Stereocomplex Films Research Articles

Robust Superhydrophobic Films Based on an Eco-Friendly Poly(l-lactic acid)/Cellulose Composite with Controllable Water Adhesion.

Poly(l-lactic acid) (PLLA) featuring desirable biodegradability and biocompatibility has been recognized as one of the promising eco-friendly biomaterials. However, low crystallization and poor mechanical and chemical performances dramatically hamper its practical application. In this work, we report that functionalized cellulose/PLLA composite superhydrophobic stereocomplex films with controllable water adhesion and protein adsorption can be fabricated by a facile approach for the first time. First, cellulose is surface-modified by means of two silanization modification methods. Then, superhydrophobic cellulose/PLLA composite films are prepared through a solvent-evaporation-induced phase separation method. The two cellulose/PLLA composite films exhibit extreme water repellency but tunable water adhesion from sticky to slippery. The protein adsorption capacity of the cellulose/PLLA composite films can also be regulated. In addition, the stereocomplexation of the composite film provides excellent mechanical properties with an elongation at break of 22.36%, which is 237.8% higher than that of a pure PLLA film, which is more suitable for biomaterials. Furthermore, good biodegradability of the PLLA composite films in nature enables the bio-based composites as alternative materials to replace conventional petroleum-based polymers. The superhydrophobic films have also been demonstrated for many applications, including slippery surfaces, liquid transportation without loss, and antifouling.

Preparation of oriented poly(lactic acid) thin films by a combination of high temperature rubbing and thermal annealing: Impact of annealing parameters on structure, polymorphism and morphology

AbstractHigh temperature rubbing is a fast and low‐cost method to prepare highly oriented films of polymers. This contribution describes the fabrication of smooth and pin‐hole‐free poly(lactic acid) (PLA) thin films of controlled structure and morphology using a combination of rubbing at moderate temperature (T ≤ 100°C) and thermal annealing. We investigate the impact of annealing temperature and duration on the structure of rubbed PLLA and stereo‐complex (SC) thin films. The importance of annealing parameters on polymorphism, crystallinity, crystal dimensions and in‐plane orientation are analyzed using Transmission Electron Microscopy, Differential Scanning Calorimetry and FTIR spectroscopy. Regarding SC PLA films, the conditions are identified to fully transform the equimolar PLLA‐PDLA blend films into pure oriented SC films without presence of homocrystals.

Characterization of Polymer Composites between Stereocomplex Polylactide Blends with Poly (methyl methacrylate)

Polylactide stereocomplex (ST) of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) (PLLA:PDLA 50:50) was blended with poly(methyl methacrylate) (PMMA) 10 – 50 wt.%. The materials were dissolved in chloroform at room temperature and the films were then cast. Differential scanning calorimetry showed a stereocomplex melting peak at 208 °C – 50 °C higher than that for neat PLLA or PDLA - confirming the polylactide stereocomplex crystallites. The PMMA content ratio of 10 – 50 wt.% in the stereocomplex showed almost complete stereocomplex crystallites. A peak at about 908 cm-1 in Fourier transform infrared spectra further confirmed the stereocomplex crystallites which indicated that PMMA could blend and efficiently bond with the stereocomplex. The X-ray diffraction analysis showed that the stereocomplex crystallinity became smaller when PMMA was added. Morphology from scanning electron microscopy revealed that phases separated in the ST/PMMA blend when the amount of PMMA was increased. Adding PMMA to stereocomplex films led to an increased elongation at break which peaked at 30 % added PMMA. Increased PMMA also led to the improved thermal stability of the stereocomplex. These properties and higher toughness are also needed in common applications, in particular films for packaging and protection of manufactured products.

