Photoinitiated Cationic Polymerization of Unconventional Monomers

Photoinitiated cationic polymerization of unconventional monomers namely, benzoxazines, monothiocarbonates and macromonomers of poly(ε-caprolactone) and poly(ethylene oxide) is described. Ring opening polymerization of benzoxazines and thiocarbonates by direct and sensitized photoinitiation using onium salts was studied. The structures of the resulting polybenzoxazine were complex and related to the ring opening process of the protanated monomer either at through oxygen or nitrogen atoms. In the case of monothiocarbonate, the polymerization was accompanied with isomerization of thiocarbonate group. The potential use of macromonomers in photoiniated cationic polymerization to design complex macromolecular structures such as graft copolymers, water-borne photoresist materials and networks with dangling chains was presented. Photoinduced oxidative polymerization of thiophene, precursor for conducting polymers, using onium salts was also demonstrated.     

Condensation polymers containing silicon and germanium in the main chain

Poly(carbonates), poly(thiocarbonates) and poly(esteres) containing silicon and/or germanium in the main chain were obtained under phase transfer conditions. Polymers were synthesized in a biphasic system NaOH/CH₂Cl₂ at 20°C using several phase transfer catalysts, and characterized by IR and ¹H and ¹³C NMR. The results were evaluated by the yields and the inherent viscosity values. The process was effective observing an increase of both parameters in comparison with the essays without catalyst. The increases depended of the nature of the polymer and the catalyst. In poly(ester) synthesis there was an increase of these parameters when the NaOH concentration was increased due to a salting out effect of the diphenolate from the aqueous phase to the organic one. Also poly(amides) containing silicon or germanium were synthesized by solution polymerization.     

Hydrocarbon versus fluorocarbon in the electrodeposition of superhydrophobic polymer films

To elaborate on superhydrophobic surfaces, we report the electrochemical synthesis, surface morphology, and wettability of hydrocarbon conductive polymer films obtained by the electrodeposition of polythiophene, poly(3,4-ethylenedioxythiophene) (i.e., PEDOT), and poly(3,4-ethylenedioxypyrrole) (i.e., PEDOP) derivatives. Highly hydrophobic films were obtained from n-C(14)H(29) and n-C(8)H(17) chains in the cases of polythiophenes and PEDOP, respectively. By contrast, superhydrophobic films were formed by the deposition of PEDOT substituted with n-C(10)H(21) chains (PEDOT-methyl undecanoate): static contact angle ≈ 160.6°, hysteresis ≈ 2°, and sliding angle ≈ 3°. Their surface properties were compared to those of previously reported fluorinated analogues. The water-repellent properties of PEDOT-methyl undecanoate were similar to the best surface properties obtained with fluorinated monomers. Even if the main approach for the chemical factor to build up superhydrophobic surfaces is via a coating of a fluorinated compound, this work confirms that the formation of fractal surfaces is able to achieve super-anti-wetting properties within a hydrocarbon series (less expensive with a favorable ecotoxic approach), and it opens a new path to bioinspired surfaces.     

Sulfur-containing polymers. X. Aromatic poly(sulfenyl thiocarbonates)

Aromatic poly(sulfenyl thiocarbonates) have been synthesized by the interfacial polycondensation of bis(dithiocarbonyl chlorides) with bisphenols. Bisphenols having the hydroxyl groups on separate rings gave polymers in high yields. The inherent viscosities of the polymers ranged from 0.22 to 0.51. In general, they were soluble in chloroform, sym-tetrachloroethane, hexamethylphosphoramide, m-cresol, and dimethylformamide and formed transparent tough films on evaporation of chloroform solutions. Almost all of the polymers were amorphous and gave melt-spun fibers. The polymer films decomposed upon ultraviolet irradiation with liberation of carbonyl sulfide.     

