Virginia Cádiz

Plant Oils as Platform Chemicals for Polyurethane Synthesis: Current State-of-the-Art

Plant oils are already one of the most important platform chemicals for the chemical industry due to its universal availability, inherent biodegradability, and low price. Nowadays, plant oils are already a commercial source of multifunctional monomers and oligomers for polyurethane synthesis, and the design of novel biobased polyols derived from them is an active area of research. By taking advantage of the wide variety of possibilities for chemical modification of plant oils, there is a broad palette of strategies to functionalize its structure with hydroxyl groups. The purpose of this review is to comprehensively overview recent developments on the preparation of biobased polyols from plant oils, covering from the general epoxidation and ring-opening approach to novel routes based on thiol-ene click chemistry as well as to highlight the properties of polyurethanes obtained from them.

Polybenzoxazines: new players in the bio-based polymer arena

Polybenzoxazines are phenol-like materials that have attracted significant attention from both academia and industry because of their unique advantages. The growth of this technology has always been linked to petro-based feedstocks. However, due to the incessant global energy crisis it is now finding a breakthrough through the preparation of their monomers from renewable resources. This mini-review focuses on the recent efforts to replace petro-based feedstocks with polybenzoxazine precursors.

Unsaturated modified poly(vinyl alcohol). Crosslinking through double bonds

Poly(vinyl alcohol) (PVA) was esterified with 10-undecenoyl chloride to give polymers with different degrees of modification which were studied in order to find how the concentration of reactive sites can influence the crosslinking process. The polymers obtained were characterized by spectroscopic techniques, elemental analysis and thermal methods. Weight average molecular weights and viscosities were determined. Thermal crosslinking of the double bonds on the side chain took place in all cases, but was overlapped by the degradation process. Thus, dicumyl peroxide had to be used to obtain the cured material and avoid degradation. Activation energies for radical initiated crosslinking were determined by means of dynamic DSC studies. Isoconversional kinetic analysis was applied to DSC data and the dependences of activation energies on conversion degrees were obtained and compared with those obtained from polymers with the same pendant chain but a more flexible polyether main chain.

Poly(vinyl alcohol) modified with carboxylic acid anhydrides: crosslinking through carboxylic groups

The reaction of carboxylic acid anhydride with poly(vinyl alcohol) (PVA) leads to vinyl alcohol—vinyl ester copolymers which contain carboxylic acid groups. Esterification enables degrees of modification to be reached which depend on the chemical structure of the anhydride introduced and the ratio of the reagents in the feed. The copolymers obtained were characterized by spectroscopic techniques, elemental analysis, and thermal methods. These half-esters reacted in a second step with aromatic diglycidyl ethers to obtain tridimensional networks. This crosslinking reaction through the carboxylic groups was studied by differential scanning calorimetry. The water absorption of the linear and crosslinked polymers was determined gravimetrically as a function of time at room temperature.

Synthesis, Characterization and Polymerization of a Novel Glycidyl Phosphinate

With the aim to obtain flame-retardant epoxy resins, a new glycidyl phosphinate, 9-(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-2,3-epoxypropyl (DOPO-Gly) was synthesized via a two-step synthesis. The subsequent reaction of DOPO-Gly with BF3·Et2O resulted in a polyether with a pendant bulky phosphorylated group. Likewise, the reaction with phthalic acid anhydride gave the expected dihydroxy ester. However, the reaction with tertiary or primary amines led to isomerization and no polymer was obtained.

Silicon-Containing Soybean-Oil-Based Copolymers. Synthesis and Properties

New silicon-containing soybean-oil-based copolymers were prepared from soybean oil, styrene, divinylbenzene, and p-trimethylsilylstyrene by cationic polymerization using boron trifluoride etherate as initiator. Soxhlet extraction and NMR spectroscopy indicate that the copolymers consist of a cross-linked network plasticized with varying amounts of oligomers and unreacted oil. This soluble fraction increases when the SiST content in the feed increases, according to a lower reactivity of this monomer. The thermal, dynamomechanical, and flame-retardant properties of these materials were examined. Thermosets with glass transition temperatures ranging from 50 to 62 degrees C, which are thermally stable below 350 degrees C, and with LOI values from 22.6 to 29.7 were obtained. Their properties suggest that these materials may prove to be useful alternatives for current non-renewable-based thermosets and that the flame-retardant properties of vegetable-oil-based thermosets can be improved by adding covalently bonded silicon to the polymer.

