Systematic Variation of the Degree of Branching (DB) of Polyglycerol via Oxyanionic Copolymerization of Glycidol with a Protected Glycidyl Ether and Its Impact on Rheological Properties

摘要

In an oxyanionic polymerization, glycidol as a latent AB2 monomer is copolymerized with the protected linear AB glycidyl ether monomer EEGE (ethoxy ethyl glycidyl ether) to generate hyperbranched polyglycerols with an adjustable degree of branching (DB) after deprotection. The DB for the random copolymers is controlled by the comonomer content (10-92 EEGE). Detailed ~(13)C NMR and 2D NMR studies are carried out for precise calculation of the actual DB, which is in the range of 0.17-0.58. The acetal protecting group of EEGE can be cleaved by acidic treatment to generate linear or terminal glycerol units with increased content of linear glycerol repeat units and thus decreased DB. The course of the DB with increasing AB comonomer content perfectly confirms the theoretical prediction, demonstrating that high AB contents (>50) are required for a significant reduction of the DB. Moderate polydispersities are obtained for the resulting polyglycerols (M_w/M_n < 2.0, Mn: 4100-5100 g mol~(-1)). The hyperbranched polyglycerols with tailored degree of branching (DB) are investigated. A pronounced dependence of the structure-property relationship on the degree of branching indicates increasing intramolecular hydrogen bonds when increasing the degree of branching.