Glycidol represents a latent cyclic AB2-type monomer that can be polymerized in a ring-opening multibranching polymerization (ROMBP). Hyperbranched aliphatic polyethers with controlled molecular weights and narrow molecular weight distribution have been prepared via anionic polymerization of glycidol with rapid cation-exchange equilibrium. 1,1,1-Tris(hydroxymethyl)propane (TMP) was partially deprotonated (10%) and used as initiator for the anionic polymerization carried out under slow addition conditions to minimize polymerization without initiator as well as cyclization. 13C NMR spectra were employed to assess the degree of branching (DB), which was in the range 0.53−0.59. 13C NMR, MALDI-TOF mass spectrometry, vapor pressure osmometry (VPO), and GPC were used to characterize molecular weights and polydispersities of the polyols formed, showing good agreement. n for the polymers prepared was in the range 15−83 (M̄ n = 1250−6500), and M̄ w/M̄ n obtained was 1.13−1.47, being exceptionally low for hyperbranched polymers. MALDI-TOF spectra evidenced complete attachment of the hyperbranched structures to the TMP initiator and the absence of macrocyclics as well as hyperbranched macromolecules without initiator, due to the slow addition. The hyperbranched polyethers prepared showed T g's between −20 and − 26 °C.
A novel synthetic procedure for the preparation of hyperbranched polymers with narrow molecular weight distribution and enhanced degree of branching (DB) has been studied, using computer simulation to model the kinetics of the process. Slow addition of AB m monomers to B f core molecules in solution (“core-dilution/slow addition technique”) can be used to prepare hyperbranched polymers in a controlled manner, provided the coupling reaction B f + AB m to B f + m -1 is rapid and quantitative. The computer simulation is based on random addition of AB m monomers to B-functionalities of the B f core molecules for m = 2, 3 and f ranging from 2 to 12, excluding sterical constraints. It is shown that this synthetic strategy permits one to (i) control molecular weights, (ii) lower polydispersity, and (iii) enhance the DB of the resulting hyperbranched polymers. In the ideal case (AB m molecules react only with core B-functionalities and not with other AB m monomers) narrow molecular weight distributions are obtained, ranging from M w/M n = 1.33 to 1.08 for f = 3 and f = 12, respectively; i.e., polydispersities are controlled by the core functionality f. Obviously, for m = 2 the polydispersity for the core-dilution/slow addition process obeys the expression M w/M n = 1 + 1/f. The DB obtained from the simulation is 2/3 for m = 2 and 3/5 for m = 3, in excellent agreement with recent theoretical predictions, showing that DB = m/(2m − 1) for slow addition of AB m monomers (Acta Polym. 1997, 48, 298). Also, the nonideal case is considered, when AB m monomers form new core molecules B m in the course of the reaction due to deactivation of the reactive A-function. In this case bimodal distributions are obtained.
Polar dyes can be solubilized in apolar media-molecular nanocapsules with hydrophilic interiors have been prepared (see schematic representation) using polyglycerols with narrow polydispersity and simple esterification with fatty acids. These unimolecular micelles offer attractive potential for a variety of applications ranging from controlled drug release to the design of microreactors and catalysts.
A combination of sedimentation field flow fractionation (SdFFF) with multiangle laser light scattering (MALLS) was applied to the grain level destructured potato and waxy corn starch in solution.The molar mass and radius distributions were obtained simultaneously. Separation was observed for a radii range of 50-500 nm. Degradation upon heat exposure was found depending mainly on the exposure time and less on the temperature. A detailed analysis of the particle scattering factors (angular dependence of the scattered light) revealed small differences in the internal structure of potato and waxy corn starches. Both starches showed the behavior of only weakly swollen, branched clusters. Potato starch appeared to be slightly more expanded than waxy corn starch. Self-similar structures were observed with fractal dimensions of 2.4 ( 0.1. The deviations from theoretical predictions using the mean field approximation could result from excluded volume effects and heterogeneity in branching.
A novel type of amphiphilic spherosilsesquioxane derivative, 1-(1,ω-propylenemethoxy)oligo(ethylene oxide)-3,5,7,9,11,13,15-heptahydridopentacyclo[9.5.13,9.15,15.17,13]octasiloxane has been prepared from (HSiO3/2)8 and allyl-functional oligo(ethyleneoxide) (M n = 750 g/mol) by hydrosilylation. The monosubstituted octahydridosilsesquioxane was characterized by 1H, 13C, and 29Si NMR spectroscopy, IR, and MALDI-TOF mass spectroscopy as well as elemental analysis. Surface tension measurements of the water-soluble amphiphile show a cmc in the range of 6 × 10-4 mol/L. Aggregation of the uncondensed amphiphile leads to micellar and vesicular structures that can be cross-linked to liposome-like silica particles at elevated pH.
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