Chemical Recycling and Physical Tuning of Necklace-Shaped Polydimethylsiloxanes Bearing Anthracene Dimer Units.

The problem of plastic waste in the environment calls for the development of new polymeric materials designed specifically for easy recycling at the end of their life cycle. Herein, a green polymer system comprising a series of necklace-shaped polydimethylsiloxanes bearing anthracene dimer units is developed. The polymers have low environmental impact and are easily recycled. Further, their flexibility and glass transition temperatures are easy to control. These necklace-shaped inorganic polymers are synthesized by photopolymerizing (dimerizing) anthracene-terminated oligo-dimethylsiloxane monomers. A key achievement of the present work is the successful chemical recovery of the monomers from the polymers through thermal depolymerization, enabling monomer-polymer recycling. By applying equilibrium polymerization with base catalysts, monomers with a controlled distributed chain length are synthesized from monomers with a constant chain length. The necklace-shaped polymers synthesized from these randomized monomers have amorphous structures and readily form transparent films. It is possible to modulate the thermal and mechanical properties of the polymers by controlling the average chain length of the polydimethylsiloxane between the anthracene dimers. This investigation presents a method for the synthesis and cyclic utilization of polymer materials with a wide range of applications, including plastics and elastomers.

In situ STM investigation of aromatic poly(azomethine) arrays constructed by "on-site" equilibrium polymerization.

Two-dimensional (2D) arrays of π-conjugated aromatic polymers produced by surface-selective Schiff base coupling reactions between an aromatic diamine and an aromatic dialdehyde were investigated in detail using in situ scanning tunneling microscopy. Surface-selective coupling was achieved for almost all diamine/dialdehyde combinations attempted, although several combinations did not proceed even in homogeneous aqueous alkaline solution. Most of the combinations of an aromatic diamine and a dialdehyde, except the combinations of 4,4'-azodianiline with mono/bithiophenedicarboxaldehyde, formed highly ordered π-conjugated polymer arrays on an iodine-modified Au(111) surface in aqueous solution at a suitable pH. The simplest polymer of the various combinations tested, obtained from the combination of 1,4-diaminobenzene with terephthaldicarboxaldehyde, gave a 2D array consisting of linearly connected benzene units. Poly(azomethine) adlayers caused a positive shift in the electrochemical potential of the butterfly shaped oxidative adsorption and reductive desorption of iodine. The acceleration of the reductive desorption of iodine suggests the existence of a weak interaction between the polymer layer and iodine. Not only the first polymer adlayers but also partially adsorbed secondary adlayers with "on-top" epitaxial behavior were frequently observed for all polymer systems. The alignment of the polymer chains in the adlayers possessed a certain regularity in terms of a regular interval between polymer chains because of repulsive interpolymer interactions.

Stimuli responsive poly(1-[11-acryloylundecyl]-3-methyl-imidazolium bromide): dewetting and nanoparticle condensation phenomena.

A stimuli-responsive homopolymer poly(ILBr) is fabricated via a "two-phase" atom transfer radical polymerization (ATRP) process, where ILBr stands for the reactive ionic liquid surfactant, 1-[11-acryloylundecyl]-3-methyl-imidazolium bromide. An extraordinarily wide molecular weight distribution (PDI = 6.0) was obtained by introducing the initiator (4-bromomethyl methyl benzoate) in a heterogeneous two-phase process. The molecular weight distribution of poly(ILBr) was characterized by size-exclusion chromatography (SEC). The resulting homopolymer was found to be surface active and stimuli responsive. Poly(ILBr) films coated on quartz exhibit stimuli-responsive dewetting after ion exchange of Br(-) by PF(6)(-). This dewetting phenomenon can be understood in chain segmental terms as a stimuli-induced structural relaxation and appears to be the first such reported stimuli-responsive polymeric dewetting. Titrating aqueous poly(ILBr) with aqueous bis(2-ethylhexyl)sulfosuccinate induces nanophase separation and results in the condensation of nanoparticles 30-60 nm in diameter.

