Molecular motion and hydrogen bond of long-chain PA1212 elastomer under thermal field

doi:10.11949/0438-1157.20211166

Abstract

Abstract:

Thermoplastic polyamide elastomers (TPAEs) have attracted extensive attention in both academia and industry due to their excellent resilience and carbon dioxide permeability. Hydrogen bond has significant influence on the phase-separated structure and mechanical properties of polyamide elastomers. In this work, a TPAE comprised of long-chain PA1212 and poly(propylene glycol)-poly(ethylene glycol)-poly(propylene glycol) was used to investigate its molecular motion and hydrogen bond during heating process by in situ FT-IR, 2D correlation FT-IR, in situ WAXD and molecular dynamic simulation. Upon heating, the mobility of the molecular chain is enhanced and the hydrogen bond of the system is weakened. The hydrogen bond between C—O—C and N—H dissociates prior to that of PA1212, whose ordered hydrogen bond transits to disordered hydrogen bond. The in situ WAXD results show that d₁₀₀ is more sensitive to heat than d_010/110 and that these two lattice distances are equal finally, where the Brill transition occurs. The WAXD results suggest that the dissociation of the hydrogen bond is promoted by heating. Molecular dynamic simulation verified the results by FT-IR. The simulation results show that hydrogen bond decreases with the increasing of its bond length during heating and that the density of hydrogen bond in the PA1212 domain is higher than that in polyether. The hydrogen bond of polyether chains reduces before that of PA1212.

Key words: long-chain polyamide elastomer, FT-IR, in situ WAXD, molecular simulation, hydrogen bond

摘要：

热塑性聚酰胺弹性体因其优异的回弹性和二氧化碳选择透过性而受到广泛关注，而材料内氢键作用对弹性体相分离行为和力学性能有决定性影响。基于PA1212聚醚型弹性体，即PA1212为硬段，聚丙二醇-聚乙二醇-聚丙二醇三嵌段共聚醚为软段，通过原位红外光谱(FT-IR)、二维相关红外光谱(2D FT-IR)、原位广角X射线衍射(WAXD)分析，结合分子动力学模拟，研究了PA1212弹性体分子链运动行为和氢键解离方式。弹性体受热导致分子链运动能力增强，体系中氢键作用减弱，有序氢键(ordered hydrogen bond)向无序氢键(disordered hydrogen bond)转变，其中软段C—O—C和N—H形成的氢键优先解离，而硬段微区PA1212中C $? ?????$ O和N—H形成的氢键解离滞后；相比形成氢键的分子链间距d₁₀₀，氢键面间距d_010/110受热变化更敏感，最终分子链间距和氢键面间距近似相等，即发生Brill转变，WAXD结果表明，加热促进了氢键的解离。分子动力学模拟结果验证了红外分析结果，氢键键长增加，氢键作用减弱，PA1212微区的氢键密度和强度总是大于聚醚微区，聚醚微区的氢键密度受加热影响下降更快。

关键词: 长碳链聚酰胺弹性体, 红外光谱, 原位WAXD, 分子模拟, 氢键

CLC Number:

TQ 323.6

Jie JIANG, Qiuyu TANG, Ling ZHAO, Zhenhao XI, Weikang YUAN. Molecular motion and hydrogen bond of long-chain PA1212 elastomer under thermal field[J]. CIESC Journal, 2022, 73(1): 425-433.

蒋杰, 唐秋雨, 赵玲, 奚桢浩, 袁渭康. 长碳链PA1212弹性体在热环境中的分子运动和氢键研究[J]. 化工学报, 2022, 73(1): 425-433.

Figures/Tables 8

Fig.1 In situ FT-IR spectra of PA1212-co-PEG elastomer during the heating process from 30℃ to 205℃ (the temperature interval is 5℃)

Table 1 Band assignments of FT-IR spectra for PA1212-co-PEG elastomer

波数(cm^-1)	峰的归属及所属软硬段相	文献
3319	ν(N—H, disordered bonded),酰胺A无序N—H伸缩振动，硬段	[23-24]
3309	ν(N—H, ordered bonded),酰胺A有序N—H伸缩振动，硬段	[13，23-24]
2920	ν_as(—CH₂—),CH₂反对称伸缩振动，硬段和软段	[13，24]
2851	ν(—CH₂—),CH₂对称伸缩振动，硬段和软段	[13，24]
1678	ν(C $? ?????$ O, free),酰胺Ⅰ的“自由”C $? ?????$ O伸缩振动，硬段	[24]
1650	ν(C $? ?????$ O, disordered bonded),酰胺Ⅰ的无序氢键键合的C $? ?????$ O伸缩振动，硬段	[24]
1633	ν(C $? ?????$ O, ordered bonded),酰胺Ⅰ的有序氢键键合的C $? ?????$ O伸缩振动，硬段	[13，24]
1536	δ(N—H, bonded),酰胺Ⅱ的有序氢键的N—H弯曲振动,硬段	[13]
1507	δ(N—H, free),酰胺Ⅱ的“自由”的N—H弯曲振动,硬段	[24]
1350	ω(—O—CH₂—),C—H摇摆振动，软段	[13，24]
1107	ν_as(C—O—C),C—O—C反对称振动，软段	[13，24]
950	Amide Ⅳ, 硬段α phase	[13，22，25-27]

Table 1 Band assignments of FT-IR spectra for PA1212-co-PEG elastomer

波数(cm^-1)	峰的归属及所属软硬段相	文献
3319	ν(N—H, disordered bonded),酰胺A无序N—H伸缩振动，硬段	[23-24]
3309	ν(N—H, ordered bonded),酰胺A有序N—H伸缩振动，硬段	[13，23-24]
2920	ν_as(—CH₂—),CH₂反对称伸缩振动，硬段和软段	[13，24]
2851	ν(—CH₂—),CH₂对称伸缩振动，硬段和软段	[13，24]
1678	ν(C $? ?????$ O, free),酰胺Ⅰ的“自由”C $? ?????$ O伸缩振动，硬段	[24]
1650	ν(C $? ?????$ O, disordered bonded),酰胺Ⅰ的无序氢键键合的C $? ?????$ O伸缩振动，硬段	[24]
1633	ν(C $? ?????$ O, ordered bonded),酰胺Ⅰ的有序氢键键合的C $? ?????$ O伸缩振动，硬段	[13，24]
1536	δ(N—H, bonded),酰胺Ⅱ的有序氢键的N—H弯曲振动,硬段	[13]
1507	δ(N—H, free),酰胺Ⅱ的“自由”的N—H弯曲振动,硬段	[24]
1350	ω(—O—CH₂—),C—H摇摆振动，软段	[13，24]
1107	ν_as(C—O—C),C—O—C反对称振动，软段	[13，24]
950	Amide Ⅳ, 硬段α phase	[13，22，25-27]

Fig.2 2D correlation spectra of PA1212-co-PEG elastomer in different regions

Fig.3 Hydrogen bond distribution of PA1212-co-PEG elastomer at different temperature

Fig.4 Density of hydrogen bonds of PA1212-co-PEG elastomer at different temperature

Fig.5 Length distribution of hydrogen bonds of PA1212-co-PEG elastomer at different temperature

Fig.6 In situ WAXD patterns of PA1212-co-PEG sample on heating from 25℃ to 200℃

Fig.7 Variation of diffraction spacing of reflection plane as a function of temperature

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