Surface properties of bottle-brush polyelectrolytes on mica: effects of side chain and charge densities

Surface properties of a series of cationic bottle-brush polyelectrolytes with 45-unit-long poly(ethylene oxide) side chains were investigated by phase modulated ellipsometry and surface force measurements. The evaluation of the adsorbed mass of polymer on mica by means of ellipsometry is complex due to the transparency of mica and its birefringence and low dielectric constant. We therefore employed a new method to overcome these difficulties. The charge and the poly(ethylene oxide) side chain density of the bottle-brush polymers were varied from zero charge density and one side chain per segment to one charge per segment and no side chains, thus spanning the realm from a neutral bottle-brush polymer, via a partly charged brush polyelectrolyte, to a linear fully charged polyelectrolyte. The adsorption properties depend crucially on the polymer architecture. A minimum charge density of the polymer is required to facilitate adsorption to the oppositely charged surface. The maximum adsorbed amount and the maximum side chain density at the surface are obtained for the polymer with 50% charged segments and the remaining 50% of the segments carrying poly(ethylene oxide) side chains. It is found that brushlike layers are formed when 25-50% of the segments carry poly(ethylene oxide) side chains. In this paper, we argue that the repulsion between the side chains results in an adsorbed layer that is non-homogeneous on the molecular level. As a result, not all side chains will contribute equally to the steric repulsion but some will be stretched along the surface rather than perpendicular to it. By comparison with linear polyelectrolytes, it will be shown that the presence of the side chains counteracts adsorption. This is due to the entropic penalty of confining the side chains to the surface region.     

Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

Thermal decomposition of s-2-benzothiazole thiocarbonates

Thermal decompositions of S-2-benzothiazole thiocarbonates have been investigated. The results are best rationalized by an Sni ion-pair return mechanism from which S-substituted benzothiazoles are the major products obtained. The ready ionization of the carbon-oxygen bond of thiocarbonates at elevated temperature renders a concerted Sni mechanism (internal substitution with allylic rearrangement) inoperative. Of particular interest is the mixed benzo-thiazole-2-thiol and 2-thione compound isolated from the decomposition of 2 (or 3)-halogen-substituted ethyl (or propyl) thiocarbonates. Evidence is presented that the thione 14 results from the nucleophilic opening of the cyclic intermediate, 2,3-dihydrothiazolo[2,3-b]benzothi-azolium chloride ( 20 ). The latter is readily formed under the experimental condition by intramolecular cyclization of the corresponding 2-(2-chloroethyl)benzothiazole ( 23 ), a primary product from the decomposition of S-2-benzothiazole 2-chloroethylthiocarbonate ( 7 ).     

Supramolecular interactions between beta-cyclodextrin and hydrophobically end-capped poly(ethylene glycol)s: a quartz crystal microbalance study

In this study, the supramolecular interactions occurring between beta-cyclodextrin-based surfaces and macromolecular chains modified at one end with naphthyl, adamantyl, or phenyladamantyl hydrophobic groups were investigated by means of a quartz crystal microbalance. beta-Cyclodextrin-functionalized gold electrodes were obtained through the amide-coupling reaction between mono-6-deoxy-6-amino-beta-cyclodextrin and 11-mercaptoundecanoic acid self-assembled monolayer allowing the reproducible preparation of densely grafted surfaces with host properties. The interaction data obtained for the three different modified poly(ethylene glycol)s are in good agreement with our previous studies performed by high performance liquid chromatography and surface plasmon resonance. This evidences that the driving force for the supramolecular interaction is based on the inclusion of the hydrophobic terminal group of the chains within the cyclodextrin cavities. The reversibility of the inclusion process was proven through the regeneration of the original host properties of the sensing surfaces using sodium dodecylsulfate as a competitor for the desorption of the poly(ethylene glycol) chains.     

