Investigating the Crystalline Structure of Poly(vinylidene fluoride) (PVDF) in PVDF/Silica Binary and PVDF/Poly(methyl methacrylate)/ Silica Ternary Hybrid Composites Using FTIR and Solid-State 19 F MAS NMR Spectroscopy Jin-Woo Park, Yun-Ah Seo, Il Kim, and Chang-Sik Ha* Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Korea Keitaro Aimi and Shinji Ando Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-Ku, Tokyo 152-8552, Japan Received September 19, 2003; Revised Manuscript Received November 12, 2003 ABSTRACT: We investigated the crystalline structures of poly(vinylidene fluoride) (PVDF) in PVDF/ silica (SiO 2) binary and PVDF/poly(methyl methacrylate) (PMMA)/SiO2 ternary hybrid composite films using infrared (IR) analysis and solid-state, high-speed magic-angle-spinning (MAS) 19 F NMR spectroscopy. These hybrid films were prepared by sol-gel processes. We used three different blending sequences to prepare the ternary hybrid composite films: (1) The “Type 1” hybrid was prepared from a one-pot mixture of PVDF, PMMA, and tetraethoxysilane (TEOS), the silica precursor, in dimethylacetamide (DMAc). (2) The “Type 2” hybrid composite was prepared by first forming a PVDF/silica hybrid and then mixing it with PMMA. (3) The “Type 3” hybrid composite was prepared by mixing a preformed PMMA/silica hybrid with PVDF. The crystallinity of the PVDF/SiO 2 hybrid composite films decreased upon increasing the silica content. By using the different methods to prepare the PVDF/PMMA/SiO2 ternary hybrid composite films, we were able to assign the γ-phase of PVDF crystals in the solid-state 19 F MAS NMR spectrum, which shows seven resonances that are attributable to an amorphous domain (-88 ppm), crystalline domains (-101.3, -93.7, -84.2, and -79.6 ppm), and regioirregular structures (-112.4 and -110.4 ppm). 19 F MAS NMR spectra of the Type 2 and Type 3 PVDF/PMMA/SiO2 hybrid composite films show two new resonances, assignable to the γ-phase at lower (-101.3 ppm) and higher (-84.2 ppm) frequencies, which show long 19 F spin-lattice relaxation times in the rotating frame (T1F F ) and chemical shifts that are significantly different from those of R- and -phases of the PVDF crystals. The disappearance of the R-phase of PVDF crystals in the Type 2 and Type 3 hybrid composite films can be explained by the large silica particles in the PVDF/PMMA matrix hindering crystallization of PVDF. Solid-state 19 F spin-lock NMR spectroscopy experiments also indicate significant differences exist between the values of T1F F of the crystalline and amorphous domains depending on the method of hybrid preparation. Introduction Poly(vinylidene fluoride) (PVDF) has remarkable electrical and mechanical properties. The discovery of its piezoelectrical 1 and pyroelectrical 2 properties has motivated most of its subsequent investigations. The poor optical clarity of PVDF, however, has limited its use as an optical material. In this regard, much em- phasis has been placed on blending PVDF with an amorphous polymer, especially poly(methyl methacry- late) (PMMA), to improve its optical properties. 3 PMMA and PVDF are molecularly miscible in the amorphous state and have been studied by thermal analysis, 4-6 dynamic mechanical spectroscopy, 5,7 X-ray scattering, 5,7 and Fourier transform IR (FTIR) spectros- copy. 8,9 Studies of PVDF/PMMA blends obtained either from the melt or from solution indicate that increasing the PMMA content results in an increase in the glass- transition temperature and a decrease in the melting and crystallization temperatures of PVDF. 6,10 PVDF crystallizes in five different polymorphs, the so-called R, , γ, δ, and ǫ forms. 11,12 The unit cell of the lattice of R-PVDF consists of two chains in tg+ tg- conformations. The dipole components are mutually antiparallel, and therefore, they neutralize each other; hence, R-PVDF exhibits nonpolar behavior. A polar analogue of R-PVDF is δ-PVDF, which is formed upon application of a high electric field. 13,14 PVDF polymorphs have been studied by a combination of differential scanning calorimetry (DSC), FTIR spectroscopy, and X-ray diffraction techniques. 15-17 Crystalline PVDF/ PMMA blends consist of crystalline PVDF phases and miscible PVDF/PMMA amorphous phases. The mor- phology that PVDF/PMMA blends adopt depends on the cooling rate and the blend composition; together, these parameters determine whether PVDF crystallizes or remains amorphous upon cooling from the melt. Solution-state 19 F NMR spectroscopy can provide insight into the chain microstructure of PVDF. 18 Re- cently, Holstein et al. 18 reported that after 1 H decou- pling, PVDF powder obtained from the melt displays a major signal at δ F )-91 ppm, two shoulders at relatively lower and higher frequencies, and a weak doublet at a significantly lower frequency. The authors demonstrated that discrimination in favor of the crys- talline domains is enhanced by a long spin-locking time. Solid-state spin-lock experiments show that significant differences exist in the 19 F spin-lattice relaxation times in the rotating frame (T 1F F ) between the immobile * To whom correspondence should be addressed. E-mail: csha@pusan.ac.kr. 429 Macromolecules 2004, 37, 429-436 10.1021/ma035402g CCC: $27.50 © 2004 American Chemical Society Published on Web 12/17/2003