Manipulation of the Glass Transition Properties of a High-Solid System Made of Acrylic Acid-N,N'-Methylenebisacrylamide Copolymer Grafted on Hydroxypropyl Methyl Cellulose

Abstract

Crosslinking of hydroxypropyl methyl cellulose (HPMC) and acrylic acid (AAc) was carried out at various compositions to develop a high-solid matrix with variable glass transition properties. The matrix was synthesized by the copolymerisation of two monomers, AAc and N,N'-methylenebisacrylamide (MBA) and their grafting onto HMPC. Potassium persulfate (K₂S₂O₈) was used to initiate the free radical polymerization reaction and tetramethylethylenediamine (TEMED) to accelerate radical polymerisation. Structural properties of the network were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), modulated differential scanning calorimetry (MDSC), small-deformation dynamic oscillation in-shear, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show the formation of a cohesive macromolecular entity that is highly amorphous. There is a considerable manipulation of the rheological and calorimetric glass transition temperatures as a function of the amount of added acrylic acid, which is followed upon heating by an extensive rubbery plateau. Complementary TGA work demonstrates that the initial composition of all the HPMC-AAc networks is maintained up to 200 °C, an outcome that bodes well for applications of targeted bioactive compound delivery.

Keywords: Hydroxypropyl methyl cellulose; N,N′-methylenebisacrylamide; acrylic acid; glass transition temperature.

Figure 1

FTIR spectra of AAc, HPMC and HPMC:AAc systems (1:3, 1:4, 1:5, 1:6, 1:7).

Figure 2

X-ray diffractograms of HPMC:AAc systems (1:3, 1:4, 1:5, 1:6, 1:7).

Figure 3

Scanning electron micrograph image of the HPMC:AAc matrix (1:3).

Figure 4

Master curve of G′, G″ and tan δ as a function of temperature for the HPMC-AAc network (1:5); scan rate 1 °C min⁻¹, frequency 1 rad s⁻¹.

Figure 5

Frequency variation of a G′ and b G″ for the HPMC-AAc network (1:5); bottom curve is taken at 48 °C (□), other curves successively upward, 44 °C (◊), 40 °C (∆), 36 °C (✕), 32 °C (✴), 28 °C (−), 24 °C (−), 20 °C (○), 16 °C (+), 12 °C (■), 8 °C (♦), 4 °C (▲), 0 °C (●), respectively, c G′_p (●) and G″_p (○) values reduced to 20 °C and plotted logarithmically against reduced frequency (ωa_T) utilising the mechanical spectra in a,b,d logarithm of the shift factor, α_T, plotted against temperature from the data of the master curve in Figure 5c.

Figure 5

Frequency variation of a G′ and b G″ for the HPMC-AAc network (1:5); bottom curve is taken at 48 °C (□), other curves successively upward, 44 °C (◊), 40 °C (∆), 36 °C (✕), 32 °C (✴), 28 °C (−), 24 °C (−), 20 °C (○), 16 °C (+), 12 °C (■), 8 °C (♦), 4 °C (▲), 0 °C (●), respectively, c G′_p (●) and G″_p (○) values reduced to 20 °C and plotted logarithmically against reduced frequency (ωa_T) utilising the mechanical spectra in a,b,d logarithm of the shift factor, α_T, plotted against temperature from the data of the master curve in Figure 5c.

Figure 6

Differential scanning calorimetry thermograms of HPMC-AAc networks (1:7, 1:6, 1:5, 1:4, 1:3); scan rate 1 °C min⁻¹.

Figure 7

Thermogravimetric analysis of HPMC-AAc matrices (1:7, 1:6, 1:5, 1:4, 1:3) and HPMC powder; scan rate 20 °C min⁻¹.