The influence of chain‐end functionalization and stereocomplexation on the degradation stability under alkaline condition

AbstractHydrolytic degradation of polylactides (PLAs) bearing cinnamic acid derivatives was conducted and their thermal degradation temperature at 10% weight loss (T10) and melting point temperature (Tm) were measured, to confirm that a PLA stereocomplex could be modified for use in a wide range of application. The improved T10 values of PLA films by chain end modification were maintained after the alkaline degradation. The increase in Tm by stereocomplex formation was also maintained after degradation with a slight change in the melting point of the attached homopolymer. The present results indicate the suitability of chain end modification for the additional functionality of PLA stereocomplex films.

Stretchable optical diffraction grating from poly(acrylic acid)/polyethylene oxide stereocomplex.

Advances in optical materials, which were initially static elements, have enabled dynamically tunable optical diffraction gratings to be designed. One common tuning strategy relies on mechanical deformation of the grating pitch to modify the diffraction pattern. In the present work, we demonstrate an all-polymer tunable diffraction grating fabricated using a modified replica molding process. The poly(acrylic acid) (PAA)/polyethylene oxide (PEO) polymer stereocomplex films exhibit optical transmittance at or above 80% from 500 nm to 1400 nm and stretchability over 800% strain with reversibility under 70% strain. The imprinted gratings are characterized at 633 nm and 1064 nm under a range of strain conditions. The measured tunability agrees with finite element method modeling.

In situ formation of PLA-grafted alkoxysilanes for toughening a biodegradable PLA stereocomplex thin film.

Poly(lactide) (PLA) has received tremendous attention recently from researchers and industrialists due to its ability to solve environmental problems related to plastic pollution. However, PLA's brittleness, poor thermal stability, low elongation at break, and poor melt processing prevent its use in a broader spectrum of applications. Herein, we produced a very tough and thermally more stable PLA stereocomplex by simply mixing PLA with organoalkoxysilane. The stereocomplex PLA/silane (sc-PLA–silane) composite was prepared by simple mixing of three types of organoalkoxysilanes in sc-PLA followed by in situ formation of a silane-based rubbery core with a cross-linked PLA shell. Mechanical and thermal properties were improved by stereocomplexation of PLA with a small amount (1–5 wt%) of PLA-grafted silanes. The addition of organoalkoxysilane with different functional groups resulted in a plasticizer of rubbery silica-PLA core–shell gel through in situ condensation and grafting of long PLA chains at the interface between the stereocomplex and silane particles. The results revealed that the toughness of sc-PLA was improved dramatically with only a small addition (only 2.5%) of 3-(triethoxysilyl)propyl isocyanate (ICPTES). The morphology and mechanical and thermal properties of the toughened stereocomplex films were characterized. The results revealed that elongation at break was increased from 16% to 120%, while other mechanical properties such as tensile strength and modulus were retained. Surface analysis confirmed that this toughness was achieved by formation of a silica-PLA core–shell gel. The mechanical properties of PLA were improved without any significant reduction in modulus and tensile strength using this simple methodology.

Supramolecular Cyclodextrin Microstructures as Novel Templates to Fabricate Hollow Polymer Cubes

A combination of an alternating layer-by-layer assembly of isotactic (it) and syndiotactic (st) poly(methyl methacrylate) (PMMA) and supramolecular cyclodextrin microcubes as a template core forms hollow microcubes composed of it-/st-PMMA stereocomplex films. Simply washing with water removes the cyclodextrin templates from the it-/st-PMMA stereocomplex film-coated particles to give hollow microcubes.

Fabrication of high-performance poly(l-lactic acid)/lignin-graft-poly(d-lactic acid) stereocomplex films

The need for green renewable alternatives such as lignin to traditional fillers has driven recent interest in polylactic acid blend materials. Herein, lignin-graft-polylactic acid copolymers (LG-g-PDLA, LG-g-PDLLA, and LG-g-PLLA) have been synthesized via ring-opening polymerization of d-, dl-, and l-lactic acid. Then poly(l-lactic acid)/lignin-graft-polylactic acid (PLLA/LG-g-PDLA, /LG-g-PDLLA, and /LG-g-PLLA) complex films have been prepared. The results showed that, compared with LG-g-PDLA and LG-g-PLLA, a small amount of LG-g-PDLA addition could improve the crystallization rate, reduce the glass transition temperature and cold crystallization temperature of PLLA due to the stereocomplex crystallites. The thermal stability, tensile strength and strain of the stereocomplex films were also enhanced. Moreover, the PLLA/LG-g-PDLA films have good ultraviolet resistance and excellent biocompatibility. This study provides a green approach to design advanced polylactic acid-based blends with renewable natural resources.

