Study on the enzymatic polymerization mechanism of lactone and the strategy for improving the degree of polymerization

Polymerization of several lactones were carried out by employing Pseudomonas sp. lipase as the catalyst. The data indicate that water is consumed at the onset of polymerization and released in part during subsequent stages, leading us to propose a complex mechanism for the enzymatic polymerization of lactone. This mechanism involves both ring‐opening and linear condensation polymerization. The former was dominant at the early stage while the latter was dominant in the later stage. In addition, the reaction media showed complex influences on enzymatic polymerization. Some organic solvents increased the degree of polymerization (DP) and decreased the molecular weight distribution. A strategy to increase the molecular weight of the polymer is introduced, which led to the synthesis of a polymer with a number‐average molecular weight (M_n) of 14,500—the highest M_n of poly(ε‐caprolactone) prepared by enzyme‐catalyzed polymerization thus far—and molecular weight distribution of 1.23. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1265–1275, 1999     

Hairpin polymer unfolding in square nanochannels

The unfolding dynamics of a flexible hairpin polymer inserted in a square nanochannel is studied using Brownian dynamics simulations of the bead‐spring model. Because the hairpin polymer is not an equilibrium configuration, the molecule starts unfolding until it reaches a stretched configuration inside the tube. We study the effect of varying the channel height and width D, and the number of monomers N in the folded arm on the unfolding times. We show that for square nanochannels, the unfolding time scales as DN2, for small values of D. The unfolding relaxation dynamics obeys similar mechanisms described in the escaping dynamics of partially inserted polymers in cylindrical nanotubes. We also show that the velocity of the polymer center of mass scales as D^?1, in agreement with DNA unfolding experiments in solid‐state nanochannels and recent computational simulations. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1411–1418     

Computational modeling of block-copolymer directed self-assembly

Directed self-assembly (DSA) is a potentially promising method of writing lithographic patterns on a sub-40 nm length-scale. While the utility of DSA has been demonstrated in principle, there are many challenges that need to be solved before its wide adoption in the semiconductor industry. Computational modeling is crucial in addressing many of those challenges, for example, optimizing polymer formulations, producing a better pattern, or predicting the defect density. In particular, the use of mesoscale approaches such as Self-Consistent Field Theory (SCFT), coarse-grained Monte Carlo, coarse-grained Molecular Dynamics, and Dynamic Density Functional Theory (DDFT) to describe polymer morphology—both bulk and in confinement—is now widespread. These models are used to predict phase behavior of block copolymers in thin films (undirected self-assembly), as well as in cases of chemo- and graphoepitaxy (DSA). In the near future, modeling is expected to be an integral part of formulation design and screening process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 90–95     

Polyaddition of bifunctional 1,3‐benzoxazine and 2‐methylresorcinol

A polyaddition system consisted of a bifunctional N‐n‐propyl benzoxazine and 2‐methylresorcinol ( MR ) that proceeds at ambient temperature has been developed. In this system, the aromatic ring of MR acted as a bifunctional monomer, reacting with a two equivalent amount of benzoxazine moieties via their ring‐opening reaction. The polyaddition gave the corresponding linear polymer bearing phenolic moieties bridged by Mannich‐type linkage in the main chain. The linear polymer had a high glass transition temperature, which was comparable to that of the linear polybenzoxazine synthesized by the ring‐opening polymerization of a monofunctional N‐n‐propyl benzoxazine. The employment of a bifunctional N‐allyl benzoxazine in the polyaddition system resulted in the formation of the corresponding polymer with allyl pendants, which exhibited improved heat resistance due to its thermally induced crosslinking reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3867–3872     

Synthetic control over the dynamics of mesoscaled cargo release from colloidal polymer vectors inside live cells

Directed delivery of mesoscaled cargo—for example, nanocrystals, proteins, or nucleic acids—to cells using polymer vectors impacts numerous biomedical fields. We introduce here the concept of dynamic complementarity as a simple, yet powerful approach to control the rate of mesoscaled cargo dissociation from colloidal polymer vectors once inside the cytosol. By tuning the degree of electrostatic reciprocity between the polymer vector and its cargo, it is possible to both deliver and release large cargo in live cells in a controllable manner over both long and short periods, pointing to a highly modular materials platform with molecularly tailored properties suited to task. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 256–264     

Influence of monomer type on miniemulsion polymerization systems stabilized by graphene oxide as sole surfactant

