Control Of Polymer Structure Research Articles

Mechanistic Insights into Oxidative Molecular Layer Deposition of Conjugated Polymers

Oxidative molecular layer deposition (oMLD) promises to enable molecular-level control of polymer structure through monomer-by-monomer growth via sequential, self-limiting, gas-phase surface reactions of monomer(s) and oxidant(s). However, only a few oMLD growth chemistries have been demonstrated to date, and limited mechanistic understanding is impairing progress in this field. Here, we examine oMLD growth using 3,4-ethylenedioxythiophene (EDOT), pyrrole (Py), p-phenylenediamine (PDA), thiophene (Thi), and furan (Fu) monomers. We establish key insights into the surface reaction mechanisms underlying oMLD growth. We specifically identify the importance of a two-electron chemical oxidant with sufficient oxidation strength to oxidize both a surface and a gas-phase monomer to enable oMLD growth. The mechanistic insights we report enable rational molecular assembly of copolymer structures to improve electrochemical capacity. This work is foundational to unlock molecular-level control of redox-active polymer structure and will enable the study of previously intractable questions regarding the molecular origins of polymer properties, allowing us to control and optimize polymer properties for energy storage, water desalination, and sensors.

Photoredox Catalysis in Photocontrolled Cationic Polymerizations of Vinyl Ethers.

Advances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.

Advances in Molecular Layer Deposition of Conductive and Redox-Active Polymer Thin-Films

Electrically-conductive and redox-active polymers such as polyethylenedioxythiophene (PEDOT), polypyrrole (PPy), and polyaniline (PANI) have appealing properties for use in electrochemical applications including energy storage, electrochemical desalination, and chemical sensors. In each of these applications, delivering conformal, thin-film polymer coatings is attractive to provide lower weight, faster charging, and higher sensitivity. Molecular layer deposition (MLD) is an attractive approach for delivering such thin-film coatings and promises to provide molecular-level control of polymer structure. Previous work has reported a scheme for MLD of conductive and redox-active polymers termed oxidative MLD or “oMLD” that employs sequential doses of monomers and a chemical oxidant. Initial work demonstrated the formation of PEDOT films using this approach. In recent work, we expanded the list of oMLD-accessible polymers to include PPy, PANI, and their derivatives. In this report, we describe efforts to better understand the oMLD growth mechanism using in situ and ex situ characterization. We also report on initial studies of the deposition of copolymer alloys of different monomer combinations using oMLD. These copolymer alloys are found to yield improved electrochemical properties over isolated monomer chemistries. Our results provide new insights into the oMLD growth mechanism, and offer the prospect for providing improved understanding of the properties of conductive polymers through bottom-up structure control by oMLD.

Controlling Polymer Composition in Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Vinylcyclopropanes.

Although radical polymerizations are among the most prevalent methodologies for the synthesis of polymers with diverse compositions and properties, the intrinsic reactivity and selectivity of radical addition challenge the ability to impart control over the polymerization propagation and produce polymers with defined microstructure. Vinylcyclopropanes (VCPs) can be polymerized through radical ring-opening polymerization to produce polymers possessing linear (l) or cyclic (c) repeat units, providing the opportunity to control polymer structure and modify the polymer properties. Herein, we report the first organocatalyzed photoredox radical ring-opening polymerization of a variety of functionalized VCP monomers, where high monomer conversions and spatial and temporal control were achieved to produce poly(VCPs) with predictable molecular weight and low dispersity. Through manipulating polymerization concentration and temperature, tunable l or c content was realized, allowing further investigation of thermal and viscoelastic materials properties associated with these two distinct compositions. Unexpectedly, the photoredox catalysis enables a postpolymerization modification that converts l content into the c content. Combined experimental and computational studies suggested an intramolecular radical cyclization pathway, where cyclopentane and cyclohexane repeat units are likely formed.

The efficiency of cytosolic drug delivery using pH-responsive endosomolytic polymers does not correlate with activation of the NLRP3 inflammasome.

