Radiation‐induced fabrication of polymer nanoporous materials from microphase‐separated structure of diblock copolymers as a template

Polymer nanoporous materials with periodic cylindrical holes were fabricated from microphase‐separated structure of diblock copolymers consisting of a radiation‐crosslinking polymer and a radiation‐degrading polymer through simultaneous crosslinking and degradation by γ‐irradiation. A polybutadiene‐block‐poly(methyl methacrylate) (PB‐b‐PMMA) diblock copolymer film that self‐assembles into hexagonally packed poly(methyl methacrylate) cylinders in polybutadiene matrix was irradiated with γ‐rays. Solubility test, IR spectroscopy, and TEM and SEM observations for this copolymer film in comparison with a polystyrene‐block‐poly(methyl methacrylate) diblock copolymer film revealed that poly(methyl methacrylate) domains were removed by γ‐irradiation and succeeding solvent washing to form cylindrical holes within polybutadiene matrix, which was rigidified by radiation crosslinking. Thus, it was demonstrated that nanoporous materials can be prepared by γ‐irradiation, maintaining the original structure of PB‐b‐PMMA diblock copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5916–5922, 2007     

Removal of poly(methyl methacrylate) in diblock copolymers films studied by grazing incidence small‐angle X‐ray scattering

Self‐assembly of diblock copolymers (BCP) into periodic arrays is a promising route to generate templates for the fabrication of nanoscopic elements, when one block is selectively removed. In cylindrical morphology polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) copolymer (BCP) films, the efficiency of different processes for removing the PMMA from cylinders is studied using grazing incidence small angle X‐ray scattering (GISAXS), x‐ray reflectivity and critical dimension scanning electron microscopy. The detailed analysis of the GISAXS patterns leads to the determination of the depth of cylindrical holes left by removal of the PMMA. It is found that the combination of a preliminary UV exposure followed by a wet treatment allows to remove totally the PMMA blocks. Furthermore, the optimization of both UV exposition time and solvent allows to preserve the PS matrix and interestingly for nanolithographic applications to decrease the process costs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1137–1144     

Surface and solution properties of polysiloxane–poly(methyl methacrylate) graft copolymer

A polysiloxane–poly(methyl methacrylate) (PMMA) graft copolymer was prepared by hydrosilylation reaction between a Si? H containing polysiloxane and an allyl-terminated PMMA. The obtained graft copolymer was blended with PMMA homopolymer. The addition of only 0.01 wt % of graft copolymer was sufficient to make PMMA surfaces hydrophobic. In acetone–cyclohexane mixed solvent, the graft copolymer formed a polymeric micelle by the aggregation of PMMA branches.     

Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.     

Crystalline structure and morphology of microphases in compatible mixtures of poly(tetrahydrofuran‐methyl methacrylate) diblock copolymer and polytetrahydrofuran

The crystalline structure and morphology of compatible mixtures of poly(tetrahydrofuran‐methyl methacrylate) diblock copolymers (PTHF‐b‐PMMA) with a polytetrahydrofuran homopolymer (PTHF) were studied with synchrotron X‐rays. Wide‐angle diffraction was used to study the crystalline structures in a confined lamellar region with a PTHF thickness ranging from 12.2 to 19.5 nm, and in a PTHF matrix with an interface distance between the PMMA cylinders ranging from 17 to 22 nm. As the above thickness values are around the long period (ca. 17 nm) of PTHF homopolymer under the crystallization condition used, the crystalline structure has been found to be very sensitive to the average thickness of the PTHF phase. The changes in the diffraction patterns with changing PTHF homopolymer content suggested a chain folding model in confined PTHF lamellae with the PTHF fiber axes being perpendicular to the thick PTHF lamella. In the case of hexagonally packed cylindrical PMMA microdomains with an interface distance ranging from 12 to 16 nm, the effects of PMMA cylinders on the crystallization morphology of PTHF in the PTHF matrix, and the effects of the PTHF crystallization on the hexagonally packed structure of PMMA cylinders were also studied. It is shown that only when the interdistance of two neighboring PMMA cylinders is comparable with the long period of the pure PTHF homopolymer, ordered PTHF stacks can be formed in the PTHF matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 779–792, 1999     

Facile control of surface wettability in TiO2/poly(methyl methacrylate) composite films

A facile method to produce very hydrophobic surface was developed simply using the mixture of TiO(2) nanoparticles and poly(methyl methacrylate) (PMMA). When the volume ratio of TiO(2) to PMMA is between 35 vol.% and 50 vol.%, the mixture of two hydrophilic materials became very hydrophobic. Analysis of the molecular structure by infrared spectroscopy shows that the preferential orientation and attachment of a carbonyl group of a polymer molecule to the surface of TiO(2) nanoparticles play a critical role in the appearance of the strong hydrophobicity. When this composite was exposed to UV light, PMMA on the surface of the mixture film was decomposed through a photocatalytic reaction and the very hydrophobic surface turned to the superhydrophilic one. The superhydrophilic property of UV-irradiated composite lasts as long as several months. This long lasting superhydrophilicity is ascribed to the porous structure, which provides high roughness and strong capillary interaction. Easy transition from strong hydrophobicity to superhydrophilicity in TiO(2)/PMMA composites could be applied to designing high contrast hydrophilic/hydrophobic patterns.     