Based on a recent report [J. Polym. Sci. Part A. Polym. Chem. 2013 , 51, 47–58] whereby we demonstrated the synthesis of polystyrene nanoparticles by miniemulsion polymerization stabilized by graphene oxide (GO) nanosheets as sole surfactant, we hereby report the synthesis of hybrid polymer nanoparticles of several members of the (meth)acrylate family as well as the cross‐linker divinylbenzene via the same approach. The nature of the resultant emulsion is strongly linked to the polarity of the monomer used; monomers with a relatively small polar component (based on Hansen solubility parameters) such as lauryl methacrylate and benzyl methacrylate, in addition to styrene, generate stable emulsions that can be effectively polymerized. Particularly polar monomers (e.g., methyl acrylate and methyl methacrylate) formed kinetically stable emulsions in the presence of GO, however rapid coagulation occurred during polymerization. Electron microscopy analysis reveals the formation of polymer nanoparticles with size distribution between 200 and 1000 nm with roughened surface morphologies, indicative of GO sheets adsorbed at the interface. The results of this work demonstrate the applicability of this synthetic route for specific monomers in the preparation of novel graphene‐based polymeric materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5153–5162     

Influence of fullerene photodimerization on the PCBM crystallization in polymer: Fullerene bulk heterojunctions under thermal stress

For an increased lifetime of polymer:fullerene bulk heterojunction (BHJ) solar cells, an understanding of the chemical and morphological degradation phenomena taking place under operational conditions is crucial. Phase separation between polymer and fullerene induced by thermal stress has been pointed out as a major issue to overcome. While often the effect of thermal stress on the morphology of polymer:fullerene BHJ is investigated in the darkness, here we observe that light exposure slows down fullerene crystallization and phase separation induced at elevated temperatures. The observed photo‐stabilizing effect on active layer morphology is quite independent on the polymer and is attributed to light‐induced dimerization of the fullerene. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1209–1214     

Allyl ethers as combined plasticizing and crosslinkable side groups in polycarbonate‐based polymer electrolytes for solid‐state Li batteries

Allyl ether‐functional polycarbonates, synthesized by organocatalytic ring‐opening polymerization of the six‐membered cyclic carbonate monomer 2‐allyloxymethyl‐2‐ethyltrimethylene carbonate, were used to prepare non‐polyether polymer electrolytes. UV‐crosslinking of the allyl side groups provided mechanically stable electrolytes with improved molecular flexibility—T_g below ?20 °C—and higher ionic conductivity—up to 4.3 × 10^?7 S/cm at 25 °C and 5.2 × 10^?6 S/cm at 60 °C—due to the plasticizing properties of the allyl ether side groups. The electrolyte function was additionally demonstrated in thin‐film Li battery cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2128–2135     

Effects of crosslinker density on the polymer network structure in poly‐N,N‐dimethylacrylamide hydrogels

To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly‐N,N‐dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1017–1027     

Synthesis and reaction of β‐hydroxyaspartic acid‐based polymethacrylate

O‐Methacryloyl‐N‐(tert‐butoxycarbonyl)‐β‐hydroxyaspartic acid dimethyl ester was synthesized by methyl esterification of β‐hydroxyaspartic acid, followed by protection of the amino group with the tert‐butoxycarbonyl group and then the reaction of the hydroxyl group with methacryloyl chloride. The monomer efficiently underwent radical polymerization to afford the corresponding polymer with a number‐average molecular weight of 42,000 in good yields. The alkaline hydrolysis of the polymer occurred not only at the methyl ester but also at the ester moiety between the main and side chains of the polymer. The methyl ester‐free polymer gradually released β‐hydroxyaspartic acid moiety in a phosphate buffer solution with pH = 7.3 and 7.8. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2782–2788, 2002     

Alternating copolymer based on sulfonamide‐substituted phenylmaleimide and vinyl monomers as polymer electrolyte membrane

The alternating copolymerization of phenylmaleimide (PMI) with a pendant sulfonamide acid group (sa‐PMI) and n‐butyl vinyl ether (BVE) as the aliphatic vinyl monomer afforded proton‐conducting polymer electrolytes—sa‐PMI‐BVEs—and their properties were compared with those of sa‐PMI‐STs that were synthesized from sa‐PMI and styrene. The ion exchange capacities (IECs) can be easily controlled by partly replacing sa‐PMI with unsubstituted PMI. sa‐PMI‐BVE is more flexible than sa‐PMI‐ST, and therefore, forms thin membranes even at high IECs, while sa‐PMI‐ST membranes are rigid and brittle. However, sa‐PMI‐BVE exhibits rather low thermal and oxidative stability. To realize polymer electrolyte membranes with reliable mechanical strength and a high IEC, gel‐filled membranes were prepared by polymerization in the presence of a small amount of a crosslinker, divinylbenzene, in porous polytetrafluoroethylene membranes. By using the gel‐filled membrane, H₂/O₂ fuel cells could be operated at 80 °C with reasonable performance. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Fluorescence recovery after photobleaching measurements of polymers in a surface forces apparatus

