Ultrasonic Micro Injection Molding of Poly(caprolactone)‐g‐Carbon Nanofibers Synthesized via Surface‐Initiated Polymerization

ABSTRACT Poly(caprolactone)‐grafted‐carbon nanofiber nanocomposites (PCL‐g‐CNF) were successfully synthesized through surface‐initiated ring‐opening polymerization (SI‐ROP) and subsequently processed by ultrasonic microinjection molding (UMIM). Carbon nanofibers were first functionalized with 2‐azidoethanol via [2 + 1] cycloaddition to introduce hydroxyl groups which were used as polymerization initiators. Raman and FTIR spectroscopy confirmed successful functionalization, while the reduced D/G intensity ratio (ID/IG) indicated preservation of the CNF graphitic structure. The extent of functionalization was determined by thermogravimetric analysis and reached a functionalization degree of 9.83 mg of 2‐hydroxyethyl groups per gram of CNF. SI‐ROP of ε‐caprolactone, catalyzed by Sn(Oct)₂, produced PCL‐g‐CNF nanocomposites containing 1, 3, and 5 wt% CNF with yields exceeding 95%. The nanocomposites were extruded, pelletized, and molded by UMIM into tensile specimens. The incorporation of 1 and 3 wt% CNF increased tensile strength by approximately 8% and 15%, respectively, while 5 wt% CNF increased Young's modulus by up to 53%. The thermal properties of the nanocomposites were not significantly affected by CNF incorporation or UMIM processing. These results demonstrate that SI‐ROP combined with UMIM is an effective strategy for producing mechanically reinforced PCL‐g‐CNF nanocomposites with potential applications in the fabrication of medical microdevices.