Network properties: 3. A pulsed n.m.r. study of molecular motions in some AB-crosslinked polymers

This paper presents the results of a pulsed n.m.r. study of molecular motions in poly (methyl methacrylate) (PMMA) and poly (methyl acrylate) (PMA) chains in a series of multicomponent network polymers consisting of poly (vinyl trichloroacetate) (PVTCA) crosslinked with PMMA and with PMA, with emphasis on segmental motions. Results of ancilliary broad line n.m.r. and dilatometric studies are included; the latter demonstrate that in PMA containing polymers microphase separation of the components is complete while in PMMA containing polymers a mixed microphase of PVTCA and PMMA and a pure PMMA microphase are formed. α-Methyl group rotations in PMMA chains and segmental motions in both PMMA and PMA chains are modified with respect to those in the corresponding homopolymers. Modifications to the segmental motions in the crosslinking chains are attributed to the fact that their chain ends are attached to PVTCA chains. It is considered that the comparative rigidity of PVTCA chains (T_g ～ 60°C) reduces segmental motions in at least portions of the PMA chains (T_g ～ 5°C) while the comparative mobility of PVTCA enhances segmental motions in PMMA (T_g ～ 100°C). Thus the molecular mobility of chains of one polymer is to some extent transmitted to chains of another polymer to which it is attached.     

Some morphological aspects of AB crosslinked polymers

The structures of multicomponent species present in AB crosslinked polymers (ABCPs) formed by the random introduction of crosslinks of polymer B into an assembly of chains of polymer A are described for different extents of crosslinking. Microphase separation has been observed in solvent cast samples of ABCPs prepared by crosslinking poly(vinyl trichloroacetate) and a styrene copolymer (A-components) with polychloroprene (B-component). The morphologies of the polymers at low and high degrees of crosslinking are presented. Polychloroprene domain sizes have been determined for various crosslink lengths and crosslink densities. Domain sizes and their variation with molecular weight of the B-chains are discussed in terms of the structures of the multicomponent species present in the ABCPs and with theoretically predicted domain sizes in linear block copolymers. Distributions of domain sizes have been determined and compared with the molecular weight distributions of the B-chains.     

Macroscopic phase separation in multicomponent polymer homopolymer blends: general considerations based on studies of AB—crosslinked polymers

This paper explores the significance of, and presents additional evidence in support of, our earlier conclusion that molecules of multicomponent polymers (i.e. copolymers consisting of long sequences of different components), such as AB-crosslinked polymers, are normally incompatible with homopolymers of the individual components. The arguments are generalized to include block copolymer systems. After a brief review of relevant previous studies, schematic phase diagrams appropriate to multicomponent polymer/homopolymer blends and common solvent are constructed. The consequences of solvent-casting mixtures of multicomponent species with one homopolymer from homogeneous dilute solution are considered for cases where equilibrium is always achieved, and more practical situations where equilibrium is not attained in bulk polymer. Electron micrographs of ultra-thin sections of solvent-cast blends of AB-crosslinked polymers with homopolymer are presented to substantiate and illustrate points made in the preceding discussion. Conclusions are drawn regarding possible morphologies which can exist in multicomponent polymer/homopolymer blends and it is proposed that unusual morphologies in block copolymer blends reported by various workers are the direct consequences of combinations of macroscopic phase separation and subsequent microphase separation within phases of different composition. We suggest that the incompatibility of chemically identical blocks and homopolymers arises from an unfavourable entropy of mixing as a result of the blocks in the vicinity of microphase interfaces adopting different sets of conformations than randomly-coiled chains in bulk polymer.     

