Effect of pendant group of polysiloxanes on the thermal and mechanical properties of polybenzoxazine hybrids

Polybenzoxazine (PBa) was successfully hybridized with polysiloxanes by synchronizing two reactions; ring-opening polymerization of benzoxazine (Ba) and sol–gel process of diethoxysilanes. Diethoxydimethylsilane, diethoxymethylphenylsilane, and diethoxydiphenylsilane were used as precursors for the formation of polydimethylsiloxane (PDMS), polymethylphenylsiloxane (PMPS), and polydiphenylsiloxane (PDPS), respectively. The effect of pendant group of polysiloxane on the optical, mechanical, and thermal properties of PBa–polysiloxane hybrids was studied. The progress of sol–gel process was confirmed by IR, ¹H NMR and size exclusion chromatography. Opaque PBa–PDMS hybrid films were obtained up to 15 wt% of PDMS content, corresponding to the phase separation with 1–2 μm domain size of PDMS as observed from the scanning electron microscope. Meanwhile, transparent PBa–polysiloxane hybrid films were obtained up to 29 wt% for PMPS and 36 wt% for PDPS, which revealed no apparent domain of PMPS and PDPS, indicating high compatibility of the polysiloxanes with PBa. Dynamic viscoelastic analysis (DMA) of the PBa–PDMS hybrid revealed two glass transition temperatures corresponding to PDMS and PBa components, while the DMA of the PBa–PMPS and PBa–PDPS hybrids revealed only one glass transition temperature. The tensile strength and elongation at break of the hybrid films increased with increasing polysiloxane content. Thermogravimetric analysis revealed high weight residue at 850 °C for PBa–polysiloxanes with phenyl group.     

Synthesis and characterisation of poly(arylene sulphides): Part 10. A comparative evaluation of the thermoanalytical behaviour and curing of poly(1,4-phenylene sulphide) and copolymers containing 1,4-phenylene sulphide and 2-methyl-1,4-phenylene sulphide repeat units

Thermogravimetry, differential scanning calorimetry and curing studies were used to assess the viability of random and block copolymers comprising 1,4-phenylene sulphide and 2-methyl-1,4-phenylene sulphide repeat units as alternatives to poly(1,4-phenylene sulphide) (PPS). The properties of the copolymers are discussed critically and compared with those of the parent homopolymers PPS and poly(2-methyl-1,4-phenylene sulphide) (PMPS). The results suggest that (a) random copolymers with low PMPS contents would offer the best compromise between PPS and PMPS properties, and (b) more desirable physical properties might be achieved from systems containing a less reactive 2-substituted-1,4-phenylene sulphide comonomer repeat unit.     

Synthesis of azobenzene‐containing side chain liquid crystalline diblock copolymers using RAFT polymerization and photo‐responsive behavior

Well‐defined azobenzene‐containing side chain liquid crystalline diblock copolymers composed of poly[6‐[4‐(4‐methoxyphenylazo)phenoxy]hexyl methacrylate] (PAzoMA) and poly(glycidyl methacrylate) (PGMA) were synthesized by a two‐step reversible addition–fragmentation chain transfer polymerization (RAFT). The thermal liquid‐crystalline phase behavior of the PGMA‐b‐PAzoMA diblock copolymers in bulk were measured by differential scanning calorimetry (DSC) and polarized light microscopy (POM). The synthesized diblock copolymers exhibited a smectic and nematic liquid crystalline phase over a relatively wide temperature range. With increasing the weight fraction of the PAzoMA block, the phase transition temperatures, and corresponding enthalpy changes increased. Atomic force microscope (AFM) measurements confirmed the formation of the microphase separation in PGMA‐b‐PAzoMA diblock copolymer thin films and the microphase separation became more obvious after cross‐linking the PGMA block. The photochemical transition behavior of the PGMA‐b‐PAzoMA diblock copolymers in solution and in thin films were investigated by UV–vis spectrometry. It was found that the trans–cis isomerization of diblock copolymers was slower than that of the corresponding PAzoMA homopolymer and the photoisomerization rates decreased with increasing either the length of PAzoMA block or PGMA block. The photo‐induced isomerization in solid films was quite different with that in CHCl₃ solution due to the aggregation of the azobenzene chromophore. The cross‐linking structures severely suppressed the photoisomerization of azobenzene chromophore. These results may provide guidelines for the design of effective photo‐responsive anisotropic materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2165–2175, 2013     

