Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO₂ films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO₂ films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO₂ film growth. The TiO₂ films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO₂ surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO₂ film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO₂ could not be deposited on the substrate and a cloudy TiO₂ film was formed due to the increase of surface roughness, respectively.     

Synthesis of amphiphilic heteroarm star‐shaped polymer via free radical polymerization using polyfunctional chain transfer agent and its self‐assembly behavior

Amphiphilic heteroarm star‐shaped polymers have important theoretical and practical significance. In this work, amphiphilic heteroarm star‐shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in two steps. First, conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′‐azobis (isobutyronitrile) (AIBN) was carried out in the presence of polyfunctional chain transfer agent, pentaerythritol‐tertrakis (3‐mercaptopropinate) (PETMP). At appropriate monomer conversion, about two‐arm s‐PMMA having two residual thiol groups at the chain center was obtained. Second, the s‐PMMA obtained above was used as macro‐chain‐transfer agent for free radical polymerization of acrylic acid (AA). The heteroarm star‐shaped polymer with the hydrophobic PMMA segment and the hydrophilic PAA segment was obtained. The successful synthesis of heteroarm star‐shaped polymers, (PMMA)₂(AA)₂, was confirmed by ¹H‐NMR and its self‐assembly behavior in different solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A novel amphiphilic AB2 star copolymer synthesized by the combination of ring-opening metathesis polymerization and atom transfer radical polymerization

A new amphiphilic AB₂ star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminating agents catalyzed by first generation Grubbs catalyst. The values of capping efficiency (CE) of the polymers were determined by NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphilic AB₂ star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly(2-(dimethylamino)ethyl methacrylate)] (PONBDM_n-b-(PDMAEMA_m)₂) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assemble spontaneously in water to form polymeric micelles, which were characterized by dynamic light scattering, atom force microscopy, and transmission electron microscopy measurements.     

Star polymers via atom transfer radical polymerization from adamantane-based cores

A series of novel multifunctional initiators derived from adamantane-based derivatives have been used in the syntheses of various styrenic and (meth)acrylic star polymers by atom transfer radical polymerization (ATRP). Conditions were identified in each system to produce star polymers with nearly monomodal molecular distributions. These synthesized star polymers have glass transition temperatures similar to those known for high-molecular-weight linear polymers. We obtained a series of adamantane-contained star polymers covering a wide range of molecular weights by adjusting the monomer-to-initiator ratio and the solvent polarity. Because of reaction heterogeneity and inevitable termination processes, the occurrence of star-star coupling led to a lower than predicted molecular weight polydispersity. When hydrolyzed from their cores by NaOH, the values of M_w of the arms of the PMMA star polymer did not change with reaction time, at least for the first 48 h of the reaction, which implies that no significant PMMA hydrolysis occurs within this interval of time.     

Intermolecular radical addition of alkoxyamines onto olefins: An easy access to advanced macromolecular architectures precursors

Novel “second generation” alkoxyamines, derived from N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (so-called SG1) as initiators for nitroxide-mediated polymerization (NMP) were synthesized by intermolecular radical 1,2-addition (IRA) of a high dissociation rate constant alkoxyamine (BlocBuilder^®, also called MAMA-SG1) onto various activated olefins, such as n-butyl acrylate, acrylic acid, dimethylacrylamide, 2-hydroxyethylacrylate and styrene. The potential of this radical addition was further applied to the synthesis of multifunctional alkoxyamines as precursors for complex macromolecular architectures, namely 3- and 4-arm star polymers. For this, tri- and tetra-acrylates were synthesized by reaction of acryloyl chloride with the 1,1,1-tris(hydroxymethyl)ethane and pentaerythritol, respectively, in the presence of triethylamine. The addition of MAMA-SG1 onto these olefins led to the tri- and tetra-functional SG1-based alkoxyamines which were further used to prepare polystyrene stars of controlled molecular weights and polydispersity values not exceeding 2. The individual arms were recovered by hydrolysis of the ester groups of the star core originating from the alkoxyamine initiator under basic conditions. The decreasing molecular weight determined by GPC during hydrolysis demonstrated the star architecture of the polymers.     

