SUPPLEMENTARY DATA

Click synthesis by Diels–Alder reaction and characterisation of hydroxypropyl methylcellulose-based hydrogels

Guo-Feng Wang, Hui-Juan Chu,Hong-Liang Wei[*], Xiao-Qian Liu,Zi-Xuan Zhao, Jing Zhu

School of Chemistry and Chemical Engineering, HenanUniversity of Technology, Zhengzhou 450001, China

Received 24 October 2013; Revised 12 February 2014; Accepted 13 February 2014

1. Thermogravimetric analysis (TGA)

Thermogravimetric analysis (TGA) was conducted to observe changes in the thermal response profiles and to estimate the composition of polymers. TGAwas performed using TA Instrument 2000 thermogravimetric analyzer in the range 25-500 °Cunder a nitrogen atmosphere.Heating rate was 20 °C/min.

The thermogravimetry curves obtained with HPMC, HPMC-SFA, HPMC-AMI, and Gel-6 are presented in Fig. S1. All four curves are similar and reveal only a minor change in thermal stability. Gel-6 shows the highest thermal stability, which indicates stability is improved after crosslinking by Diels-Alder reaction.The first phase of the weight loss (25-100 °C)indicates evaporation of water and shows that the samples are hygroscopic.The second stage is due to thermal degradation of the samples, which started at about 214 °C and attains a maximum at around 320 °C, after which degradation continues until near to 400°C, where the mass loss is due to the loss of CO2 from the polysaccharide.This should be the typical degradation mechanism of cellulose where depolymerization, dehydration and consequently,decomposition of the glycosidic structure take place in parallel.

Fig.S1 TGA curves of HPMC(black line), HPMC-SFA (red line), HPMC-AMI(blue line), and Gel-6(green line)

2. Hydrolytic degradation in vitro

The in vitro degradation studies were performed at 37°C in buffer solutions of pH= 7.4 and pH=9. To calculate the percent mass loss of each sample (Mloss), the samples were each weighed(m2), andimmersed in 5 mL buffer solutions of pH=7.4 and pH=9 at 37℃incuvettes, respectively.At specified time points, the hydrogels were taken out from the cuvettes, and washed with distilled water and then dried under vacuum to constantweight (m3).The Mloss was calculated according to the following equation.

Mloss = (m2-m3)×100%/m2

The mass loss rate (Mloss) against degradation time is plotted in Fig.S2. It was observed that the hydrogel degraded quickly at a solution of pH=9, and more than 90% of its weight was lost after 14hours.Whereas hydrogel degraded slowly at a solution of pH=7.4, its weight only lost 25% in 5 days. Evidently, the degradation rate was faster in pH=9 than in pH=7.4. The reason should be that the ester bonds at the hydrogel are easy to break in basic solution.

Fig.S2 Degradation curves of Gel-6 at pH=9(a) and pH=7.4 (b) at 37℃

3. Disassembly by retro-DA reaction

10 mL of DMF, water were put into two 50 mL flasks, respectively, then added 0.15 g of dry gel (Gel-4) to each flask. After heated to a preset temperature, disassembly time based on retro-DA reaction was determined when the gel disappeared.

When the temperature is 70°C, the gel was not disassembled in water after 20 h but the gel disappeared in DMF. The results indicate the gel is stable in water and retro-DA reaction is interrelated with the solvents used. Bigger polarity of organic solvents is of advantage to disassembly of the gel. The result was the same as our previous report (H-L Wei, Z Yang, L-M Zheng, Y-M Shen.Polymer,2009, 50: 2836-2840)

4. NMR of SFA

Fig.S3 1H NMR spectrum of SFA in DMSO-d6

Fig.S413C NMR spectrum of SFA in DMSO-d6

[*]Corresponding author, e-mail: