Preparation And Properties Of AN/MAA/AMS Copolymers And Their Foams

Polymethacrylimide(PMI)foams were widely used in aerospace,transportation and many other fields due to its excellent mechanical strength and thermal stability.However,the polymerization process is difficult to control and the catastrophe phenomenon is easy to take place when PMI copolymer is prepared with acrylonitrile(AN)and methacrylic acid(MAA)as main monomers.It is useful to solve this problem by adding third-party monomers.In this paper,PMI copolymer was modified by methylstyrene(AMS)as a third-party monomer.The effects of different contents of AMS on the properties of the modified copolymer was studied.Based on this situation,the AMS modified foams were prepared.Firstly,the AN/MAA copolymer was prepared by a free radical prepolymerization.The results of the mechanical properties test and TGA test showed that the mechanical properties and heat resistance of copolymers can be improved by increasing heat treatment temperature.As the heat treatment temperature rised from 140 ~oC to 160 ~oC,the tensile strength of the AN/MAA copolymer increased from 96.32 MPa to 108.54 MPa.And the thermal decomposition residue of the copolymer at 600°C increased from 36.91%to 39.13%.The results of FTIR,DSC and TGA test showed that the main reaction of AN/MAA copolymer during heat treatment was the imide ring-forming reaction between adjacent-CN groups and-COOH groups on the copolymer molecular chain.Secondly,the theoretical research of radical copolymerization via Q-e equation and these modified copolymers with different content of AMS were prepared.The test results showed that the content of AMS will affect the properties of the modified copolymers.When the content of AMS in the copolymer was low,the modified copolymer had a delamination phenomenon.And the modified copolymer is uniformly transparent when the content of AMS in the copolymer increased to 9 wt%.The results of ultra-depth of field and SEM test showed that the modified copolymer with low content of AMS was prone to tensile fracture due to poor compatibility of the layered material,and the compatibility of the modified copolymer improved with the increase of AMS content.The results of the mechanical properties and TGA test showed that as the increase of the AMS content in the modified copolymer will reduce the tensile strength and thermal stability of the modified copolymer,but it can improve the toughness of the modified copolymer.As the content of AMS in the modified copolymer increased from 0 wt%to 9 wt%,the tensile strength of the modified copolymer decreased from 96.32 MPa to 84.29 MPa,and the thermal decomposition residue of the modified copolymer decreased from 36.91%to7.60%.However,the toughness of the modified copolymer increased from 275.90 MPa to439.16 MPa.The results of FTIR,DSC and TGA test indicated that AMS participated in the polymerization process of the modified copolymers as a third-party monomer.However,AMS did not react with the molecular groups in the copolymers during heat treatment.Finally,the AMS modified foams with excellent properties were prepared by adjusting the formulation and process.The results of SEM test showed that the AMS modified foam had a complete proe structure and the distribution of the proe was uniform.The results of the apparent density test and the mechanical properties test showed that the density of the foams can be adjusted by changing the content of the foaming agent and the crosslinking agent.The crosslinking degree of the foam can be increased by a small amount of Bismaleimide(BMI),which will affect the density and mechanical properties of the foam.The carboxamide as a nucleating agent can effectively reduce the pore size of the foam and make the pore distribution more uniform.The order of influence of technological parameters on the density and mechanical properties of foam plastics is foaming temperature,heat treatment temperature and pre-heat treatment temperature.