Hyperbranched PEG by Random Copolymerization of Ethylene Oxide and Glycidol

The synthesis of hyperbranched poly(ethylene glycol) (hbPEG) in one step was realized by random copolymerization of ethylene oxide and glycidol, leading to a biocompatible, amorphous material with multiple hydroxyl functionalities. A series of copolymers with moderate polydispersity ($\overline {M} _{{\rm w}} /\overline {M} _{{\rm n}} $ < 1.8) was obtained with varying glycidol content (3-40 mol-%) and molecular weights up to 49 800 g mol(-1) . The randomly branched structure of the copolymers was confirmed by (1) H and (13) C NMR spectroscopy and thermal analysis (differential scanning calorimetry). MTS assay demonstrated low cell toxicity of the hyperbranched PEG, comparable to the highly…

Ring-Opening Multibranching Polymerization

Phase behavior of the system hyperbranched polyglycerol+methanol+carbon dioxide

Abstract Phase equilibrium data have been measured for the ternary system hyperbranched polyglycerol + methanol + carbon dioxide at temperatures of 313–450 K and pressures up to 13.5 MPa. Phase changes were determined according to a synthetic method using the Cailletet setup. At elevated temperatures the system shows a liquid–liquid–vapor region with lower solution temperatures. Besides the vapor–liquid and liquid–liquid equilibria, the vapor–liquid to vapor–liquid–liquid and vapor–liquid–liquid to liquid–liquid phase boundaries are reported at different polymer molar masses and can serve as test sets for thermodynamic models. A distinct influence of the polymer molar mass on the vapor–liqu…

Nonlinear Macromolecules by Ring-Opening Polymerization

Ring-opening polymerization (ROP) is a well-established method for the controlled synthesis of linear polymers, which can be found in various everyday applications. However, during the past decades, there has been an increasing interest in the generation of nonlinear highly branched polymers, profiting from the fascination created by the structurally perfect dendrimers. The applicability of various heterocyclic monomers renders the ring-opening multibranching polymerization (ROMBP), a versatile tool for the generation of multifunctional hyperbranched polymers. First, the historical key steps leading to the development of ROMBP are described, which is the basis for the controlled synthesis o…

Can Hyperbranched Polymers Entangle? Effect of Hydrogen Bonding on Entanglement Transition and Thermorheological Properties of Hyperbranched Polyglycerol Melts

Melt rheology and thermal phase transition of a series of hyperbranched polyglycerol samples (hbPG) (DB ≈ 60%) in a broad molecular weight range (Mn = 600–440 000 g/mol) were investigated and correlated to both molecular weight and nature of the end group (hydroxyl vs permethylated and trimethylsilylated). The well-characterized and defined flexible polyethers are particularly suitable to shed light on the linear viscoelastic behavior with respect to (i) hyperbranched topology and (ii) hydrogen bond interactions, particularly in comparison to the perfectly linear polyglycerol counterparts studied recently [Osterwinter, C.; Macromolecules 2015, 48, 119−130]. We present a detailed examination…

Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor

The paper describes the living anionic polymerization of styrenes to homo- and diblock copolymers in continuous flow, using a microstructured mixing set-up ("microreactor"). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by "break-seal" and "high vacuum" techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g.h -1 . Facile molecular weight adjustment is achieved by variation of the flow rates of initiato…

Ionic Liquids on Demand in Continuous Flow

We report on the development of an alternative protocol for the facile, solvent-free synthesis of various novel imidazolium-based ionic liquids (ILs) that affords highly pure products without the necessity of subsequent purification steps. The continuous approach is based on the combination of HPLC pumps with a micromixer and a capillary residence tube. Our system provides a high degree of control over the alkylation reactions due to a high surface-to-volume ratio and superior heat and mass transport. Within the scope of our studies, we focused on ionic liquids containing differently substituted phenyl rings and characterized these compounds with respect to further use for direct applicatio…

Microstructured Reactors for Polymer Synthesis: A Renaissance of Continuous Flow Processes for Tailor-Made Macromolecules?

Organic synthesis in microfluidic devices has attracted increasing interest in recent years. However, little efforts had been undertaken to exploit this novel technology for polymer chemistry until several recent studies demonstrated the interesting potential of microreactors for the synthesis and modification of polymers. In fact, anionic polymerizations in continuous capillary flow-tube systems were established already in 1962 in pioneering work by Szwarc. Subsequent work focused on detailed kinetic analyses in such reactors. The present article explores different current strategies developed by several research groups to realize bulk and solution polymerizations using continuous flow mic…

Hyperbranched Polyglycerols: From the Controlled Synthesis of Biocompatible Polyether Polyols to Multipurpose Applications

