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Summary:In this work an investigation of the chain end groups produced in the free radical copolymerization of vinilydene fluoride (VDF) and hexafluoropropylene (HFP) is performed. Type and amount of chain end groups are evaluated by a meticulous analytical characterization of VDF/HFP copolymer. At first pulsed gradient spin-echo nuclear magnetic resonance (spin-echo NMR) is used to identify all the chain end groups also at very low concentration (equal to 0.1 mmol Á Kg À1). The instrument sensitivity is increased of an order of magnitude in comparison with the traditional NMR. Moreover potentiometric titration and ion chromatography (IC) are also used to study the chain end groups and, as a consequence, the nature and the amount of the acidity showed by the polymer chains. In details two intensity of acidity are detected by potentiometric titration, namely strong and weak. The strong acidity is associated to the presence of residual surfactant and can be removed washing the polymer, while the weak acidity is due to free molecules of fluoride acid (HF). The standard ion chromatography facility is properly modified to quantify the fluoride in the polymer matrix without any pre extraction in water. Thanks to this the HF concentration in the polymer is evaluated with high accuracy. A detailed kinetic scheme for the VDF/HFP polymerization is also proposed taking into account all the findings obtained studying the chain end groups.

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A 19F, 'H, and 13C NMR structural study is presented for a selected sample of a perfluoropolyether macrodiol (ZDOL), as well as one of its copolymers with formaldehyde. From their l9F spectra the average composition of perfluorooxymethylene and -0xyethylene units along the chain is clearly evaluated; the end group analysis allows the calculation of the number average molecular weight and functionality of samples of the macrodiol and, to a first approximation, those of the copolymer. The lH and 13C NMR spectra are studied also in order to clarify the nature of the bridging units in the copolymer between perfluoropolyether segments; in particular the absence of oligo(oxymethy1ene) sequences -(OCH&-is verified. A comparison is also made with the spectroscopic data of a corresponding low molecular weight compound, which was prepared by reaction of trifluoroethanol with paraformaldehyde. For that reference compound the heteronuclear shift correlation 2D NMR spectrum is also reported and discussed.

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