Vegetable Oils as Platform Chemicals for Polymer Synthesis

The replacement of petroleum-based raw materials by renewable resources constitutes a major contemporary challenge in terms of both economical and environmental aspects. Natural vegetable oils are considered to be one of the most important classes of renewable sources because of the wide variety of possibilities for chemical transformations, universal availability, and low price and they are preferred by the chemical industry as alternative. The main components of the triglyceride vegetable oils are saturated and unsaturated fatty acids which in its pure form are also available as platform chemicals for polymer synthesis
The purpose of our research is to develop new biobased thermosetting polymers from vegetable oils and its derivatives as renewable resources. Recently there have been many attempts to convert vegetable oils and fatty acids to useful polymers and several different approaches have been described.
The direct polymerization of vegetable oils themselves is generally considered difficult due to their lack of active functional groups. Moreover the aliphatic nature and the light crosslinking that characterize the triglyceride-based materials make them incapable of displaying the necessary rigidity and strength required for structural applications by themselves. These drawbacks can be overcome for instance by cationic copolymerization of natural oils with styrene and divinylbenzene. Even the resulting materials have the appropriate properties for a specific application, they must be inherently safe to be commercialized which involves to posses flame resistance and non toxic characteristics. Vegetable oil-based materials, like many other organic polymeric materials, are inherently flammable and so the use of flame retardant additives or the copolymerization with flame retardant monomers are common strategies used in the industry to overcome this shortcoming. Phosphorus, silicon and boron-containing polymers are well recognized for their flame retardant properties, and they are increasingly becoming more popular than their halogen counterparts, as they generally give off nontoxic combustion products. In this work we describe the preparation and characterization of styrene-soybean oil based copolymers containing phosphorus, silicon or boron as effective environmentally friendly flame-retardant systems.
The functionalization of the triglyceride double bonds is another common strategy for obtaining high performance polymeric materials and various chemical pathways for functionalising triglycerides have been described. - We developed an environmentally friendly chemical procedure to obtain an enone-containing triglyceride from high oleic sunflower oil that could be an interesting alternative to epoxidized vegetable oils to produce thermosets. We studied their chemical crosslinking through aza-Michael and phospha-Michael reactions using aromatic diamines and aromatic secondary phosphine oxides in order to infer flame retardancy to the final materials. The curing of this enone-containing triglyceride with aromatic amines at high temperatures has been found to proceed through a complex cascade mechanism which leads to the formation of quinoline moieties that notably enhances the physical properties of the resulting thermosets.
The use of fatty acids or its chemical derivatives to obtain useful polymers has been also considered. Starting from 10-undecenoic acid or 10-undecenoyl alcohol, we synthesized a set of glycerol derived -dienic monomers containing free hydroxylic groups. Acyclic diene metathesis (ADMET) polymerization of ,-dienes has been shown as an efficient tool for the synthesis of a wide variety of linear polymers and polymer architectures that are not available using other polymerization methods. It has been demonstrated that ADMET polymerization can proceed in the presence of heteroatoms and a variety of functional groups, as long as the terminal olefins are far enough apart from them. So we used this synthetic procedure to prepare a set of lineal polyether and polyester polyols with different molecular weight and hydroxyl content from the above undecenoyl-based ,-dienes. In the case of the 10-undecenoic acid-derived ,-diene, the copolymerization with a phosphorus containing ,-diene has been also carried out. The resulting P-containing polyester-polyols have been acrylated and radically crosslinked to obtain a set of flame retardant thermosets. In the case of polyether-polyols thermosetting polyurethanes have been prepared.
Finally, 10-undecenoic, 10-undecynoic and oleic acid derivatives have been exploited as platform chemicals to obtain renewable diols and polyols to produce linear and crosslinked polyurethanes. The coupling between a thiol and a carbon double or triple bond has received recently a growing interest. Thiol-ene coupling complies with most of the requirements of the concept of a click reaction and so it has been used with hydroxyl and carboxyl-functionalized thiols such as 2-mercaptoethanol, 1-thioglycerol and thioglycolic acid to obtain well defined functionalized structures.

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