Stereocomplex poly(lactic acid) nanocoated chitosan microparticles for the sustained release of hydrophilic drugs

In this work, novel chitosan based microparticles were developed by the layer-by-layer deposition of poly(lactic acid) stereocomplex films on their surface in the view of controlling the release of encapsulated hydrophilic drugs. As first step, the quartz crystal microbalance technique was used to monitor the step-by-step deposition of the stereocomplex layers onto chitosan by evaluating the deposited mass for each layer. Chitosan microparticles, with a size ranging between 40 and 90μm, were then produced by an aerodynamically-assisted jetting technique and covered by a poly(lactic acid) stereocomplex shell. Infrared spectroscopy, wide X-ray diffraction, field emission scanning electron microscopy and contact angle measurements were used to verify the effective poly(lactic acid) adsorption onto chitosan microparticles and the stereocomplex formation. Finally, the release of a hydrophilic local anesthetic, procaine hydrochloride, from uncoated and stereocomplex-nanocoated microparticles was preliminary evaluated over a period of 15days.

Thermal and Mechanical Properties of Biodegradable Star-Shaped/Linear Polylactide Stereocomplexes

The 6-arm star-shaped poly(L-lactide) (6PLL)/linear poly(D-lactide) (1PDL) stereocomplex films were prepared by the solvent casting method. The influences of the 6PLL/1PDL blend ratios (75/25, 50/50, and 25/75 w/w) and 1PDL molecular weights (15,000, 30,000, and 60,000 g/mol) on the thermal and mechanical properties of the stereocomplex films were investigated. The 6PLL and 1PDLs had a single melting temperature (Tm) of homocrystallites at 174°C and 167°C, respectively. The 6PLL/1PDL blends had twoTms: a lowerTmof homocrystallites (160–173°C) and a higherTmof stereocomplex crystallites (219–228°C). The stereocomplex crystallinity and mechanical properties of the 6PLL/1PDL blend films were higher than those of 6PLL and 1PDL and were the highest in the 50/50 (w/w) blend ratio. However, the stereocomplex crystallinity of the 50/50 (w/w) 6PLL/1PDL blend films decreased and the mechanical properties increased as the molecular weight of 1PDL increased.

Temperature effect on template polymerization of methacrylic acid using stereocomplex formation on quartz crystal microbalance substrates

ABSTRACTThe radical polymerization of methacrylic acid (MAA) at 0, 20, 40, and 70 °C was achieved in porous isotactic (it‐) poly(methyl methacrylate) (PMMA) films on quartz crystal microbalance (QCM) substrates, which were prepared by layer‐by‐layer assembled stereocomplex films of it‐PMMA and syndiotactic (st‐) poly(methacrylic acid) (PMAA), followed by the subsequent extraction of st‐PMAA. The MAA polymerization yields increased from 35 to 75%, as the polymerization temperature increased from 0 to 70 °C. Furthermore, infrared spectroscopy revealed that a higher polymerization temperature is necessary to form it‐PMMA/st‐PMAA stereocomplexes via stereoregular polymerization manner that resemble native it‐PMMA/st‐PMAA stereocomplexes. X‐ray diffraction pattern of porous it‐PMMA were also investigated for reaction fields. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3032–3036

