Introduction
Due to the depletion of environmental resources and fossil fuels, the development of new coating systems derived from renewable resources to replace petroleum-based coatings is becoming increasingly important [[1], [2], [3], [4]]. Vegetable oils are among the most attractive renewable raw materials, because they are readily available and inexpensive [[5], [6], [7]]. Vegetable oils have unique chemical structures with hydroxyl groups, esters, unsaturated sites, and a variety of other functionalities. Their unique structures can undergo various chemical transformations for use in polymeric materials [[8], [9], [10]].
Acetoacetate chemistry is attractive for the preparation of thermoset resins, because acetoacetate functional groups can react with a variety of chemicals, including acrylates [11], amines [12], aldehydes [13] and isocyanates [14]. Although many thermoset resins have been prepared using acetoacetate chemistry, only a few bio-based coating materials have been reported. Trumbo et al. added multifunctional amines to acetoacetylated castor oil to obtain coating materials that could be cured to make films. They discovered that the properties of the coating could be improved by increasing the temperature [15]. Webster et al. developed bio-based coating materials with acetoacetylated sucrose and multifunctional amines, and they obtained coatings with desirable properties by adjusting the degree of substitution in the acetoacetylated sucrose [16]. Our group recently synthesised a series of bio-based coating materials using modified acetoacetylated castor oil (MACO), and the properties of the coatings could be controlled by adjusting the proportion of acetoacetate groups [[17], [18], [19]]. Although the reaction between acetoacetyl functionalities and isocyanate has been widely employed in the development of coating technologies (Scheme 1) [[20], [21], [22], [23]], the preparation of resins from acetoacetylated plant-based materials and isocyanate has not yet been reported.
Herein we describe the synthesis of novel bio-based coating materials from MACO and isocyanates. The bio-based coating materials could be cured with a mixed catalyst loading of PTSA (2.5 wt %) and DBTDL (2.5 wt %) to fabricate biobased films with excellent mechanical and chemical properties. More importantly, the bio-based coating material crosslinked with 4,4′-diphenylmethane diisocyanate exhibited good shape memory.