Synthesis and hydrolysis behaviour of poly(ester anhydrides) from polylactone precursors containing alkenyl moieties

Hydroxyl-group functional polylactones were prepared and converted to acid- terminated polyesters in a reaction with a series of alkenylsuccinic anhydrides containing 8, 12, or 18 carbons in their alkenyl chains. These polyester precursors were then linked into higher molecular weight poly(ester anhydrides) containing alkenyl moieties in their polyester blocks. The hydrolysis behaviour of the poly(ester anhydrides) was found to depend on the thermal properties of the polyester precursors. For poly(ester anhydrides) prepared from low molecular weight prepolymers with thermal transitions below 37 degrees C, the presence of hydrophobic alkenyl chains in the polyester precursors slowed the rate of weight loss. Poly(ester anhydrides) prepared from higher molecular weight prepolymers showed the opposite weight-loss behaviour; i.e., the crystallinity and thermal transitions of the alkenyl chain-containing poly(ester anhydrides) were low, and the weight loss was faster than for poly(ester anhydrides) without the alkenyl chains. The differences in length of the alkenyl chain, as such, had little effect on the hydrolysis behaviour and thermal properties of the poly(ester anhydrides).     

Photoinduced phospholipid polymer grafting on Parylene film: advanced lubrication and antibiofouling properties

Poly(p-xylylene) (Parylene C) coatings have been applied in implantable electronic devices because of their electrical insulation and moisture barrier properties. To provide lubrication and an antibiofouling surface, a biomimetic phospholipid polymer--poly(2-methacryloyloxyethyl phosphorylcholine (MPC))--was grafted from the surface using UV irradiation with benzophenone as an initiator. The poly(MPC) grafting on the Parylene C films was confirmed by attenuated total reflection-Fourier transfer inflated irradiation, X-ray photoelectron spectroscopy and ellipsometry. These analyses indicated that the Parylene C films were completely covered by the poly(MPC)-graft layer with an average thickness of 140 nm under dry condition. The atomic force microscope (AFM) images revealed that the poly(MPC)-graft chains extended under wet condition. However, they formed globular structures under dry condition. Water contact angle measurements revealed a decreased receding angle of 29.5 degrees on the poly(MPC)-grafted surface with a high hysteresis of 41.4 degrees. These results indicate that the poly(MPC)-graft chains gain mobility in a wet environment. The average kinetic friction coefficient of the poly(MPC)-grafted surface in water was 0.018, which was 90% lower than that of the original surface. The in vitro single protein adsorption reduced by over 70% due to the poly(MPC) grafting. The hydrated poly(MPC)-graft chains are considered to provide lubrication and antibiofouling properties. The surface zeta potential measurement clarified the electroneutrality of the poly(MPC)-grafted surface. We concluded that the poly(MPC) grafting from the Parylene C layer significantly improved its surface properties and, subsequently, its biological properties.     

Photocrosslinked hydrogels based on copolymers of poly(ethylene glycol) and lysine

A group of new, water-soluble poly(ether-urethane)s, derived from poly(ethylene glycol) and the amino acid L -lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. the crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64–88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1M, pH 7.4, 37°C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly(ethylene glycol)-lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful properties. © 1994 John Wiley & Sons, Inc.     

Spectroelectrochemical properties of poly(4,4'-dialkyl-2,2'-bithiophenes) and poly( 3-alkylthiophenes): A comparative study

The influence of alkyl side chain distribution patterns on the Spectroelectrochemical properties of poly(alkylthiophenes) has been studied. Two types of compounds were studied as representing different coupling patterns:(i) poly(4,4'-dialkyl-2,2'-bithiophenes), which represent head-to-head and tail-to-tail coupled poly(al-kylthiophene) chains; and(ii) poly(3-alkylthiophenes), which represent head-to-tail coupled poly(alkylthiophene) chains.Both types of polymers can be obtained chemically or electrochemically by the constant potential method or the potential scanning method. Poly(4,4'-dialkyl-2,2'-bithiophenes) differ significantly from poly(3-alkylthiophenes) in their voltammetric and spectroelectrocheinical properties. The oxidative doping of these compounds occurs in a very narrow potential range (35 mV as determined by static Spectroelectrochemical studies) and is significantly retarded in dynamic measurements. Analysis of the changes in absorption in the 500 nm spectral region and the observation of an induction period in the oxidation at constant potential seem to indicate that the oxidative doping is preceded by structural changes which facilitate the oxidation.Although in the neutral state poly(4,4'-dialkyl-2,2'-bithiophenes) absorb at 390 nm, i.e. their π→π^* transition is blue-shifted as compared to poly(3-alkylthiophenes), the polaronic states included by doping are located in the same spectral region for both families of polymers. This observation is consistent with the postulate of significant changes induced by doping in poly(4,4'-dialkyl-2,2'-bithiophenes). The more twisted head-to-head and tail-to-tail coupled poly(alkylthiophene) chains must adopt a more planar structure, similar to poly(3-alkylthiophenes), in order to create polaronic states and accommodate the charge-compensating anions.     