Cationic polymerization of α-methyl styrene from polydienes. II. Tensile properties of poly(butadiene-g-α-methyl styrene) and poly(styrene-b-butadiene-g-α-methyl styrene) copolymers

Tensile properties of poly(butadiene-g-α-methyl styrene) copolymers have been investigated on molded samples. These graft copolymers show thermoplastic elastomer behavior because of their graft copolymer structure. Both modulus and strength increase with increasing α-methyl styrene content and tensile strength is highest at the 45–50% by weight α-methyl styrene level. Tensile strength at elevated test temperatures is considerably higher for these poly(butadiene-g-α-methyl styrene) copolymers than for styrene-butadiene-styrene triblock polymers. This is attributed to the higher glass transition temperature for poly(α-methyl styrene) segments compared to polystyrene segments. The oil acceptance of these graft copolymers appears to depend on the number of loose polybutadiene chain ends. Thus, the tensile strength of oil-extended poly(butadiene-g-α-methyl styrene) copolymers was considerably lower than oil-extended poly(styrene-b-butadiene-g-α-methyl styrene) copolymers even though both copolymers contained equal hard segment contents.     

Thermal Expansion of Thin Diblock Copolymer Films

The thermal expansion of thin films of symmetric diblock copolymers of polystyrene (PS) and poly(methyl methácrylate) (PMMA) was investigated by X-ray reflectivity. The confinement of the copolymer to the substrate, coupled with the multilayering of the copolymer where PS and PMMA layers are oriented parallel to the substrate, gives rise to unusual thermal expansion characteristics. The total thickness of the film increases as 3α_L, where α_L is the linear thermal expansion coefficient of the copolymer. Unlike homopolymer films, the thermal expansion of an ordered block copolymer film results in an excessive stretching of the copolymer chains at the interface between the PS and PMMA layers. This excess stretching is a result of the confinement of the junction points of the copolymer chains to the interfaces and the suppression of the lateral expansion of the copolymer. When the stretching of the chains becomes too high, relaxation occurs by transporting copolymer chains to the surface. This is evidenced by a reduction in the period of the multilayer. After the copolymer chains have relaxed, the change in the multilayer period with temperature closely follows α_L.     

Enhanced light emission of nano-patterned GaN via block copolymer thin films

We demonstrate that the nanoscopic block copolymer patterns on GaN can enhance light extraction efficiency of GaN-based light emitting diodes. Nanoporous patterns were fabricated on a bare GaN substrate via self-assembly of poly(styrene-b-methyl methacrylate) block copolymers from which PMMA microdomains were selectively removed later on. A bare GaN surface was treated with a photo-crosslinkable thin layer of poly(styrene-r-methyl methacrylate) random copolymers to tune the cylindrical microdomain orientations. The nanoporous block copolymer thin film was controlled to be thicker than its typical repeat period in bulk by incorporating PMMA homopolymer into block copolymer. Consequently, the light extraction efficiency in photoluminescence spectra could be tuned with the thickness of nanopatterned thin film on GaN. This paper is dedicated to Professor Chul Soo Lee on the occasion of his retirement from Korea University.     

Temperature influence and CO2 transport in foaming processes of poly(methyl methacrylate)–block copolymer nanocellular and microcellular foams

Fabricated by high-pressure or supercritical CO₂ gas dissolution foaming process, nanocellular and microcellular polymer foams based on poly(methyl methacrylate) (PMMA homopolymer) present a controlled nucleation mechanism by the addition of a methylmethacrylate–butylacrylate–methylmethacrylate block copolymer (MAM), leading to defined nanocellular morphologies templated by the nanostructuration of PMMA/MAM precursor blends. Influence of the CO₂ saturation temperature on the foaming mechanism and on the foam structure has been studied in 90/10 PMMA/MAM blends and also in the neat (amorphous) PMMA or (nanostructured) MAM polymers, in order to understand the role of the MAM nanostructuration in the cell growth and coalescence phenomena. CO₂ uptake and desorption measurements on series of block copolymer/homopolymer blend samples show a competitive behavior of the soft, rubbery, and CO₂-philic block of PBA (poly(butyl acrylate)) domains: fast desorption kinetics but higher initial saturation. This competition nevertheless is strongly influenced by the type of dispersion of PBA (e.g. micellar or lamellar) and a very consequent influence on foaming.CO₂ sorption and desorption were characterized in order to provide a better understanding of the role of the block copolymer on the foaming stages. Poly(butyl acrylate) blocks are shown to have a faster CO₂ diffusion rate than poly(methyl methacrylate) but are more CO₂-philic. Thus gas saturation and cell nucleation (heterogeneous) are more affected by the PBA block while cell coalescence is more affected by the PMMA phases (in the copolymer blocks + in the matrix).     

