Weight sequence distributions, theoretical

Figure 18. Theoretical weight sequence distributions (Equation 8) for samples of Table V (Wn,i, and W j/Wn,i are shown beside each curve)...

Monomer Sequence Distribution in the Copolymer by C NMR. The latex samples which were precipitated in the mixed solvent (ispropanol/hexane = 45/55 and dried in a vacuum oven at 45-50°C, were used for the C NMR study. The polymer samples were dissolved (5-7% weight volume) in deuterated pyridine (PYR d%) with tetramethylsilane (TMS) as a zero external reference. The NMR measurement and the theoretical calculation were carried out in CNRS, Laboratoire des Matriaux Organiques, in Lyon, France using C NMR 30 MH (Bruker). 

Radical Addition to C=C Bonds. Radical addition to C=C bonds are of importance for free-radical polymerization as this reaction forms the propagation step, and thus influences the reaction rate and molecular weight distribution in both conventional and controlled free-radical polymerization, and the copolymer composition and sequence distribution in free-radical copolymerization. Numerous studies have examined the applicability of high level theoretical methods for stud5dng radical addition to C=C bonds in small radical systems (32,33,37,93,94). The most recent study (37) included W1 barriers and enthalpies, and geometries and frequencies at the CCSD(T)/6-31 lG(d,p) level of theory, and is the highest level study to date. The main conclusions from this study, and (where still relevant) the previous lower level studies, are outlined below. 

As seen in Scheme 5.1, preparation of the IG polymer in this synthesis involved the ROP of cCL and subsequent chain-end modification. Conversion of the terminal hydroxyl group to two hydroxyl functions enabled further ROP to the 2G polymer. The IG polymer synthesized by this procedure was a 6-arm star-branched PcCL. The target dendrimer-like star-branched polymer was obtained as a 2G polymer by the second iteration and possessed a minimum architectural unit. One more repetition of the synthetic sequence involving the two reaction steps resulted in a 3G dendrimer-like star-branched PaCL. The 3G polymer possessed six branches at the core and two branches at the junctions in both the 2G- and 3G-based layers, composed of 42 arm segments (6 (IG) + 12 (2G) + 24 (3G) = 42). The observed M value was 96 000 g/mol, close to the theoretical value, and the molecular-weight distribution was not narrow, but an acceptable value of 1.14. 

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