By the polymer coupling reaction with a tetrafunctional silyl enol ether [1; C{CH2OC6H4C-(OSiMe3)dCH2}4], amphiphilic tetraarmed star polymers (6) with R-methylstyrene-2-hydroxyethyl vinyl ether (RMeSt-HOVE) block arm chains have been synthesized: C{CH2OC6H4COCH2-[CH(OCH2CH2-OH)CH2]n-[C(CH3)(C6H5)CH2]m-}4. The synthesis consisted of the following steps: (i) the sequential living cationic polymerization of RMeSt and 2-[(tert-butyldimethylsilyl)oxy]ethyl vinyl ether (SiVE) into an RMeSt-SiVE living block copolymer (4); (ii) the coupling of four chains of 4 with the quencher 1 into a tetraarmed polymer (5); and (iii) the transformation of the poly(SiVE) segment into the poly(HOVE) chain by the fluoride-catalyzed deprotection. In step i the living polymerization was carried out at -78°Cin methylene chloride with a binary initiating system comprising tin tetrabromide and the hydrogen chloride adduct of 2-chloroethyl vinyl ether. After step iii, the tetraarmed amphiphile 6 (RMeSt/HOVE ) 27/27 in DPn in each arm) was soluble in ethanol and chloroform, in which its 1 H NMR spectra changed dramatically by responding to solvent polarity. For example, in the former polar solvent, the signals of the hydrophobic RMeSt units were hardly detectable, whereas they were clearly observed in chloroform. This responsiveness was attributed to the rigidity of the poly(RMeSt) segment, which contrasts with the more flexible poly(vinyl ether) arm chains in the previously reported tetraarmed amphiphiles.
An airway tree is a fractal object. We showed that the distribution of minimal inner cross-sectional area (iCSA) of airway branches can be expressed by a fractal index, D, of minimal iCSA. This D was correlated with airflow limitation and future body mass index reduction in chronic obstructive pulmonary disease patients, as predicted by Hess–Murray’s law.
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