A series of poly(A-block-B-block-A) copolymers based on biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and amorphous polystyrene (PS) were synthesised by atom transfer radical polymerisation (ATRP). The chemical structure, molecular weight and distribution were systematically characterised by Fourier transform infrared, 1 H nuclear magnetic resonance ( 1 H NMR) and gel permeation chromatography (GPC). The melting and crystallisation behaviours, and thermal stabilities of copolymers were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); the degradation activation energy was calculated by Horowitz-Metzger method. Results showed that the maximum yield of triblock copolymer was 88%. DSC curves revealed that the triblock copolymers had their cold crystallisation temperature from 50?83 to 65?67uC, and the crystallinity from 55?60 to 12?60. TG curves showed that the thermal stabilities of triblock copolymers were enhanced, and its degradation activation energy decreased from 428 to 197 kJ mol 21 .
To solve the high viscosity of bisphenol A glycerolate dimethacrylate (Bis-GMA), its derivate AcBis-GMA substituting acetyl groups for hydroxyl groups was synthesised by the esterification reaction and mixed with tri(ethylene glycol) dimethacrylate (TEGDMA) as polymer matrix to fabricate dental resin restorative composites. To improve the degree of conversion (DC), polymerization shrinkage (PS) and wear resistance of resin-based composite (RBC) 58-12 filled with commercial microsize and nanosize (M/N) SiO 2 particles, bimodal silica nanostructures consisting of SiO 2 nanoparticles (NPs) and SiO 2 nanoclusters (NCs) were introduced as inorganic fillers. Resin composites with different mass ratios of silanized SiO 2 NPs and SiO 2 NCs were fabricated under the light polymerisation, and the effect of filler compositions on these two properties, wear resistance (wear volume and worn surface morphology), and cytotoxicity assay of resin composites was investigated in this work. The results suggested that resin composites reinforced with bimodal silica nanostructures at the optimum ratio presented the improved performance, especially for RBC 35-35 (SiO 2 NPs:SiO 2 NCs535:35, wt/wt), which resulted in 16% enhancement in DC and 19% reduction of PS, the smoother and flatter worn surface after 10 000 wear cycles, as well as the excellent cytocompatibility, compared with those of RBC 58-12.This effective and facile way might provide a new sight to develop dental resin restorative composites for clinical application.
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