Photostabilization of poly (vinyl chloride) by 1,3,4-thiadiazole and 1,3,4-oxadiazole chelate complexes and some of their free ligands

In the work described in this thesis, 2-thioacetic acid-5-phenyl-1,3,4- oxadiazole chelate complexes, 2N-salicylidene-5-(p-nitro phenyl)-1,3,4- thiadiazole chelate complexes and four Schiff base compounds, were synthesized and characterized and their activity in photstabilization of poly(vinyl chloride) is
investigated. These compounds and complexes are: 1- 2-thioacetic acid-5-phenyl- 1,3,4-oxadiazole, (OX) 2- - Bis[2-thioacetic acid-5-phenyl-1,3,4- oxadiazole]tin(II),Sn(OX)2-) 3- Bis[2-thioacetic acid-5-phenyl-l,3,4- oxadiazole]barium(II), Ba(OX)2. 4-Bis[2-thioacetic acid-5-phenyl-1,3,4- oxadiazole]nickel(II), Ni(OX)2. 5-Bis [2-thioacetic acid-5-phenyl-1,3,4- oxadiazole]zinc(II), Zn(OX)2. 6-Bis[2-thioacetic acid-5-phenyl-l,3,4-
oxadiazole]copper(II),Cu(OX)2. 7-Bis[2-thioacetic acid-5-phenyl-l,3,4- oxadiazole]calcium(II),Ca(OX)2. 8-2N-salicylidene-5-(cinnamyl)-l,3,4-thiadiazole, (SA). 9- 2N-salicylidene-5-(p-nitro phenyl)-1,3,4-thiadiazole,(SN). 10 - 2Nsalicylidene- 5-(p-methoxy phenyl)-1,3,4-thiadiazole, (SE). 11- 2N- salicylidene-5-
(phenyl)- 1,3,4-thiadiazole, (SP). 12- Bis[2N-salicylidene-5-(p-nitro phenyl)-!,3,4- thiadiazole] tin(II), Sn(SN)2. 13- Bis[2N-salicylidene-5-(p-nitro phenyl)-1,3,4- thiadiazole]nickel(II), Ni(SN)2. 14- Bis[2N-salicylidene-5-(p-nitro phenyl)-1,3,4- thiadiazole] copper(II), Cu(SN)2. 15-Bis[2N-salicylidene-5-(p-nitro phenyl)-1,3,4-thiadiazole] zinc(II), Zn(SN)2. Infrared and ultraviolet-visible spectrophotometry techniques, mole ratio method, and other physical properties were used to characterize the above free ligands and chelate complexes. All these compounds were act as stabilizer in PVC films, and from ultraviolet-visible spectral changes, the first order specific rate constants values were determined. The rate of photodegradation and photostabilization of PVC film (thickness 30μm) were monitored with irradiation time by measuring the carbonyl and polyene indices (Ico and Ipo) values with irradiation time using different concentrations of additive ranged from 0.1% to 0.5% wt/wt. The light of wavelength 313 nm with intensity (1.052*10 8" ein.dm-³.S-¹ ) is used for irradiation of polymer films at temperature about 45°C. It is found that the carbonyl index (Ico) or polyene index (Ipo) values increased with irradiation time, and this increase depend on the type and wt% of additives (free ligand and complexes). The following trend is obtained for the photostabilization effect of PVC film in presence of these additives: (a) For 2-thioacetic acid-5-phenyl-l,3,4-oxadiazole complexes. PVC (control) > (OX) > Ca(OX)2 > Cu(OX)2 > Zn(OX)2 > Ni(OX)2 > Ba(OX)2 > Sn(OX)2 (b) For 2N-salicylidene-5-(p-nitro phenyl)-l,3,4-thiadiazole complexes. PVC (control) > SN > Zn(SN)2 > Cu(SN)2 > Ni(SN)2 > Sn(SN)2 (c) For 2Nsalicylidene- 5-(substituted)-1,3,4-thiadiazole compounds. PVC (control) > SP > SE >SN > SA. The effect of additives concentration, ranged from 0.1%-0.5wt%, on the rate of photostabilization was also monitored, for PVC films. The rates were decreased with increasing additive concentration. The effect of film thickness is also studied, and results show that increasing film thickness the rate of photodegradation is decreased. The kinetic of photodegradation of PVC also investigated and show the usual kinetic in degradation process, since the linear relation between square root of carbonyl index (Ico)'/2 and irradiation time is obtained. The mode of chain scission was also investigated by measuring the variation of average viscosity molecular weight with irradiation time for PVC. The degree of deterioration (a) and the average number of chain scission (S) values were also calculated, and it was concluded that branching or cross-linking also occur. According to the experimental results obtained several mechanisms were suggested depending on the structure of the additives. Therefore HC1 scavenging, UV absorption, peroxide decomposer and radical scavenger for photostabilizer additives were suggested. The quantum yield of the chain scission (Φcs) of these complex in PVC films, were evaluated and found to be ranged between 5.71 xl0-8 9.7xl0-8 in 2-thioacetic acid-5-phenyl-l,3,4-oxadiazole complexes, and in the range from 5.71 xl0-8 to 8.7x10-8 for the 2N-salicylidene-5-(p-nitro phenyl)-l,3,4-thiadiazoie complexes and in the range from 1.71xl0-7 to 1.37xl0-7 2N-salicylidene-5- (substituted)-1,3,4-thiadiazole compounds.