Polymeric materials are promising next-generation materials for different applications due to their unique properties largely influenced by the type of molecules being bonded and the bonding methods. Over the past decades, extensive research has been conducted to fabricate new polymers, improve the performance of the existing ones and expand their applications. In particular, polymers containing fluorine have attracted research attention due to their high performance and exceptional properties like good chemical resistance and high thermal stability. Unlike hydrocarbon polymers, fluoropolymers are generally inert. This can be attributed to the strong C – F bonds, making fluoropolymers a good candidate for different practical applications in biomedical and photonics industries.
To date, various methods for preparing fluoropolymers have been proposed. However, most of the existing fluoropolymers are synthesized by chain-growth polymerization of fluorooleefins. Other preparation strategies such as step-growth polymerization, particularly those starting from fluoroalkenes, are sparsely explored despite their potential practical implications. Lately, the feasibility of the one-step polymerization method has been successfully demonstrated, providing a new path for preparing perfluoropolyether fluids with remarkable chemical and thermal resistance properties. Moreover, the previously reported semi-fluorinated arylene vinylene ether (FAVE) polymers exhibited telechelic nature and good film-forming and ductility properties, but their glass transition temperature (Tg) value remained undesirably low. Therefore, developing more feasible and efficient step-growth polymerization strategies for fluoroalkenes.
Motivated by the previous research findings, Mississippi State University researchers: Dr. Karl M. Mukeba, Mr. Behzad Faradizaji, Dr. Ketki E. Shelar, Dr. Charles U. Pittman Jr. and Professor Dennis W. Smith Jr synthesized FAVE telechelic polymers and their extended chain perfluorocyclobutyl (PFCB) polymers via a base-catalyzed step-growth polymerization of polycyclic aromatic hydrocarbon (PAH) bisphenols and aromatic trifluorovinyl ethers (TFVE). The original research article is currently published in the journal, Polymer.
In their approach, the step-growth polymerization strategy used in this experiment involved the elimination/addition polymerization of 4,4ꞌ-bis(4-trifluorovinyloxy)biphenyl (TFVE-BP) monomer with commercially available bisphenols. The properties of the resulting polymers were characterized using different techniques, including differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Finally, the properties of the new aromatic FAVE polymers were presented and discussed in detail.
The authors findings demonstrated the successful synthesis of processable FAVE polymers with backbones containing reactive and crosslinked fluoroalkenes. The polymers were obtained in good yields and were soluble in common solvents to form transparent free-standing films with remarkably high toughness and thermal stability in the air, making them easily characterizable using different methods and techniques. Furthermore, the new aromatic FAVE polymers demonstrated high telechelic properties and possessed TFVE end groups that formed PFCB aryl ether polymers with a glass transition temperature between 149 °C to 174 °C when subjected to thermal chain extension. It was worth noting that the FAVE polymer contained a controllable terminal and enchained fluoroalkenylenes for potential latent reactivity.
In a nutshell, the step-growth polymerization of TFVE – BP monomer with PAH bisphenols to synthesize polycyclic aromatic core-containing FAVE telechelomers as well as their extended chain PFCB polymers were reported. The resulting aromatic FAVE telechelic polymers demonstrated exceptional solubility and thermal stability. Besides, they recorded all-time high glass transition temperature, thereby addressing the vital challenge reported in prior studies. The DSC revealed glass transition temperature values in the range 150 – 168 °C higher than those of previously reported polymers. In a statement to Advances in Engineering, Professor Dennis Smith explained, “Our semi-fluorinated telechelic polymers present unique opportunities for chain extension, functionalization, and thermal cross-linking for high temperature stability required for thin film electronics/photonics applications or the extreme environments demanded for gas separation membranes.”
Mukeba, K., Faradizaji, B., Shelar, K., Pittman, C., & Smith, D. (2020). Semi–fluorinated arylene vinylene ether (FAVE) telechelic polymers from polycyclic aromatic hydrocarbon bisphenols and trifluorovinyl aryl ethers. Polymer, 209, 122955.