Synthesis, characterization, and properties of chain terminated polyhedral oligomeric silsesquioxane-functionalized perfluorocyclobutyl aryl ether copolymers

A new class of perfluorocyclobutyl (PFCB) polymers covalently functionalized with polyhedral oligomeric silsesquioxane (POSS) is presented. Three discreetly functionalized POSS monomers possessing thermally reactive trifluorovinyl aryl ether (TFVE) were prepared in good yields. The POSS TFVE monomers were prepared by initial corner-capping of cyclopentyl (-C5H9), iso-butyl (-CH2CH(CH3)(2)), or trifluoropropyl (-CH2CH2CF3) functionalized POSS trisilanols with acetoxyethyltrichlorosilane followed by sequential acid-catalyzed deprotection and coupling with 4-(trifluorovinyloxy)benzoic acid. TFVE-functionalized POSS monomers were thermally polymerized with 4,4'-bis(4-trifluorovinyloxy)biphenyl or 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomers via a condensate-free, [2+2] step-growth polymerization. The polymerization afforded solution processable PFCB polymers with POSS macromer installed on the polymer chain ends. POSS monomers and their corresponding copolymers were characterized by H-1, C-13, F-19, and Si-29 NNIR, GPC, ATR-FTIR, and elemental combustion analysis. GPC trace analysis showed agreeable number-average molecular weight for various weight percent of cyclopentyl or iso-butyl and trifluoropropyl chain terminated POSS PFCB copolymers. DSC analysis showed the introduction of increasing POSS weight percent in the endcapped PFC13 copolyrners lowers the glass transition temperatures as high as 31 degrees C. On the other hand, the trifluoropropyl POSS endcapped PFC13 polymer glass transition temperature was unaffected when copolymerized with the more fluorinated 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomer. TGA analysis of POSS PFC13 copolymers showed step-wise decomposition of copolymers resulting from the initial degradation of the POSS cages at 297-355 degrees C in nitrogen and air which was confirmed by pyrolysis coupled with GC-NIS. This initial weight loss was proportional to the weight percent of POSS incorporated into the polymer. The balance of decomposition was observed at 450-563 degrees C in nitrogen and air which is higher than the PFCB homopolymers in most cases. Polymer surface characterization was performed on spin cast transparent, flexible films. These composite films exhibited good POSS dispersion within the matrix PFC13 polymer as was shown by TEM analysis. (c) 2007 Elsevier Ltd. All rights reserved.