Study On Preparation And Properties Of Polydicyclopentadiene Nanocomposites

Polydicyclopentadiene（PDCPD）with excellent properties is a non-polar thermosetting engineering plastic obtained by the ring-opening metathesis polymerization of monomeric dicyclopentadiene（DCPD）.In this paper,the spherical silica and rod-like multi-walled carbon nanotubes were selected as fillers to prepare fillers/PDCPD composite.Firstly,in order to address the issues of dispersion and compatibility between the SiO₂ and PDCPD,non-polar groups（vinyl,phenyl）were introduced onto the surface of fillers.Then fillers/PDPCD composites were prepared by in situ polymerization,to study the effect of different fillers and different non-polar groups on mechanical properties of PDCPD composite.In the first part of the study（chapter 3）,vinyl functionalized silica（V-SiO2）was synthesized by sol-gel method.Then V-SiO₂/PDCPD composites with different contents of V-SiO₂ were prepared by in-situ polymerization and pouring process.The V-SiO₂ was characterized with respect to the content of vinyl group,particle size and morphology by fourier transform infrared spectroscopy（FTIR）,thermogravimetric analysis（TGA）,dynamic light scattering（DLS）and field-emission scanning electron microscopy（FE-SEM）.Mechanical properties of composites were investigated by universal testing machine（UTM）and dynamic mechanical analysis（DMA）.The toughness of PDCPD composites was significantly improved by the addition of V-SiO₂.The tensile toughness increased by 14 times compared to neat PDCPD when just 0.2 wt%V-SiO₂ was added.The dramatic toughness enhancement is attributed to the formation of microvoids and microcracks during the process of stretching,which can absorb lots of energy.Meanwhile,because of the covalent bonding between the vinyl group on surface of V-SiO2 and the double bond in DCPD,the crosslinking degree of the material is reduced.In the second part of the study（Chapter 4）,the phenyl-functionalized silica（P-SiO₂）was synthesized and the P-SiO₂/PDCPD composites were prepared by the same method as the first part to compare the effects of different groups on the surface of silica SiO₂ on the mechanical properties of PDCPD composites.TG results showed that the content of phenyl in P-SiO₂ was about 22%.The mechanical properties of P-SiO2/PDCPD composites were studied.The results showed that the tensile strength and impact strength of the composites were increased with increasing P-SiO2content,and the elongation at break decreased slightly.With addition of 0.3 wt%P-SiO₂,the tensile strength and impact strength were increased by about 56%and 2 times,respectively.The reason for the increasment of tensile strength is that the movement of molecular chains in the tensile process is hindered because of the higher content of rigid phenyl group and high interfacial bonding strength between PDCPD and P-SiO₂.In the third part of the study（Chapter 5）,in order to study the effect of different fillers and same groups on the mechanical properties of PDCPD composites,multi-walled carbon nanotubes functionalized hydroxyl（MWNT-OH）were modified by grafting vinyl groups with vinyltrimethoxysilane（VTMS）.The vinyl functionalized MWNT was successfully synthesized by controlling synthesis process,improving dispersion and compatibility between the MWNT and PDCPD.The f-MWNT was measured by FTIR and SEM.The results showed that the vinyl group was grafted onto the surface of MWNT and a coating was formed on the surface of MWNT.f-MWNT/PDCPD composites were prepared by in-situ polymerization.The results of mechanical properties showed that the tensile strength and toughness of PDCPD were improved by adding f-MWNT,and the tensile strength and toughness of PDCPD were increased by about 48%and94%,respectively,when the tensile strength and toughness reached the maximum.The impact strength reached the maximum and increased by about 96%when 0.4 wt%f-MWNT was added.