Cover Picture: Macromol. Rapid Commun. 15/2006Benkoski, Jason J.; Hu, Hua; Karim, Alamgir
doi: 10.1002/marc.200690028pmid: N/A
Cover: Hierarchical assemblies can be built up from nanoscale building blocks through manipulation of the oil/water interface. By choosing a monomer as the oil phase, one can preserve a rich variety of structures by UV flash curing. We show here a surface created by iteratively crosslinking several generations of particle‐stabilized emulsions. Further details can be found in the article by J. J. Benkoski,* H. Hu, and A. Karim on page 1212.
A New Approach to Prepare Poly(ethylene terephthalate)/Silica Nanocomposites with Increased Molecular Weight and Fully Adjustable Branching or Crosslinking by SSPBikiaris, Dimitris; Karavelidis, Vassilis; Karayannidis, George
doi: 10.1002/marc.200600268pmid: N/A
Summary: In the present study, it has been unexpectedly found that solid‐state polycondensation (SSP) can act as a facile method to prepare poly(ethylene terephthalate)/silica (PET/SiO2) nanocomposites with high molecular weight and an adjustable degree of branching or crosslinking. Fumed silica, with its surface silanol groups, seems to participate in some kind of reaction, probably esterification with the hydroxy end‐groups of PET, during SSP, to act as a multifunctional chain extender. Differential scanning calorimetry and FT‐IR spectroscopy reveal this ability of the silanol groups. The molecular weight increase depends on the used temperatures of SSP as well as on the amount of SiO2 added. As the amount of silica increases the rate of increase of the intrinsic viscosity slows because of the higher extent of branching. At 5 wt.‐% SiO2 the extensive branching produces a crosslinked polymeric material. Such polyesters with increased molecular weight and low silica content could be suitable for blown bottle production, while the high SiO2 content and adjustable branching or crosslinking could make them ideal high‐melt‐strength resins suitable for the preparation of low‐density closed‐shell foams.
Polyacetylene and Polynorbornene Derivatives Carrying TEMPO. Synthesis and Properties as Organic Radical Battery MaterialsKatsumata, Toru; Satoh, Masaharu; Wada, Jun; Shiotsuki, Masashi; Sanda, Fumio; Masuda, Toshio
doi: 10.1002/marc.200600286pmid: N/A
Summary: 2,2,6,6‐Tetramethylpiperidine 1‐oxyl (TEMPO)‐containing N‐propargylamide HCCCH2NHCO‐4‐TEMPO (1), propargyl ester HCCCH2OCO‐4‐TEMPO (2), phenylacetylene derivative HCCC6H3‐3,4‐(CO2‐4‐TEMPO)2 (3), and norbornene diester monomers, NB‐2,3‐exo,exo‐(CH2OCO‐4‐TEMPO)2 (4), NB‐2,3‐endo,exo‐(COO‐4‐TEMPO)2 (5a), NB‐2,3‐endo,endo‐(COO‐4‐TEMPO)2 (5b) (NB = norbornene, TEMPO = 2,2,6,6‐tetramethyl‐1‐piperidinyloxyl) were synthesized and polymerized with rhodium and ruthenium catalysts. Monomers 2, 5a, and 5b gave polymers with number‐average molecular weights of 47 000–185 000 in 59–100% yields, while 1, 3, and 4 gave polymers insoluble in common organic solvents in 88–100% yields. The capacities of cells fabricated with poly(1), poly(2), and poly(3) were 67, 82, and 23 Ah · kg−1 based on the weight, respectively. The capacity of poly(5a)‐based cell reached the theoretical value (109 Ah · kg−1) of the polymer.
Generation of Hierarchical Topologies from Photocrosslinkable, Particle‐Stabilized EmulsionsBenkoski, Jason J.; Hu, Hua; Karim, Alamgir
doi: 10.1002/marc.200600272pmid: N/A
Summary: We describe a way to obtain biomimetic, hierarchical surface morphologies. In order to mimic natural surfaces more accurately such as lotus leaves and gecko feet, we employ a strategy that bears many of the attractive characteristics of natural materials synthesis. The system in question consists of a photocurable monomer and water. To this quasi‐two‐component system we add polymer latex spheres. The monomer–water interface is then manipulated according to the well‐established science of complex fluids. Drawing from the rich phase behavior of particle‐stabilized emulsions, we demonstrate the creation of complex biomimetic morphologies over many length scales. The resulting structures are then solidified by crosslinking the monomer with UV light.
Chain Orientation in Polyethylene Fibers Prepared by Ethylene Nanoextrusion PolymerizationYe, Zhibin; Zhu, Shiping; Britten, James F.
doi: 10.1002/marc.200600179pmid: N/A
Summary: Ethylene nanoextrusion polymerization has been demonstrated to be a novel nanofabrication concept for the preparation of polyethylene (PE) fibers directly from ethylene monomers without any post‐processing procedures. For PE fibers, chain orientation is a critical parameter that affects performance and application of the fibrous materials. In this communication, we report an investigation on chain orientation in PE fibrous samples prepared through nanoextrusion polymerization using a two‐dimensional wide angle X‐ray diffraction (2D WAXRD) technique. Two types of fibrous samples, including individual microfibers and microfiber aggregates, were sampled randomly and studied. For individual PE microfibers, anisotropic diffraction patterns were observed, suggesting chain orientation along the microfiber axial direction. Some microfibers showed the most desired diffraction pattern often found in high‐modulus high‐strength PE fibers. These samples possessed a very high degree of chain orientation along the fiber axis. Owing to a random aggregation of anisotropic microfibers, microfiber aggregates exhibited isotropic diffraction patterns. This work provided further experimental evidence for the proposed nanoextrusion polymerization concept.
A Mechanistic Interpretation of Initialization Processes in RAFT‐Mediated PolymerizationMcLeary, James B.; Tonge, Matthew P.; Klumperman, Bert
doi: 10.1002/marc.200600238pmid: N/A
Summary: The presence of strong chain length selectivity behavior during initialization in the RAFT process is an experimental observation. The mechanistic underpinning of the observation is, however, open to interpretation. The rates and concentration profiles for the cyanoisopropyl‐dithiobenzoate‐mediated polymerization of styrene at 70 °C can be relatively well reproduced by either the slow fragmentation or intermediate radical termination models. The use of modeling that provides a fit to the data is an important tool, but should be considered as additional evidence in support of experimental data rather than as experimental evidence in and of itself.
Catch and Release of DNA in Coacervate‐Dispersed GelsOhsugi, Asami; Furukawa, Hidemitsu; Kakugo, Akira; Osada, Yoshihito; Gong, Jian Ping
doi: 10.1002/marc.200600234pmid: N/A
Summary: We have synthesized novel coacervate‐droplet gels, which were applied to controlling the transportation of DNA in electrophoresis. Coacervate droplets are colloidal particles and they are usually composed of positive and negative polyelectrolytes. However, the polyzwitterion (polyampholyte) PDMAPS can form coacervate droplets in water by itself, since PDMAPS has both positive and negative charges in each side group of main chain. Coacervate droplets have a unique nature and can catch charged macromolecules such as DNA. In order to utilize the nature of the PDMAPS coacervate droplets for the catch and release of DNA, we stabilized PDMAPS droplets in gels. The droplets catch the DNA in electrophoresis and the release of DNA can be controlled by temperature and salt addition.