Liquid phase peptide synthesis by fragment condensation on a soluble polymer support, 6. The influence of peptide-chain lengths of Boc-oligopeptides on the coupling efficiencies of their C-terminal amino acids in coupling reactions with polymer-bound amino acids

The influence of both the peptide-chain lengths of Boc-oligopeptides and the degree of crosslinking of polymer supports on the coupling efficiencies of the C-terminal amino acids of Bocoligopeptides in the coupling reactions with terminal free amino groups of amino acids linked to polymer supports was investigated. The coupling efficiencies of Boc-oligopeptides (consisting of 3 to 10 amino acid residues) relative to those of Boc-Val-OH or Boc-Met-OH were determined by competitive coupling reactions with amino acids anchored to soluble and crosslinked polystyrene supports, using four systems of coupling reagents dicyclohexylcarbodiimide (DCC) + 1-hydroxy-1 H-benzotriazole, DCC + N-hydroxysuccinimide, DCC + N-hydroxy-5-norbornene-2,3-dicarboximide, and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline. In the coupling reactions on soluble polystyrene supports, containing 1 mol-% of an amino acid (per styrene monomeric unit), and on poly(styrene-co-divinylbenzene (1%)), containing 1 or 10 mol-% of an amino acid, little influence of peptide-chain lengths was observed. In reactions with amino acids anchored to poly(styrene-co-divinylbenzene (2%)) (containing 2 or 20 mol-% of terminal amino groups), an increase in peptide-chain length of Boc-oligopeptides was found to reduce remarkably the coupling efficiencies of their C-terminal amino acids. With poly(styrene-co-divinylbenzene (2%))s as supports, it was detected that amino groups are present which are sterically inaccessible for peptide fragments such as Boc-Ala-Ala-Leu-Leu-Leu-OH and Boc-Ala-Ala-Leu-Leu-Leu-Pro-Pro-Leu-Leu-Leu-OH.     

Photo-induced in situ crosslinking of polymer brushes with dimethyl maleimide moieties for dynamically stimulating stem cell differentiation

We designed photo-crosslinkable polymer brushes with dimethylmaleimide moieties, in order to demonstrate dynamic stimulation of cell differentiation in mesenchymal stem cells (MSCs). The polymer brushes were synthesized by surface-initiated reversible addition fragmentation chain transfer polymerization using dimethylmaleimide ethyl methacrylate and methyl methacrylate on a chain transfer agent-immobilized glass surface. The polymer brushes were crosslinked by photodimerization of the dimethylmaleimide moieties within polymer chains with stem cells present on the surface. In order to evaluate the effects of in situ photo-induced crosslinking of the polymer brushes on gene expression of stem cells, human bone marrow MSCs were cultured under static and dynamic culture conditions for 7 days. Expression of the osteocalcin (Ocn) gene in MSCs was used as an indicator of osteoblast differentiation under dynamic culture conditions. Structural conversion from non-crosslinked polymer brushes to crosslinked polymer brushes increased the expression of Ocn by 1.4-fold in the presence of adhered cells, compared with non-crosslinked polymer brushes under static culture conditions. These results suggest that MSCs recognized surface conversion from non-crosslinked to crosslinked structures, which resulted in altered differentiation lineages. Therefore, photo-crosslinkable surfaces with dimethyl maleimide moieties are potential novel materials for dynamically stimulating MSC differentiation.     

Poly(methyl methacrylate)-supported isoxazolinium permanganates: preparation and application as oxidising reagents

Divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA) and N,N′-methylenebis(acrylamide) (N,N′MBA) crosslinked poly(methyl methacrylate) (PMMA) was functionalised to generate isoxazolinium permanganate resins. These resins were found to selectively oxidise alcohols to the corresponding carbonyl compounds in appreciable yields. These reagents were found to possess the characteristics of polymeric reagents including operational simplicity.     

Darstellung und Derivatisierung von linearem Polyvinylamin zur selektiven Komplexbildung in homogener Phase

Poly(1-aminoethylene) (polyvinylamine) ( 4 ) was prepared by hydrazinolysis of poly(1-succinimidoethylene) ( 2 ) [poly(N-vinylsuccinimide)]. The water-soluble polymer 4 , with more than 95% of primary amino groups, was used as basic material for the synthesis of macromolecular complex forming reagents. By the reaction of poly(1-ammonioethylene chloride) ( 3 ) [poly(vinylamine hydrochloride)] with 2-pyridinecarbaldehyde a complex forming polymer 5 was obtained, which is highly selective for iron. Poly{1-[bis(carboxymethyl)amino]ethylene} ( 6 ) from 4 and chloroacetic acid is a reagent for copper, whereas poly[1-(3-methylthioureido)-ethylene] ( 7 ) from 4 and N-methylisothiocyanate shows a good selectivity for mercury. The ultrafiltration technique allows a continuous procedure for the separation of the polymer complexes. The formation and stability of the prepared complexes of 4 and its derivatives 5, 6 , and 7 in homogeneous phase are investigated and discussed.     