The surface forces apparatus has been combined with fluorescence recovery after photobleaching to measure translational diffusion of polymer confined between mica sheets. This article presents findings using polydimethylsiloxane with number‐average molecular weight M_n = 2200 g mol^?1, the chains end‐labeled with soluble fluorescent dye. Melts with thickness 10 nm display a translational diffusion coefficient (D) with a bulk component and a slower component assigned to surface diffusion. Reduction of thickness to 1.8 nm causes mobility to split into two populations—an immobile fraction (immobile on the time scale of 30–60 min) and a mobile fraction who's D slow only weakly with diminishing film thickness. However, when load causes the confining mica sheets to flatten, D of the mobile fraction drops by up to an additional order of magnitude, depending on the local pressure that squeezes on the polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Ordered nanostructures at two different length scales mediated by temperature: A triphenylene‐containing mesogen‐jacketed liquid crystalline polymer with a long spacer

A mesogen‐jacketed liquid crystalline polymer (MJLCP) containing triphenylene (Tp) moieties in the side chains with 12 methylene units as spacers (denoted as PP12V) was synthesized. Its liquid crystalline (LC) phase behavior was studied with a combination of solution ¹H NMR, solid‐state NMR, gel permeation chromatography, thermogravimetric analysis, polarized light microscopy, differential scanning calorimetry, and one‐ and two‐dimensional wide‐angle X‐ray diffraction. By simply varying the temperature, two ordered nanostructures at sub‐10‐nm length scales originating from two LC building blocks were obtained in one polymer. The low‐temperature phase of the polymer is a hexagonal columnar phase (Φ_H, a = 2.06 nm) self‐organized by Tp discotic mesogens. The high‐temperature phase is a nematic columnar phase with a larger dimension (a′ = 4.07 nm) developed by the rod‐like supramolecular mesogen—the MJLCP chain as a whole. A re‐entrant isotropic phase is found in the medium temperature range. Partially homeotropic alignment of the polymer can be achieved when treated with an electric field, with the polymer in the Φ_H phase developed by the Tp moieties. The incorporation of Tp moieties through relatively long spacers (12 methylene units) disrupts the ordered packing of the MJLCP at low temperatures, which is the first case for main‐chain/side‐chain combined LC polymers with MJLCPs as the main‐chain LC building block to the best of our knowledge. The relationship of the molecular structure and the novel phase behavior of PP12V has implications in the design of LC polymers containing nanobuilding blocks toward constructing ordered nanostructures at different length scales. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 295–304     

Polymer brushes containing sulfonated sugar repeat units: Synthesis,characterization, and in vitro testing of blood coagulation activation

A new polymer brush chemistry containing sulfonated carbohydrate repeat units has been synthesized from silicon substrates using ATRP methods and characterized both in bulk and using surface analysis. The polymer brush was designed to act as a mimic for the naturally occurring sulfonated glycosaminoglycan, heparin, commonly used for modifying blood‐contacting surfaces both in vitro and in vivo. Surface analysis showed conversion of brush saccharide precursor chemistry to the desired sulfonated polymer product. The sulfonated polymer brush surface was further analyzed using three conventional in vitro tests for blood compatibility—plasma recalcification times, complement activation, and thrombin generation. The sulfonated polymer brush films on silicon oxide wafers exhibited better assay performance in these blood component assays than the unsulfonated sugar functionalized polymer brush in all tests performed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7713–7724, 2008     

Tuning the frontier molecular orbital energy levels of n‐type conjugated copolymers by using angular‐shaped naphthalene tetracarboxylic diimides,and their use in all‐polymer solar cells with high open‐circuit voltages

An angular‐shaped naphthalene tetracarboxylic diimide (NDI) was designed and synthesized as a new building block for n‐type conjugated polymers to tune their energy levels. Three n‐type copolymers incorporating this angular‐shaped NDI as the acceptor moiety were obtained by Stille coupling reactions and had number average molecular weights of 18.7–73.0 kDa. All‐polymer bulk‐heterojunction solar cells made from blends of these polymers with poly(3‐hexylthiophene) gave a power conversion efficiency up to 0.32% and exhibited an open‐circuit voltage (V_oc) up to 0.94 V due to their relative high‐lying lowest unoccupied molecular orbital energy levels. The high V_oc of 0.94 V is higher than that of solar cells based on linear‐shaped NDI‐containing polymers (<0.6 V). The results indicate that the angular‐shaped NDI is a promising building block for constructing nonfullerene polymer acceptors for solar cells with high open‐circuit voltages. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Solvent‐assisted prototyping of microfluidic and optofluidic microsystems in polymers