Solvent-induced self-assembly of mixed poly(methyl methacrylate)/polystyrene brushes on planar silica substrates: molecular weight effect

The effect of molecular weight on the solvent-induced self-assembly of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes on silicon wafers was studied. For a series of mixed brushes with a fixed PMMA M(n) and systematically changed PS M(n), a transition in water advancing contact angle (theta(a)) from 74 degrees, the value for a flat PMMA surface, to 91 degrees, the value for a flat PS film, was observed with increasing PS M(n) after treatment with CHCl(3). Atomic force microscopy studies showed smooth surfaces for all samples. While no significant changes in surface morphologies were observed after treatment with cyclohexane, a selective solvent for PS, contact angle and XPS studies indicated that the mixed brushes with a PS M(n) slightly smaller than that of PMMA underwent self-reorganization, exhibiting a different theta(a). Intriguing surface morphologies composed of relatively ordered nanoscale domains were found from mixed brushes with PS M(n) slightly smaller than or similar to that of PMMA after treatment with acetic acid, a selective solvent for PMMA. The nanodomains are speculated to be of a micellar structure, with PS chains forming a core shielded by PMMA chains.     

Synthesis and characterization of linear ABC triblock copolymer of ethylene oxide,methyl methacrylate,and styrene

A well‐defined linear ABC triblock copolymer of ethylene oxide (EO), methyl methacrylate (MMA), and styrene (St) was prepared by sequential living anionic and photo‐induced charge transfer polymerization (CTP) using p‐aminophenol as parent compound. In the first step, the diblock copolymer of PEO‐b‐PMMA with a protected aniline end group at PEO end was prepared by initiating of phenoxo‐anion the polymerization of EO and MMA successively, then the diblock copolymer of PEO‐b‐PMMA via deprotection of aniline at PEO end constituted a binary initiation system with benzophenone (BP) by charge transfer complex mechanism to initiate the polymerization of St under UV‐irradiation. The GPC and NMR measurements support that in copolymerization, either in the first or second step, neither homopolymer nor side reactions, such as chain transfer or chain termination, was found. The effect of the concentration of PEO_a‐b‐PMMA and St, and the polarity of solvent on the polymerization rate (R_p) of CTP is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 825–833, 1999     

PS-PMMA嵌段共聚物/PMMA在选择性溶剂中的自组装行为

用动态光散射和透射电镜研究了嵌段共聚物聚苯乙烯-聚甲基丙烯酸甲酯(PS-b-PMMA)和其对应的均聚物聚甲基丙烯酸甲酯(PMMA)在选择性溶剂四氢呋喃/环己烷(THF/CYH)中的自组装行为.选择性溶剂对PS嵌段是良溶剂,对PMMA嵌段和均聚物PMMA是非良溶剂,实验结果表明,在适当的分子量及组成条件下,PS-PMMA/PMMA在选择性溶剂中形成了单分散的纳米胶束,均聚物PMMA与PMMA嵌段一同形成了胶束的核,通过控制均聚物PMMA的量可以在较大的范围内调整胶束的尺寸.     

Ring-shaped morphology in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films

We report observation of ring-shaped morphology formed in thin films of a cylinder-forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer cast from 1,1,2,2-tetrachloroethane (Tetra-CE) solution via relatively fast solvent evaporation rates, in which Tetra-CE is a good solvent for both blocks but preferential affinity for the minority PMMA block. We studied the microstructure of a set of solution-cast block copolymer films dried with different solvent evaporation rates, R. The control with different R leads to keeping microstructures in different solution concentrations (phi) and bringing mechanical strain fields with different strength in the film, for which faster evaporation rates result in microstructures of lower solution concentrations and mechanical strain fields of higher strength. As R decreases from rapid evaporation (approximately 0.1 mL/h), the film microstructure evolved from an intermediate ringlike morphology sequentially to ring-shaped morphologies including loose and tight rings and then inverted phase of PS spheres in a PMMA matrix and finally reached the equilibrium phase, namely, cylinders of PMMA in a PS matrix. In view of the influence of the film constraints, the microstructure of a film with a terraced free surface profile has been examined. The results indicate that the ring-shaped morphology can form as long as the film thickness is larger than a critical value of about one microdomain spacing. In the case where the film thickness is larger than that value, the nature of solvent and the kinetics of solvent evaporation are shown to be mainly responsible for the ring-shaped morphology formation.     

