Hyperbranched poly(butylene oxide) polyols have been synthesized by multibranching anionic ring-opening copolymerization of 1,2-butylene oxide and glycidol. Systematic variation of the composition from 24 to 74% glycidol content resulted in a series of moderately distributed copolymers (Đ = 1.41–1.65, SEC), albeit with limited molecular weights in the solvent-free batch process in the range of 900–1300 g mol–1 (apparent M n determined by SEC with PEG standards). In situ monitoring of the copolymerization kinetics by 1H NMR showed a pronounced compositional drift with respect to the monomer feed, indicating a strongly tapered microstructure caused by the higher reactivity of glycidol. In the case of slow monomer addition considerably higher apparent molecular weights up to 8500 g mol–1 were obtained (SEC). By alteration of the comonomer ratio, aqueous solubility of the hyperbranched copolymers could be tailored, resulting in well-defined cloud points between 20 and 84 °C. Glass transition temperatures between −60 and −29 °C were observed for the resulting polyether polyols. High degrees of branching (DB) between 0.45 and 0.77 were calculated from inverse gated (IG) 13C NMR. Online viscosimetry and analytical ultracentrifugation (AUC) were employed to study hydrodynamic properties and to establish a universal calibration curve for the determination of absolute molecular weights. This resulted in M w values between 2100 and 35 000 g mol–1 that were generally 2–3 times higher than the apparent values determined by SEC with linear PEG standards.
Hyperbranched, multifunctional polycarbonate polyols based on CO2, cyclohexene oxide (CHO), and the “inimer” (initiator–monomer) (4-hydroxymethyl)cyclohexene oxide (HCHO) were prepared in one-pot syntheses. The related linear poly(hydroxymethyl cyclohexene carbonate) structures based on protected HCHO and postpolymerization deprotection were also synthesized as model compounds. The content of hydroxyl functionalities was adjustable for both linear and hyperbranched terpolymer systems. All CO2/epoxide polymerizations were catalyzed by the (R,R)-(salcy)-Co(III)Cl complex. The polycarbonates obtained were comprehensively investigated using various 1D and 2D NMR techniques, SEC, FT-IR, UV–vis spectroscopy, and contact angle measurements. Rigid polyols with molecular weights between 3600 and 9200 g mol–1 and moderate dispersity between 1.18 and 1.64 (M w/M n) were obtained. In addition, the materials were examined with respect to their thermal properties, intrinsic viscosity, and their three-dimensional structure. Glass transition temperatures in the range of 113–141 °C (linear) and 72–105 °C (hyperbranched) were observed. The intrinsic viscosity of the hyperbranched systems is in the range of 5.69–11.51 cm3 g–1 and mirrors their compact structure. The hyperbranched polyols were also studied regarding their successful reaction with phenyl isocyanate to convert the free hydroxyl groups into urethanes.
Multiarm star copolymers, consisting of hyperbranched poly(ethylene oxide) (hbPEO) or poly(butylene oxide) (hbPBO) polyether copolymers with glycerol branching points as a core, and linear aliphatic polycarbonate arms generated from carbon dioxide (CO2) and epoxide monomers, were synthesized via a “core-first” approach in two steps. First, hyperbranched polyether polyols were prepared by anionic copolymerization of ethylene oxide or 1,2-butylene oxide with 8–35% glycidol with molecular weights between 800 and 389,000 g·mol–1. Second, multiple arms were grown via immortal copolymerization of CO2 with propylene oxide or 1,2-butylene oxide using the polyether polyols as macroinitiators and (R,R)-(salcy)-CoCl as a catalyst in a solvent-free procedure. Molecular weights up to 812,000 g·mol–1 were obtained for the resulting multiarm polycarbonates, determined by online viscometry with universal calibration and 1H NMR. Comparing the synthesis of different multiarm star polycarbonates, a combination of a highly reactive macroinitiator with a less reactive epoxide monomer was found to be most suitable to obtain well-defined structures containing up to 88 mol% polycarbonate. The multiarm star copolymers were investigated with respect to their thermal properties, intrinsic viscosity, and potential application as polyols for polyurethane synthesis. Glass transition temperatures in the range from −41 to +25 °C were observed. The intrinsic viscosity could be adjusted between 5.4 and 17.3 cm3·g–1 by varying the ratio of polyether units and polycarbonate units.
Efficient coupling of sterically demanding polystyryllithium (PS-Li) chain ends is achieved using tetra[3-(chloro-dimethylsilyl)propyl]silane (TCDMSPS) as a linking agent. This general approach is employed for the rapid synthesis of tapered star copolymers.
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