Inefficient cytosolic delivery has limited the development of many promising biomacromolecular drugs, a long-standing challenge that has prompted extensive development of drug carriers that facilitate endosomal escape. Although many such carriers have shown considerable promise for cytosolic delivery of a diversity of therapeutics, the rupture or destabilization of endo/lysosomal membranes has also been associated with activation of the inflammasome with attendant risk of inflammation and toxicity. In this study, we investigated relationships between pH-dependent membrane destabilization, cytosolic drug delivery, and inflammasome activation using a series of well-defined poly[(ethylene glycol)-block-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)] copolymers of variable second block composition and pH-responsive properties. We found that polymers that demonstrated the most potent membrane-destabilizing activity at early endosomal pH values in an erythrocyte hemolysis assay were most efficient at delivery of siRNA, yet tended to be associated with the least amount of NOD-like related protein 3 (NLRP3) inflammasome activation. By contrast, polymers that displayed minimal hemolysis activity and poor siRNA knockdown, and instead mediated lysosomal rupture likely due to a proton sponge mechanism, strongly induced NLPR3 inflammasome activation in a caspase- and cathepsin-dependent manner. Collectively, these findings reinforce the importance of early endosomal escape in minimizing inflammasome activation and also demonstrate the ability to tune the degree inflammasome activation via control of polymer structure with potential implications for design of vaccine adjuvants and immunotherapeutics.

Investigation on thermal properties of Styrene Acrylonitrile (SAN) matrix with Polytetrafluroethylene (PTFE) particle reinforced composites

Temperature utilization of composites materials depends on its thermal conductivity and co-efficient of thermal expansion. Polymers are exceptionally combustible because of their structure and they can’t fulfill a few applications. Thermal treatment of soften polymer because of the preparing setup by injection molding fabrication process able to control polymer structure (fitting) and in this manner deciding its thermal conduct. The fundamental point of this work is to contemplate the impact of Polytetrafluroethylene polymer (PTFE) as particle with Styrene Acrylonitrile polymer (SAN) as matrix to examine its thermal properties. Samples of 100% SAN and 10% PTFE by weight, 20% PTFE by weight blended specimens with SAN are prepared successfully by Injection molding process. Heat capacity, Thermal expansion, Thermal conductivity and Thermal degradation are the thermal properties examined. From the observations it was found that PTFE particles blended samples exhibits maximum thermal conductivity and good dimensional stability.

Photocontrolled Interconversion of Cationic and Radical Polymerizations.

The ability to combine two polymerization mechanisms in a one-pot setup and switch the monomer selectivity via an external stimulus provides an excellent opportunity to control polymer sequence and structure. We report a strategy that enables monomer incorporation to be determined via the selection of the wavelength of light through selective activation of either cationic or radical processes. This method enables the synthesis of varying polymeric structures under identical solution conditions but with simple modulation of the external stimulus. Additionally, changes in the ratios of the two photocatalysts afford complementary chemical control over these reactions to design elaborated polymeric structures. Our strategy takes advantage of the unique regulation that can be accessed through light.

Libraries of modified polyacrylamides using post‐synthetic modification

ABSTRACTPolyacrylamide‐based (PAM) polymers are the most widely used synthetic water‐soluble polymer so they are applied in a range of industries. However, they suffer from a number of limitations which requires the development of synthetic routes that can accurately control polymer structure and hence function. This study describes a carbodiimide mediated coupling reaction (CMC) that is used to generate modified polyacrylamide (PAM) including hydrophobically modified water‐soluble polymers (HMWSP). The reaction proceeds efficiently in water and does not require organic solvents or high temperatures. The approach is flexible due to the efficiency of the CMC reaction allowing for accurate control over polymer structure and function. This is confirmed using acid‐base titration, spectroscopy, viscometry, and rheology. The viscosity of the polymers varies over a broad range with those containing larger hydrophobic group (dodecyl) showing the highest viscosity. The hydrophobicity of the pendent group determines how it influences viscosity and using this new synthetic approach polymer with the same molecular weight can be compared. Linear hydrocarbon pendent groups are more hydrophobic than the cyclic versions resulting in higher viscosity. However, the spatial arrangement of the pendent group (linear or cyclic) also affects the viscosity at higher pendent group contents. The number of modified PAMs that can be generated is expansive because the approach works with a number of different functional groups and base polymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42797.