Reversible crosslinking-decrosslinking of polymers having bicyclo orthoester moieties in the side chains

Radical polymerizations of methacrylate- and styrene-based bicyclo orthoesters (BOEs), and their copolymerization with methyl methacrylate and styrene were carried out with 2,2′-azoisobutyronitrile (AIBN, 5 mol-%) as an initiator in N,N-dimethylformamide (DMF, 2 M ) at 70°C for 15 h to afford the corresponding polymers in 64–96% yields having BOE moieties in the side chains. Crosslinking of the polymers was carried out in the presence of BF₃·OEt₂ (3 mol-%) as a cationic catalyst in CH₂Cl₂. The yield of the crosslinked polymer increased with increasing initial concentration of the polymer and increasing crosslinking temperature. Decrosslinking of the crosslinked polymers was carried out in the presence of trifluoroacetic acid (TFA, 5 mol-%) as a cationic catalyst in CH₂Cl₂ to regenerate the starting linear polymers. The recovery of the starting linear polymer increased with decreasing concentration of the initially crosslinked polymer and with increasing decrosslinking temperature.     

Polymer ester von sären des phosphors, 7. Polymerisation des 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.1]heptans

1-Oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.1]heptane is transformed in situ (prepared from trimethyl phosphite and glycerol) at ?78°C in the presence of a trace of water into a crosslinked polymer containing constitutional repeating units with 5- and 6-membered rings. The reaction with reagents containing hydroxyl groups (water, acetic acid, alcohol) leads to the degradation of the network with the formation of soluble fragments with P _n = 35–50. This reactivity and the possibility to obtain other derivatives from the fragments make this polymer a carrier for pharmacologically active polymers with the advantage of decomposing only into the innocuous components phosphoric acid and glycerol.     

Synthesis of polymers with primary amino end groups, 2. Synthesis of polyisoprene with primary amino end groups and poly(isoprene-b-γ-benzyl-L-glutamate)s

Primary amine terminated polyisoprene 2 was produced by reaction of anionic living polyisoprene with one of the following protected aminating reagents: N-(benzylidene)trimethylsilylamine ( 1a ). N-(1-phenylpentylidene)trimethylsilylamine ( 1b ), N-benzylidenebenzenesulfeneamide ( 1c ), or N,N-bis(trimethylsilyl)-2-bromoethylamine ( 3 ). Especially with 1a , the terminal amino group was quantitatively introduced at the end of the polymer chain. 2 was found to initiate the polymerization of the N-carboxy anhydride of γ-benzyl-L -glutamate 5 to afford poly(isoprene-b-γ-benzyl-L -glutamate) ( 6 ).     

Synthesis and characterization of a rubber incorporated polyamideimide

A new flexible and crosslinkable copolyimide was prepared by low temperature polycondensation between bis [4-(4-chloroformylphthalimido)phenyl] ether ( 1 ), bis(4-aminophenyl) ether and liquid α,ω-bis[2-(4-piperazinyl)ethylaminocarbonyl]poly(butadiene-co-acrylonitrile) in DMAc solution. The polymer is soluble in DMF, DMAc, NMP, m-cresol, DMSO and concentrated sulfuric acid. On heating with or without dicumyl peroxide the polymer was crosslinked.     

New second-order nonlinear optical (NLO) epoxy polymer treated by sol-gel processing

We have demonstrated a novel approach to achieve a stable second-order NLO polymer by incorporating NLO moieties into a processable epoxy polymer and hardening with crosslinkable sol-gel technique. The crosslinked polymer showed high nonlinearity (d₃₃ = 41 pm/V) and better thermal stability compared to the prepolymer, which maintained its nonlinearity up to 100°C without significant loss of NLO activity.     

Crosslinkable PEO-PPO-PEO-based reverse thermo-responsive gels as potentially injectable materials

This paper describes the functionalization and crosslinking of PluronicRTM derivatives in aqueous solution at 37° C. Pluronic dimethacrylate was obtained by reacting native PEO-PPO-PEO triblocks with methacryloyl chloride and then crosslinking them by free radical polymerization at 37° C, using a redox system. The resulting gel and its rheological behavior were characterized by different techniques. The swelling study of the crosslinked polymer was indicative of its reverse thermo-responsive behavior, as illustrated by the almost 800% water uptake of the polymer at 37° C, as opposed to the 1600% attained by the polymer at 25° C. As expected, while the Pluronic dimethacrylate gel displayed an E _c value of 142.5 ± 29.7 kPa at 37° C, the crosslinked system attained a Young's modulus three times higher: 415.2 ± 45.7 kPa. Finally, the environmental SEM analysis revealed the porous microstructure of the crosslinked gels.     

