Macromolecules,Vol.38.No.5,2005 Communications to the Editor 1543 GPC results morphologv [MI (mol/L) ISk (wt) M4 (kg/mol) SEM images appearances 26 6 163 0.6 333 me particles 0.6 a 898 6 42 Mon agitation at 30 T (PDMS- polar solve and PVDF is a Therefo ns)in the ring.CH (on proton)linked t r isa dipole interactio in the bacl gPEP四 th mplished at 80C with MWD standa graft degree =1.99 h NMr.IF NMR.and C NMR w the eetnmateiah F-g-PMV MA material P with a diffuse reflectance chain.Ho ver.C NMR an Results and Di n9 PMVE-M PMVE-NA S Char n the polytic for ain at o pe rbon ba oe(CO-phobic moiety).To ess PFOL (n a white F&-PM n the 19 mixture of PMVE-MA 72h.the graft chain atin at the F-PVE- ubility ofF-g-PMVE-MA in 1na1001 The rea ion t continued for 14 days to obtain VDF.and a mixture (see Supp ortingnf 4000 psi (27. MA revealed three characteristic peaks in the carbor in the FPMVE-MA OR COUE-PMVe-MA DF in t 101 85 single phas o th grafting in the the ous and pr ipi tted polymer mater POL and the ed sta ontrast in the sence of FPMVE-MA. stabl The d after 30 thests tha A of t mfor the OCE in the fluorinate &-PMVE 15 min.? kept the PVDtapolar solvent, and PVDF is a polar polymer. Therefore, there is a dipole interaction that occurs, causing arti￾ficial shoulders to appear on the high molecular weight end of the distribution. This interaction is eliminated by the addition of lithium bromide. The calibration was accomplished at 80 °C with narrow MWD standards of poly(methyl methacrylate) (PMMA) (Polymer Labora￾tories Ltd). The morphology of the PVDF product was determined using a Philips XL30 ESEM-FEG machine. 1H NMR, 19F NMR, and 13C NMR were performed for F-g-PMVE-MA and the starting materials using a Bruker 300 MHz spectrometer. Infrared analysis for F-g-PMVE-MA and the starting material PMVE-MA was carried out using a Perkin-Elmer system 2000 FTIR spectrometer equipped with a diffuse reflectance infra￾red spectroscopy (DRIFTS) attachment (Spectratech). Results and Discussion. a. Synthesis and Char￾acterization of F-g-PMVE-MA Stabilizer. The sta￾bilizer F-g-PMVE-MA was synthesized by a thermal ring-opening esterification reaction (Figure 1), leading to a fluorinated graft chain (CO2-philic segment) and a hydrocarbon backbone (CO2-phobic moiety). To obtain a high percentage of graft chain (formation of diester for every repeat unit of PMVE-MA), excess PFOL (mole ratio of PMVE-MA to PFOL is 1:5) was used. The mixture of PMVE-MA and PFOL formed a white slurry, indicating that PMVE-MA was not soluble in the PFOL. After 72 h, the mixture turned into a brown homoge￾neous solution, demonstrating that the F-g-PMVE-MA was soluble in the excess PFOL at elevated tempera￾ture. The reaction was continued for 14 days to obtain a fully grafted sample. The FTIR spectrum (see Supporting Information) obtained using DRIFTS for the starting material PMVE￾MA revealed three characteristic peaks in the carbonyl region.29 Following nucleophilic ring-opening in the presence of fluorinated alcohol (PFOL), the carbonyl region revealed only one distinct peak in a position typical of an ester (1738 cm-1). To determine the degree of grafting in the stabilizer, the 1H NMR spectra (see Supporting Information) for both the starting material PFOL and the ring-opened stabilizer product F-g-PMVE-MA were obtained in an octafluorotoluene/ CDCl3 (50/50, v/v) mixture. The 1H NMR spectrum (see Supporting Information) for the starting material PMVE￾MA was obtained in deuterated acetone. The integration of the peak at 4.5 ppm for the OCH2 in the fluorinated graft chains is 100 (two protons). The total integration of peaks in the range of 4.0-3.0 ppm for CH (two protons) in