Synthesis, Characterization Of A HBPE-b-PMMA Block Copolymer And Its Effection In Noncovalently Functionalizing MWCNTs

Noncovalent functionalization of carbon nanotubes (CNTs) with polymersto improve its dispersibility in polymer matrix and interfacial compatibility withpolymer matrix is of great importance for achieving advanced polymer/CNTsnanocomposites of better performance. Herein, a series of hyperbrancedpolyethylene-b-poly (methyl methacrylate) block copolymer (HBPE-b-PMMA)samples were successfully synthesized via a tander synthesis strategy with afunctionalized Pd-Diimine catalyst with acyl bromide group. The noncovalentfunctionalization of multi-walled carbon nanotubes (MWCNTs) with thesynthesized HBPE-b-PMMA block coplymer in organic solvents was carriedout to give a MWCNTs@HBPE-b-PMMA composite and a series of PMMA/MWCNTs@HBPE-b-PMMA nanocomposites were rendered by adding theMWCNTs@HBPE-b-PMMA composite powder into PMMA matrix by meltingand solution blending process, respectively. Characterizations on the structuresand performance for the nanocomposites were performed.(1) A composite Pd-Diimine catalyst functionalized with an acyl bromidegroup was first synthesized via the reaction between the acetonitrile Pd-Diimineand acryloyl group from BIEA. Then the synthesized Pd-Diimine catalyst wasused for catalyzing ethylene polymerization to give a HBPE-ATRP, whichcontains an ATRP initiating group as a end-group and subsequently the ATRP ofMMA with the HBPE-ATRP was performed to render the HBPE-b-PMMAblock copolymer.1HNMR, TGA, FTIR and DSC indicated that the copolymerHBPE-b-PMMA possesses typical block structure composed of a HBPE andPMMA block. The HBPE block was testified to have typical hyperbranchedchain topology with a branch density of85-90/1000C based on1H NMR spectra. It is also found that the composition of the block copolymer could beadjusted by controlling polymerization time.(2) Noncovalent functionalization of MWCNTs with the as-synthesizedHBPE-b-PMMA block copolymer was performed in organic solvents and thedispersibility of MWCNTs in organic solvents and interactions between theMWCNTs surface with polymer. UV-Vis, HRTEM, TGA and FTIR etc indicatedthat the HBPE-b-PMMA block copolymer exhibits a better ability insolubilizing MWCNTs in THF, chloroform and toluene. Especially, as comparedto the HBPE homopolymer, the HBPE-b-PMMA block coploymer was found tohave significantly improved ability in solubilizing MWCNTs in toluene,probably due to the introduction of PMMA block. Also the interactions betweenthe MWCNTs surface with the copolymer was testified by TGA and FTIRanalysis, which could be ascribed to the noncovalent nonspecific CH-πinteractions. It is found that the PMMA block from the HBPE-b-PMMAcopolymer could be attached noncovalently to MWCNTs surface by means ofthe above interactions between MWCNTs surface and HBPE block.(3) A series of PMMA/MWCNTs@HBPE-b-PMMA nanocomposites weresuccessfully achieved by introducing the MWCNTs@HBPE-b-PMMAcomposite into PMMA matrix via melt and solution blending process,respectively. The MWCNTs@HBPE-b-PMMA composite could be obtained bynoncovalent functionalization of MWCNTs with the HBPE-b-PMMA blockcopolymer in organic solvents. TEM, SEM, DMA, DSC and conductivity testindicated that the dispersibility of the MWCNTs in PMMA matrix could beimproved to an extent by functionalization with the HBPE-b-PMMA copolymerand the PMMA/MWCNTs@HBPE-b-PMMA nanocomposite with enhancedperformace, including mechanical, thermal and electrical properties, could beachieved.