Solid-state NMR Study on the Dynamics of Thermo-sensitive Cellulose/Poly(N-isopropylacrylamide) Composite Hydrogel†

doi:10.7503/cjcu20150174

Abstract

Abstract:

The cellulose/poly(N-isopropylacrylamide)(PNIPAM) composite thermo-sensitive hydrogel was prepared by interpenetrating polymer network(IPN) approach. Various solid-state nuclear magnetic resonance(NMR) methods including ¹³C cross polarization/magic angle spinning nuclear magnetic resonance(CP/MAS NMR), ¹³C quantitative cross polarization(QCP) NMR, static ¹H NMR and ¹H filtering-spin diffusion NMR experiments were performed to analyze the structure, content, property and dynamics of the composite thermo-sensitive hydrogel. The results show that the cellulose/PNIPAM composite hydrogels have obvious temperature sensitivity. Cellulose molecules are relatively rigid while PNIPAM molecules are flexible. The space between cellulose and PNIPAM chains are very close.

Key words: Solid-state NMR, Thermo-sensitive hydrogel, Cellulose, Poly(N-isopropylacrylamide), Molecular dynamics

CLC Number:

O631

TrendMD:

WANG Min, GE Hao, SONG Jianhui, XU Min. Solid-state NMR Study on the Dynamics of Thermo-sensitive Cellulose/Poly(N-isopropylacrylamide) Composite Hydrogel^†[J]. Chem. J. Chinese Universities, 2015, 36(7): 1422.

Figures/Tables 17

Scheme 1 Fabrication process of CL/PNIPAM composite hydrogel

Fig.1 SEM images of net cellulose gel(A) and CL/PNIPAM composite gel(B)

Fig.2 DSC thermogram curves of LCST of net cellulose hydrogel and CL/PNIPAM compositesa. Cellulose; b. 2%C/PNP; c. 4%C/PNP; d. 6%C/PNP; e. 8%C/PNP.

Fig.3 Temperature responsive on swelling behavior of net cellulose hydrogel(a) and cell/PNIPAM composite hydrogel(b)

Fig.4 Solid-state 13C CP/MAS NMR spectra of neat PNIPAM(a), neat cellulose(b) and CL/PNIPAM composite polymer(c)The peaks labeled with “*” are sidebands.

Fig.5 Experimental results of the normalized CP and CDP dynamics from C1'—C6' of CL/PNIPAM gel

Table 1 Quantitative results of cellulose/PNIPAM from QCP NMR*

Sample	t_CDP/μs	η(C5,6)	η(C1'—C6')	n(AGU)/n(NIPAM)
2%C/PNP	200	1.28	1.27	0.96
4%C/PNP	200	1.83	1.85	0.80
6%C/PNP	100	1.72	2.23	0.73
	200	2.46	2.33	0.72
8%C/PNP	200	1.40	1.37	0.69
10%C/PNP	200	1.90	1.83	0.67

Fig.6 Static 1H NMR spectra of net cellulose gel(a) and CL/PNIPAM composite gel(b) at 298 K

Fig.7 Standard 1H NMR spectrum of PNIPAM

Fig.8 Static1H NMR spectra signal belonging of CL/PNIPAM composite gel at 298 K

Table 2 Nonlinear least squares fitting(NLSF)results of static 1H NMR spectra of CL/PNIPAM composite gel*

Label of peak	δ	Fitting area(%)	Attribution	Label of peak	δ	Fitting area(%)	Attribution
1	-0.30	1.65	Few impurity	5	3.83	7.56	b
2	1.05	46.21	a	6	4.78	5.54	H₂O
3	1.95	25.36	c,d	7	5.65	5.77	CL
4	2.80	7.91	CL

Fig.9 Static 1H NMR spectra of net cellulose gel(A) and CL/PNIPAM composite gel(B) at different temperatures

Fig.10 Static 1H NMR spectra of CL/PNIPAM composite gel fitting with Gauss(a) and Lorentz(b)

Table 3 Gauss and Lorentz fitting results of static 1H NMR spectra of CL/PNIPAM gel at different temperature*

Temperature/K	Δδ		Fitting area(%)
Temperature/K	Wide peak	Narrow peak	Wide peak	Narrow peak
298	145.94	3.62	26.82	73.18
304	142.68	3.63	27.20	72.80
306	115.08	4.60	41.65	58.35
307	100.98	6.50	56.52	43.48
308	93.85	6.91	63.35	36.65
310	88.46	6.60	68.28	31.72
312	85.39	6.26	70.70	29.30

Fig.11 Data processing results of static 1H NMR spectrum of CL/PNIPAM composite gel at different temperature

Fig.12 1H NMR spectra of CL/PNIPAM composite gel before filtering(a), after filtering(b) and after filtering-spin diffusion(c) at 298 K

Table 4 Static 1H NMR spectra of CL/PNIPAM gel at different temperatures before and after spin diffusion intensity ratio

Temperature/K	298	302	304	305	306	307	308	310
Intensity ratio	4.5	4.2	4.1	4.4	5.5	4	3.8	3.8

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