Tunable mesoscale-structured self-assembled hydrogels synthesized by organocatalytic ring-opening polymerization

A class of tunable, mesostructured self-assembled hydrogels has been developed based on a library of π–π stacking ABA-type telechelic triblock copolymers prepared by organocatalytic ring-opening polymerization (ROP). Poly(ethylene glycol) (PEG) served as a macroinitiator for ROP of methylene tricarbonate-benzyl ester (MTC-OBn), a benzyl-ester functionalized cyclic carbonate monomer, resulting in polymers with well-defined length and narrow polydispersity. Self-assembled hydrogels were formed by dissolving poly(MTC-OBn)-b-PEG-b-poly(MTC-OBn) copolymers in water. Physical cross-links in the hydrogels formed through hydrophobic and π–π stacking intermolecular interactions between poly(MTC-OBn) segments. The mesoscale material properties were probed using small angle X-ray scattering (SAXS) and dynamic mechanical measurements. SAXS spectra show a scattering peak, corresponding to a molecular domain spacing of 20–25 nm, which we attribute to the formation of electron-dense poly(MTC-OBn) assemblies. Results from oscillatory shear experiments were analyzed in conjunction with SAXS data in order to develop an understanding of the influence that nanoscale structure has on the mechanical properties of self-assembled gels. Modeling of scattering peaks using the Bragg spacing model demonstrated that the hydrophilic PEG network chains connecting the scattering moieties behaved as a two-dimensional self-avoiding walk. We compared the observed microstructural features with the mechanical properties of self-assembled gels and determined that the molecular weight of the polycarbonate and PEG segments controls the gel structure on both the mesoscale and macroscale. A central contribution of this work is a synthetic strategy that utilizes ROP to control polymer structure, which in turn controls both the structure and mechanical properties of these biodegradable self-assembled hydrogels.

Solid-State Polycondensation via Ionic-to-Covalent Bond Transformation to Control Polymer Structure: Preparation of Porphyrin-Based Ladder Polymer.

The controlled formation and the regular arrangement of polymer chains have been performed by novel solid-state polycondensation including the ionic-to-covalent bond transformation in the ionic molecular crystals. The combination of the tetra-anion and -cation of tetraphenylporphyrin derivatives, tetrakis(benzylpyridinium carboxylate), was found to form layered crystal structures and underwent thermal solid-state polycondensation, thus, releasing the pyridine and forming the benzyl ester linkages. Powder X-ray diffraction, when compared to the monomer crystal structure data, suggested that the ladder polymer was produced with a layered structure.

Divergent Macrocyclization Mechanisms in the Cationic Initiated Polymerization of Ethyl Glyoxylate

We recently discovered that the cationic polymerization of o-phthalaldehyde generates cyclic poly(phthalaldehyde) in high yield, high molecular weight, and a high degree of cyclic purity. Given this surprising result, we pursued the cationic polymerization of ethyl glyoxylate to determine if the macrocyclization outcome is, in fact, a general trend of low ceiling temperature polyacetals. Using NMR spectroscopy, MALDI-TOF mass spectrometry, and triple detection GPC, we have uncovered divergent macrocyclization mechanisms in the cationic polymerization of ethyl glyoxylate. Backbiting is observed either via the backbone acetal or via the pendant ester to give disparate polymer products and unique polymer architectures. The favored route for cyclization is found to depend on both the monomer concentration and the initiating species. Understanding the underlying mechanisms of polymerization and the ability to rigorously control polymer structure has important implications for the design of new transient materials.