The design of polymer microcarrier surfaces for enhanced cell growth.

A variety of neutral and cationic polymers based on polyamino acids were prepared and investigated as microcarriers for cell attachment and growth. Among neutral polymer particles including the alkylated poly(gamma-methyl L-glutamate) (PG) particles, in which the hydrophobicity changes as a function of the length of the alkyl groups, and hydroxy terminal PG particles, the PG particle with the longest alkyl chain (PG-C12) demonstrated the highest cell attachment rate and highest rate of cell growth. Moreover, the introduction of hydroxyl groups (PG-OH) led to a deterioration of cell growth. Cell growth on cationic particles having primary amino groups was drastically dependent upon the anion exchange capacity (AEC). A higher AEC for aminated PG microcarriers inhibited cell growth. In contrast, a higher AEC for cross-linked poly( epsilon -lysine) (PL) microcarriers facilitated cell growth. Cell growth on cationic particles clearly showed a good correlation with the pK(a,app) of the microcarriers, but not with their AEC. The particles with low and high pK(a) values possessed toxically acidic and basic pH microenvironments near the surface, respectively. These microenvironments had cytotoxic effects. On the other hand, no correlation between attachment rate constants and high cell growth was observed. The aminated particles, in which pK(a) were controlled at neutral pH, and PG-C12 produced obviously higher cell growth than did a commercially available microcarrier.

Permselective monolayer membrane based on two-dimensional cross-linked polysiloxane LB films for hydrogen peroxide detecting glucose sensors.

Novel two-dimensional (2D) cross-linked polysiloxane LB films were prepared and applied for glucose sensing as H2O2-permselective films in order to block other electroactive interferences, such as L-ascorbic acid, L-cysteine, uric acid and acetaminophen; the 2D cross-linked polysiloxane monolayers were remarkably effective in eliminating interfering responses and had a rapid response for glucose, even though the films were only a monolayer thick.

Polymer dewetting via stimuli responsive structural relaxation-contact angle analysis.

Thin films of a stimuli-responsive homopolymer dewet as a stimulus response after anion exchange of the imidazolium's counter anion. Contact angle analysis and interfacial energy considerations indicate dewetting goes counter to increasing spreading coefficient. Intrafilm stress arising from structural relaxation drives the dewetting.

Sparsely-distributed silica/PMMA composite particles prepared by static polymerization in aqueous silica dispersion.

Silica/poly(methyl methacrylate) (PMMA) composite particles, in which silica particles are sparsely distributed in the surface of PMMA particles, were formed by static dispersion polymerization of methyl methacrylate (MMA) in aqueous dispersions of submicron silica particles. The silica-modified PMMA particles were constructed via Pickering emulsion-like silica/PMMA aggregation based on weak interaction between PMMA and silica. The morphology of the composite particles is governed by the adsorption/partition equilibrium of PMMA with the silica surface.

Limulus amebocyte lysate assay for endotoxins by an adsorption method with polycation-immobilized cellulose beads.

To assay lipopolysaccharides (LPSs) in solutions containing Limulus amebocyte lysate (LAL)-inhibiting or LAL-enhancing compounds, we developed a selective endotoxin (LPS) assay using poly(epsilon-lysine)-immobilized cellulose beads (PL-Cellufine) and LAL. The PL-Cellufine can adsorb LPSs in a solution containing certain compounds (NaCl, proteins and amino acids) at an ionic strength of mu = 0.05-0.4 at neutral pH. The LPSs adsorbed on the PL-Cellufine were separated from the compounds by centrifugation and then the PL-Cellufine was suspended in LPS-free water. The LPS activities of the suspension are directly assayed by a turbidimetric time assay with the LAL reagent. The accuracy of the adsorption method was high compared with those of common solution methods. As for the common method, the apparent recovery of LPS from the compounds was 40-95%. This suggests that these compounds inhibit the LAL procedure. By contrast, the adsorption method showed good LPS recovery (88-120%) in all cases, without being inhibited or enhanced by the compounds.