High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films

A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.     

Computer modeling study on the phase morphology of PS‐b‐PMMA copolymers

The phase morphologies of six kinds of designed poly(styrene‐block‐methyl methacrylate) copolymers were studied at 383, 413, and 443 K by mesoscopic modeling. The values of order parameter depended on both the structures of block copolymers and the simulation temperatures, whereas values of order parameter of the long chains were higher than those of the short ones; temperature showed a more obvious effect on long chains than on the short ones. These plain copolymers doped with PS or PMMA homopolymer showed different order parameter values. When the triblock copolymer was composed of the same component at both ends and was doped with a homopolymer with the same component as that in the middle of triblock copolymer, such as B6A3B6 doped with A3, B12A6B12 doped with A6, A6B12A6 doped with B12, and A3B6A3 doped with B6, it showed the highest order parameter values. The study of copolymers doped with nanoparticles showed that the mesoscopic phase was influenced by not only the properties of the nanoparticles, such as the size and density, but also the compositions of copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of incorporation of POSS units on polymer blend compatibility

In this work, the compatibility of poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers with their polyhedral oligomeric silsesquioxane (POSS) copolymers combined by solution blending is investigated, to determine the effect of incorporation of the POSS unit on polymer compatibility. The morphology of these tethered POSS copolymer/polymer blends was studied by electron microscopy, thermal analysis, and density. Although the basic PS/PMMA blend was clearly immiscible, it was also found that the incorporation of POSS into the PS chain led to incompatibility when the POSScoPS copolymer was blended with PS homopolymer. However, conversely, in the case where the POSS moiety was included as part of a copolymer with PMMA, the copolymer was miscible with the PMMA homopolymer. The presence of isobutyl units on the corners of POSS cage is clearly sufficient to encourage miscibility with PMMA. Interestingly, blends of the two different POSS copolymers led to an immiscible structure, despite having the common POSS units, the interactions between the POSS moieties clearly not being sufficient to drive compatibility. The POSS copolymers have also been used as interfacial agents in immiscible PS and PMMA blend, and it has been found that the appearance of the interface bonding is improved, although the phase morphology is only slightly changed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of triblock copolymers containing PDMS via AGET ATRP

The bromo-terminated macroinitiator was prepared by direct addition reaction of difunctional poly(dimethylsiloxane) (PDMS) containing methyl methacrylate end groups with hydrobromic acid in acetic acid under mild conditions, and well-defined triblock copolymers of poly(methyl methacrylate-b-dimethylsiloxane-b-methyl methacrylate) (MMA-b-DMS-b-MMA) were synthesized via activators generated by election transfer atom transfer radical polymerization (AGET ATRP). The gel permeation chromatography data obtained verified the polymerization and showed the well controlling of the reaction. FTIR and ¹H NMR measured the structure of the macroinitiator and copolymers. The contact angle measurement indicated that the water contact angles decreased gradually with the increasing of PMMA block content. The self-assembly behaviors of the triblock polymer were studied by transmission electron micrograph, scanning electron microscopy, and dynamic light scattering measurement. The results indicated that the polymers could self-assemble into various complex morphologies in different solvents and the morphologies depended on the properties of solvents. The possible molecular packing models for self-assembly behaviors of the ABA triblock polymers were proposed.     

Characterization of the collagen–vinyl graft copolymers prepared by the ceric ion method. II. Infrared spectra and electron microscopy

Collagen powder and goat skins were grafted with different vinyl monomers using the ceric ion technique. The graft copolymers were characterized by infrared spectra and electron microscopy. The collagen–vinyl graft copolymers were hydrolyzed by both acid and enzymatic hydrolysis, and the grafted vinyl polymer side chains were isolated. In the grafted poly(methyl methacrylate) (PMMA) side chains isolated by acid hydrolysis, the characteristic amide absorption bands at 1550 and 1660 cm^?1 were not seen prominently. However, in PMMA side chains isolated by enzymatic methods, the amide absorption bands were more prominent as these isolated side chain polymers contained longer fragments of the peptide backbone attached to them. Electron-microscopic observations of grafted collagen fibrils and ultrathin sections of grafted goat skin fibrils did not show any cross-striations. These various evidences indicate that the polymers formed on collagen have penetrated into the fibrils and that they were chemically bound to the collagen molecules.     

