Critically branched polyester

Universal scaling curves for the molar mass distribution of randomly branched polyesters with many different samples in each class. The filled symbols have Nq = 2 monomers between branch points and correspond to critical percolation in three dimensions. The open symbols have Nq — 900 monomers between branch points and obey the mean-field percolation model. Data of C. P. Lusignan ei al., Phys. Rev. E 52, 6271 (1995) 60, 5657(1999). 

Here, Me is the critical molecular weight for entanglement of random branches, Mr is the molecular weight of the Kuhn segment, A is a constant determined by the chemical stracture of the chain and temperature, and B is a constant specific to the chemical structure. Equation [72] allows us to estimate Mb from the j/o data, M data (determined from SEC-LALS), and Mk data (determined from the characteristic ratio C ) given that the chains in the sample are randomly branched (no regular branches such as star branches) and that the values of A and B are known (which was the case for randomly branched polyesters examined in Reference 141). 

Ester-based cascades (e.g., 107) have been prepared[77 80i by using 5-(tert-butyldime-thylsiloxy)isophthaloyl dichloride (108), which was synthesized in high yield from 5-hydroxy-isophthalic acid (Scheme 5.26). The dendron wedges were prepared by treatment of siloxane 108 with phenol to give bis(aryl ester) 109, which was hydrolyzed, or desilylated (HC1, acetone), to generate a new phenolic terminus. Treatment of this free phenolic moiety with monomer 108, followed by hydrolysis, afforded the next tier (110). Repetition of the sequence followed by reaction of the free focal phenols with a triacyl chloride core, (e.g., 86), afforded the fourth tier dendrimer 107 of the polyester aryl series. It was noted that the choice of base (N, A-dimethylaniline) used in the final esterification was critical, since with pyridine bases (pyridine or 4-(dimethylamino)pyridine) facile transesterification resulting in branch fragmentation occurred. 

Figure 24.10 Molar mass [M ) versus elution volume for linear and branched polymers at critical conditions of the linear polyester (94% acetone and 6% THF). (Reprinted with permission from Ref [161] 2010, American Chemical...

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