Two-dimensional supramolecular arrangements of enantiomers and racemic modification of 1,1'-binaphthyl-2,2'-dicarboxylic acid.

Formation of adlayers of the optically active compound 1,1'-binaphthyl-2, 2'-dicarboxylic acid (BINAC) on iodine-modified Au (111) surfaces in perchloric acid was investigated by in situ scanning tunneling microscopy (STM). Highly ordered arrays formed on the surfaces via simple spontaneous adsorption from a solution of enantiomers or the racemic BINAC, in spite of the fact that BINAC has a three-dimensionally complex stereochemical structure. Adlayers of both enantiomers essentially shared the same enantiomorphous structure. Observed parameters of the rectangular unit cell lattice for arrays of both enantiomers of BINAC were a = 2.3 +/- 0.2 nm and b = 0.7 +/- 0.2 nm. On the other hand, racemic modification formed an entirely different adlayer, which consisted of an alternate alignment of the two enantiomers, with an oblique unit cell lattice with parameters of a = 1.2 +/- 0.2 nm, b = 0.8 +/- 0.1 nm, and 74 +/- 3 degrees . No domain composed of a single enantiomer was observed. The stronger hetero-intermolecular interactions of enantiomer couples led to the formation of an alternate arrangement in the array prepared by racemic modification.

Fullerene adlayers on various single-crystal metal surfaces prepared by transfer from L films.

Fullerene adlayers prepared by the simple Langmuir-Blodgett (LB) method onto various well-defined single-crystal metal surfaces were investigated by in situ scanning tunneling microscopy (STM). The surface morphologies of fullerene adsorbed onto metal surfaces depended largely on the adsorbate-substrate interactions, which are governed by the types of surfaces. Too weak adsorption of C60 molecules onto iodine-modified Au(111) (I/Au(111)) allows surface migration of the molecules, and then, STM cannot visualize the C60 molecules. Stronger and appropriate adsorption onto bare Au(111) leads to highly ordered arrays relatively easily due to the limited surface migration of C60. On iodine-modified Pt(111) (I/Pt(111)) and bare Pt(111) surfaces, which have stronger adsorption, randomly adsorbed molecular adlayers were observed. Although C60 molecules on Au(111) were visualized as a featureless ball due to the maintenance of the rapid rotational motion (perturbation) of C60 on the surface at room temperature, those on I/Pt(111) revealed the intramolecular structures, thus indicating that the perturbation motion of molecules on the surface was prohibited.

Poly(ethyleneimine)-immobilized-cloth enzyme immunoassay for the detection of Salmonella lipopolysaccharide.

Poly(ethyleneimine) (PEI) was immobilized on non-woven polyester cloth and examined for application on a simple, rapid and economical "cloth enzyme immunoassay (CEIA)" which was developed originally as polymyxin-CEIA for the detection of Salmonella lipopolysaccharide (LPS). PEI-cloth regardless of the PEI molecular weight, but with the amine group contents of 0.1 to approximately 0.35 meq/g immobilized either in a physisorption-like or chemisorption-like manner, adsorbed LPS rapidly, preferentially and effectively. The captured LPS was then able to be detected qualitatively and quantitatively as an antigen by enzyme immunoassay. PEI-CEIA had a detection limit for Salmonella LPS of 10 ng/ml, which was equivalent to 1.6 x 10(5) cell/ml and was ten times more sensitive than polymyxin-CEIA. It was possible to detect Salmonella LPS in the presence of a 100-fold excess of E. coli LPS. PEI-CEIA was found to be more sensitive and much easier to carry out than polymyxin-CEIA but had the same advantages as polymyxin-CEIA.