Synthesis and characterization of organic-inorganic hybrid thin films from poly(acrylic) and monodispersed colloidal silica

Hybrid thin films containing nano-sized inorganic domain were synthesized from poly(acrylic) and monodispersed colloidal silica with coupling agent. The 3-(trimethoxysilyl)propyl methacrylate (MSMA) was bonded with colloidal silica first, and then polymerized with acrylic monomer to form a precursor solution. Then, the precursor was spin coated and cured to form the hybrid films. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results showed that the coverage area of silica particle by the MSMA decreased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. Thus, the silica domain in the hybrid films was varied from 20 to 35 nm by the different mole ratios of MSMA to silica. The results of scanning electron microscope, transmission electron microscope, and elemental analysis support the above results. The prepared hybrid films from the crosslinked acrylic polymer moiety showed much better film uniformity, thermal stability and mechanical properties than the poly(methyl methacrylate) (PMMA) based hybrid materials. Large pin-holes were found in the PMMA-silica hybrid films probably due to the significant difference on thermal properties between the two moieties or the evaporation of solvent. The refractive index decreased linearly with increasing the silica fraction in the hybrid films. Excellent optical transparence was obtained in the prepared hybrid films. These results show that the hybrid thin films have potential applications as passive films for optical devices.     

Preparation,morphology and sonication time dependence of silver nanoparticles in amphiphilic block copolymers of PEO with polystyrene or PMMA

Composite materials comprising arrays of silver nanoparticles in amphiphilic copolymers have been prepared by sonochemically enhanced borohydride reduction of precursor silver nitrate (AgNO₃). The precursor was incorporated into the cores of polymeric micelles formed from block copolymers of polystyrene (PS) or poly(methyl methacrylate) (PMMA) with poly(ethylene oxide) (PEO). The copolymers were synthesised with varying hydrophobic block lengths from a PEO macroinitiator by atom transfer radical polymerization (ATRP). UV/visible spectroscopy was used to confirm the formation of elemental silver and the effect of sonication time on the appearance of the silver nanoparticles was determined. The growth was faster than when gold nanoparticles are formed in comparable block copolymers. Nanoparticles formed in copolymers with PMMA blocks were more stable to agglomeration than when polystyrene was used. Electron microscopy revealed the morphology of the nanocomposites which confirmed that both block copolymers are vehicles for the formation of well-defined films containing nanoparticulate silver. However, AgNP formation shows some significant differences from previous reports of gold NP containing materials formed under similar conditions.     

Preparation and characterization of poly(ethylene glycol)-block-poly[ε-(benzyloxycarbonyl)-l-lysine] thin films for biomedical applications

The nanoscale architectures evident in the thin films of self-assembling hybrid block copolymers—which are tailored to inherit the advantageous properties of their constituent synthetic (homo)polymer and polypeptide blocks—have continued to inspire a variety of new applications in different fields, including biomedicine. The thin films of symmetric hybrid block copolymer, α-methoxy-poly(ethylene glycol)-block-poly[ε-(benzyloxycarbonyl)-l-lysine], MPEG₁₁₂-b-PLL(Z)₁₇, were prepared by solvent casting in five different solvents and characterized using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy, Thermogravimetric analysis, Derivative Thermogravimetric analysis, Differential Scanning Calorimetry, Contact Angle goniometry, Wide-Angle X-ray Diffraction, and Scanning Electron Microscopy. Film thickness was estimated to be 51 ± 23 μm by the “step-height” method, using a thickness gauge. Although no significant change to the block copolymer’s microstructure was observed, its solvent-cast films displayed divergent physical and thermal properties. The resulting cast films proved more thermally stable than the bulk but indicated greater block miscibility. Additionally, the thin films of MPEG₁₁₂-b-PLL(Z)₁₇ preserved the microphase separation exhibited by the bulk copolymer albeit with appreciable loss of crystallinity. The surface properties of the polymer–air interface were diverse as were the effects of the casting solvents. Oriented equilibrium morphologies are also evident in some of the as-cast thin films.     

