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首页> 外文期刊>Macromolecular symposia >Comprehensive Characterization of Chain End Groups of Vinylidene Fluoride Based Polymers
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Comprehensive Characterization of Chain End Groups of Vinylidene Fluoride Based Polymers

机译：偏二氟乙烯类聚合物链端基的综合表征

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摘要

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 · Kg~(-1)). 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.
机译：在这项工作中，进行了对氟乙烯基芳烃（VDF）和六氟丙烯（HFP）的自由基共聚过程中产生的链端基的研究。链端基的类型和数量通过VDF / HFP共聚物的精细分析表征进行评估。首先，使用脉冲梯度自旋回波核磁共振（spin-echo NMR）来鉴定所有链端基团，而且浓度也很低（等于0.1 mmol·Kg〜（-1））。与传统NMR相比，仪器灵敏度提高了一个数量级。此外，电位滴定法和离子色谱法（IC）也用于研究链端基，结果是研究了聚合物链显示出的酸度的性质和数量。详细地，通过电位滴定法检测到两种酸度，即强和弱。强酸度与残留表面活性剂的存在有关，可以通过洗涤聚合物除去，而弱酸度是由于氟酸（HF）的自由分子引起的。对标准离子色谱仪设备进行了适当的修改以定量聚合物基质中的氟化物，而无需在水中进行任何预萃取。因此，可以高精度评估聚合物中的HF浓度。考虑到研究链端基的所有发现，还提出了用于VDF / HFP聚合的详细动力学方案。

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