Crystallization by thermal processing of Poly(lactide) stereocomplex thin films

Various properties of polymers such as optical, barrier and mechanical properties are substantially anisotropic, since molecular orientations of polymer chains strongly affect the physical properties. Controlling the chain orientation in the semicrystalline polymers can thus lead us to valuable technological breakthroughs. Polymer ultrathin films have attracted great attention due to their vast applications. In thin films, the molecular chain orientation depends on the method of processing, thickness and substrate interactions. In the present study, we report on the crystallization condition dependent molecular chain orientation and crystallinity peculiar to the ultrathin films of biodegradable Poly(lactide) (PLA) stereocomplex (SC) with thicknesses ranging from several nm to several hundred nm. Equimolar solution of two enantiomers of PLA, poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) has attracted great attention because of the formation of SC which shows decent physical properties better than PLLA and PDLA. Combination of surface sensitive X-ray diffraction and scattering techniques, including grazing incidence wide angle X-ray diffraction (GIWAXD), X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) measured at synchrotron radiation facility (SPring-8, Japan) and infrared reflection absorption spectroscopy (IR-RAS) were used to characterize the film structures. In the SC films, two different polymer chain configurations, i.e., lying molecules and standing molecules revealed to be controlled by simple thermal processes.

Controlled Release Using a Polymer Stereocomplex Capsule through the Selective Extraction and Incorporation of One Capsule Shell Component

Isotactic poly(methyl methacrylate) (it-PMMA)/syndiotactic poly(methacrylic acid) (st-PMAA) stereocomplex hollow capsules were fabricated by the deposition of stereocomplex films of it-PMMA and st-PMAA on silica particles by alternate layer-by-layer assembly and the subsequent removal of the silica particles with aqueous HF. The selective extraction of st-PMAA from the it-PMMA/st-PMAA stereocomplex capsule shells was successfully carried out by immersion in a pH 6-9 aqueous solution. The incorporation of st-PMAA into the resulting porous capsule shells was performed by immersion in an acetonitrile/water (1/1) solution of st-PMAA. The controlled release of an encapsulated dye from the it-PMMA/st-PMAA hollow capsules was achieved by combining the selective extraction of st-PMAA from the capsule shells and the incorporation of st-PMAA into the resulting porous shells.

Surface modification of stereoregular and stereocomplex poly(methyl methacrylate) films with biologically identified peptides

Biologically identified peptides that bind to the surfaces of isotactic poly(methyl methacrylate) (PMMA), syndiotactic PMMA, and their assembled stereocomplex films were used as noncovalent surface modifiers. Each peptide was biotinylated and immobilized onto the PMMA films to function as a linker for the subsequent immobilization of streptavidin. We demonstrated that the PMMA species had a great impact on the peptides' abilities to functionally modify the film surfaces.

Fusion of Porous Isotactic Poly(methyl methacrylate) Thin Films Fabricated on Silica Nanoparticles with Stepwise Stereocomplex Assembly

Structures of silica nanoparticles coated with stereocomplex thin films composed of isotactic (it) poly(methyl methacrylate) (PMMA) and syndiotactic (st) poly(methacrylic acid) (PMAA) and with porous it-PMMA thin films under gentle stirring or static conditions were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), respectively. The porous it-PMMA films were fabricated by stepwise stereocomplex assembling of it-PMMA and st-PMAA, and subsequent extraction of the st-PMAA from the films. From DLS results, an evident difference was not observed between the it-PMMA films and the stereocomplex films, whereas the it-PMMA films after 10 h of stirring in acetonitrile/water (4/6, v/v) and drying on a SEM stage fused to form nanostructured networks. The fusion of the it-PMMA films on the silica nanoparticles occurred not by the dissolution of it-PMMA in the mixed solvent, but rather by an interaction of the it-PMMA chains driven by the slight solvation of acetonitrile without dissolution. Thus, leaving the solution at rest would be important for film fusion on the particles, and multiple spherical substrates could promote the crosslinking of the it-PMMA chains on the particles.

Nanotube Formation through the Continuous One-Dimensional Fusion of Hollow Nanocapsules Composed of Layer-by-Layer Poly(lactic acid) Stereocomplex Films

Hollow nanocapsules composed of a poly(lactic acid)s (PLAs) stereocomplex can be fabricated by a combination of the layer-by-layer assembly technique and the silica template method. These hollow capsules one-dimensionally fuse together to generate novel PLA nanotubes. The formation of nanotubes was affected by the molecular weights of PLAs constituting the hollow capsules.

