Extrusion foaming by injection of inert gases (carbon dioxide, nitrogen, argon) in the polymer melt is increasingly finding applications for a wide variety of resins, competing with chemical blowing agents, volatile organic compounds or microcellular foaming. The molecular weight and molecular weight distribution of the resin affect its rheological characteristics (shear and elongational viscosity, melt elasticity, melt strength), its process characteristics and control cell size and stability of the resulting foam. In the present work, a variety of PET resins (including virgin materials, recycled and post-reactor modified) having different rheological characteristics were foamed by direct carbon dioxide injection and through the use of chemical blowing agents. Formability as related to density and cell size and distribution was evaluated and correlated with rheological characteristics of the particular resin, process conditions and type of blowing agent.

In this paper silane coupling agents A151, A171, A174 and A187 were used to modify the surface of nanosilica (SiO 2 ) and polybutadiene (PB)/SiO 2 nanocomposites (NC) had been prepared by in situ anionic polymerization. The morphology and chemical constitution of NC were characterized by Transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR); Thermogravimetric analysis (TGA) was used to investigate the thermal properties of NC; the molecular weight and molecular weight distribution of NC were characterized by gel permeation chromatography (GPC). The effect of different SiO 2 and silane coupling agents on the molecular weight and distribution of PB, microstructure and properties were studied. The results showed that the hydrophobicity of SiO 2 was increased after the surface modification by silane coupling agents and can disperse in PB matrix uniformly. The thermal stability of NC also increased.