Molecular-Mass and Its Distribution Analysis of n-Alkylated Poly（p-phenylene terephthamide）

doi:10.19894/j.issn.1000-0518.220366

Chinese Journal of Applied Chemistry ›› 2023, Vol. 40 ›› Issue (6): 853-859.DOI: 10.19894/j.issn.1000-0518.220366

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Molecular-Mass and Its Distribution Analysis of n-Alkylated Poly（p-phenylene terephthamide）

Lin-Tao YANG¹^,², Mao LI¹^,²()

^1.State Key Laboratory of Polymer Physics and Chemistry，Changchun Institute of Applied Chemistry，Chinese Academy of Sciences，Changchun 130022，China
^2.University of Science and Technology of China，Hefei 230026，China

Received:2022-11-11 Accepted:2023-04-05 Published:2023-06-01 Online:2023-06-27
Contact: Mao LI
About author:limao@ciac.ac.cn

Abstract

Abstract:

The molecular-mass and its distribution of poly（p-phenylene terephthamide）（PPTA） directly affect the spinning performance of aramid fiber. The hydrogen bonds between PPTA backbones make PPTA insoluble in common organic solvents such as chloroform， which cannot meet the test requirements of proton magnetic resonance， mass spectroscopy， and gel permeation chromatography （GPC）. The soluble n-alkylated PPTAs are obtained by grafting a series of alkyl chains with different lengths and degrees of supersede on the N-position of PPTA backbones. The influence of alkyl lengths and alkylation conditions on relative molecular-mass and its distribution are further studied. Ethyl alkylated PPTA with the highest substitution degree of 98.6% enables to provide the lowest polydispersion coefficient and the more accurate molecular-mass distribution. The relationship between the average relative molecular-mass and the intrinsic viscosity in a specific viscosity range is obtained according to the Makhovink equation ［η］=9.96×10^-3 $M w 1.08$ . These results could be utilized for optimizing PPTA synthesis and improving the performance of aramid fiber.

Key words: Poly（p-phenylene terephthamide）, Aramid fiber, Alkylation, Molecular-mass distribution

CLC Number:

O631.6

Lin-Tao YANG, Mao LI. Molecular-Mass and Its Distribution Analysis of n-Alkylated Poly（p-phenylene terephthamide）[J]. Chinese Journal of Applied Chemistry, 2023, 40(6): 853-859.

Figures/Tables 7

Fig.1 （A） Infrared absorption spectra of PPTA and n-alkylated PPTA：（a） PPTA，（b） n-decyl PPTA，（c） n-hexyl PPTA，（d） n-butyl PPTA，（e） ethyl PPTA；（B） 1H NMR spectrum of n-butyl PPTA

Table 1 Degree of different n-alkylated PPTA

	Alkyl chains	DS/%	η_inh/（dL·g^-1）
1	—	—	2.82
2	Ethyl	98.6	1.02
3	n-Butyl	96.2	1.06
4	n-Hexyl	93.5	1.06
5	n-Decyl	91.2	1.09
6	n-Hexadecyl	84.9	1.14

Table 2 The relatrve molecular-mass and its distribution of ethyl PPTA （ηinh=3.3） with different substitution degrees

	DS/%	M_n/（g·mol^-1）	M_w/（g·mol^-1）	PDI
1	43.6	14 100	31 200	2.21
2	59.9	12 800	25 300	1.98
3	82.3	12 000	20 800	1.73
4	98.6	11 900	19 900	1.68

Fig.2 （A） The intrinsic viscosity of different PPTA：（a） η=1.23，（b） η=1.68，（c） η=2.27，（d） η=2.82，（e） η=3.68；（B） The relationship between the molecular-mass of PPTA and the intrinsic viscosity

Table 3 The relatrve molecular-mass and distribution of ethyl PPTA with different viscosity

	η_inh/（dL·g^-1）	M_n	M_w	［η］/（mL·g^-1）
1	1.25	3 960	6 260	122
2	1.68	5 350	8 620	164
3	2.27	9 090	14 600	297
4	2.82	10 600	18 200	369
5	3.68	12 500	22 800	507

Fig.3 （A） Comparison of GPC results of n-alkylated PPTA：（a） ethyl PPTA，（b） n-butyl PPTA，（c） n-hexyl PPTA，（d） n-decyl PPTA，（e） n-hexadecyl PPTA；（B） Comparison of GPC results of PPTA with different degrees of substitution：（a） 43%，（b） 59%，（c） 82%，（d） 96%

Table 4 The relative molecular-mass and distribution of n-alkylated PPTA with different lengths of alkyl chains

	Alkyl chain	M_n	M_w	PDI
1	Ethyl	10 500	18 200	1.72
2	n-Butyl	10 600	18 200	1.72
3	n-Hexyl	10 600	18 400	1.74
4	n-Decyl	10 700	18 600	1.75
5	n-Hexadecyl	10 800	19 400	1.81

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Molecular-Mass and Its Distribution Analysis of n-Alkylated Poly（p-phenylene terephthamide）

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