Solvent-free esterification of poly(vinyl alcohol) and maleic
anhydride through mechanochemical reaction
Bo Zhao, Can Hui Lu *, Mei Liang
State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute, Sichuan University, Chengdu 610065, China
Received 13 July 2007
Abstract
A solid-state mechanochemical processing, that is, pan-milling, was used to conduct the esterification of poly(vinyl alcohol)
(PVA) with maleic anhydride (MA) through stress-induced reaction. FTIR spectrum study indicated the presence of ester linkages
and olefinic double bonds in maleic anhydride cross-linked PVA. Thermal properties of the cross-linked product were characterized
by DSC. The results showed its glass transition temperature was 20 8C higher than the original linear PVA and the thermal stability
was also improved.
# 2007 Can Hui Lu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Mechanochemical synthesis; Esterification; Poly(vinyl alcohol); Maleic anhydride
The chemical modification of poly(vinyl alcohol) (PVA) is important to expand its application. The presence of its
hydroxyl groups makes it possible to react with appropriate reagents under certain conditions. Many
literatures reported the esterification or grafting reaction between various acids and hydroxyl groups in PVA to
produce new products [1–5]. However, most of them need more than one step to achieve the cross-linked structures for
application in membrane modifier. The mechanochemical synthesis, including the mechanical alloying, is a
heterogeneous solid-phase reaction, in which several processes occur: dispersion of the components, generation of the
contacts between them and the mass transfer at the contact zones. All these processes are caused only by the
mechanical impact on the mixture of solid reagents [6]. Previously, we studied the stress-induced mechanochemical
reactions of solid polymer and organic reagents without solvent and heating [7–9]. Solvent-free mechanochemical
reaction may appear to be an energy intensive technique when compared with the conventional solvent-based chemical
synthesis [10].
In this work, we reported the solvent-free preparation of PVA ester during mechanical processing of solid reactants
at ambient conditions through our self-designed disc-type mechanochemical reactor without heating or catalysts.
Furthermore, the structures of the esterified products of PVA with maleic anhydride were investigated by FTIR and
DSC.
The experimental procedure was as follows, original PVA was immersed in water for 12 h to remove the solvable
impurities in order to reduce the effect of side reactions. Then, the PVA was dried in oven at 120 8C for 10 h. PVA/MA
(4:1, w/w) particles were fed into the inlet in the middle of the pan-mill equipment at a rotation speed of 60 rpm and in
www.elsevier.com/locate/cclet
Available online at www.sciencedirect.com
Chinese Chemical Letters 18 (2007) 1353–1356
* Corresponding author.
E-mail address: [email protected] (C.H. Lu).
1001-8417/$ – see front matter # 2007 Can Hui Lu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2007.09.019
a specific gap distance between the moving and stationary pans. Milled particles were discharged from the brim of the
pans, and collected for the next milling cycle. The operation was performed at ambient temperature and the heat
generated during milling was removed by cooling water. The products were extracted with acetone for 72 h to remove
the unreacted maleic anhydride, and subsequently evacuated at 80 8C for 4 h. Pan-milled PVA is markeded as nC, and
co-milled PVA/maleic anhydride is marked as MnC, in which the n denotes the pan-milling cycle number.
The chemical structures of original PVA, PVA treated with maleic anhydride samples were studied by FTIR spectra.
From Fig. 1, the appearance of absorption peak between 3000 and 3500 cm�1 indicates the presence of strong
intermolecular and intramolecular hydrogen bonding among hydroxyl groups. The C–H stretching vibration is
observed at about 2930 cm�1 and in spectrum of milled sample (B) the peak at 2930 cm�1 becomes weaker than that
of the original PVA. The C–H stretching vibration band (2930 cm�1) changes and the peak at 1640 cm�1 indicates the
generation of a C C structure in the PVA chains. The peaks at 1718 and 1260 cm�1 may be attributed to the stretching
vibration of C O and C–O of the modified sample. The disappearance of the bands associated with anhydride at 1834
and 1768 cm�1 indicates the absence of the anhydride in the structure. As the mark of the crystalline PVA [10], the
absorption peak of 1141 cm�1 becomes weaker in the spectrum of modified sample, implies the crystallinity of PVA is
decreased after solid-state mechanochemical reaction. In addition, there is no absorption between 955 and 915 cm�1
(assigned to characteristic bands of the carboxylic group) observed in the FTIR spectrum of the mechanochemically
synthesized product, which indicates no carboxylic acid generated in the product. Based on the spectral results, it is
reasonable to conclude that maleic anhydride cross-linked PVA is prepared by solid-state mechanochemical reaction
successfully (Fig. 2).
