Solid-state 19F MAS and 1H → 19F CP/MAS NMR study of the phase transition behavior of vinylidene fluoride-trifluoroethylene copolymers:: 1.: Uniaxially drawn films of VDF 75% copolymer
Solid-state 19F MAS and 1H → 19F CP/MAS NMR study of the phase transition behavior of vinylidene fluoride-trifluoroethylene copolymers:: 1.: Uniaxially drawn films of VDF 75% copolymer
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DOI：
10.1016/j.polymer.2004.01.005
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发表时间：
2004-03-29
期刊：
影响因子：
4.6
通讯作者：
Harris, RK
中科院分区：
文献类型：
--
作者：
Aimi, K;Ando, S;Harris, RK
采用变温（VT）固态F-19 MAS和H-1—> F-19 CP/MAS NMR谱分析了偏氟乙烯（VDF）和三氟乙烯（TrFE）共聚物P（VDF75/TrFE25）铁电-准电相变引起的相结构和分子迁移率的变化。在43 ~ 92°c温度范围内，VDF链序列的CF2信号和VDF- trfe序列首尾联动处的CHF信号频率变化较大，而VDF- trfe首尾联动处的CHF信号在92°c温度范围内没有变化。因此，VT F-19 MAS光谱显示，VDF-TrFE从头到尾序列是聚合物链中最稳定的部分，在加热时的相变温度（居里温度，T-c）低于反式-间扭构象交换运动。然而，包括TrFE单元在内的所有链序列都发生构象。在T-c左右交换。在F-19光谱形状中可以清楚地识别出相变行为，其中铁电不动相的宽信号在115°和119°之间消失。此外，所有峰的T-1rho(F)在119°c时减小到一个独特的值（约20 ms），表明在该温度下发生了均匀的分子运动并伴有完整的链旋转。在环境温度下，拟电相中（119度）所有峰的T-1rho(F)（约20 ms）明显大于非晶畴（< 4 ms），这支持了聚合物链在拟电相中围绕链轴的旋转运动受到限制的结论。当温度从119℃降至85℃时，VDF序列中CF2信号的低频位移，伴随着T-1(F)和T-1rho(F)的轻微下降，证实了近电相中间扭构象的逐渐减少。在85 ~ 77°c之间观察到相变，其中准电相特征信号消失，各峰的T-1rho(F)值迅速升高，77°c处突然出现宽晶信号。(C) 2004年Elsevier Ltd.出版
The changes in the phase structures and molecular mobility caused by the ferroelectric-paraelectric phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer, P(VDF75/TrFE25), were analyzed using variable temperature (VT) solid-state F-19 MAS and H-1 --> F-19 CP/MAS NMR spectroscopy. The CF2 signal of the VDF chain sequence and the CHF signal at the head-to-head linkage of VDF-TrFE sequence showed higher frequency shift in the temperature range 43-92degreesC, whereas no change was found for the CHF signal at the head-to-tail linkage of VDF-TrFE up to 92degreesC. Hence, VT F-19 MAS spectra revealed that the VDF-TrFE head-to-tail sequence is the most stable part in polymer chains against trans-gauche conformational exchange motions below the phase transition temperature (Curie temperature, T-c) on heating. However, all chain sequences including TrFE units undergo conformational. exchange at around T-c. The phase transition behavior is clearly recognized in the F-19 spectral shapes, in which the broad signals of the ferroelectric immobile phase disappeared between 115 and 119degreesC. In addition, T-1rho(F) for all peaks decreased to a unique value (ca. 20 ms) at 119degreesC, indicating that uniform molecular motion accompanied by a full chain rotation occurred at the temperature. The significantly longer T-1rho(F) for all peaks (ca. 20 ms) in the paraelectric phase (119degreesC) than that in the amorphous domain ( < 4 ms) at ambient temperature supports the conclusion that there is restricted rotational motion of polymer chains around the chain axis in the paraelectric phase. On cooling from 119 to 85degreesC, a gradual decrease in gauche conformers in the paraelectric phase was confirmed by the low-frequency displacement of CF2 signals in VDF sequences accompanied by slight decreases in T-1(F) and T-1rho(F). The phase transition was observed between 85 and 77degreesC on cooling, in which the characteristic signals of the paraelectric phase disappeared, the T-1rho(F) values of all peaks quickly increased, and the broad crystalline signals abruptly appeared at 77degreesC. (C) 2004 Published by Elsevier Ltd.