Dendritic macromolecules with random branch-on-branch topology, termed hyperbranched polymers in the late 1980s, have a decided advantage over symmetrical dendrimers by virtue of typically being accessible in a one-step synthesis. Saving this synthetic effort once had an unfortunate consequence, though: hyperbranching polymerization used to result in a broad distribution of molecular weights (that is, very high polydispersities, often M(w)/M(n)5). By contrast, a typical dendrimer synthesis yields a single molecule (in other words, M(w)/M(n) = 1.0), albeit by a labor-intensive, multistep process. But 10 years ago, Sunder and colleagues reported the controlled synthesis of well-defined hyperb…

Correlations between Ion Conductivity and Polymer Dynamics in Hyperbranched Poly(ethylene oxide) Electrolytes for Lithium-Ion Batteries

Poly(ethylene oxide)s with varying degrees of hyperbranching are effective at preventing the crystallization of PEO and lead to approximately a 100-fold increase in the Li-ion conductivity below 50 °C as compared with linear PEO. The Li-ion conductivities, which increase further upon permethylation of the hydroxyl termini, are found to correlate quantitatively with the fast segmental dynamics of PEO as measured by inelastic neutron scattering.

Rheological Consequences of Hydrogen Bonding: Linear Viscoelastic Response of Linear Polyglycerol and Its Permethylated Analogues as a General Model for Hydroxyl-Functional Polymers

Viscoelastic properties of linear, hydroxyl-functional polymers are only little understood with respect to the effect of functional group interactions. Melt rheology and thermal phase transitions of linear polyethers (polyglycerol, linPG-OH) and their methylated analogues (linPG-OMe) in a broad molecular weight range (Mn = 1–100 kg/mol) with low polydispersities (PDI) have been investigated as a general model for hydroxyl-functional polymers with respect to their functionality and hydrogen bond interactions. We provide detailed insight into the rheodynamics of nonentangled and well-entangled polyethers bearing one functional group per monomer unit. Booij–Palmen plots (BBP) revealed failure …

Multihydroxyl-Functional Polystyrenes in Continuous Flow

We describe the synthesis of end-functionalized polystyrenes by living anionic polymerization in a microstructured reactor via termination by acetal-protected functional epoxides. Initiation of styrene polymerization by alkyllithium takes place in a micromixing device with efficient heat and mass transfer properties. A newly developed continuous polymerization−termination sequence enabled quantitative functionalization of the living carbanions by nucleophilic displacement with different, specifically designed glycidyl ethers (ethoxy ethyl glycidyl ether (EEGE), 1,2-isopropylidene glyceryl glycidyl ether (IGG), and trans-2-phenyl-1,3-dioxane glycidyl ether (PDGE)). Upon acidic hydrolysis the…

Entanglement Transition in Hyperbranched Polyether-Polyols

Are hyperbranched polymers capable of forming entanglements? This is the central issue of this contribution. Hyperbranched polyglycerol (hbPG) samples with different molecular weights (600-106 000 g · mol(-1) ), narrow polydispersities (1.2-1.8) and high degrees of branching (≈0.6) were prepared by anionic ring-opening polymerization. The viscoelastic properties of these polymers with respect to molecular architecture and molar mass were investigated. At low molecular weights "classical" scaling behavior between zero shear viscosity and molecular weight can be observed, whereas between 3 000 and 10 000 g · mol(-1) a plateau-like area is found. The results indicate entanglement dynamics when…

Synthesis of Hyperbranched Polyglycerol in a Continuous Flow Microreactor

Hyperbranched polymers have been synthesized in a microreactor for the first time, employing the known ring-opening multibranching polymerization of glycidol. Microreactors are well-known to be beneficial for highly exothermic reactions because of their capability to enhance mass and heat transfer due to short diffusion pathways and large interfacial areas per volume. The characteristics of the microstructured reaction system were utilized to engineer a continuous flow process for the preparation of well-defined hyperbranched polyglycerols with molecular weights up to 1,000 g/mol. Increased flow rates, as well as the use of highly polar solvents, led to the partial formation of very narrowl…

Hyperbranched Polyglycerols with Elevated Molecular Weights: A Facile Two-Step Synthesis Protocol Based on Polyglycerol Macroinitiators

Hyperbranched polyglycerol (PG) is established as one of the few hyperbranched polymers that offer the possibility to control molecular weight up to Mn = 6000 g/mol. This work introduces a facile 2-step strategy that relies on the use of a low molecular weight PG (Mn = 500 and 1000 g/mol) as a macroinitiator for the slow addition of glycidol, permitting to overcome previous limitations concerning molecular weights and molecular weight control. A systematic investigation of the effect of the degree of deprotonation on the control of the polymerization reaction has been carried out. A series of hyperbranched PGs with molecular weights up to Mn = 24000 g/mol has been obtained under fully contr…