Polymer blend/organoclay nanocomposite with poly(ethylene oxide) and poly(methyl methacrylate)

A series of polymer blend/organoclay nanocomposite at a fixed blending ratio was prepared using equal ratio of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) via solvent casting method. With respect to nanoscale internal structure, we found that PMMA chains have better affinity with organoclay than PEO, based on the results from X-ray diffraction. Direct visualization via transmission electron microscopy (TEM) also supported the better affinity of PMMA with organoclay by indicating the existence of hybrid structures of mainly intercalated but with some exfoliated forms. The miscible nature of the blend and homogeneous dispersion state of layered silicate in the blend system were investigated via the microscopic fractured surface morphologies. From rheological measurements (storage and loss modulus), we discovered the role of the physical network structure between polymer and organoclay to be a main factor for the enhancement of elastic properties.     

Spectral and kinetic characteristics of formyl-substituted spiropyran in poly(methyl methacrylate) modified with elastomers

The efficiency of photochemical transformations of 1′,3′,3′-trimethyl-6′-formyl-8′-allylspiro[2H-1-benzopyran-2,2′-indoline] in PMMA modified with small amounts of poly(ethyl acrylates) of different structures is studied. It is shown that, in the presence of these additives, the quantum yield of the coloring reaction of the photochromic compound under UV irradiation and the rates of photochemical reactions (forward and back) increase. The maximum efficiency of photochemical parameters is observed for PMMA containing small amounts of linear poly(ethyl acrylate) occurring as a microphase in a glassy matrix.     

Structures and thermal properties of chitosan-modified poly(methyl methacrylate)

The emulsion polymerization of methyl methacrylate in the presence of chitosan with potassium persulfate (KPS) as an initiator was examined in a previous article. The free radicals that dissociated from KPS not only initiated the polymerization but also degraded the chitosan molecules. Therefore, in addition to its role as a cationic surfactant, chitosan also participated in the polymerization reaction. When the polymerization was complete, the latex polymer consisted of poly(methyl methacrylate) (PMMA) homopolymer and chitosan–PMMA copolymer. In this article, the structures and thermal properties of latex polymers are examined. Gel permeation chromatography was used to measure the molecular weight of the PMMA homopolymer, with the copolymer composition determined by an elemental analyzer. Scanning and transmission electronic microscopes were used to measure the size of latex particles from different reaction systems. The surface charges of latex particles at several different pH values were determined by the measurement of the ζ potential. All results agreed with the reaction mechanism proposed in the previous article. Finally, the presence of rigid chitosan increased the glass-transition temperature of the final latex polymers. Thermogravimetric analysis showed that the degradation behavior of latex polymers was similar to the unzipping mechanism of PMMA, yet the presence of chitosan units hindered the unzipping of the main chains in chitosan–PMMA copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1646–1655, 2001     

Direct spincasting of polystyrene thin films onto poly(methyl methacrylate)

The low vapor pressure solvent 1‐chloropentane was used to directly spincast polystyrene (PS) films onto poly(methyl methacrylate) (PMMA) with smooth surfaces and sharp interfaces. Interface roughness after removal of the PS layer with cyclohexane was determined with scanning force microscopy to be <1 nm. Dynamic secondary mass spectroscopy revealed an interfacial width below the resolution limit of ～10 nm. Large area bilayers with smooth surfaces could be created. In addition, direct spincasting with 1‐chloropentane allows the production of thin PS films (<15 nm) and films of low molecular weight (<5 kDa) PS, all of which would be impossible to produce for this important model system by the traditional water‐transfer method. 1‐chloropentane was confirmed to be a sufficiently selective solvent for PS by measuring the Flory–Huggins χ parameters of 1‐chloropentane with PS and PMMA, respectively, with inverse gas chromatography. In the search for a suitable selective solvent, the authors have also examined the role of vapor pressure in spin casting smooth films over a wider molecular weight (4.3–190 kDa) and thickness range (～5–500 nm) than previously reported. Only solvents with low vapor pressure produced high quality PS films. Methylcyclohexene can also be used to produce excellent, directly cast PS/PMMA bilayers, but with a smaller molecular weight and thickness window compared with 1‐chloropentane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3234–3244, 2006     

An optical waveguide study on the nanopore formation in block copolymer/homopolymer thin films by selective solvent swelling

Thin films of mixtures of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) diblock copolymers and PMMA homopolymers with cylindrical PMMA microdomains oriented normal to the substrate surface were used to couple optical modes in the Kretschmann configuration, and their optical properties were investigated by optical waveguide spectroscopy (OWS). The nanopore formation in the block copolymer (BCP) waveguide layer via selective solvent swelling and subsequent reannealing was monitored in terms of shifts in the coupling mode angles. The sequential swelling/reannealing of the initial mixture film resulted in a number of discrete or partially interconnected pores instead of cylindrical pores with a high aspect ratio. The simultaneous processes occurring inside and on top of the BCP waveguide layer were discerned independently with high selectivity for p- and s-polarization.     