Thermal and dynamic mechanical analysis of cross-linked poly(esterurethanes)

New cross-linked poly(esterurethanes) (PEU) based on unsaturated olygo(alkyleneester)diol (OAE), 4,4’-diphenylmethane diisocyanate (MDI) and styrene or methyl methacrylate as curing monomers were prepared. The synthesis of PEU was performed in two steps. In the first step OAE was obtained from adipic acid, maleic anhydride and ethylene glycol. In the second step a prepolymer was obtained in a reaction of OAE with different amounts of 4,4’-diphenylmethane diisocyanate followed by crosslinking using previously mentioned curing monomers. The influence of structure of the poly(esterurethanes) on thermal and dynamic mechanical properties is studied. Thermogravimetric analysis shows that cross-linked poly(esterurethanes) demonstrate high thermal stability. Moreover the dynamic mechanical thermal analysis shows that the presence of styrene cross-linking chains in polymers lead to the phase separation in cross-linked poly(esterurethanes).     

聚乙烯醇／明胶复合型吸附树脂的合成及其对鞣酸的吸附性能

用反相悬浮聚合法合成了聚乙烯醇／明胶复合型吸附树脂,研究了该类树脂对鞣酸的吸附性能。结果表明,树脂中聚乙烯醇组分的引入,能有效地阻止明胶链之间氢键的形成,使树脂能通过氢键作用选择性吸附鞣质。模拟的应用实验说明,这类吸附树脂可用于某些中药剂型,如口服液,针剂生产中有害及不稳定成分鞣质的选择性去除。     

全共轭聚噻吩类和聚硒吩类嵌段共聚物的凝聚态结构调控

嵌段共聚物可发生微相分离形成丰富的介观尺度上的相结构,而共轭聚合物是一类具有特殊的力学、导电性能或光电功能的半刚性链高分子.全共轭嵌段共聚物因其兼具两者的特性而备受瞩目.本文着重介绍了近年来课题组在基于全共轭聚(3-烷基噻吩)和聚(3-烷基硒吩)嵌段共聚物体系的研究进展,通过改变体系的分子结构包括主侧链结构、侧链的烷基长度及取代基团等以及对体系在溶液状态及薄膜状态进行后处理包括改变溶剂、热处理、溶剂蒸气处理等来调控体系的微相分离行为和结晶行为,实现对材料凝聚态结构的调控.在此基础上,以有机场效应晶体管和聚合物太阳能电池器件作为最终体现聚噻吩或聚硒吩类体系凝聚态结构与性能关系的平台,将获得的调控体系凝聚态结构的有效策略用于实现其半导体材料物理性能的提升.     

Photochemically prepared polysulfone/poly(ethylene glycol) amphiphilic networks and their biomolecule adsorption properties

Polysulfone/poly(ethylene glycol) amphiphilic networks were prepared via in situ photo-induced free radical crosslinking polymerization. First, the hydrophobic polysulfone diacrylate (PSU-DA) oligomer was synthesized by condensation polymerization and subsequent esterification processes. Then, the obtained oligomer was co-crosslinked with the hydrophilic poly(ethylene glycol) diacrylate (PEG-DA) or poly(ethylene glycol) methyl ether acrylate (PEG-MA) at different feed ratios. In the case of PEG-MA, the resulting network possessed dangling pendant hydrophilic chains on the crosslinked surface. The structure and the morphology of the membranes were characterized by attenuated total reflection infrared spectroscopy (ATR-IR) and scanning electron microscopy (SEM). The enhancement of surface hydrophilicity was investigated by water contact angle measurements. The biomolecule adsorption properties of these networks were also studied. The biomolecules easily adsorbed on the surface of the hydrophobic polysulfone networks whereas dangling hydrophilic chains on the surface prevented the adsorption of the biomolecules.     