Affinity of amine-functionalized plasma polymers with ionic solutions similar to those in the human body

This work presents a study on the synthesis and on the interaction of allylamine, pyrrole and ethylenglycol polymerized by plasma with solutions of ionic composition similar to those in the nervous system. These polymers are attractive substrates to interact with the ionic pulses of the spinal cord due to their electrical and biocompatible characteristics. The ionic solutions were prepared with aqueous combinations of NaCl, MgSO₄, KH₂PO₄, KCl, CaCl₂, and NHCO₃. The polymers were prepared as thin films on glass substrates. The results indicated that some of the most important physical characteristics in the hydrophilicity of the polymers, roughness, porosity and functional groups, can be controlled with the energy of polymerization. The interaction between polymers and solutions was studied measuring the contact angle at the solid–liquid interface and the electrical conductivity of the polymers wet with these solutions. The contact angles were between 8° and 38°, and the electrical conductivity was in the 10^?8 to 10^?9 S/cm interval. The general tendencies indicate that the amine-functionalized polymers of this work are good materials to interact with the spinal cord system.     

Synthesis of multi‐arm star polystyrene with hyperbranched polyester initiators by atom transfer radical polymerization

Multi‐arm star polystyrenes with hyperbranched polyester (HP3) core were prepared by atom transfer radical polymerization (ATRP). The structures of the polymers were investigated with FTIR and ¹H NMR. GPC results showed that the resultant polymers had relatively broad polydispersity indices that arouse from the macromolecular initiator (HP3‐Br). The thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis indicated that polystyrene star polymers had only the glass transition temperatures (T_g), which changes with the weight ratio of multi‐functional macroinitiator‐to‐monomer. In addition, these star polymers could form the spherical micelles in the selected solvent (THF/n‐hexane). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 728–733, 2006     

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

Well-defined photo-responsive alternating copolymers, poly(4-(N-maleimido)azobenzene-alt-styrene)s (PMSts), were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. A divinyl monomer was used in this polymerization to prepare high molecular weight azobenzene polymers. These polymers had good solubility in most organic solvents, formed films well, and had high glass transition temperatures (T_g = 174–250 °C) and were heat resistant (T_d > 320 °C). The photo-induced trans–cis isomerization of the copolymers was examined in chloroform solution. Surface-relief-gratings (SRGs) formed on the polymer films were also investigated using illumination from a linearly polarized Kr⁺ laser beam.     

Ring-opening metathesis polymerization of norbornene derivatives for multifunctionalized all-optical photorefractive polymers with a non-conjugated main chain

With the aim of multifunctionalized all-optical photorefractive polymers bearing a non-conjugated main chain (NCMC), four novel norbornene-containing monomers were synthesized by introduction of different alkyl spacers between the functional chromophore and norbornene group. The polymers were prepared via ring-opening metathesis polymerization (ROMP) and characterized by IR, UV–Vis, GPC, DSC, TG, etc. Their number average molecular weights (M_n) are higher than 1.0 × 10⁴, and their glass transition temperatures are in the range from 75 °C to 153 °C depending on the volume of functional group and spacer length. The polymers have good thermal stability up to 280 °C and excellent solubility in THF. Optically transparent films were fabricated with N-ethyl-carbazole (ECZ) as a plasticizer and C₆₀ as a charge generator. Their photorefractive performance was evaluated at 633 nm by two-beam-coupling (TBC) experiment at a zero electrical field. TBC signals were observed from these films without prepoling, indicating that the synthesized NCMC polymers bear an all-optical photorefractive property.     

Preparation and ionic conductive properties of all‐solid polymer electrolytes based on multiarm star block polymers

A series of star block polymers with a hyperbranched core and 26 arms are successfully synthesized by atom transfer radical polymerization of styrene (St), and poly(ethylene glycol) methyl ether methacrylate from a hyperbranched polystyrene (HBPS) multifunctional initiator. All‐solid polymer electrolytes composed of these multiarm star polymers and lithium salts are prepared. The influences of polyoxyethylene (PEO) side‐chain length, PEO content, lithium salt concentration and type, and the structure of polymer on ionic conductivity are systematically investigated. The resulting polymer electrolyte with the longest PEO side chains exhibits the best ionic conductive properties. The maximum conductivity is 0.8 × 10^?4 S cm^?1 at 25°C with EO/Li = 30. All the prepared multiarm star block polymers possess good thermal stability. The mechanical property is greatly improved owing to the existence of polystyrene blocks in the multiarm star polymer molecules, and flexible films can be obtained by solution‐casting technique. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Scale-up precision synthesis of octa-arm polyisobutylene stars

Summary This paper concerns the scale-up precision synthesis of octa-arm polyisobutylene (PIB) stars. Specifically, we have optimized to the 100–200 g scale the preparation of star polymers consisting of eight PIB arms radiating from a calix[8]arene core. The synthesis strategy involved the use of a calix[8]arene fitted with eight p-C(CH₃)₂OCH₃ groups as the initiator in conjunction with mixed BCl₃/TiCl₄ coinitiators in hexanes/methyl chloride solvent systems at − 80 °C. Various possible side-reactions have been identified and means for their suppression/elimination were developed. Received: 29 December 1999/Revised version: 22 May 2000/Accepted: 22 May 2000     

