Abstract
PMMA/PAN core/shell microspheres were synthesised by polymerising methyl methacrylate (MMA) or acrylonitrile(AN) at 75 °C for 5 h in a soapless emulsion system, using ammonium persulfate (APS) as a radical initiator. It has been shown that in the first-stage reaction the initiator APS significantly accelerated the reaction rate. However, when the APS concentration reached 0.9% (based on the amount of the monomers), this tendency lessened.
In the second-stage core/shell reaction, the effect of initiator on reaction rate was not so pronounced. Transmission electron microscope (TEM), fourier transform infrared (FT-IR), thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were used to characterise the structure and properties of seeded PMMA core and/or PMMA/PAN core/shell polymers. The core/shell morphology was clearly displayed and the diameter of the core is ca. 350 nm whereas the shell thickness was ca. 100 nm. Both the PMMA core and the PMMA/PAN core/ shell polymers had weak and strong endothermic peaks when heated in the range of 340–390 °C, but the latter showed a characteristic exothermic peak which corresponded with the crosslinking reaction of polyacrylonitrile macromolecules at ca. 600 °C. A mixture was obtained by blending the core/shell polymers with high density polyethylene, then spinning to form composite fibres, which were thermally stabilised in air at 180 °C for 1 h and carbonised in nitrogen at 1000 °C to obtain nanometre-sized carbon fibres.