The differential scanning calorimeter (DSC) data of PVA and mechanochemically modified PVA are shown in
Table 1. The strong intermolecular and intramolecular hydrogen bonding of PVA leads to a high glass transition
temperature. Usually, solid-state process can break down chemical or hydrogen bondings and reduce the glass
transition temperature (Tg) as well as the degree of crystallinity of polymers. However, for a cross-linked polymer, Tg
depends on the cross-linking density and the chemical structure of the crosslinker. As the introduction of the cross-
linked structure limits the mobility of polymeric chain and leads to the increase of Tg value [12]. The increase of glass
B. Zhao et al. / Chinese Chemical Letters 18 (2007) 1353–13561354
Fig. 1. FTIR spectra of of poly(vinyl alcohol): (A) before mechanochemical treatment) and PVA/maleic anhydride mixture milled 30 cycles (B).
Table 1
DSC data of PVA and PVA/MA esterified product
Sample PVA 0C 20C M20C M40C M60C
Xca (%) 44.1 34.5 26.3 20.9 16.0
Tg (8C) 81.9 59.1 85.6 84.9 88.7
Tm (8C) 230.5 231.3 228.8 227.3 228.3
a The enthalpy of fusion for 100% crystalline PVA is 156 J/g [13].
transition temperature is observed in each modified PVA. The results showed that the glass transition temperature of
maleic anhydride cross-linked PVA was 20 8C higher than the original linear PVA and the thermal stability was also
improved.
The effects on cross-linking reaction and mechanochemical effects induced by mechanical stress during pan-
milling, led to the deterioration of chain regularity and reduced the values of degree of crystallinity (Xc) in each
mechanochemically modified product, which agree with the values of Xc from the crystalline sensitive wavenumber of
1141 cm�1 in the FTIR spectrum [11]. From the DSC curves as displayed in Fig. 2, it is found that the melting
temperature of milled and original PVA tend to a stable value, and the milled PVA decomposed more rapidly after
melting, compared with esterified samples obtained through mechanochemical synthesis.
Based on the experimental results described above, a possible mechanochemical esterification procedure of
poly(vinyl alcohol) and maleic anhydride can be deduced as follows [12,14], the more detailed reaction mechanism is
under investigation.
In comparison with conventional methods for the esterification of poly(vinyl alcohol), the mechanochemical solid-
state reaction reported here is proved to be viable and environmentally friendly. It is an effective and alternative
technique for the chemical modification of polymers.
Acknowledgment
This study was supported by the National Natural Science Foundation of China (No. 10476014).
B. Zhao et al. / Chinese Chemical Letters 18 (2007) 1353–1356 1355
Fig. 2. DSC spectrum of PVA and PVA/MA esterified product: (A) (PVA 0C), (B) (PVA 20C), (C) (PVA-MA M20C), (D) (PVA-MA M40C) and (E)
(PVA-MA M60C).
References
[1] F.J. Liou, Y.J. Wang, J. Appl. Polym. Sci. 59 (1996) 1395.
[2] A.M. Atta, K.F. Arndt, Polym. Int. 54 (2005) 448.
[3] R.Y.M. Huang, J.J. Shieh, J. Appl. Polym. Sci. 70 (1998) 327.
[4] V. Gimenez, A. Mantecon, V. Cadiz, J. Polym. Sci. Part A: Pol. Chem. 34 (1996) 934.
[5] I. Ikeda, H. Taniguchi, H. Okamoto, K. Suzuki, Polym. Int. 49 (2000) 824.
[6] P. Butyagin, J. Mater. Synth. Process 8 (2000) 211.
[7] C.S. Liu, Q. Wang, J. Appl. Polym. Sci. 78 (2000) 2197.
[8] H.S. Xia, Q. Wang, K.S. Li, G.H. Hu, J. Appl. Polym. Sci. 93 (2004) 386.
[9] C.H. Lu, Q. Wang, Chin. J. Struct. Chem. 21 (2002) 12.
[10] V.P. Balema, J.W. Wiench, M. Pruski, V.K. Pecharsky, Chem. Commun. (2002) 724.
[11] S.K. Mallapragada, N.A. Peppas, J. Polym. Sci. B 34 (1996) 1346.
[12] J.M. Gohil, A. Bhattacharya, P. Ray, J. Polym. Res. 13 (2006) 169.
[13] C. Seoul, S.I. Mah, Polymer 38 (1997) 5555.
[14] M.A. Mikhailenko, et al. Chem. Sustain. Dev. 12 (2004) 371.
B. Zhao et al. / Chinese Chemical Letters 18 (2007) 1353–13561356
Recommended
