Dynamics near the Glass Temperature of Low Molecular Weight Cyclic Polystyrene

Photoresponsive Amphiphilic Macrocycles Containing Main-Chain Azobenzene Polymers

Herein, the first example of photosensitive cyclic amphiphilic homopolymers consisting of multiple biphenyl azobenzene chromophores in the cyclic main chain tethered with hydrophilic tetraethylene glycol monomethyl ether units is presented. The synthetic approach involves sequentially performed thermal catalyzed "click" step-growth polymerization in bulk, and Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) intramolecular cyclization from α-alkyne/ω-azide linear precursors. It is observed that such amphiphilic macrocycles exhibit increased glass transition temperatures (Tg ), slightly faster trans-cis-trans photoisomerization, and enhanced fluorescence emission intensity compared with the corresponding linear polymers. In addition, the cyclic amphiphilic homopolymers self-assemble into spherical nanoparticles with smaller sizes which possess slower photoresponsive behaviors in a tetrahydrofuran/water mixture compared with those of the linear ones. All these interesting observations suggest that the cyclic topology has a great influence on the physical properties and self-assembly behavior of these photoresponsive amphiphilic macrocycles in general.

Self-assembly of cyclic polymers

This review describes the self-assembly of polymers with a cyclic topology and highlights how cyclization affects the resulting assemblies.

Glass Transition Temperature of Cyclic Stars

Cyclic homo- and diblock copolymers with different topologies were synthesized using a combination of "living" radical polymerization and "click" coupling reactions. The topologies included 2- and 3-arm stars, with the arms consisting of either cyclic or linear polystyrene. In addition, a diblock consisting of a cyclic polystyrene and a cyclic poly(acrylic acid) was also made. The topologies by imposing topological constraints due to the presence of cyclic polymers and branch points had a marked influence on the glass transition temperature (T_g). It was found that for the polystyrene topology series, the T_g increased above the glass transition temperature at infinite molecular weight for a linear chain (i.e., T_g^∞) and correlated to the more compact nature of cyclic polymers. For the cyclic diblock of polystyrene and poly(acrylic acid), the T_g increased significantly due to separation of the blocks into their pure phases. This resulted in significant stretching of the chains and thus loss of conformation entropy.

Dynamics and thermodynamics of polymer glasses

The fate of matter when decreasing the temperature at constant pressure is that of passing from gas to liquid and, subsequently, from liquid to crystal. However, a class of materials can exist in an amorphous phase below the melting temperature. On cooling such materials, a glass is formed; that is, a material with the rigidity of a solid but exhibiting no long-range order. The study of the thermodynamics and dynamics of glass-forming systems is the subject of continuous research. Within the wide variety of glass formers, an important sub-class is represented by glass forming polymers. The presence of chain connectivity and, in some cases, conformational disorder are unfavourable factors from the point of view of crystallization. Furthermore, many of them, such as amorphous thermoplastics, thermosets and rubbers, are widely employed in many applications. In this review, the peculiarities of the thermodynamics and dynamics of glass-forming polymers are discussed, with particular emphasis on those topics currently the subject of debate. In particular, the following aspects will be reviewed in the present work: (i) the connection between the pronounced slowing down of glassy dynamics on cooling towards the glass transition temperature (Tg) and the thermodynamics; and, (ii) the fate of the dynamics and thermodynamics below Tg. Both aspects are reviewed in light of the possible presence of a singularity at a finite temperature with diverging relaxation time and zero configurational entropy. In this context, the specificity of glass-forming polymers is emphasized.

Zwitterionic polymerization of glycidyl monomers to cyclic polyethers with B(C6F5)3

Glycidyl monomers react with B(C₆F₅)₃ to generate cyclic polyethers decorated with functional groups.

Viscosity of ring polymer melts

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as function of the number of entanglements Z. In the unentangled regime η0,linear/η0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/η0,ring=2. In the entanglement regime, the Z-dependence of rings viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 Collapse

Key Words

• entanglements
• molecular weight
• purification
• ring polymers
• viscosity

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Grants

• P01 HL108808 NHLBI NIH HHS
• P50 HL107168 NHLBI NIH HHS

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Affiliation(s)

Rossana Pasquino FORTH, Institute for Electronic Structure and Laser, Heraklion 71110, Greece
Thodoris C Vasilakopoulos University of Athens, Department of Chemistry, Athens 15771, Greece
Youn Cheol Jeong Pohang University of Science and Technology, Division of Advanced Materials Science and Department of Chemistry, Pohang 790-784, Korea
Hyojoon Lee Pohang University of Science and Technology, Division of Advanced Materials Science and Department of Chemistry, Pohang 790-784, Korea
Simon Rogers FORTH, Institute for Electronic Structure and Laser, Heraklion 71110, Greece
George Sakellariou University of Athens, Department of Chemistry, Athens 15771, Greece
Jürgen Allgaier Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Atsushi Takano Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Ana R Brás Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Taihyun Chang Pohang University of Science and Technology, Division of Advanced Materials Science and Department of Chemistry, Pohang 790-784, Korea
Sebastian Gooßen Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Wim Pyckhout-Hintzen Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Andreas Wischnewski Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Nikos Hadjichristidis University of Athens, Department of Chemistry, Athens 15771, Greece ; King Abdullah University of Science and Technology, Division of Physical Sciences & Engineering, KAUST Catalysis Center, Polymer Synthesis Laboratory, Thuwal, Kingdom of Saudi Arabia
Dieter Richter Forschungszentrum Jülich GmbH, Jülich 52428, Germany
Michael Rubinstein Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA
Dimitris Vlassopoulos FORTH, Institute for Electronic Structure and Laser, Heraklion 71110, Greece ; University of Crete, Department of Materials Science & Technology, Heraklion 71003, Greece

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