| Dendritic polymers have received increasing attention in recent years becausethey are expected to have unique properties when compared to their linearanalogues.The highly branched structure and a large number of terminal functionalgroups are two importantstructural features of dendritic polymers, which clearlydistinguish them from linear (nonbranching) polymers. Dendrimers are perfectlybranched and monodispered macromolecules. The synthesis of a dendrimerinvolvesmultistep procedures (i.e., protection, coupling, anddeprotection cycles),leading to high cost and difficulty in large-scale preparation. Hyperbranchedpolymers do not have the well-defined (perfect) architectures as dendrimers, andthey are generally comprised of three parts: linear (L), dendritic (D), and terminal(T) units.Nevertheless, hyperbranched polymers are thought to have similar physicalproperties to dendrimers and can be used to replace dendrimers for most cases.Since hyperbranched polymer can be simply prepared by direct "one-step"polymerization of multifunctional monomers,they are of more significance thandendrimers from the viewpoint of industrial applications.The widespread interest in hyperbranched polymers stems from theiruniquechemical and physical characteristics, based on their nanosizedspherical-shaped structures with many branches radiating from the centers.1Recently,a great deal of attention has centered on using degradablehyperbranched polymers as a template to create nanometer-sized cavities forseparation.Moreover, Gref etal. considered the possibility of applying dendrimersasinjectable biodegradable nanospherical carriers for drug delivery or medicalimaging.Dendrimersand hyperbranched polymers have alsobeen used ascrosslinking agents. Hyperbranched polymers are generally prepared by one-pot self-Polymerization of the AB2 monomers.Since the AB2 monomers are not alwayscommercially available and their preparation sometimes involves in synthetic effort,a facile A2 + B3 approach was put forward recently.The hyperbranched polymer byA2 + B3 polymerization was found to have a loose-packing,low branching densitytopology with a high solution viscosity. The polymerization of a difunctional monomer(A2) and a trifunctionalmonomer (B3) can also lead to soluble hyperpranched polymers. The potentialadvantage of A2-B3 polymerization lies in the use of commercially availablemonomers. It is the most important that the trait of the obtained polymer possess ofthe adjustable terminal group and the degree of branching. In this study, a newtrifluoro-end groups containing an aryl ether ketone structure, 1,3,5-tris[4-(4-flourobenzoyl)phenoxy]benzene was intentionally synthesized. Fluorin-Terminated HPAEK was synthesized by 3,3',5,5'-tetramethylbiphenol (A2 typemonomer)and1,3,5-tris[4-(4-flourobenzoyl)phenoxy]benzene(B3 type monomer).Fluorin-Terminated HPAEK was end-capped with 4-phenyl ethynyl phenol.Wereceived Phenylethynyl-Terminated HPAEK. Phenylethynyl-Terminated polymers can self-crosslink ,they have highthermal stability.We can control the reactant and Tgs.For high-temperatureapplications,phenylethynyl groups are good candidates because of their high curingtemperatures,which provide broad processing windows. The structure of monomer and polymers were confirmed by FTIR and1H-NMR The final results are consistent with our prediction . Firstly, we carried out further research about the polymer's crosslinkingproperties .The polymer was procured with different time and temperaturesrespectively. The comparisons of Phenylethynyl-Terminated HPAEK before and aftercuring were performed. The glass transition temperature(Tg) of Phenylethynyl-Terminated HPAEK was larger than Fluorin-Terminated HPAEK. The glasstransition temperature(Tg) and solubility of polymer changed greatly after fullycrosslinked, in another word, we got a solvent-resistant HPAEK with high Tgafter curing. The thermal stability of polymer was increased after crosslinking. Secondly, we employed FTIR instrument to trace the crosslinking reaction.The absorption of ethynyl groups at 2215cm-1 was faded away with longer curingtime and higher curing temperature, which could prove that the crosslinkingreaction had occurred. At the same time, we investigated other factors such as the curing time,temperature and curing atmosphere how to influence the crosslinking rate. Theresult was that the crosslinking degree was increased with the elevating curingtemperature; the similar situation appeared in the relationship between... |
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