A simple and efficient concept has been developed for the synthesis of pH‐responsive molecular nanocarriers based on commercially available hyperbranched polymers. These dendritic core‐shell architectures can encapsulate, transport, and selectively release polar guest molecules in an acidic environment (pH 3–6, see scheme). The observed release properties render these molecular nanocarriers promising candidates for controlled drug and gene delivery.

Summary: Thin films of nematic and cholesteric side‐chain polymers containing reactive benzophenone units can be macroscopically oriented by electric/magnetic fields or surface interactions. After UV‐irradiation, liquid single crystal elastomers (LSCEs) are formed. With this simple, new pathway, macroscopically ordered free‐standing LSCE films are easily accessible having a thickness in the range of about 100 nm to 100 μm as outlined in Figure. magnified image

Smectic‐A liquid single crystal elastomers (SA‐LSCE) are materials where the rubber elasticity of the polymer network is combined with the one‐dimensional positional long‐range order of mesogenic groups which are covalently attached to the network. In the systems investigated so far, a mechanical deformation of the network causes significant reorientation processes of the layered structure. We present a new type of SA‐LSCE in which this structure remains unaffected on mechanical deformation both parallel and perpendicular to the director. The thermoelastic behavior, macroscopic dimensions, and stress–strain measurements parallel as well as perpendicular to the director are investigated. X‐ray studies confirm that a deformation parallel and perpendicular to the layer normal does not alter the macroscopically ordered lamellar structure with respect to the order parameter and the layer correlation length. We propose a simple picture where defects within the lamellar structure might account for these findings.magnified image

Cover: Smectic-A Liquid Single Crystal Elastomers exhibiting optical transparency and spontaneous shape change are presented on the cover. Additionally, a simple model of the liquid crystalline phase is presented. The background shows a beautiful S A texture of the monomer taken between crossed polarizers. Further details can be found in the article by A. Komp, and H. Finkelmann* on page 55.

Summary: Fourier transform infrared (FTIR) spectroscopy with polarized light is employed to study the segmental orientation and the order of a nematic liquid crystalline elastomers (NLCEs) with a monodomain structure in response to an external mechanical field. The reorientation and the order parameter of the different molecular moieties are analyzed in detail, revealing information about angular excursion in the rearrangement of the mesogens, the spacer molecules, and the main‐chain. In case of an elongation of the NLCE films perpendicular to the initial mesogen orientation, no reorientation or change of order is observed for an elongation ratio less than 1.3. At higher strain, a molecular reorientation process is induced on all molecular segments and the order of alignment is decreased. When the NLCE‐films are stretched parallel to the mesogens, no molecular reorientation takes place and the order parameters show no significant change.Angular reorientation of different molecular moieties at mechanical strain perpendicular to the initial mesogen orientation.magnified imageAngular reorientation of different molecular moieties at mechanical strain perpendicular to the initial mesogen orientation.

(2) H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d(6) and hexamethylbenzene-d(18) , at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase.

Physikalische Aggregate von amphiphilen Molek¸len, z. B. micellare Strukturen, werden h‰ufig f¸r den Wirkstofftransport vorgeschlagen. [1] Diese Aggregate kˆnnen jedoch aufgrund ihrer schwachen Wechselwirkungskr‰fte bei Scherkr‰ften oder anderen ‰u˚eren Einfl¸ssen zerfallen. Auch sind sie weniger f¸r die aktive Freisetzung verkapselter Molek¸le geeignet, die durch externe Signale wie pH-aenderungen ausgelˆst wird. Besonders f¸r den Wirkstofftransport in biologischen Systemen muss sich die Freisetzung von verkapselten Molek¸len auf der Basis schwacher externer Signale ereignen, z. B. einer pH-Erniedrigung in Tumor-oder infiziertem Gewebe bei pH 5±6. [2, 3] Ferner wurde gezeigt, dass Nanopartikel grˆ˚er als 5 nm, z. B. Liposomen und polymere Tr‰ger, biologische Membranen im Vergleich zu kleinen Molek¸len¸ber andere Mechanismen passieren und damit die Spezifit‰t von Wirkstoffen f¸r bestimmtes Gewebe [4±6] (z. B. Tumor) verbessern kˆnnen.Im Unterschied zu physikalischen Aggregaten amphiphiler Molek¸le kˆnnen durch die kovalente Modifizierung dendritischer Makromolek¸le [7] mit entsprechender Schale stabile micellartige Strukturen erhalten werden, welche f¸r die nichtkovalente Verkapselung von Gastmolek¸len geeignet sind. [8] W‰hrend die Verkapselung und der Transport der Gastmolek¸le in solchen dendritischen Architekturen von mehreren Arbeitsgruppen untersucht wird, [9±16] ist relativ wenig¸ber die aktive Freisetzung der verkapselten Gast-molek¸le ± ausgelˆst durch pH-abh‰ngige Spaltung der Schale ± unter physiologischen Bedingungen bekannt. Bisher wurde von einer pH-abh‰ngigen Freisetzung aus dendritischen Architekturen nur unter relativ drastischen Bedingungen [17] oder durch Protonierung von Polypropylenimin-Dendrimeren [18] und deren Derivaten berichtet. [19, 20] ZUSCHRIFTEN 4426

Polarized Fourier transform infrared (FTIR) spectroscopy is employed to study the segmental orientation and mobility of liquid-crystalline elastomers (LCEs) with a monodomain structure in response to external mechanical fields parallel and perpendicular to the initial nematic director. The mean orientation and the molecular order parameter of the different molecular moieties referring to the mesogen, the spacer and the network are analyzed in detail. Parallel stretch leaves the mean orientation of the different molecular moieties and its molecular order parameter nearly uninfluenced. Perpendicular stretch results in a threshold-like dependence: for elongation ratios lambda < or = lambda(c) = 1.3 (10 mol% crosslinker density), respectively lambda < or = lambda(c) = 1.6 (5 mol% crosslinker density) no change of the mean orientation and the molecular order parameters is observed, while for lambda > or = lambda(c) all molecular units reorient and their molecular order parameters are strongly decreased. The present studies give no indications that the reorientational dynamics of the network and the mesogens differ as long as the elongation ratio is smaller than lambda(c).