Ordering in thin films of block copolymers: Fundamentals to potential applications

The ordering of block copolymers in thin films is reviewed, starting from the fundamental principles and extending to recent promising developments as templates for nanolithography which may find important applications in the semiconductor industry. Ordering in supported thin films of symmetric and asymmetric AB diblock and ABA triblock copolymers is discussed, along with that of more complex materials such as ABC triblocks and liquid crystalline block copolymers. Techniques to prepare thin films, and to characterise ordering within them, are summarized. Several methods to align block copolymer nanostructures, important in several applications are outlined. A number of potential applications in nanolithography, production of porous materials, templating, and patterning of organic and inorganic materials are then presented. The influence of crystallization on the morphology of a block copolymer film is briefly discussed, as are structures in grafted block copolymer films.     

Synthesis of poly(methylphenylsiloxane)/phenylene‐silica hybrid material with interpenetrating networks and its performance as thermal resistant coating

In this study, poly(methylphenylsiloxane) (PMPS) and phenylene‐silica based hybrid material with interpenetrating networks was prepared by a two‐step sol–gel process. Firstly, in the presence of H₂SO₄, the phenylene‐silica was formed as sol particles with high branching degree by cohydrolysis and condensation of phenylene‐bridged monomer, tetraethoxysilane (TEOS), and hexamethyldisiloxane (MM). Then, the intermediate transformed into gel framework in polymer matrix using alkali catalyst, in order to produce a homogenous hybrid material with interpenetrating networks. The structure of prepared hybrid material was characterized by FTIR and NMR, suggesting that phenylene‐silica framework was imported into polymer matrix and the hybrid products have a much higher network chain density than neat PMPS. The thermogravimetric analysis (TGA) shows that the prepared materials start to degrade at around 490°C. The results of tensile test indicate that the typical PMPS/phenylene‐silica hybrid material has a tensile strength up to 26 MPa and demonstrate a certain degree of flexibility. An increase of phenylene content in phenylene‐silica particles tends to produce hybrid materials with improved thermal stability and tensile strength. The hybrid coating films after calcinating at 350 and 400°C for 2 h exhibit a good mechanical performance on adhesion, impact strength and flexibility. Electrochemical impedance spectroscopy (EIS) measurements show that the investigated films have an extremely high electric resistance (10¹⁰ Ohm·cm²) and a satisfied impermeability to 3.5 wt % sodium chloride solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Double-brush Langmuir-Blodgett monolayers of α-helical diblock copolypeptides

The synthesis of amphiphilic diblock copolypeptides consisting of poly(α-l-glutamic acid) (PLGA) and poly(γ-methyl-l-glutamate-ran-γ-stearyl-l-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) and their monolayer behavior at the air-water interface have been studied. PLGA-b-PMLGSLG was synthesized via a diblock copolymer precursor consisting of poly(γ-tert-butyl-l-glutamate) (PtBuLG) and PMLGSLG blocks, with the tert-butyl group as a mild acid-labile protecting group for the carboxylic acid. The polymerization conditions were found to influence the α-helix to β-sheet content ratio and can be tuned to significantly enhance the diblock copolypeptide helicity. Purely α-helical PtBuLG-b-PMLGSLG diblock copolymers were successfully prepared. After removal of the tert-butyl group, the study of the PLGA-b-PMLGSLG amphiphilic diblock copolymers in Langmuir monolayers and Langmuir-Blodgett films demonstrated the formation of a stable α-helical double-brush structure, with the helices tilted away from the substrate surface. These double-brush monolayers combine the unique properties arising from the unidirectionally aligned helix macrodipole and the liquid-like features of the side chain mantle of the PMLGSLG block. Such systems are promising for thin film applications requiring incorporation and orientation of bio- and optical molecules.     

