Percentage Grafting

Table I. Effect of Grafting Time on Percentage Grafting and Molecular Weight...

The addition of organic acids or anhydrides to the grafting solution enhances the yields, especially above 50% monomer concentration. If the data in Table I are graphed (Figure 1), the percentage graft curves for the three carboxylic acids converge and become virtually parallel. 

Another method of graft copolymer synthesis is a combination of microwave-based and conventional synthesis, i.e. using both microwave radiation as well as a chemical free radical initiator (e.g. ceric ammonium nitrate) together. This process is referred to as microwave assisted synthesis [47]. Although it yields a higher percentage grafting than the microwave initiated synthesis, the rehability of the synthesis process is low. 

It is obvious from Table 5.1 that with the increase in exposure time (1-4 minutes), the percentage grafting increased up to 3 minutes (which is optimized) after which it decreased. This may be because of the fact that, beyond an exposure time of 3 minutes, the prolonged exposure to microwave irradiation may have degraded the polysaccharide backbone. Hence, the percentage grafting and intrinsic viscosity decreased. 

The correlation between percentage grafting and intrinsic viscosity in case of polyacrylamide grafted carboxymethylstarch (CMS-g-PAM) is evident in Figure 5.6. 

Elemental Analysis (C, H, N, O S) helps us understand the actual extent of grafting. From the synthesis details (Table 5.1) we get the percentage grafting. Now from percentage grafting and from the known elemental composition of the polysaccharide and that of the graft polymer, we can calculate the theoretical elemental composition, which we can simply compare with that actually obtained from the elemental analyzer. 

In Mishra s work [41], an environmentally benign and efficient route of synthesis of polyacrylic acid grafted carboxymethyl cellulose (CMC-g-PAA) is developed using microwave radiation alone to initiate the grafting reaction. The synthesis is optimized in terms of percentage grafting and intrinsicviscositybyvaryingthe microwave... 

Higher reproducibility of percentage grafting in the final product,... 

Functionalization of PLA by grafting of maleic anhydride (MAn) by reaction extrusion in the presence of free radical initiators tert-h xiy peroxide) has also been carried out. The presence of high succinic anhydride units in the grafts was confirmed by FTIR and NMR studies. Low percentage grafting was observed in PLA due to presence of limited free radical sites [69, 70]. 

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