Due to their low‐cost and processing simplicity, polymers have made a substantial impact on everyday life and scientific discoveries. Such discoveries include the use of microanalysis and optical microsystems, which—albeit simpler to prototype than their inorganic counterparts—still require dedicated procedures at high temperatures and pressures. Here, recent developments in microsystem prototyping are highlighted, based on solvent‐assisted polymer stimulation. These developments—largely inspired by the earlier demonstration of solvent‐assisted micromolding (SAMIM) for nanoimprinting—enable micronscale imprinting, but also bonding to substrates and three‐dimensional chemical functionalization via strict benchtop procedures. These solvent‐assisted strategies are categorized into two groups: those based on solvent immersion and those based on complete polymer dissolution. Recent embodiments within each group are discussed and compared in performance. Solvent‐assisted prototyping further narrows the gap of processing complexity and costs between the PDMS elastomer and thermoplastic polymer microfluidics, and also enables novel architectures and thus new opportunities in microscale Life Sciences and Chemistry investigations. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1681–1686     

Remarkably stable amphiphilic random copolymer assemblies: A structure–property relationship study

Synthesis of a library of amphiphilic random copolymers from a single reactive pre‐polymer and their self‐assembly is reported. Post‐polymerization modifications of the parent polymer containing pendant N‐hydroxy succinimide (NHS) ester groups with various oligooxyethylene (OE) amines produce amphiphilic random copolymers with same degree of polymerization and equal extent of randomness. ¹H‐NMR and FT‐IR data indicate quantitative substitution in all cases. The critical aggregation concentration (CAC) for all the polymers is estimated to be in the range of 10^?5 M. Stability of these nano‐aggregates is studied by photoluminescence using time dependent F—rster Resonance Energy Transfer (FRET) between co‐encapsulated lipophilic dyes namely DiO and DiI in the hydrophobic pocket of the aggregates. These studies suggest remarkably high stability for all systems. However those with shorter hydrophilic pendant chains are found to be even more robust. Morphology is examined by high resolution transmission electron microscopy (HRTEM) which reveals multi‐micellar clusters and vesicles for polymers containing short and longer OE segments, respectively. Encapsulation efficacy is tested with both hydrophobic and hydrophilic guest molecules. All of them can encapsulate hydrophobic guest pyrene while a hydrophilic dye Calcein can be sequestered only in vesicle forming polymers. Lower critical solution temperature (LCST) is exhibited by only one polymer that contains the shortest OE chains. All polymers exhibit excellent cell viability as determined by MTT assay. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4932–4943     

A helical chiral polymer‐based chromo‐fluorescence and CD response sensor for selective detection of trivalent cations

A novel chiral (S)‐BINAM‐based fluorescent polymer sensor was designed and synthesized by the polymerization of 4,4′‐((2,5‐dibutoxy‐1,4‐phenylene)bis(ethyne‐2,1‐diyl))‐dibenzaldehyde ( M‐1 ) with (S)‐2,2′‐binaphthyldiamine (S‐BINAM, M‐2 ) via Schiff's base formation. The resulting helical chiral polymer sensor exhibited remarkable “turn‐on” bright blue fluorescence color upon the addition of trivalent metal ions under a commercially available UV lamp; this change can be clearly observed by the naked eye for direct visual discrimination at low concentration. More importantly, the addition of trivalent metal cations can lead to a most pronounced change of CD spectra of the chiral polymer indicating this kind chiral sensor can also be used as a sole probe for selective recognition of trivalent metal cations based on CD spectra. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4070–4075     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure

A styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure, 4‐vinylbenzyl 1,3‐oxathiolane‐2‐thione‐5‐ylmethyl ether (VBTE), was synthesized from 4‐vinylbenzyl glycidyl ether (VBGE) and carbon disulfide in the presence of lithium bromide in 86% yield. Radical polymerization of VBTE in dimethyl sulfoxide by 2,2′‐azobisisobutyronitrile was carried out at 60 °C to afford the corresponding the polymer, polyVBTE, in 64% yield. PolyVBTE with number‐averaged molecular weight higher than 31,000 was obtained. The glass transition temperature (T_g) and 5 wt % decomposition temperature (T_d5) of the polyVBTE were evaluated to be 66 and 264 °C under nitrogen atmosphere by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBTE repeating unit could also be obtained via polymer reaction, that is, a lithium bromide‐catalyzed addition of carbon disulfide to a polyVBGE prepared from a radical polymerization of VBGE. Copolymerization of VBTE and styrene with various compositions efficiently gave copolymers of VBTE and styrene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013