Preparation of oil-modified polycaprolactone and its further modification with benzoxazine for coating purposes

Sunflower oil-modified polyester (SOMPE) was prepared via the ring opening polymerization of ɛ-caprolactone (CL) using partial glycerides (PGs) and stannous octoate (SO) as the initiator and catalyst, respectively. In addition to being the initiator, PGs participate in the drying process of the film sample for coating purposes. The structure of the sample was characterized by FT-IR and 1H NMR. The film of SOMPE cannot reach a fully dried state as a result of its less oil moiety content. By increasing the oil fraction, the chain length of polycaprolactone (PCL) decreased by changing the [monomer]/[initiator] mol ratio and shortening the reaction time. Even with these precautions, the molecular weight of SOMPE could not be reduced below 5000 g/mol, and this caused the film to become soft. Therefore, hydroxy-functional benzoxazine monomer (HFB-a) was prepared and used in a further modification of SOMPE. HFB-a was chemically combined with SOMPE via the urethane linkage formed from the reaction of 2,4-toluene diisocyanate, yielding SOMPE-HFB-a. Because the SOMPE-HFB-a sample also had a soft film, additional HFB-a was used to prepare the SOMPE-HFB-a/HFB-a blend. The cured blend prepared with SOMPE-HFB-a and HFB-a in a weight ratio of 1/8, [SOMPE-HFB-a/HFB-a:1/8], had good film properties. The cured film was examined by FT-IR and DSC following the curing process. After our modifications were applied, PCL and polybenzoxazine lost their softness and brittleness, respectively, and a binder with good film properties was formed.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Partial glycerides were used as an initiator in the ROP of caprolactone. ► Oil-modified polyester was chemically modified with benzoxazine. ► Benzoxazine modified polyester can be used as a binder for organic coatings.