Characterization of High Polymerization Degree Ammonium Polyphosphate and Its Chain Structure by 31P NMR†

doi:10.7503/cjcu20180019

Abstract

Abstract:

Ammonium polyphosphate(APP) of high polymerization degree is an kind of important inorganic polymer flame retardant. Characterization of APP with high polymerization degree and its solution property are a meaningful topic. In this paper, quantitative liquid ³¹P nuclear magnetic resonance(NMR) is used to characterize APP polymerization degree and chain structures. A method of preparing aqueous APP solution by adding NaCl in water to auxiliary dissolving was established without resulting in APP degradation. The effects of different dissolution and testing temperature, and different NMR parameters were studied on the characterization of APP polymerization degree. Finally, The method to accurately characterize the APP polymerization degree was suggested based on liquid ³¹P NMR, that is: dissolving APP could be in water at 36 ℃ with auxi-liary NaCl salt, setting the temperature as 26 ℃ in ³¹P NMR testing. In this case, the good solubility of APP could be achieved, at same time no degradation of APP happened, the measurement of APP polymerization degree can be stable and accurate. The relaxation time(T₁) of terminal phosphorus(P_end) and middle phosphorus(P_mid) at different temperatures were determined by liquid ³¹P NMR, and the relationship between T₁ and temperature was found to be linear. The relaxation time parameter(D₁) in ³¹P NMR has a great effect on the characterization of APP polymerization degree, and the polymerization degree of APP will be inaccurate when the setting of D₁ could not meet the T₁ required for phosphorus. Characterization of APP chain structures by ³¹P NMR showed that there are three kinds of chemical environments in the terminal phosphorus of APP, that is the P connecting with two N $H 4 +$ , one N $H 4 +$ and one H⁺, and two H⁺, respectively. The NaCl concentration and testing temperature obviously influence the chemical shift of terminal phosphorus in the three chemical environments. It was verified that there was the middle phosphorus connecting with H⁺ in APP as well.

Key words: Ammonium polyphosphate, Polymerization degree, Chain structure, ³¹P nuclear magnetic resonance(NMR), Relaxation time

CLC Number:

O631.6

TrendMD:

LIU Yina,YANG Rongjie,LI Dinghua,LIANG Jiaxiang,HU Weiguo. Characterization of High Polymerization Degree Ammonium Polyphosphate and Its Chain Structure by ³¹P NMR^†[J]. Chem. J. Chinese Universities, 2018, 39(9): 2080.

Figures/Tables 18

Fig.1 31P NMR spectra of APP1# solution with 10 mg NaCl at 36 ℃(a) and NH4H2PO4(b)

Table 1 Characteristic phosphorous and polymerization degree(n) of APP1# at different testing conditions

Preparation conditon	Dissolving temperature/℃	Testing temperature/℃	P_free		P_end		P_mid		n
Preparation conditon	Dissolving temperature/℃	Testing temperature/℃	S_free	Ratio(%)	S_end	Ratio(%)	S_mid	Ratio(%)	n
NaCl auxiliary	26	26	6.69	0.64	2.62	0.25	1034.62	99.11	792
dissolving	36	26	6.77	0.61	2.46	0.22	1099.07	99.17	893
	36	36	6.92	0.66	2.71	0.26	1040.72	99.08	770
100 ℃ High temperature dissolving	100	26	7.21	7.20	3.83	3.82	989.34	98.89	519

Table 2 Polymerization degree of APP1# solution(10 mg NaCl) experiencing preservation for different time

Preservation temperature/℃	Polymerization degree, n
Preservation temperature/℃	2 h	5 h	8 h	11 h
26	792	782	764	754
36	770	773	513	460

Table 3 Repeatability of polymerization degree(n) of APP1# in 31P NMR tests

Testing number	n	Testing number	n
1	893	6	838
2	883	7	857
3	878	8	865
4	866	Average	865
5	840