Synthesis of double hydrophilic graft copolymer containing poly(ethylene glycol) and poly(methacrylic acid) side chains via successive ATRP

A well‐defined double hydrophilic graft copolymer, with polyacrylate as backbone, hydrophilic poly(ethylene glycol) and poly(methacrylic acid) as side chains, was synthesized via successive atom transfer radical polymerization followed by the selective hydrolysis of poly(methoxymethyl methacrylate) side chains. The grafting‐through strategy was first used to prepare poly[poly(ethylene glycol) methyl ether acrylate] comb copolymer. The obtained comb copolymer was transformed into macroinitiator by reacting with lithium diisopropylamine and 2‐bromopropionyl chloride. Afterwards, grafting‐from route was employed for the synthesis of poly[poly(ethylene glycol) methyl ether acrylate]‐g‐poly(methoxymethyl methacrylate) amphiphilic graft copolymer. The molecular weight distribution of this amphiphilic graft copolymer was narrow. Poly(methoxymethyl methacrylate) side chains were connected to polyacrylate backbone through stable C? C bonds instead of ester connections. The final product, poly[poly(ethylene glycol) methyl ether acrylate]‐g‐poly(methacrylate acid), was obtained by selective hydrolysis of poly(methoxymethyl methacrylate) side chains under mild conditions without affecting the polyacrylate backbone. This double hydrophilic graft copolymer was found be stimuli‐responsive to pH and ionic strength. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4056–4069, 2008     

Phospha-S-triazines. VI. Polymeric systems

Two types of polymeric phospha-s-triazines were synthesized: poly(perfluoroalkylethermonophospha-s-triazines) and monocyclic mono- and diphospha-s-triazines substituted on the carbon ring atoms by poly- (perfluoroalkylether) chains. The polymeric system consisting of the monophospha-s-triazine rings joined by perfluoroalkylether chains were found to have lower thermal oxidative stability than that shown by the corresponding dumbbell compounds. The monocyclic materials substituted by poly(perfluoroalkylether) chains possessed good thermal and oxidative stability, in addition to exhibiting anticorrosive and antioxidative properties.     

Synthesis and Characterization of New Functional Poly(ester-anhydride)s Based on Succinic and Sebacic Acids

Summary: New functional poly(ester-anhydride)s with allyl pendant groups in the side chains were obtained by polycondensation of sebacic acid (SBA) and poly(3-allyloxy-1,2-propylene succinate) (OSAGE) terminated with carboxyl groups. The carboxyl groups in OSAGE and in SBA were converted to mixed anhydride groups by acetylation with acetic anhydride. After that, prepolymers obtained were condensed in vacuum to yield higher molecular weight poly(ester-anhydride)s. The influence of SBA and OSAGE content in poly(ester-anhydride)s on their selected properties e.g. molecular weight, thermal and solubility characteristics as well as degradation rate and mode, were examined. Poly(ester-anhydride)s were degraded in aqueous buffer of pH 7.4 at 37 °C. The hydrolytic degradation was monitored by determination of weight loss of samples and by determination of ester to anhydride groups ratio.     

Electrostatic force microscopy measurements of CdSe-PS nanoparticles and CdSe-PS/poly(styrene-b-butadiene-b-styrene) nanocomposites

Electrostatic force microscopy (EFM) measurements were performed to analyze the conductive properties of CdSe nanoparticles functionalized with polystyrene (PS) brushes and embedded in a poly(styrene-b-butadiene-b-styrene) triblock copolymer. CdSe nanoparticles were synthesized aqueously and functionalized with polystyrene chains by the grafting through technique. CdSe-PS nanoparticles obtained after 5 and 8 h of polymerization were analyzed, in order to study the effect of the molecular weight of PS chains on conductive properties. EFM results showed the maintenance of the conductive properties of CdSe nanoparticles through functionalization reactions and even when they were confined in the block copolymer. Due to the low differences between the values obtained in the response of the samples to the charged tip, no effect of the molecular weight of brushes was confirmed.