Synthesis of heat- and solvent-resistant polymers by radical polymerization of trifluoromethyl-substituted N-phenylmaleimides

The radical polymerization of the three kinds of fluorine-containing maleimides, that is, N-[2-(trifluoromethyl)phenyl]maleimide (2TFPhMI), N-[3-(trifluoromethyl)phenyl]maleimide (3TFPhMI), and N-[4-(trifluoromethyl)phenyl]maleimide (4TFPhMI) was carried out in the presence of a radical initiator in benzene at 60°C. The polymerization reactivity of these fluorine-containing maleimides and the properties of the resulting polymers were examined in comparison with the results for the methyl-substituted phenylmaleimides. The trifluoromethyl-substituted maleimides readily polymerized to give polymers in high yields as well as a methyl-substituted one. The resulting polymers showed an excellent resistance against organic solvents; especially, poly(4TFPhMI) was insoluble in the most common solvents. The onset temperature of thermal decomposition of the fluorine-containing polymers (T_init> = 352–368°C) was similar to that of poly(N-phenylmaleimide) (T_init = 364°C) and slightly lower than those for the methyl-substituted one (T_init = 388–402°C). The glass transition temperature of the polymers was dependent on the position of the trifluoromethyl group. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1703–1708, 1998     

Block polymers of poly(para-xylelene) and polystyrene or poly(vinyl pyridine) prepared by anionic polymerization

Anionic polymerization of para-xylelene, p-X, may be initiated in solution at a low temperature (～?70°C) by electron-transfer process. The spontaneous formation of diradicals through dimerization of p-X monomers is too slow at these temperatures to initiate the radical polymerization of p-X. The anionic polymerization yields a living poly(p-xylelene) which is capable of growing further by the addition of vinyl pyridine, VP. In this way block polymers PVP-P_pX-PVP were prepared. Alternatively, the addition of p-X monomers to living polystyrene, PS, or living poly(vinyl pyridine), PVP, yields at low temperatures the block polymers P_pX-PS-P_pX or P_pX-PVP-P_pX. The block polymers prepared by this approach were isolated and characterized. Even small blocks of P_pX attached to polystyrene or poly(vinyl pyridine) make the resulting polymers insoluble in boiling solvents below 200°C.     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Surface grafting of polymers onto glass plate: Polymerization of vinyl monomers initiated by initiating groups introduced onto the surface

The surface grafting of polymers onto a glass plate surface was achieved by the polymerization of vinyl monomers initiated by initiating groups introduced onto the surface. Azo groups were introduced onto the glass plate surface by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with isocyanate groups, which were introduced by the treatment with tolylene-2,4-diisocyanate. The radical polymerization of various vinyl monomers was initiated by azo groups introduced onto the glass plate surface and the corresponding polymers were grafted from the surface: The surface grafting of polymers was confirmed by IR spectra, and the contact angle of surface, with water. The contact angle of the glass plate increased by the grafting of hydrophobic polymers, but decreased by the grafting of hydrophilic polymers. The radical postpolymerization was successfully initiated by the pendant peroxycarbonate groups of grafted polymer on the surface to give branched polymer-grafted glass plate. The cationic polymerization of vinyl monomers was also successfully initiated by benzylium perchlorate groups introduced onto the glass plate surface and the corresponding polymers were grafted onto the surface. The contact angle of the glass plate surface obtained from the cationic polymerization of styrene was larger than that obtained from the radical polymerization. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2165–2172, 1997     

Synthesis and characterization of phosphorus containing aromatic poly(amide-imide)s copolymers for high temperature applications

A series of novel thermally stable poly(amide-imide)s (PAIs) based on non-coplaner diimide-diacid (DIDA) monomer is synthesized. These polymers are characterized by elemental analysis, FT-IR, ¹H-NMR, ¹³C-NMR and ³¹P-NMR spectroscopic techniques and their physical and thermal properties are also studied. Four different dianhydrides pyromellitic anhydride (PMDA)/3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA)/1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA)/4,4′-oxydiphthalic anhydride (ODPA) and amino acid l-tryptophan are used to synthesize DIDA. The polymerization of DIDA with phosphorus containing triamines having phenyl moieties gives poly(amide-imide)s. The synthesized polymers are obtained in high yield and possessed inherent viscosity in the range 0.66–0.98 dL/g. These polymers display higher solubility in polar aprotic solvents, such as DMSO, NMP and DMF. In addition, the absorption edge values (λ _o) obtained from their UV curves are determined, and all the resulting poly(amide-imide)s films exhibited high optical transparency. The glass transition temperature (T _g) of these polymers is recorded in the range 211–265 °C, initial decomposition temperature in excess of 435 °C and char yield at 800 °C in nitrogen ranged from 52 to 70 %. Wide angle X-ray diffraction showed that all the polymers are almost amorphous.     

