1. Multifunctional Initiators. 3749 2. Multifunctional Linking Agents 3751 3. Use of Difunctional Monomers 3754 B. Star−Block Copolymers 3754 C. Functionalized Stars 3755 1. Functionalized Initiators 3755 2. Functionalized Terminating Agents 3756 D. Asymmetric Stars 3757 1. Molecular Weight Asymmetry 3757 2. Functional Group Asymmetry 3760 3. Topological Asymmetry 3761 E. Miktoarm Star Polymers 3761 1. Chlorosilane Method 3761 2. Divinylbenzene Method 3766 3. Diphenylethylene Derivative Method 3766 4. Synthesis of Miktoarm Stars by Other Methods 3770

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Polymers with Complex Architecture by Living Anionic Polymerization

Macromolecular Architectures by Living and Controlled/Living Polymerizations

http://www.materials.uoi.gr/polymers/files/PapersPDF/PPS2005.pdf

Linear and non-linear triblock terpolymers. Synthesis, self-assembly in selective solvents and in bulk

Semi-crystalline polymers containing amorphous and crystalline regions usually have intimately mixed chains. The resulting topological constraints (entanglements) in the amorphous regions limit the drawability in the solid state. By controlled synthesis the number of entanglements can be reduced. Ultimately, crystals composed of single chains are feasible, where the chains are fully separated from each other. If such separation can be maintained in the melt a new melt state can be formed. Here we show that through slow and carefully controlled melting such polymer crystals form a heterogeneous melt with more entangled regions, where the chains are mixed, and less entangled ones, composed of individually separated chains. Chain reptation, required for the homogenization of the entanglement distribution, is found to be considerably hindered. The long-lived heterogeneous melt shows decreased melt viscosity and provides enhanced drawability on crystallization. This novel route to create heterogeneous melt should be applicable to polymers in general.

Heterogeneity in polymer melts from melting of polymer crystals

In this paper, we examine the melt rheology of well-defined, model polymers where the long chain branching (LCB) is precisely known from the synthesis. All of these are made by the hydrogenation of polybutadiene, but they vary greatly in the level and type of LCB present. We find that all polymers that have LCB show a greater degree of shear thinning than linear chains. This applies both to those with a single branch (stars) and also to those with multiple branches per chain (such as combs). However, only molecules with multiple branches induce extensional thickening in a sample. Only a small amount of these comblike molecules, on the order of 5%, are needed to show this effect. We also show here how a new method of treating the shear data, the so-called Van Gurp−Palmen analysis, can give a more easily interpreted form of the results that can reveal the length and amount of branches in a sample. The insights generated from this work show the importance of access to well-defined polymers with several kinds...

Well-Defined, Model Long Chain Branched Polyethylene. 2. Melt Rheological Behavior

We describe the synthesis and characterization of a number of polymers with well-defined structures that serve as models for polyethylene with long chain branching. All of them have been made by using anionic polymerization techniques and controlled chlorosilane chemistry to give nearly monodisperse polybutadienes with precise control of the number, length, and placement of long (Mw > 1500 g/mol) branches on each chain. This was followed by hydrogenation to give saturated polymers with the same well-defined long chain branching and the local structure of a typical linear low-density polyethylene. That is, both the backbones and the long branches had 17−25 ethyl branches per 1000 total carbons. Among the structures made were some with no long branches (“linears”), some with a single long branch (“stars”), others with exactly two branch points (the α−ω type, “H's”, “super-H's”, and “pom-poms”), and some with several long branches randomly distributed along the backbone (“combs”). Essentially all types of b...

Well-Defined, Model Long Chain Branched Polyethylene. 1. Synthesis and Characterization

Synthesis of an exact graft copolymer of isoprene and styrene with two branches

We introduce a new combination of diene/diene microstructures to form microphase-separated ABC terpolymers. The synthesis and morphology of two triblock terpolymers of the poly(butadiene-b-styrene-b-isoprene) (BSI) type and one poly(styrene-b-butadiene-b-isoprene) (SBI) type are reported. The microstructure for the PB block was 92 wt % 1,4- and 8 wt % 1,2- and for the PI block 54 wt % 3,4-, 16 wt % 1,2-, and 30 wt % 1,4-. A three-component microphase-separated system occurred even when the two diene blocks were adjacent, as in the SBI sequence, leading to the conclusion that the PB:PI 1,4/3,4 diene combination has a larger Flory−Huggins χ parameter than the other three possible combinations of PB:PI diene microstructures. A new type of cylindrical microdomain structure with alternating types of diene regions along the cylinder axis is observed.

Synthesis and Microphase Separation of Linear Triblock Terpolymers of Polystyrene, High 1,4-Polybutadiene, and High 3,4-Polyisoprene

Dielectric spectroscopy has been employed to study selectively the local and global dynamics of polyisoprene (PI) in three microphase separated star diblock copolymers (SI)4, where PI and polystyrene (PS) form the core and corona, respectively. The thermally induced order-to-disorder transition (ODT) has been identified by rheology and small-angle x-ray scattering (SAXS). All dielectric measurements were made at temperatures well below the ODT and the polystyrene glass transition temperatures, where the four PI chain ends are tethered by the glassy polystyrene domains. The ordered state morphology, studied by SAXS, revealed the formation of PS spheres (fPS=0.25, where fPS is the polystyrene volume fraction), polyisoprene cylinders (fPS=0.68), and a lamellar structure (fPS=0.41) in the three copolymers. In contrast to the local segmental motions, the chain orientational dynamics associated with the amplitude and the characteristic relaxation time are strongly influenced by the spatial confinement. The main...

Stella Paraskeva

Papers

Well-Defined, Model Long Chain Branched Polyethylene. 1. Synthesis and Characterization

Synthesis of an exact graft copolymer of isoprene and styrene with two branches

Synthesis and Microphase Separation of Linear Triblock Terpolymers of Polystyrene, High 1,4-Polybutadiene, and High 3,4-Polyisoprene

Dynamics of polyisoprene in star block copolymers confined in microstructures: A dielectric spectroscopy study