Research On Blends Of DAOP Prepolymer With PPO For Improved Processing And Properties

The high melt viscosity of polyphenylene oxide(PPO) resulted in many difficulties in processing. At present by adding crosslinkable monomer can improve the processing of PPO and preserve its thermodynamic properties at the same time. However, crosslinkable monomers are mostly liquid, which may be inconvenient to operate and easily volatile in processing. What's more, in order to meet the requirements in processing, the crosslinkable monomer usually is low active, so it may eventually lead to the lower degree of cure and residual small molecule droplets will have a greater impact on the thermodynamic properties of PPO. In this paper the DAOP prepolymer with appropriate molecular weight was polymerized by bulk polymerization with high-temperature initiator DMDPB in order to make up for deficiencies of DAOP monomer in improving the processability. Through studying the thermodynamic properties, rheological properties, phase separation structure of DAOP prepolymer/PPO blends, the paper discussed the feasibility of DAOP prepolymer for improving processability of PPO in the premise of retaining its thermodynamic properties.By studying the influence of initiator content, reaction temperature, reaction time, reaction atmosphere and other polymerization conditions on molecular weight, molecular weight distribution and DAOP prepolymer conversion. Determined the best polymerization condition for DMDPB content is 0.8%, reaction time is 40 min, reaction temperature is 180 ?, reaction atmosphere is nitrogen. The molecular weight and molecular weight distribution of DAOP prepolymer are moderate and the conversion is relatively high. TG/DSC and rheological tests show that the glass transition temperature of DAOP prepolymer is 74.4 ?. DAOP prepolymer also has good thermal stability, it began to degrade when temperature was raised to 339 ? and degradation of 25% at a temperature close to 364 ?. The gel-temperature,curing temperature and post-curing temperature of 3%DMDPB/DAOP prepolymer are 170.866 ?, 181.243 ?, 197.578 ? respectively. Moreover DAOP prepolymer also has excellent rheological properties and good processing adaptability.The rheological tests of DAOP prepolymer/PPO blends show that DAOP prepolymer can effectively improve the processability of PPO. With the increase of DAOP prepolymer, the initial viscosity of the blends decreased and the balanced viscosity increases. Wherein compared to the blends containing 20% DAOP prepolymer, the processing temperature of blends containing 40% DAOP prepolymer can be reduced by about 40 ? in the same processing. DMA results show that DAOP prepolymer has good compatibility with PPO, and its cross-linking curing reaction can play a role in enhancement of PPO substrate. When the content of DAOP prepolymer is 40%, the glass transition temperature of blends is 182.17 ?. Furthermore the heat resistance after curing has little difference compared with pure PPO, and compared to the blends with lower content of DAOP prepolymer the mechanical properties has improved. So DAOP prepolymer can improve the processing of PPO and preserve its thermodynamic properties at the same time.SEM observations of the DAOP prepolymer/PPO blends in different situations indicated the effect of the gelation and the shear on the morphology development of thermosetting/thermoplastic blend, thereby affecting product performance. Before the gel, the introduction of shear even lead to the agglomeration of DAOP prepolymer. But once the shear is removed, DAOP prepolymer will immediately resume the original morphology. The irreversible agglomeration of DAOP prepolymer under the effect of shear will influence drastically the development of the morphology around the gel point, forming irregular and larger particles. After gel the coalescence and agglomeration of DAOP prepolymer will not occur, even if introducing the effect of shear, it will not have a significant impact on microstructure of blends.