Macromolecular Chemistry and Physics

Front Cover: Density functional theory calculations reveal a detailed normal amine mechanism of a ring-opening reaction of the α-amino acid N-carboxyanhydride (NCA). Three steps are involved including addition, ring-opening, and decarboxylation. The first step, in which C⁵ the carbonyl group of NCA is attacked by an NH₂ group, is rate-determining. Further details about this widely used reaction can be found in the article by J. Ling^* and Y. Huang on page 1708.

FTIR spectroscopic imaging is shown to be a valuable tool for the investigation of structures and orientations of solid polymers. Poly(3-hydroxybutyrate) and isotactic poly(propylene oxide) serve as well-understood examples for the demonstration of this technique.

The effect of incorporation of clay particles on the orientation of thermotropic liquid crystal polymer (LCP) is studied. The unique uplifting nature of both storage and loss moduli of LCP and its clay-containing nanocomposites in the low-frequency region during the frequency sweep was supported nicely by the two-dimensional small- and wide-angle X-ray scattering patterns.

A simple, green synthesis technique for preparing Au nanoparticle-PDMS composites is described. The solid solution nature of the PDMS combined with the surface properties of the nanoparticles imparts unique properties to this composite. We demonstrate the utility of this material for water purification and for chemically-triggered storage and release of compounds toward-drug delivery applications.

Pentynyldextrans form silver acetylides, from which Ag nanoparticles can be obtained. Alkynylglucans have been synthesised and various types of deviation from a random substitution pattern have been found for propargyl-and higher alkynyldextrans.

The electrochemical, thermal, structural, morphological, and electrical properties of both doped and undoped poly[N-(2-cyanoethyl)pyrrole] have been examined. Results indicate that this material is suitable for specific applications in electronics. Systems made of alternated layers poly(3,4-ethylenedioxythiophene) and poly[N-(2-cyanoethyl)pyrrole] have been analyzed for their use as molecular condensers.

The defined insertion of acrylic acid into poly(tert-butyl acrylate) via RAFT polymerization considerably affects the relaxation characteristics determined via dynamic-mechanical analysis compared to the homopolymer. The ABA-type copolymers exhibit two additional relaxations due to the presence of hydrogen bonds, which are formed by the acrylic acid in the outer A-blocks and chemically confine the inner poly(tert-butyl acrylate) segments.

Liquid chromatography coupled with FT-IR spectroscopy and MALDI-TOF MS are applied for the separation and characterization of PVP/PVAc copolymers. The obtained structural data are used to elucidate the mechanism of a controlled radical polymerization, and clearly show a change from a RAFT mechanism to a conventional free radical polymerization dominated by irreversible chain transfer.

A novel low-bandgap conjugated polymer PDDTP has been synthesized and studied in polymer/fullerene bulk heterojunctions. Solar cells have been optimized according to their fullerene content and the active layer thickness. The photovoltaic performance is highly correlated with the crystallinity of the polymer as detected by grazing-incidence X-ray diffraction. The maximum power conversion efficiency coincides with a clear peak in the photocurrent generation.

The synthesis of the foamable polyelectrolyte poly(2-tert-butoxy-N-[2-(methacryloyloxy)ethyl]-N,N-dimethyl-2-oxoethanammonium chloride) is described. TGA, DSC, IR and GC/MS measurements confirm the cleavage of isobutylene at temperatures above 160 °C, which leads to the foaming of the polymer. In addition, a LCST behaviour can be obtained and varied by copolymerization with NiPAAm.

Conjugated polymer electrochromic devices can be used as infrared shutters in imaging and detection systems where all light is either completely absorbed or transmitted. The quality of operation of a mid-infrared shutter device is determined by film thicknesses, electrolyte composition, and electrolyte concentration.

The detailed polymerization mechanism of α-amino acid N-carboxyanhydride initiated by primary amines is calculated using density functional theory. Separate addition, ring-opening and decarboxylation steps are involved in a monomer ring-opening cycle; the addition step is rate-determining.

The synthesis of new polyurea networks by organic sol/gel chemistry is presented. For the first time, amino-terminated polymer melts with reactivity slowed by a capping process allow the well-defined polymer networks to be obtained when crosslinked with triisocyanates. The resulting elastomers have both chemical and physical crosslinks that enhance the mechanical properties of common polyurethanes or thermoplastic block copolymers.