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Lutz J.-F.,Charles Sadron Institute
Accounts of Chemical Research | Year: 2013

Synthetic polymer materials are currently limited by their inability to store information in their chains, unlike some well-characterized biopolymers. Nucleic acids store and transmit genetic information, and amino acids encode the complex tridimensional structures and functions within proteins.To confer similar properties on synthetic materials, researchers must develop" writing" mechanisms, facile chemical pathways that allow control over the primary structure of synthetic polymer chains. The most obvious way to control the primary structure is to connect monomer units one-by-one in a given order using iterative chemistry. Although such synthesis strategies are commonly used to produce peptides and nucleic acids, they produce limited yields and are much slower than natural polymerization mechanisms. An alternative strategy would be to use multiblock copolymers with blocks that have specified sequences. In this case, however, the basic storage element is not a single molecular unit, but a longer block composed of several repeating units. However, the synthesis of multiblock copolymers is long and tedious. Therefore, researchers will need to develop other strategies for writing information onto polymer chains.In this Account, I describe our recent progress in the development of sequence controlled polymerization methods. Although our research focuses on different strategies, we have emphasized sequence-regulation in chain-growth polymerization processes. Chain-growth polymerizations, particularly radical polymerization, are very convenient methods for synthesizing polymers. However, in most cases, such approaches do not lead to controlled monomer sequences. During the last five years, we have shown that controlled/living chain-growth polymerization mechanisms offer interesting advantages for sequence regulation. In such mechanisms, the chains form gradually over time, and therefore the primary structure can be tuned by using time-controlled monomer additions. For example, the addition of small amounts of acceptor comonomers, such as N-substituted maleimides, during the controlled radical polymerization of a large excess of donor monomer, such as styrene, allows the writing of information onto polymer chains in a robust manner. Even with these advances, this strategy is not perfect and presents some of the drawbacks of chain-growth polymerizations, such as the formation of chain-to-chain sequence defects. On the other hand, this approach is experimentally easy, rapid, scalable, and very versatile. © 2013 American Chemical Society. Source

Lutz J.-F.,Charles Sadron Institute
Advanced Materials | Year: 2011

We describe here the advantages of oligo(ethylene glycol)-based (co)polymers for preparing thermoresponsive materials as diverse as polymer-enzyme bio-hybrids, injectable hydrogels, capsules for drug-release, modified magnetic particles for in vivo utilization, cell-culture substrates, antibacterial surfaces, or stationary phases for bioseparation. Oligo(ethylene glycol) methacrylates (OEGMAs) can be (co)polymerized using versatile and widely-applicable methods of polymerization such as atom transfer radical polymerization (ATRP) of reversible addition-fragmentation chain-transfer (RAFT) polymerization. Thus, the molecular structure and therefore the stimuli-responsive properties of these polymers can be precisely controlled. Moreover, these stimuli-responsive macromolecules can be easily attached to-or directly grown from-organic, inorganic or biological materials. As a consequence, the OEGMA synthetic platform is today a popular option for materials design. The present research news summaries the progress of the last two years. The (controlled) radical polymerization of oligo(ethylene glycol) methacrylates (OEGMAs) is a new construction platform in materials science. Indeed, thermoresponsive polymers constructed with OEGMAs allow design of a wide variety of smart materials such as polymer-enzyme bio-hybrids, injectable hydrogels, capsules for drug-release, modified magnetic particles for in vivo utilization, cell-culture substrates, antibacterial surfaces, or stationary phases for bioseparation. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Lutz J.-F.,Charles Sadron Institute
ACS Macro Letters | Year: 2014

Current polymer terminology only describes very simple copolymer structures such as block, graft, alternating periodic, or statistical copolymers. This restricted vocabulary implies that copolymers exhibit either segregated (i.e., block and graft), regular (i.e., alternating and periodic), or uncontrolled (i.e., statistical or random) comonomer sequence distributions. This standard classification does not include many new types of sequence-controlled copolymers that have been reported in recent years. In this context, the present viewpoint describes a new category of copolymers: aperiodic copolymers. Such structures can be defined as copolymers in which monomer sequence distribution is not regular but follows the same arrangement in all chains. The term aperiodic can be used to describe encoded comonomer sequences in monodisperse sequence-defined copolymers but also the block sequence of some multiblock copolymers. These new types of copolymers open up very interesting perspectives for the design of complex materials. Some recent relevant literature on the topic is discussed herein. (Figure Presented). © 2014 American Chemical Society. Source

Rhamnogalacturonans-I (RGs-I) are complex structural components of the (primary) cell wall. Their backbone, composed of the repeating diglycosyl [→2)-α- L-Rhap-(1→4)-α-D-GalpA-(1→], is believed to be branched at O-4/O-3 positions by 4 different side chain types, viz. (1→5)-α-L-arabinan, (1→4)-β- D-galactan, arabinogalactan-I, and sometimes with arabinogalactan-II. However, the fine structure of RGs-I remains somewhat enigmatic, as shown by various continuous findings, such as branches of galactoarabinan, arabinogalactan with a (1→6) - D-galactan core, and possibly (1→3)-rhamnan. This timely review is the first of its kind, highlighting the freak structural diversity and the functional versatility of RG-I, one of the two major structural domains of complex pectins. © 2011 Copyright Taylor and Francis Group, LLC. Source

Brinkmann M.,Charles Sadron Institute
Journal of Polymer Science, Part B: Polymer Physics | Year: 2011

This review focuses on the structural control in thin films of regioregular poly(3-hexylthiophene) (P3HT), a workhorse among conjugated semiconducting polymers. It highlights the correlation existing between processing conditions and the resulting structures formed in thin films and in solution. Particular emphasis is put on the control of nucleation, crystallinity and orientation. P3HT can generate a large palette of morphologies in thin films including crystalline nanofibrils, spherulites, interconnected semicrystalline morphologies and nanostructured fibers, depending on the elaboration method and on the macromolecular parameters of the polymer. Effective means developed in the recent literature to control orientation of crystalline domains in thin films, especially by using epitaxial crystallization and controlled nucleation conditions are emphasized. © 2011 Wiley Periodicals, Inc. Source

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