Morphological investigations of self-assembled films from a pyridine -incorporated poly (p -phenylene)

Well-organized structures of polymers in thin films have been widely investigated. Amphiphilic polymers, star-shaped polymers and modified polystyrene-based polymers have been shown to form self-assembled honeycomb patterns on substrates. Herein, we report a poly (p-phenylene) derivative capable of producing self-assembled regular structures. Highly fluorescent honeycomb structures were observed on various substrates. The nature of the substrate and polymer influences the morphology of the film.     

Grafted polytriphenylamines synthesized by atom transfer radical polymerization in tandem with oxidative polycondensation

Arylamine polymers are among the most studied conducting polymers due to a whole range of interesting properties and applications. In this paper, we describe the synthesis of soluble and processable electroactive poly(triphenylamine-g-oligostyrene) by two polymerization methods in tandem. In the first step, oligostyrene macromonomers with well-defined molecular weight, polydispersity and chain-end functionality were obtained by radical-controlled polymerization (i.e., atom transfer radical polymerization, ATRP) of styrene. The styrene oligomerization was carried out using a new triphenylamine-based initiator, [4-(diphenylamino)benzyl 2-bromo-2-methylpropanoate], cuprous bromide as co-initiator and bipyridine as ligand, at 100 °C, in bulk. Using two feed molar ratios of components: [styrene]₀:[initiator]₀:[CuBr]₀:[bipyridine]₀, two macromonomers with M _n = 9,900; M _w/M _n = 1.25 and M _n = 3,460; M _w/M _n = 1.22, respectively, were synthesized. The presence of triphenylamine moiety at one end of the macromonomer allowed the chemical and electrochemical polymerization of macromonomers to polytriphenylamine brushes having short oligostyrene grafts in every structural unit. The oligostyrene substituents confer processability and good solubility in common organic solvent characteristics for polystyrene while preserving the optoelectronic properties of arylamine-conjugated main chain. The chemical oxidative polymerization of macromonomer was carried out using iron (III) chloride dissolved in nitrobenzene. The redox behavior of the initiator, macromonomer and graft polymer was investigated by cyclic voltammetry. In all cases, it was observed that the reversible oxido-reduction of arylamine sites was accompanied by irreversible oxidative electropolymerization by free-para positions of triphenylamine substituents and deposition of thin films on working electrode. The structures of the initiator, macromonomers and graft copolymers were determined by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy. The absorption and fluorescence spectroscopy have revealed absorption and emission maxima characteristics for triphenylamine group. DSC studies have confirmed glass transitions characteristics for styrene oligomers.     

Facile synthesis and promising antibacterial properties of a new guaiacol-based polymer

A new acrylamide-type monomer (N-(4-hydroxy-3-methoxy-benzyl)-acrylamide) derived from guaiacol was successfully synthesized. Polymers containing guaiacol moiety were obtained via conventional radical polymerization of this monomer with AIBN as initiator. The influence of reaction time, initiator concentration and temperature on polymers characteristics was studied. Evaluation of the termination mode in free-radical polymerization was performed by MALDI-TOF mass spectrometry. Termination occurs mainly by disproportionation reaction. Additional peaks in the spectrum were attributed to side chain reactions implying phenoxy radicals. This new polymer exhibits a potential antibacterial activity against Bacillus subtilis by using anti-adhesion and anti-biofilm tests. After an adhesion time of 3 h, compared to a non-coated glass slide, there was a decrease of bacteria of 99% on the polymer coated glass slide. After three days of culture in a bacterial suspension, no biofilm was observed on the polymer coated surface.     

Controlled radical polymerization of p-(iodomethyl)styrene—a route to branched and star-like structures

p-(Iodomethyl)styrene was polymerized under the action of a radical initiator (AIBN). The polymerization proceeds with degenerative chain transfer and leads to well defined branched polymers with functional primary and secondary iodomethyl groups as revealed by NMR studies. The obtained polymer can be further used as macroinitiator for radical polymerization of styrene. This polymerization proceeds in controlled way to polystyrene star polymers with reactive groups at the end of their arms. The characterization of branched and star structures was performed by NMR and GPC with absolute molar mass detection (MALLS).