Reorganization and improvement of bulk polymers by processing with their cyclodextrin inclusion compounds

The formation of polymer-cyclodextrin inclusion compounds of polycarbonate (PC), poly(methylmethacrylate) (PMMA) and poly(vinylacetate) (PVAc) guests with host γ-cyclodextrin (γ-CD) have been successfully achieved. Coalesced bulk polymer samples were obtained by removal of γ-CD from their inclusion compounds (ICs). The chemical and crystalline structures of ICs and coalesced PC, PMMA and PVAc were studied by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). The thermal transitions, thermal stability, and degradation mechanisms of the samples were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and direct insertion probe pyrolysis mass spectrometry (DIP-MS). FTIR findings indicated that the chain conformations of the bulk polymers were altered when they were included inside the CD channels and extended chain conformations were retained when coalesced from their ICs. Significant improvements were observed in the thermal transitions observed for the coalesced polymers, with glass transitions shifted to higher temperatures. The TGA results reveal that the thermal stabilities of coalesced polymers increased slightly compared to the corresponding as-received polymers. The DIP-MS observations indicated that the thermal stability and degradation products of the polymers are affected once the polymers chains are included inside the γ-CD-IC cavities.     

Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process

Use of supercritical carbon dioxide (scCO₂) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO₂ process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO₂ solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO₂ concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO₂ can be achieved through judicious polymer blending.     

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low‐density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt‐blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano‐ to micron‐sized cells. This gradient structure is attributed to a non‐constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained.     

Particle morphology and NMR structure of polymethylmethacrylate/polystyrene emulsifier‐free core–shell cationic latices in the presence of DBMEA

In the absence of emulsifier, we prepared stable emulsifier‐free polymethylmethacrylate/polystyrene (PMMA/PSt) copolymer latex by batch method with comonomer N,N‐dimethyl, N‐butyl, N‐methacryloloxylethyl ammonium bromide (DBMEA) by using A1BN as initiator. The size distribution of the latex particles was very narrow and the copolymer particles were spherical and very uniform. Under the same recipe and polymerization conditions, PMMA/PSt and PSt/PMMA composite polymer particle latices were prepared by a semicontinuous emulsifier‐free seeded emulsion polymerization method. The sizes and size distributions of composite latex particles were determined both by quasi‐elastic light scattering and transmission electron microscopy (TEM). The effects of feeding manner and staining agents on the morphologies of the composite particles were studied. The results were as follows: the latex particles were dyed with pH 2.0 phosphotungestic acid solution and with uranyl acetate solution, respectively, revealing that the morphologies of the composite latex particles were obviously core–shell structures. The core–shell polymer structure of PMMA/PSt was also studied by ¹H, ¹³C, 2D NMR, and distortionless enhancement by polarization transfer, or DEPT, spectroscopy. Results showed that PMMA/PSt polymers are composed of PSt homopolymer, PMMA homopolymer, and PMMA‐g‐PSt graft copolymers; results by NMR are consistent with TEM results. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1681–1687, 2005     

Effects of mechanical properties of polymer on ceramic-polymer composite thick films fabricated by aerosol deposition

ABSTRACT: Two types of ceramic-polymer composite thick films were deposited on Cu substrates by an aerosol deposition process, and their properties were investigated to fabricate optimized ceramic-based polymer composite thick films for application onto integrated substrates with the advantage of plasticity. When polymers with different mechanical properties, such as polyimide (PI) and poly(methyl methacrylate) (PMMA), are used as starting powders together with α-Al2O3 powder, two types of composite films are formed with different characteristics - surface morphologies, deposition rates, and crystallite size of α-Al2O3. Through the results of micro-Vickers hardness testing, it was confirmed that the mechanical properties of the polymer itself are associated with the performances of the ceramic-polymer composite films. To support and explain these results, the microstructures of the two types of polymer powders were observed after planetary milling and an additional modeling test was carried out. As a result, we could conclude that the PMMA powder is distorted by the impact of the Al2O3 powder, so that the resulting Al2O3-PMMA composite film had a very small amount of PMMA and a low deposition rate. In contrast, when using PI powder, the Al2O3-PI composite film had a high deposition rate due to the cracking of PI particles. Consequently, it was revealed that the mechanical properties of polymers have a considerable effect on the properties of the resulting ceramic-polymer composite thick films.     