Thiol–yne reaction of alkyne-derivatized fatty acids: biobased polyols and cytocompatibility of derived polyurethanes

With the goal of obtaining renewable diols and polyols for polyurethane (PU) technology, the thiol–yne coupling reaction was applied to alkyne-derivatized fatty acids derived from naturally occurring oleic and 10-undecenoic acids. The resulting monomers were then polymerized with 4,4′-methylenebis(phenylisocyanate) to produce the corresponding PUs. The chemical structures and thermal and mechanical properties of the synthesized PUs have been evaluated by FTIR and NMR spectroscopy, DSC, TGA and tensile tests respectively. Moreover, the biocompatibilities of the synthesized PUs with human osteoblast-like cell line (MG63) have also been evaluated for tissue engineering purposes.

“Click” Synthesis of Fatty Acid Derivatives as Fast-Degrading Polyanhydride Precursors

Fast-degrading linear and branched polyanhydrides are obtained by melt-condensation of novel di- and tri-carboxylic acid monomers based on oleic and undecylenic acid synthesized using photoinitiated thiol-ene click chemistry. (1)H NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, thermogravimetric analysis, and FT-IR spectroscopy have been used to fully characterize these polymers. The hydrolytic degradation of these polymers was studied by means of weight loss, anhydride bond loss, and changes in molecular weight, showing fast degrading properties. Drug release studies from the synthesized polyanhydrides have also been conducted, using rhodamine B as a hydrophobic model drug, to evaluate the potential of these polymers in biomedical applications.

Convenient and solventless preparation of pure carbon nanotube/polybenzoxazine nanocomposites with low percolation threshold and improved thermal and fire properties

This work contemplates the use of pristine multiwalled carbon nanotubes (MWNTs) as nanofillers in the preparation of bisphenol A-based polybenzoxazine and diphenolic acid derived polybenzoxazine. These materials were prepared by using a solventless method varying the MWNT amount from 0.1 to 1.0 wt%. MWNTs were found to disperse well within both benzoxazine monomers and the dispersion also appears to be good in the cured system. Rheological and electrical percolation thresholds were obtained for MWNT concentrations lower than 0.1 wt% indicating the existence of good affinity between MWNTs and polybenzoxazine matrices. The characterization of the resulting nanocomposites revealed that MWNTs affected polybenzoxazines differently. The limiting oxygen index of the nanocomposites increased as a function of the nanotube content, from 35.2 to 38.7 for a bisphenol A-benzoxazine based system (BPA-PBz) and from 31.2 to 37.4 for a methyl-4,4′-bis-[6-(3-phenyl-3,4-dihydro-2H-1,3-benzoxazine)]pentanoate based system (MDP-PBz), respectively. Moreover, MWNTs positively influenced the thermo-mechanical, thermal and mechanical properties of the nanocomposites. The resulting attractive properties have been attributed to good interaction between the polybenzoxazines and the finely dispersed nanofillers.

Studies on the microstructure of poly(phenyl glycidyl ether) using the 13C nuclear magnetic resonance technique

Abstract Microstructural details of poly(phenyl glycidyl ether) (PPGE) and its optically active form obtained by the aluminium isopropoxide (AIP)/ZnCl2 ionic-coordinative initiator were analysed by nuclear magnetic resonance techniques. In order to assign the soluble fraction signals unmistakably, PPGE samples had to be synthesized using various cationic initiator systems. Several modifications were studied in the AIP/ZnCl2 initiator system (such as the use of various zinc salts and the addition of water) and the tacticity and irregularity contents of the polymers were determined.