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Poly(vinylidene fluoride)-b-poly(styrene) Block Copolymers by Iodine Transfer Polymerization (ITP):  Synthesis, Characterization, and Kinetics of ITP

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journal contribution
posted on 12.12.2006, 00:00 by David Valade, Cyrille Boyer, Bruno Ameduri, Bernard Boutevin
The syntheses of poly(vinylidene fluoride)-b-poly(styrene) (PVDF-b-PS) block copolymers, from the iodine transfer polymerization (ITP) of styrene, in the presence of PVDF−I, are presented. In a first step, considering that the radical polymerization of vinylidene fluoride can lead to two different isomeric oligomers, bearing either −CH2I or −CF2I end groups, the kinetics of ITP of styrene in the presence of two chain transfer agents, C6F13−CH2CF2−I and HCF2−CF2CH2−I, were achieved as model reactions. The characterization of sampled aliquots by 19F NMR spectroscopy could monitor the average degree of polymerization in number (DPn) vs styrene conversion (αStyrene). ITPs of styrene with both these chain transfer agents showed two opposite behaviors, also confirmed by MALDI−TOF spectroscopy and SEC chromatography. (i) on the one hand, in the presence of C6F13−CH2CF2−I, the controlled character of ITP of styrene was evidenced (a linear dependence of DPn vs αStyrene was observed), theoretical DPn values were close to those of the targeted ones, with low polydispersity indexes (PDI = 1.5) and the transfer constant value was assessed (CTr ≅ 1); (ii) on the other hand, using HCF2−CF2CH2−I as the chain transfer agent, ITP of styrene did not occur since only a direct initiation for the polymerization of styrene was noted, with DPn value higher than the targeted one and a broad polydispersity distribution (PDI > 2). In a second part, PVDF-b-PS block copolymers were synthesized via a two step-procedure, ITP of VDF in the presence of C6F13I as the chain transfer agent leading to C6F13(VDF)n−I oligomers and, subsequently, ITP of styrene using those latter oligomers as macromolecular chain transfer agents. These block copolymers were characterized by 19F and 1H NMR and MALDI−TOF spectroscopies, and by SEC chromatography. Their morphological and thermal properties were also studied by atomic force microscopy (AFM) and by differential scanning calorimetry (DSC), respectively.