Study On Reinforced Modification And Self-immolative Performance Of Polyphthalaldehyde

Self-immolative polymers are unique macromolecules that can undergo end-to-end depolymerization when subjected to external stimuli.Its unique properties make it have many practical applications in transient devices,sensors,drug delivery and so on.Polyphthalaldehyde(PPHA)is an important type of self-immolative polymers,and its ceiling temperature(T_c)is-43°C.PPHA’s low T_c and highly acid-sensitive characteristics enable it to quickly and completely depolymerize at room temperature.In addition,PPHA also has the advantage of being easy to synthesize,so it is favored by researchers.However,the poor mechanical properties of PPHA have restricted the application and development of it,so it is particularly important to improve the mechanical properties of PPHA.In this paper,the mechanical properties of PPHA were enhanced by blending methods,and self-immolative materials with excellent self-immolative properties and good mechanical properties were prepared.In this paper,PPHA was synthesized by cationic polymerization,and the influence of monomer/initiator ratio and reaction time on the molecular weight of PPHA was explored.It was found that when the monomer/initiator ratio was 30 and the reaction time was 15 min,the molecular weight of the prepared PPHA was the highest,which was 17948 Da.Then the PPHA film was prepared by solvent casting method.The influence of solvent type,plasticizer and photoacid concentation on the mechanical properties of the film was studied.When dichloromethane was used as the solvent,and 7 wt%of plasticizer and 8 wt%of photoacid were added,the mechanical properties of the film were the best.The tensile strength of the film was0.43 MPa,the modulus of elasticity was 19.9 MPa,and the elongation at break was214.57%.At the same time,PPHA film exhibited excellent self-immolative properties under ultraviolet light,heat and acid stimuli.After 6 minutes of ultraviolet irradiation,the film could be completely liquefied and disappeared;when kept at200°C for 10 minutes,the mass percentage of the film dropped to about 2.7%;in a solution with an acid concentration of 0.1 mol/L,the film could completely self-immolate within 90 s.Regarding the problem of poor mechanical properties of PPHA,this paper systematically studied the effects of polylactic acid,polycaprolactone,and polyimine on the mechanical properties of PPHA through the method of blending.Research results showed that polylactic acid(25%),polycaprolactone(50%),and polyimine(50%)could increase the tensile strength of PPHA film to 1.46 MPa,4.31 MPa,18.18MPa,and increase the modulus of elasticity to 36.85 MPa,239.62 MPa,483.85 MPa,which had a very good effect of enhancing mechanical properties.It could be found that the mechanical properties of the 50%polyimine blend film had been improved by 42 times.In addition,these three blended films also had good self-immolative properties.The blend film made of polylactic acid(25%)and polycaprolactone(50%)could self-immolate within 32 minutes and 6 minutes under ultraviolet light,respectively.The blend film made of polyimine(50%)would self-immolate within30 minutes in the acid solution.