Coatable Photomobile Polymer Films Using Spring‐Like Photochromic Compounds

Photoinduced macroscopic deformation behavior of crosslinked liquid‐crystalline polymer is induced in crosslinked N‐benzylideneaniline polymer films. The film is prepared by in situ polymer reaction using polymethacrylate‐containing phenylaldehyde side chains and o‐tolidine crosslinker. The film exhibits macroscopic bending upon exposure to UV light and then immediately reverts to the initial shape when the light is turned off. The bending behavior is strongly affected by the fabrication conditions; the changes in the macroscopic shape and photomechanical properties in response to UV light for the film prepared from a mixture solution are small, while those for the film prepared by top coating the crosslinker solution onto the prepolymer substrate are large.     

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Two different, novel approaches to crosslink fully aromatic, rigid‐rod aramid chains were studied. First, the new rigid‐rod aramid poly[1,4‐phenylen‐2,5‐bis(prop‐2‐ynyloxy)‐terephthalamide] with an inherent viscosity of η_inh = 2.74 dL/g was synthesized by low temperature polycondensation of p‐phenylendiamine and 2,5‐bis(prop‐2‐ynyloxy)‐terephthaloylchloride. The pendant alkinyl moieties allowed thermally induced crosslinking at temperatures higher than 200°C. No weight loss was found due to this treatment, but curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insufficient stability of the polymer chains against degradation when being dissolved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide containing pyrimidine moieties, produced by polycondensation of bis‐silylated 2,5‐diaminoprimidine and terephthaloyl dichloride, were spun from nematic solutions. Fibers were crosslinked by complexation with nickel(II)‐ions in the swollen state. Both crosslinked and non‐crosslinked, otherwise identically processed samples, were characterized by wide‐angle X‐ray‐diffraction (WAXD) measurements and mechanical tests. A post‐spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers in general showed. The dominating crystal structures of both fiber samples are similar to “Modification II” of the well characterized fibers from poly(p‐phenylene‐terephthalamide) (PPTA). The number and size of the morphological defects in the crosslinked fibers was significantly higher than in the non‐crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was investigated. The values of all mechanical parameters were considerably lower in the case of the crosslinked fibers, probably due to the collapse of the entire supramolecular order and fiber morphology.     

Funktionalisierung heterogen-vernetzter polyvinylalkohol-gele

Cross-linked poly(vinyl alcohol) beads were functionalized by derivatization of their hydroxyl groups with succinic acid anhydride, 1,6-hexamethylene diisocyanate, 3-aminopropyltriethoxysilane, 2-chlorophenylbis(1,2,4-triazol-4-yl) phosphate and different sulfhydryl reagents. The resulting 8 gels carry isocyanato, carboxyl, amino, phosphate and mercapto residues in concentrations of 1 to 3 mmol per gram of polymer. The derivatives obtained from the starting poly(vinyl alcohol) beads are mechanically stable, resistent to hydrolysis in the pH range between 1 and 14 and stable up to 100°C. The functionalized, cross-linked polymer beads, applicable in aqueous systems as well as in organic solvents, should find a wide application in chromatography, as supports in the preparative solid phase synthesis and as basic carriers for polymeric reagents.     

Enzyme-analogue built polymers, 26. Enantioselective synthesis of amino acids using polymers possessing chiral cavities obtained by an imprinting procedure with template molecules

The asymmetric synthesis of a-amino acids within chiral cavities of special crosslinked polymers was investigated. Chiral cavities prossessing definite shapes and specific arrangements of the functional groups were obtained by preparation of crosslinked polymers in the presence of suitable templates. Best results with an enantiomeric excess of 36% were obtained by using a polymer which was imprinted by L -DOPA. The cavities contained a salicylaldehyde and a phenylboronic acid moiety each. L -Threonine was prepared by reaction of the polymer bound anion of a salicylideneglycine nickel complex with acetaldehyde.     

