoctyl)-2,4,6-octylbenzene) were synthesized through the transition-metal-catalyzed cyclotrimerization of two alkyne fatty acid methyl esters (methyl 10-undecynoate and methyl 9-octadecynoate) followed by the reduction of the ester groups to give terminal primary hydroxyl groups. A series of biobased segmented polyurethanes based on these triols, 1,4-butanediol as a chain extender and 4,4'-methylenebis(phenyl isocyanate) as a coupling agent, were synthesized. Samples were prepared with hard-segment contents up to 50%. The morphologies and thermal properties of these polyurethanes were studied by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. Partial crystallinity and phase separation were detected in samples with hard-segment content of 50%.

Preparation of bio-polymeric materials, their microstructures and physical functionalities

“…Alkyne fatty derivatives were obtained in moderate yields from the corresponding fatty acids by bromation, dehydrobromination, and esterification using well-established procedures (Scheme1). 9,12 Cyclotrimerization of the 10-undecyn-1-ol 3' and behenolic ester 3'' were carried out using PdCl 2 as a transition-metal catalyst. However, when cyclotrimerization of stearoyl alcohol 3 was carried out under the same conditions, some side products were slowly generated or no indication of the trimer formation was obtained.…”

“…10,11 Transition-metal-catalyzed cyclotrimerization of alkynes can be considered as one of the most powerful and general methodologies used to assemble arene rings, and a large number of transition-metal catalysts have been developed for alkyne cyclotrimerization in organic media. 12,[24][25] A simple method utilizes a heterogeneous Pa/C catalyst in a nitrogen atmosphere with refluxing THF as the solvent and commercial grade chlorotrimethylsilane. 10,26 Cyclotrimerization of Stearoyl alcohol 3 was carried out following this procedure, and the symmetric and asymmetric isomers, such as aromatic triols 4a and 4b, have almost identical IR or 13 C NMR spectra in CDCl 3 .…”

“…[8][9][10] The use of vegetable oils and natural fatty acids as starting raw materials offers numerous advantages: for example, inexpensive, abundant, low toxicity, and inherent biodegradability, thus they are considered to be one of the most important classes of renewable resources for the production of bio-based polymeric materials. [11][12][13][14][15][16][17] Polyurethanes (PUs) form a versatile class of polymers, which are used in a broad range of applications, for example, as elastomers, sealants, fibers, foams, coatings, adhesives, and biomedical materials. The industrial production of PUs is normally accomplished through the polyaddition reaction between organic isocyanates and compounds containing active hydroxyl groups, such as polyols.…”

“…Comparing with polyurethanes derived from petrochemical polyols, the vegetable-oil-based polyols used to produce polyurethanes have been the subject of many studies. [9][10][11][12] Moreover, due to the hydrophobic nature of triglycerides, vegetable oils produce PUs that have excellent chemical and physical properties, such as enhanced hydrolytic, high tensile strength and elongation, high tear strength, and thermal stability. [13][14][15][16][17][18] Vegetable oils are one of the most important sources of renewable raw materials for the chemical industry and provide versatile opportunities for a transformation to meet specific applications.…”

“…Based on these studies, now it has become a main research field to functionalize vegetable oils by the introduction of aromatic co-monomers into the polymer structure, which could be suitable in the search for new viable polymeric materials. 12 The transition-metal-catalyzed trimerization of alkyne fatty acid compounds provides an alternative method for the preparation of highly functionalized aromatic polyols. 10,11 In the present study, we have synthesized three kinds of bio-based aromatic triols prepared by oleic acid, 10-undecenoic acid, and erucic acid, which could be obtained from sunflower oil, castor oil, and rapeseed oil, respectively.…”