Evaluation of Schiff bases of 2,5-dimercapto-1,3,4-thiadiazole as photostabilizer for poly(methyl methacrylate)

The photostabilization of poly(methyl methacrylate) (PMMA) films by Schiff bases of 2,5-dimercapto-1,3,4-thiadiazole compounds was investigated. The PMMA films containing concentration of complexes 0.5% by weight were produced by the casting method from chloroform solvent. The photostabilization activities of these compounds were determined by monitoring the hydroxyl index with irradiation time. The changes in viscosity average molecular weight of PMMA with irradiation time were also tracked (using benzene as a solvent). The quantum yield of the chain scission (Φ_cs) of these complexes in PMMA films was evaluated and found to range between 4.19 × 10^?5 and 8.75 × 10^?5. Results obtained showed that the rate of photostabilization of PMMA in the presence of the additive followed the trend:[1] > [2] > [3] > [4] > [5].According to the experimental results obtained, several mechanisms were suggested depending on the structure of the additive. Among them, UV absorption, peroxide decomposer, and radical scavenger for photostabilizer mechanisms were suggested.     

注塑型聚甲基丙烯酸甲酯多通道微流控芯片的研制及其性能考察

微流控芯片技术因具有微量、快速、高效和高通量等特点,已成为分析化学领域中的研究热点之一．在微流控芯片中,最常见的可用作芯片的材料为玻璃、石英和各种塑料．玻璃和石英有很好的电渗性和光学性质,可采用标准的刻蚀工艺加工和用化学方法进行表面改性,但加工成本较高,封接难度较大．     

Properties of matrix-grafted multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposites synthesized by in situ reversible addition-fragmentation chain transfer polymerization

Multi-walled carbon nanotubes (MWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by the in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in the presence of MWCNTs, at which the bulk polymer was grafted onto the surface of nanotubes through the ??grafting through?? strategy. For this purpose, MWCNTs were formerly functionalized with polymerizable MMA groups. MMA and PMMA-grafted MWCNTs were characterized by Fourier-transform infrared spectroscopy, Raman, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Dissolution of nanotubes was examined in chloroform solvent and studied by UV?Cvis spectroscopy. Thermogravimetric and degradation behavior of prepared nanocomposites was investigated by TGA. MWCNTs had a noticeable boosting effect on the thermal stability of nanocomposites. TGA thermograms showed a two-step weight loss pattern for the degradation of MWCNT-PMMA/PMMA nanocomposites which is contrast with neat PMMA. Introduction of MWCNTs also improved the dynamic mechanical behavior and electrical conductivity of nanocomposites. TEM micrograph of nanocomposite revealed that the applied methods for functionalization of nanotubes and in situ synthesis of nanocomposites were comparatively successful in dispersing the MWCNTs in PMMA matrix.     

Synthesis of poly(methyl methacrylate) macromonomer

Anionic polymerization of methyl methacrylate (MMA) was carried out in tetrahydrofuran (THF) or THF/toluene mixture at ?78°C initiated by triphenylmethyl sodium or lithium as initiators. Highly syndiotactic PMMA of low polydispersity (M _w/m _n = 1.11–1.17) could be prepared with triphenylmethyl lithium in THF or THF/toluene mixture at ? 78°C. Moreover, PMMA macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMMA initiated by triphenylmethyl lithium with p-chloromethyl styrene (CMS) at ?78°C. The coupling reaction of living PMMA initiated by triphenylmethyl sodium with CMS was scarcely occurred.     

Solvent bonding of poly(methyl methacrylate) microfluidic chip using phase-changing agar hydrogel as a sacrificial layer

In this report, a solvent bonding method based on phase-changing agar hydrogel has been developed for the fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Prior to bonding, the channels and the reservoir ports on PMMA channel plates were filled with molten agar hydrogel that could gelate to form solid sacrificial layers at room temperature. Subsequently, PMMA cover sheets were covered on the channeled plates and 1,2-dichlororethane was applied to the interspaces between them. The agar hydrogel in the channels could prevent the bonding solvent and the softened surface of the PMMA cover sheets from filling in the channels. After solvent bonding, the agar hydrogel in the channels and the reservoir ports was melted and removed under pressure. The sealed channels in the complete microchips had been examined by an optical microscope and a scanning electron microscope. The results indicated that high-quality bonding was achieved at room temperature. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of three cations in combination with contactless conductivity detection.