GAMMA-RAY POLYMERIZATION OF LYOTROPIC SOLUTIONS OF CELLULOSE DERIVATIVES UNDER RETENTION OF THE MACROSCOPIC ORDER

Two new lyotropic solutions of cellulose derivatives are reported whic h can be polymerized upon gamma-irradiation. The first solution consis ts of hydroxypropylcellulose (HPC) in N,N-dimethylacrylamide (DMAcr) a nd the second of 2-(acryloyloxy)propylcellulose (APC; degree of substi tution (DS) = 0.18) in water. Both solutions were characterized using refractive index measurements, polarizing microscopy and diffuse refle ction spectroscopy. For solutions of HPC in DMAcr, it was demonstrated that they exhibit anisotropic phase behaviour at concentrations highe r than 45 wt.-% within a limited temperature range. Highly concentrate d solutions of about 70 wt.-% also showed cholesteric phase behaviour with iridescent colours. Upon gamma-irradiation, the solvent DMAcr rap idly polymerized. A conversion to 90% of polymer was reached at a dose of 5 kGy. Molecular composites of HPC in polymerized DMAcr were obtai ned in which the macroscopic order was preserved. Shear-deformed sampl es were still birefringent and exhibited band textures, when viewed be tween crossed polarizers, and light reflection of the cholesteric samp les still occurred at the same wavelength as before irradiation. The p olymerized samples showed an extended temperature stability, the aniso tropy being stable up to approximately 150 degrees C. The second solut ion of APC in water also exhibits cholesteric phase behaviour at a con centration of 61.5 wt.-%. Upon gamma-irradiation, the polymer chains u ndergo rapid cross-linking via the reactive acrylate groups and form a network in which the cholesteric order is preserved. The cross-linked APC films are swellable in water and retain their anisotropic order w hen the concentration of the solution is varied between 40 and 100 wt. -% of APC. The materials properties of the two systems after polymeriz ation are compared.