# Bio-Based Polymers with Potential for Biodegradability
## 1 Introduction  
Polymeric materials can be classified into either thermoplastics or thermosetting polymers. Thermoplastic polymers consist of well-packed, non-covalently bound polymer chains that can melt and flow when heated above the polymer's melting point, while thermosetting polymers consist of networks of polymer chains interconnected through covalent bonds. The latter structures do not melt when heated, and cannot be dissolved in a solvent. These differences between thermoplastic and thermosetting polymers have a direct impact on polymer recyclability. It is well accepted that thermoplastics can be easily melted and re-processed during recycling, whereas thermosetting polymers require harsher conditions in order to be converted into other value-added products. Because of its crosslinked chemical structure, thermosetting polymers often exhibit superior mechanical properties, making their breaking down more challenging than that of thermoplastics. Naturally, such aspect is also reflected on the thermal stability of thermoplastics and thermosetting polymers. It is therefore expected that thermosetting polymers be physically harder to degrade than thermoplastics. The versatility of thermosetting polymers lies in the possibility of easily adjusting their properties by simply changing crosslink density without a need for modification of the overall chemical structure [1]. Most thermoplastics and thermosetting resins in current industrial use are derived from petroleum, imposing a limitation to the polymer industry due to the continuous depletion of crude oil, frequent oscillation in oil price, and various environmental concerns with sustainability, gas emissions, disposal, and recyclability [2; 3]. In this context, increasing efforts have been made to date in designing polymeric materials from renewable resources [4]. A variety of renewable starting materials, such as sugars and polysaccharides, vegetable oils, lignin, pine resin derivatives, and proteins, have so far been investigated for the preparation of bio-based polymers [5; 6]. Among the various sources of bio-based feedstock, vegetable oils are the most widely used starting materials in the polymer industry due to their easy availability, low toxicity, and relative low cost [4]. Since the year 2000, the chemical industry alone was responsible for consuming more than 15% of the yearly global production of vegetable oils [7]. Unsaturated vegetable oils have been used in the formulation of paints and coatings due to their ability to react with molecular oxygen in the air and form cross-linked materials [8; 9]. A variety of thermosetting polymers obtained from the reaction of carbon-carbon double bonds in the fatty acid chains of vegetable oils have been proposed to date [10]. Despite the lack of sufficient literature on the biodegradability properties of vegetable oil-based thermosetting resins, the possibility of cross-linking the carbon-carbon double bonds in polyunsaturated oils through free radical [11], or cationic [12] polymerizations makes the design of bio-based thermosetting polymers from vegetable oils an interesting alternative to petroleum-derived materials. Other approaches for the preparation of vegetable oil-based polymers involve more significant structural changes, such as grafting of acrylate groups for free radical polymerization [13], epoxidation of carbon-carbon double bonds followed by cure with various nucleophiles [14], acyclic diene metathesis polymerization (ADMET) [15], and ring-opening metathesis polymerization (ROMP) [16]. Finally, polyesters, one of the main classes of biodegradable polymers, and polyurethanes have been prepared from the reaction of vegetable oil-based polyols with anhydrides [17], diacids [17], or diisocyanates [18].