Effect of nanoparticle surface functionality on microdomain orientation in block copolymer thin films under electric field

The electric field induced microdomain orientations has been an interesting research topic. In this article, the effect of nanoparticle surface functionality on microdomain alignments in block copolymer/nanoparticle hybrid thin films was investigated with transmission electron microscopy experiments. The presence of gold nanoparticles influenced the microdomain orientation behaviors of block copolymer/nanoparticle thin films. The possibility for complete alignment normal to the substrate was illustrated by controlling electric field strength, concentration, and surface ligands of nanoparticles. This work provides basic and essential data to understand the properties and behaviors of emerging block copolymer/nanoparticle hybrid thin films.     

Rod-rod and rod-coil self-assembly and phase behavior of polypeptide diblock copolymers

Poly(γ-benzyl l-glutamate) (PBLG) forms a rigid helical rod in organic solvents. Cholesteric liquid crystalline ordering of these rods has been observed in PBLG solutions and cast films. In this research, peptidic block copolymers were created using PBLG in order to determine the effect of an added block on the classic cholesteric ordering. Peptide blocks with varied lengths and inherent secondary structures, random coil or rigid rod, were attached to PBLG molecules. The self assembly/liquid crystalline ordering of these molecules in films cast from various organic solvents was probed with transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). In pure PBLG and PBLG diblock copolymers with relatively small additional blocks, cholesteric liquid crystalline ordering was observed in bulk films. However, depending on the kinetics of film formation and the amount of non-PBLG block, significant changes in the nanostructure and microstructure were observed. These purely peptidic block molecules provide the opportunity to pattern materials with peptidic functionalities by taking advantage of block copolymer phase behavior and liquid crystal ordering.     

Characterization on polymerized thin films for low-k insulator using PECVD

Plasma polymerized cyclohexane and TEOS hybrid thin films have been deposited on silicon substrates at room temperature with varying RF power by plasma-enhanced chemical vapor deposition (PECVD) method. As-grown thin films were annealed in vacuum. Cyclohexane monomer was utilized as organic precursor and TEOS monomer as inorganic precursor. Hydrogen and argon were used as bubbler and carrier gases, respectively. The as-grown plasma polymerized hybrid thin films were analyzed by FT-IR spectroscopy, hardness and modulus measurements, and electrical properties. Annealed hybrid thin films were also analyzed. The dielectric constant of thin films increases with increasing plasma power.     

Effect of sequence distribution of PES/PEES random,block, and alternative copolymers on excimer formation in solution

Three copolymers of poly(ether sulfone) and poly(ether ether sulfone) with the same composition but different sequence distribution were synthesized by three kinds of methods. Their molecular aggregation in dichloromethane was studied by fluorescence spectrophotometer and electron microscope. The experimental results revealed that the formation of intermolecular excimers in alternative copolymer (A50) dichloromethane solution were observed at a A50 concentration about 1.6 × 10^?2 g/mL by the fluorescence analysis, but the formation of intermolecular excimers in dichloromethane were not found for random copolymer (R50) and block copolymer (B50). The electron micrograph of three copolymer films, heat‐treated at 200°C for 7 days, presented a diffraction micrograph, which suggest that three copolymer molecular aggregation is changed from a randomly coiled amorphous phase to an ordered one, and the order structure of alternative copolymer (A50) was the most distinct in three copolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Corrosion and thermal characterization of styrene based copolymers

Films from copolymers with resistance to wear, corrosion and thermal degradation as well as other important functions have been applied in many fields. It is known that the introduction of anionic hydrophilic groups in the polymer enhances its adhesion to substrates and protective function. In the present work, copolymers of styrene with acrylic, methacrylic and itaconic acids were prepared by polymerization in toluene with benzoyl peroxide initiation (BPO) and have been tested as anticorrosive films. The copolymers were analyzed by FTIR and TGA methods. Polarizing microscope images were employed to characterize the anticorrosive properties of the formed films. All copolymers produced in this work show strong adhesion to the substrate.     