Table 4 Characteristic phosphorus and polymerization degree of different APP samples with 10 mg NaCl auxiliary dissolving at 36 ℃

APP sample	S_free(%)	S_end(%)	S_mid(%)	n
5125#	0.52	0.17	98.64	1162
61231#	0.10	0.06	95.74	3193
714#	0.16	0.02	94.17	9419
715#	0.08	—	102.6	—

Fig.2 31P NMR spectra of 714#(a), 715#(b), 5125#(c) and 61231#(d) APP samples with 10 mg NaCl auxiliary dissolving at 36 ℃

Table 5 Characteristic phosphorus and polymerization degree of APP1# with 10 mg NaCl auxiliary dissolving at 36 ℃ at different relaxation time parameters

D₁/s	S_end	S_mid	n
1	1.68	957.85	1142
10	2.48	1058.56	855
20	2.54	1058.78	835
30	2.54	1058.77	835

Table 6 Relaxation time(T1) of phosphorus at different testing temperatures in 31P NMR for APP1# with 10 mg NaCl auxiliary dissolving at 36 ℃

Testing temperature/℃	T₁/s
Testing temperature/℃	P_free	P_end	P_mid
26	8.32	2.99	0.52
31	8.52	4.54	0.55
36	8.89	5.60	0.59
41	10.70	6.81	0.63
46	10.68	7.99	0.66
51	10.21	8.97	0.69
56	11.20	10.10	0.73

Fig.3 Relationship between temperature and relaxation time T1 of Pmid of APP1# with 10 mg NaCl auxiliary dissolving at 36 ℃

Fig.4 Phosphorous resonance peaks of APP1# with 10 mg NaCl auxiliary dissolving at 36 ℃ at different testing temperatures in 31P NMR (A) Pfree; (B) Pend; (C) Pmid. Temperature/℃: a. 26; b. 36; c. 46; d. 56.

Fig.5 Pend resonance peaks in three kinds of APP1# solutionsa. Ion exchange method; b. NaCl auxiliary dissolving at 36 ℃; c. dissolving at 100 ℃.

Table 7 Characteristic phosphorus in APP1# solution with acetic acid added

Acetic acid content(%)	P_freeratio(%)	P_end ratio(%)			Short chain P_midratio(%)	Long chain P_mid ratio(%)
Acetic acid content(%)	P_freeratio(%)	Peak 1	Peak 2	Peak 3	Short chain P_midratio(%)	Long chain P_mid ratio(%)
0	1.18	0.14	0.14	0.16	0.21	98.2
30	1.40	0.13	0.22	0.20	0.21	97.8
50	1.41	0.12	0.32	0.37	0.27	97.5

Fig.6 Pend resonance peaks in APP1# solutions with different acetic acid contentAcetic acid content(%): a. 0; b. 30; c. 50.

Fig.7 Pend structure of APP1# solution with 10 mg NaCl auxiliary dissolving at 36 ℃

Fig.8 Pend characteristics of of APP1# solutions with out NaCl dissolving at 100 ℃(a) and with 10 mg NaCl auxiliary dissolving at 36 ℃(b)

Fig.9 Pend characteristics of of APP1# solutions with different NaCl concentrationsNaCl concentration/(mg·mL-1): a. 0(100 ℃); b. 5; c. 10; d. 15; e. 20; f. 25.

Fig.10 Pend characteristics of APP1# solutions at different testing temperatures (A) NaCl auxiliary dissolving at 36 ℃; (B) high temperature dissolving at 100 ℃. Testing temperature/℃: a. 26; b. 31; c. 36; d. 41; e. 46; f. 51; g. 56.

Fig.11 Resonance peaks at different testing temperature of middle phosphorus Pmid in APP1# solution with 10 mg NaCl auxiliary dissolving at 36 ℃Testing temperature/℃: a. 26; b. 31; c. 36; d. 41; e. 46.

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Characterization of High Polymerization Degree Ammonium Polyphosphate and Its Chain Structure by ³¹P NMR^†

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