Synthesis and characterization of new 4-vinylsilylbenzocyclobutene/vinylsilylbenzene random copolymers

In this work, a copolymerization of 4-(1′,1′-dimethyl-1′-vinyl) silylbenzocyclobutene (4-DMVSBCB) and CH2=CHSiMe2Ph (DMVSPh), which have similar structure, was performed by the anionic polymerization method, leading to a synthesis of a series of cross-linkable random copolymers. Attractively, the 4-DMVSBCB/DMVSPh ratio in the copolymer was almost consistent with the DMVSPh/4-DMVSBCB feed ratio, which allows the control of polymer structure. Most importantly, the replacement of partial 4-DMVSBCB by DMVSPh units provided relatively economical materials which were capable of preserving almost all the advantages of poly(4-DMVSBCB). Furthermore, the curing dynamic of copolymers can be tuned by varying 4-DMVSBCB incorporation ratio.

触媒による加熱過程における高分子構造制御

触媒による加熱過程における高分子構造制御

Molecular Recognition and Polymers – Control of Polymer Structure and Self‐Assembly

Macromolecular Chemistry and PhysicsVolume 210, Issue 16 p. 1349-1349 Book Review Molecular Recognition and Polymers – Control of Polymer Structure and Self-Assembly Christoph Weder, Christoph Weder Fribourg (Switzerland) and Shaker Heights (USA)Search for more papers by this author Christoph Weder, Christoph Weder Fribourg (Switzerland) and Shaker Heights (USA)Search for more papers by this author First published: 14 August 2009 https://doi.org/10.1002/macp.200900342Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume210, Issue16August 21, 2009Pages 1349-1349 RelatedInformation

Book Review of Molecular Recognition and Polymers: Control of Polymer Structure and Self-Assembly

Book Review of Molecular Recognition and Polymers: Control of Polymer Structure and Self-Assembly

Glycolipid Polymer Synthesized from Natural Lactonic Sophorolipids by Ring-Opening Metathesis Polymerization

NSF-I/UCRC Center for Biocatalysis and Bioprocessing ofMacromolecles, Department of Chemical and BiologicalSciences, Polytechnic UniVersity, Six Metrotech Center,Brooklyn, New York 11201, and Department of PolymerScience and Engineering, UniVersity of Massachusetts,120 GoVernors DriVe, Amberst, Massachusetts 01003-4530ReceiVed September 1, 2006ReVised Manuscript ReceiVed December 2, 2006In the past two decades, ring-opening metathesis polymeri-zation (ROMP) has proven to be an efficient method for controlof polymer structure and bulk properties.

Polymerization in Coordination Nanospaces

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Polymerization in Coordination Nanospaces

Inspired by elegant polymerizations in biological systems, polymer synthesis in confined artificial nanospaces is a key challenge in the control of polymer structures and the design of well-defined nanostructures. In this regard, porous coordination polymers (PCPs) have a wide range of advantages, such as regular channel structures, controllable pore size, dynamic and flexible pores, and unique surface potentials and functionality, which can be utilized for precisely controlled polymerization and polymer arrangement. This Focus Review describes recent progress in polymerization in the nanochannels of PCPs and demonstrates why this polymerization system is so attractive and promising, from the viewpoints of three essential polymerization processes in PCPs, that is, monomer arrangement, polymerization methods, and control of polymer structure.

ポリマー構造を制御した新規顔料分散剤

ポリマー構造を制御した新規顔料分散剤

MALDI-TOF Detection of Olefin Structural Isomerization in Metathesis Chemistry

MALDI-TOF mass spectrometry has been employed to examine polymers generated via acyclic diene metathesis (ADMET) polymerization using a ruthenium metathesis catalyst at 50 °C, a study which targets the analysis of ADMET polymers having amino acid pendant groups placed at specific positions along the polyolefin backbone. The MALDI spectra clearly delineate olefin isomerization chemistry which competes with propagation when catalyst 2 is employed, the result being loss of precise control of polymer structure. The distribution of peaks in the MALDI spectra matches the distribution pattern of gas chromatography (GC) peaks obtained for other ADMET polymers, leading to the following conclusions. First, structural isomerization and metathesis occur concurrently rather than in any kind of sequence. Second, the relative amount of isomerized chains produced dominates over the amount of nonisomerized products. In contrast to GC, MALDI analysis unequivocally identifies the mass of the oligomeric chains, allowing for increased confidence in assignment of the possible chain structures.