Synthesis And Characterization Of ?,?-Bis(2,6-dimethylphenyl)-Poly(2,6-dimethyl-1,4-phe Nylene Oxide) Oligomer In Fe(?)-salen/Hydrogen Peroxide System

Poly(2,6-dimethyl-1,4-phenyl ether)(PPE)also referred to as Poly(2,6-dimethyl-1,4-phenyl oxide)(PPO).It is one of the five general engineering plastics.PPO has excellent advantages of low moisture absorption,low dielectric constant and dielectric loss,good resistance to high and low temperature,mechanical properties and dimensional stability.It can be widely used in electronic equipment,automotive parts,commercial machinery,aerospace and other fields.In recent years,with the rapid development of 5G high-frequency and high-speed electronic circuit substrate field,PPO has been widely used in PCB due to its excellent performance.However,PPO also has some deficiencies,such as high melt viscosity,small liquidity,poor processability and low reactivity.The?,?-Bis(2,6-dimethylphenyl)-Poly(2,6-dimethyl-1,4-phenylene oxide)oligomer(PPO-2OH)can solve these problems and maintain the other advantages.In this paper,PPO-2OH was synthesized by the oxidative coupling copolymerization of 2,6-dimethylphenol(DMP)and tetramethylbisphenol A(TMBPA),which using Fe(?)-Salen complex as catalyst and hydrogen peroxide instead of conventional oxygen.FT-IR and 1H-NMR spectra showed that the product was PPO-2OH and TMBPA(diphenol monomer)was in the middle,the end and the penultimate structure of the chain.The effects of the types of diphenols,the molar ratio of DMP/TMBPA,the types of phase transfer agents and different Fe(?)-salen on the PPO-2OH were discussed.98%of PPO-2OH can be obtained by TMBPA with methyl substitutions at 2,6 positions,while the proportion of PPO-2OH is very small by the monomers with no substituents or few substituents.When the molar ratio of DMP/TMBPA is 4:1,the product is almost PPO-2OH.With the increase of the mole monomer ratio,the molecular weight is increased,but the proportion of PPO-2OH decreased.In addition,the effects of phase transfer agents and salen ligands on PPO-2OH were also studied.The results showed that the cationic phase transfer agent(DDAC)was the best with high yield of 77.99%.When the steric hindrance of salen ligand is small,it is favorable for the oxidative copolymerization of DMP and TMBPA to form PPO-2OH,and the catalyst with high steric hindrance is inhibited or has no catalytic effect.The polymerization conditions have an important influence on the polymerization of PPO-2OH oligomer.The copolymerization of DMP and TMBOA can be terminated at a specific time,and PPO-2OH with low molecular weight of about 1 600-3 000 can be obtained;With the extension of reaction time,the molecular weight of the product increased gradually,but the molecular weight increased slowly when the reaction time was too long.The molecular weight of PPO-2OH increases with the increase of reaction temperature,but the yield decreases.When the reaction temperature is controlled at 30?,the yield can reach 77.99%,and the number average molecular weight is 1 707.With the concentration of hydrogen peroxide was increased from 15%to 30%,the yield of PPO-2OH was increased from 67.63%to77.99%,and the molecular weight of PPO-2OH was decreased.The increase of the amount of Fe(?)-salen will increase the yield,increase the molecular weight and widen the molecular weight distribution;However,when the amount of catalyst is more than 1.11%(0.30 g)of the total mass of monomer,the yield will be reduced.According to the Fox-Flory equation,the K value obtained by fitting is smaller,and the relationship between Mn and[?]is consistent withlog M_n=1.36log[?]+4.73.