The influence of different surface functional groups of nano-SiO2 on nylon 6 in situ polymerization was investigated．FTIR and TGA measurements of silicas isolated from the composites showed that surface grafting was formed during polymerization of silica particles with or without silane pretreatment on the surface

and the percentage of grafting increased with increasing amount of surface functional groups．Compared with pure nylon 6

the presence of silicas with various functional groups resulted in a decreasing tendency of the average molecular weight of nylon 6 in the composites．According to the possibly occurred reactions in the composite systems several bonding styles of surface grafting were proposed．Mechanical tests revealed that the addition of silane treated silica improved the strength and toughness of the composite materials simultaneously

whereas the addition of untreated silica improved the strength at the sacrifice of toughness

indicating the importance of the flexible interlayers introduced by silane treatment.