the ring, CH (one proton) linked to OCH3 in the backbone, and CH3 (three protons) is 151 (a total of six protons). Therefore, the graft degree of F-g-PMVE-MA is The molecular weight of F-g-PMVE-MA was esti￾mated as ca. 400 kg/mol, based on the Mn of PMVE-MA (79.8 kg/mol) and the degree of grafting (1.99) for F-g-PMVE-MA. If there is a partially grafted one-arm structure in F-g-PMVE-MA, carboxylic acid end groups should exist in the polymer chain. However, 13C NMR analysis (see Supporting Information) of the product F-g-PMVE-MA failed to detect the presence of a carboxylic acid group in the polymer chain at 175 and 177 ppm, which are characteristic for carboxylic acid groups. Moreover, 19F NMR (see Supporting Information) was also per￾formed for F-g-PMVE-MA product and the starting material PFOL; typical broader peaks were observed for F-g-PMVE-MA copolymer. However, it is impossible to obtain the graft degree from the 19F NMR spectrum of F-g-PMVE-MA because there are no other characteristic fluorine atoms in the product apart from the fluorinated graft chain. The solubility of F-g-PMVE-MA in a mixture of VDF and CO2 was examined in a 100 mL cylindrically shaped view cell. The stabilizer was found to be miscible in pure scCO2, VDF, and a mixture of VDF/scCO2 at the reaction conditions (5 wt % of F-g-PMVE-MA relative to VDF monomer, 55 °C, 4000 psi (27.2 MPa)). b. Dispersion Polymerization of VDF in scCO2 in the Presence of F-g-PMVE-MA. Observations in View Cell. The polymerizations of VDF in the presence and absence of F-g-PMVE-MA were observed in the view cell. The reactions started as a single phase. In the absence of stabilizers, the system became heteroge￾neous, and precipitated polymer particles were observed immediately after the injection of the initiator solution.27 By contrast, in the presence of F-g-PMVE-MA, a stable milky emulsion formed after the initiator solution was charged, and after 30 min polymer particles were observed. This suggests that F-g-PMVE-MA acts as a stabilizer in the polymerization of VDF in scCO2. F-g-PMVE-MA showed better stabilization than PDMS￾ma; the latter kept the PVDF emulsion stable for ca. 15 min.27 Table 1. Experimental Data for the Dispersion Polymerization of Vinylidene Fluoride (VDF) Using the Fluorinated Graft Poly(methyl vinyl ether-alt-maleic anhydride) (F-g-PMVE-MA) Stabilizera GPC results morphology entry [M]b (mol/L) [S]c (wt %) monomer conversion (%) Mwd (kg/mol) PDIe SEM imagesf appearanceg 1 2.6 13.5 49 1.5 agglomerated fine powder 2 2.6 0.6 17.0 163 2.7 agglomerated fine powder 3 2.6 2.0 14.1 84 1.9 agglomerated fine powder 4h 2.6 0.6 5.0 180 2.8 agglomerated, some particles fine powder 5 9.8 4.0 216 2.3 agglomerated spongy solid 6 9.8 0.6 5.7 385 3.2 well-defined particles fine powder 7 9.8 2.0 3.5 183 4.3 well-defined particles fine powder 8i 9.8 0.6 4.0 243 2.5 particles coarse powder 9j 9.8 0.6 14.1 350 3.7 agglomerated, some particles fine powder 10j 9.8 5.0 14.2 130 3.9 well-defined particles fine powder a Reactions were carried out at 55 °C, initial pressure P0 4000 psi, initiator concentration [I] 1.0 mmol/L, agitation at 300 rpm, solid contents of final product in the autoclave ∼33 g/L. b Monomer concentration. c F-g-PMVE-MA concentration, percentage of weight/weight relative to VDF monomer. d Weight-average molecular weight. e Polydispersity. f Determined by scanning electron microscopy (SEM) analysis. g Visual observation. h Solid contents 8.3 g/L. i Poly(dimethylsiloxane) monomethacrylate macromonomer (PDMS-ma) was used as the stabilizer. j Solid contents 89 g/L. graft degree ) 100/2 151/6 ) 1.99 Macromolecules, Vol. 38, No. 5, 2005 Communications to the Editor 1543