In turn, the homopolymers prepared under microwave conditions were employed as macro-chain-transfer agents (macroCTAs) for subsequent block copolymerization. It was stressed that the microwave procedure was 150-fold faster in comparison to those described in literature under conventional conditions. The resin with a 7.25-fold increase in the mass was obtained. 47 The resin was prepared in a neat reaction of TEMPO-methyl resin with styrene derivatives. Solid-supported TEMPO-mediated controlled polymerization was also described for the preparation of novel high-loading functionalized styrenyl resins. Furthermore, it was proved by successful chain extension polymerization and NMR spectrum analysis that the nitroxide moiety did exist at the end of polymeric chain. The polymerization rates at appropriate power of microwave irradiation were faster than that under conventional heating conditions at the same reaction temperature with or without benzoyl peroxide. Similar results were obtained for ATRP of n-octyl acrylate in an acetonitrile solution in the presence of 2-bromobutyrate, CuBr, and 2,2′-pyridine under microwave conditions. It was found that microwave irradiation enhanced the rate of polymerization for example, after 150 min of microwave irradiation, the monomer conversion reached 27%, and the polymers were afforded with a number-average molecular weight of 57 300 g mol −1 and a PDI of–1.19, while under conventional conditions a similar conversion was achieved after 16 h, and the polymers were characterized by a number-average molecular weight of 64 000 g mol −1 and a PDI of –1.19 ( Figure 12). 41,42 Linear first-order rate plots, linear increase of the number-average molecular weight with conversion, and low polydispersities were observed. In a similar paper, ATRP of MMA under microwave irradiation was also studied in a solution in the presence of a small amount of CuCl, N,N,N′, N″, N″-pentamethyldiethylenetriamine, and ethyl 2-bromobutyrate (i.e., activator–initiator system). (2015) stated that a suspension will be mono-disperse if the PDI value is lower than 0.3 and with a single peak in size distribution curve. 3-29, the PDI values were within 0.25 for the ultrasonication period of 1–5 h. A similar trend has also been reported in the literature ( Kwak & Kim, 2005). Moreover, longer ultrasonication could re-agglomerate the nanoparticles again. It is known that ultrasonication can break down the cluster, however further agglomeration could be the result of prolonged ultrasonication ( Taurozzi et al., 2012). 3-26 show that the range of the cluster sizes of nanoparticles were further increased after 2 h of ultrasonication. Further ultrasonication after 2 h showed that PDI was increased with sonication period. It could be noted that the lowest PDI value is close to the mono-disperse state. 3-9 show that there were fewer clusters of particles in the nanofluid prepared by 2 h of ultrasonication. The cluster sizes of nanoparticles for 2 h of sonication were within the range of 119–150 nm, which is the smallest range of the results.
The distribution of cluster sizes reported in Fig. PDI was decreased with an increase of ultrasonication duration until 2 h and the lowest PDI value was found to be 0.22 for 2 h of ultrasonication. 3-13 also support this, as broad sizes (6–20 nm) of particles existed for 0 h of sonication. The results of average particle size reported in Fig. 3-7 also show that there were a large number of agglomerations exited in the nanofluid prepared with 0 h of ultrasonication. 3-26 also support this, as the range of cluster size for nanofluid prepared by 0 h of ultrasonication was 92–300 nm, which is the widest range among the results of Fig. 3-29, it can be seen that the highest PDI value was found to be 0.34 for the nanofluid prepared without ultrasonication (0 h). The relation of ultrasonication durations on the polydispersity index (PDI) studied for 50% amplitude sonicator power and reported in Fig.
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