Effect of Crosslinking on the Stretch-Induced Polymorphic Transition of Trans-1,4-Polyisoprene

Trans-1,4-polyisoprene (TPI) is a typical polymorphic polymer with two crystal modifications. The transition between two crystal modifications (α to β) occurs during stretching. The underlying mechanism is still under debate. In this work, the effects of crosslinking and strain rates on the crystal transition are studied. The TPI, which mainly contains α crystal (α−TPI), is crosslinked by γ-ray radiation. The results show that crystalline morphology does not change after radiation. The melting temperature and yield stress of crosslinked α−TPI decrease with the irradiation dose. The structural evolution is studied by in situ wide-angle X-ray diffraction and small-angle X-ray scattering. During stretching, the content of β crystal (X_β) of crosslinked α−TPI increases in the strain-hardening region. The X_β is lower in the sample with a higher radiation dose under the same strain. On the other hand, with increasing strain rate, the X_β of the crosslinked sample exhibits a non-monotonic variation. A parallel mechanical model consisting of amorphous and crystal fibrils is proposed to explain the experimental observations.     

Crosslinkable Polyphenols from Urushiol Analogues

Synthesis and curing behaviors of polyphenol from urushiol analogues have been examined. The analogues were synthesized by lipase‐catalyzed esterification of 4‐hydroxyphenethyl alcohol with unsaturated fatty acids, in which the primary hydroxy group was regioselectively acylated to give the phenol derivatives having the unsaturated group in the para position. The oxidative polymerization of the analogues was performed using iron‐salen or peroxidase as catalyst. Under appropriate reaction conditions, an oily soluble polymer was obtained in high yields. NMR analysis of the product polymer showed that only the phenolic moiety was polymerized and the unsaturated group was not involved in reaction during the polymerization. The polymer was subjected to the hardening by cobalt naphthenate catalyst or thermal treatment, yielding crosslinked film (artificial urushi) with high gloss surface.     

Grafting on polybutadiene with macro or macromonomer initiators containing poly(ethylene glycol) units

Crosslinked poly(ethylene glycol)-blockpolybutadience block copolymers were obtained by coupling reaction of polybutadiene (PBd) with macromonomer azo initiators (macroinimers) or polyazoesters (PAE) in moderate yield (22–75%). NMR and FT-IR spectroscopy measurements were used to characterize and determine the poly(ethylene glycol) (PEG) contents (20–66%). The latter depends on the initial concentration of the azo compounds. Broad melting peaks appear in the DSC curves in a temperature range from about 65–130°C. The crosslinked polymers containing PEG-1500 units showed sharp melting transitions and the second heating cycle showed that recrystallization rates are very high. Swelling ratios of the polymer networks were determined in water (1,22–2,96) and in CHCl₃ (7,81–20,84). The morophology of the cold fractured area of the crosslinked polymers was analyzed by scanning electron microscopy (SEM).     

Concentration effect in acceptor-catalytic polyesterification

The effect of the concentration of reagents on the kinetics of acceptor-catalytic esterification is investigated for a homologous series of poly(oxyethylene)s 1 (number of oxyethylene units in the polymer chain: n is between 1 and 68). The reaction rate constant, k₀, is found to be dependent on the concentration of the reagents and on the length of the polymer chain. The effect of concentration is most pronounced in the case of low-molecular-weight 1 (n = 1; 3). With an increase in the polymer chain length the concentration effect on the reactivity of the end groups decreases and is practically nil for oligomers containing 45 and 68 oxyethylene units.     

Monodisperse,full‐IPN Structured Polymer Particles in Micron‐Sized Range by Seeded Polymerization

Monodisperse micron‐sized poly(styrene/divinylbenzene) particles of an interpenetrated polymer network (IPN) were produced by the seeded polymerization in the presence of slightly crosslinked polystyrene seed particles. In order to evaluate the two‐stage swelling of the monomer emulsion in the case of utilizing the crosslinked seed particles, a thermodynamic equation was proposed with the crosslinking degree of the seed particles and the droplet size of the second monomer emulsion (styrene and divinylbenzene). In the light of thermodynamics, it was elucidated that an effective diffusion of monomers during swelling could be achieved in the conditions of lower crosslinking degree of the seed particles and smaller droplet size of monomer emulsions than that of seed particles. After the polymerization, the poly(styrene/divinylbenzene) particles having full‐IPN structure were obtained around 5 μm, consequently displaying a good thermal stability.     

Trifluoracetylierung von aminosäureestern und dipeptidestern mit N-trifluoracetyl-polyamid 66.

N-Trifluoroacetyl-Polyamid 66 ( 1 ) is used for the trifluoroacetylation of amino acid- and dipeptide esters. Advantages and limitations of the polymeric reagent compared with low molecular trifluoroacetylating reagents are discussed. A mixture of amino acid methyl esters can be converted by 1 to the N-trifluoroacetyl derivatives, which are separated and identified by gas chromatography.