Synthesis and Optical Properties of Poly(BPDA-ODA)/Silica Hybrid Thin Films

Poly(BPDA-ODA)/silica hybrid optical thin films were synthesized using a sol-gel reaction combined with spin coating and multi-step baking. The hybrid thin films were prepared by the precursors of aminoalkoxysilane capped poly(BPDA-ODA) amic acid and tetramethoxysilane (TMOS). Highly transparent hybrid thin films were obtained at a silica content of 0–51.9 wt%. The prepared hybrid thin films showed homogeneous structures and excellent surface planarity. The refractive index of the prepared hybrid thin films decreased linearly with increasing the silica content while the Abbe number showed the opposite trend. The prepared hybrid films also exhibited a much smaller optical birefringence than the parent poly(BPDA-ODA) because of the reduction of the rigid backbone by incorporating the silica moiety. Optical planar waveguides were prepared from the prepared hybrid thin films. The optical losses of the planar waveguides at 1310 nm were in the range of 0.5–1.3 dB/cm, which were reduced significantly by increasing the silica moiety. The reduction of the C–H bonding density and excellent surface planarity by incorporating the silica moiety explain the trend of optical loss. These results suggest that the prepared polyimide-silica hybrid thin films have potential applications for optical devices.     

Premade vs. reactively formed compatibilizers for PMMA/PS melt blends

The efficiency of two compatibilization methods, adding premade copolymers versus in situ formation of copolymers, were compared by evaluating the minor phase size and size distribution. Premade diblock copolymers were formed by coupling amine terminal polystyrene (PS-NH₂) with anhydride terminal poly(methyl methacrylate) (PMMA-An) in solution. Mid-functional PMMA was coupled with the PS-NH₂ to form graft copolymers. The same block and graft copolymers were formed in situ during melt blending. After mixing, the particle size and distribution were analyzed by transmission electron microscope (TEM). While both methods compatibilized blends, in situ formation reduced the minor phase size further. For the reactive case, graft copolymers are slight better than the block ones. This is attributed to a greater capacity for reducing interfacial tension. For the premade case, block copolymers compatibilize better at low copolymer concentration while graft copolymers work better at high concentration. As the amount of block copolymers added into the blends increases, the number of micelles increases significantly. This is believed to be the reason why premade copolymers are less capable of compatibilizing blends than the reactively formed ones.     

The preparation and characterization of high‐performance and thermally stable electroluminescent poly(p‐phenylene‐vinylene‐b‐oligoethylene oxide)

Two luminescent block copolymers (PPVPEO₂₀₀ and PPVPEO₆₀₀), composed of poly(p‐phenylene‐vinylene) (PPV) segments with three phenylene vinylene units and poly(ethylene oxide) (PEO) segments with molecular weight of 200 and 600, respectively, have been successfully synthesized. The structures of the copolymers were verified using FTIR, ¹H‐NMR, and elemental analysis. Single‐layer polymer light‐emitting electrochemical cells (LEC) devices fabricated on the bases of thin films of PPVPEO₆₀₀ and on the bases of thin films of blends of PPVPEO₂₀₀ with additional PEO both demonstrated good electroluminescent (EL) performance with the onset voltage of 2.6 V and EL efficiency of 0.64 cd/A and 0.68 cd/A at 3.2 V, respectively. Thermal analysis shows that the decomposition temperature of PPVPEO₆₀₀ is about 305°C, which is higher than that of PPVPEO₂₀₀ and PEO. AFM studies of PPVPEO₆₀₀ thin films exhibits that the block copolymer self‐assembles to form nanoscale network structures with pseudo‐cross‐linking points, thus accounting for its high thermal stability and good EL performance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1118–1125, 2007     