Elongational viscosity for miscible and immiscible polymer blends. II. Blends with a small amount of UHMW polymer

The effect of miscibility on elongational viscosity of polymer blends was investigated in homogeneous, miscible, and immiscible states by the blend of 1.5 wt % of ultrahigh‐molecular‐weight (UHMW) polymer. The matrix polymer was either poly(methyl methacrylate) (PMMA), or poly(acrylonitrile‐co‐styrene) (AS) that has a comparable elongational viscosity value. The homogeneous blend consisted of 98.5 wt % of PMMA and 1.5 wt % of UHMW–PMMA. The miscible blend was composed of AS and UHMW–PMMA at the same ratio. The immiscible blend was a combination of AS and UHMW–polystyrene (PS) at the same ratio. The strain‐hardening behavior of the different blends were compared with that of pure PMMA. It was demonstrated that 1.5 wt % of UHMW induces a strong strain‐hardening property in the homogeneous and miscible blends but was hardly changed in the immiscible blend. The optical microscope observation of the immiscible blend suggested that the UHMW domains were stretched, but that the degree of domain deformation was less than a given elongational strain. It was concluded that the strain‐hardening property is strongly affected by the miscibility of UHMW chain and matrix. The strong strain‐hardening property is caused by the deformation of the UHMW polymer. UHMW chains are stretched when they are entangled with surrounding polymers. However, UHMW chains in an immiscible state are not so deformed because of viscosity difference and no entanglements between domain and matrix. A smaller degree of UHMW chain deformation in immiscible state results in weaker strain‐hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 961–969, 1999     

Improvement of plasma etching durability of positive working resist by copolymerization,blending, and crosslinking

The plasma etching durability of O₂ and CCl₄ was investigated for copolymer and polymer blend of poly(methyl methacrylate) (PMMA) and poly(α-methylstyrene) (PMSt) as a function of MSt content. Further, the effects of crosslinking on plasma etching were studied by incorporating N-methylolated methacrylamide into the copolymer as a crosslinkable site during prebaking. The plasma-etching resistance of PMMA was largely improved by incorporating or adding only a small amount of MSt. Especially in the case of the CCl₄ plasma etching, the copolymer and the polymer blend with 10 mol% of MSt showed etching resistance as great as that of PMSt homopolymer. Stabilization of the polymers against the plasma etching can be explained by the sponge effect, the energy migration followed by the quenching by the phenyl ring. The polymer blend offered similar etching resistance as the copolymer, indicating an effective occurrence of the energy migration between the polymer chains. Etching resistance was also improved by crosslinking, also due to the enhancement of the sponge effect.     

Effects of additives on the morphologies of thin titania films from self-assembly of a block copolymer

The effects of additives of poly(methyl methacrylate) (PMMA) and HAuCl₄ on the morphologies of hybrid titania films formed via co-assembly of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers, titania sol-gel precursor in a selective solvent were investigated. The results show that addition of PMMA or HAuCl₄ has an important influence on the morphologies of hybrid titania films. Addition of PMMA or HAuCl₄ can induce the morphology transition of the PS-b-PEO/titania sol-gel mixture from spherical micelles to vesicles. Therefore, the morphologies of the hybrid films formed on silicon substrate surfaces by spin-coating can be controlled by the addition of homopolymer (PMMA) or inorganic precursor (HAuCl₄) into the PS-b-PEO/titania sol-gel mixtures, allowing access to nanoparticles or nanoporous films. After removing the polymer matrix, nanoparticle aggregates or nanobowl-like structures are left behind on the substrate surfaces.