Block copolymers of n-propyl p-styrene sulfonate with isoprene and styrene: Synthesis,characterization, and phase separation behavior

A series of ABA block copolymers based on n-propyl p-styrene sulfonate (A block) and isoprene or styrene (B block) were synthesized and characterized. The synthesis was based on methods developed previously for the anionic polymerization of n-propyl p-styrene sulfonate [S. J. Whicher and J. L. Brash, J. Polym. Sci., Polym. Chem. Ed., 19 , 1995 (1981)], and consisted of forming a polyisopryl dianion by initiation with sodium naphthalene in THF at 0°C. n-Propyl p-styrene sulfonate was then added and propagated at ?94°C. As was the case for n-propyl p-styrene sulfonate alone, it was found that only limited chain growth of this monomer initiated by living polyisoprene was possible, resulting in maximum A block molecular weights of about 10,000. The phase separation behavior of copolymers having a range of composition, as well as that of a blend of polyisoprene and poly(n-propyl p-styrene sulfonate) was investigated by examining thin films in the electron microscope. In the copolymers, phase separation was observed with transmission EM when THF was used as the solvent for film casting. Domain morphology was as expected for the various copolymer compositions. When films were cast from chloroform, phase separation was minimal, although it could be improved by annealing. Annealing produced relatively diffuse intermixed domains which occasionally formed unusual triangular patterns. Phase separation of the blend of homopolymers gave domains that were large enough to be mapped with SEM using both secondary electron and EDXA detectors.     

均聚物调控的PS-b-P4VP薄膜的微相分离形貌

分别以聚丙烯酸(PAA)和聚氧化乙烯(PEO)与苯乙烯与4-乙烯基吡啶二嵌段共聚物(PS-b-P4VP)进行溶液共混并且旋涂成膜,采用原子力显微镜(AFM)研究了这两种均聚物对PS-b-P4VP薄膜微相分离形貌的调控作用。结果表明,PAA与P4VP链段之间强烈的氢键作用使得P4VP链段对PS链段的热力学排斥作用增强,当PAA质量分数为10%时,PS分散相区以规则的柱体垂直分布于由P4VP/PAA链段相互溶解所形成的连续相基体中。对于PS-b-P4VP/PEO共混体系,共混薄膜形成了PEO/P4VP分散相以柱状形态垂直分布在以PS链段聚集区为薄膜连续相基体中的微相分离形貌,由于PS链段无法在PEO/P4VP柱状微区上方形成覆盖,导致共混薄膜表面出现许多孔洞,孔洞底部伴有PEO链段部分结晶形成的锥状突起。随PEO含量增加,孔洞直径增大,孔洞底部的锥状突起也增大。     

Synthesis and luminescent properties of block copolymers based on polyfluorene and polytriphenylamine

For the preparation of block copolymers containing polyfluorene (PF) and hole transporting segment, PF homopolymers with diphenylamine terminals were synthesized by Suzuki coupling polymerization. The terminals of PF were converted to polytriphenylamine (PTPA) block by C–N coupling polymerization to give PTPA-block-PF-block-PTPA (PF-PTPA) triblock copolymers with different PTPA chain lengths. These polymers were soluble in common organic solvents and readily formed thin films by solution processing. All of the polymers exhibited similar UV absorption and PL emission properties both in chloroform solution and in film state. PF-PTPA block copolymers showed relatively high HOMO compared with that of PF by cyclic voltammetry. Compared with corresponding PF homopolymers, the EL devices based on PF-PTPA block copolymers showed higher luminance and current efficiency than those of PF homopolymers because of the improvement of hole injection by the introduction of PTPA segment.