Morphological changes of isotactic poly(methyl methacrylate) thin films via self-organization and stereocomplex formation

Morphological changes of macromolecularly porous thin films during isotactic (it) poly(methyl methacrylate) (PMMA) crystallization and the subsequent syndiotactic (st) poly(methacrylic acid) (PMAA) incorporation are described herein. Porous it-PMMA thin films were prepared on a gold substrate by the selective extraction of st-PMAA from stereocomplex films composed of it-PMMA/st-PMAA using layer-by-layer assembly. it-PMMA crystallization occurred when the porous it-PMMA films were immersed in a mixed solvent of acetonitrile/water (4/6, v/v). Surface analyses of films were performed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS) and static contact angles. Dotted aggregates of it-PMMA appeared on crystallized films, whereas networks composed of crystallized it-PMMA and the stereocomplex were observed on st-PMAA incorporated films. Gold substrate peaks were observed not on porous it-PMMA films, but on crystallized it-PMMA films by XPS, indicating that homogeneously broadened it-PMMA in porous films was localized because of its crystallization. The static contact angle of crystallized it-PMMA films was 36.5±1.6°, which was smaller than that of porous it-PMMA films (49.2±1.9°). This difference resulted from the surface morphology of the thin films. Dotted it-PMMA aggregates were also observed when spin-coated films were immersed in the mixed solvent. Morphological changes of macromolecularly porous thin films in it-PMMA crystallization and subsequent st-PMAA incorporation

A Polymer Platform Composed of Structurally Well-defined Stereocomplex Structures for Efficient Enzymatic Reactions

Previously we reported that p-galactosidase immobilized on the structurally well-defined poly(methyl methacrylate) (PMMA) stereocomplex films fabricated by layer-by-layer (LbL) assembly of isotactic (it) and syndiotactic (st) PMMAs on solid substrates were highly active when compared to the enzyme immobilized on the single-component films, and that a slight difference of polymer surface structures strongly affects activities of immobilized enzymes, even though polymers have the same chemical component (Chem. Mater., 19, 2174-2179 (2007)). In this paper, we demonstrated activities of other enzymes immobilized on the PMMA films. Activities of immobilized alkaline phosphatase (ALP) were measured by following hydrolysis rate of fluorescence substrate 4-methylumbelliferyl phosphate (4-MUP). Initial velocity of ALP hydrolysis reaction immobilized on the complex film was approximately 2-fold faster than those on the single-component it-PMMA and atactic (at) PMMA films. Michaelis-Menten analyses revealed that catalytic efficiency (kcat/Km) of ALP was strongly dependent on conformational regulation of PMMA chains at film surfaces. Quartz crystal microbalance (QCM) analyses revealed that immobilization amount of ALP on the complex was greater than those on the single-component films. Similar dependencies were also observed in the case of cellulases that degrade polymeric cellulose under acidic condition. Secondary structural analyses using an attenuated total reflection infrared (ATR-IR) spectroscopy revealed that structural denaturation of the enzyme after immobilization processes was well-suppressed on the complex film, although the enzymes on the single-component PMMA films were relatively denatured. We propose here that PMMA stereocomplex films are a generally convenient platform for immobilization of functional proteins and could be used under various conditions without loss of their activities.

Superior Activities of Enzymes Physically Immobilized on Structurally Regular Poly(methyl methacrylate) Surfaces

Ultrathin poly(methyl methacrylate) (PMMA) stereocomplex films with macromolecularly double-stranded regular nanostructures were prepared by layer-by-layer (LbL) assembly of isotactic (it) and syndiotactic (st) PMMAs on solid substrates, and these films were used for enzyme immobilization supports. Hydrolysis of p-nitrophenyl-β-d-galactopyranoside (PNPG) by the immobilized β-galactosidase (β-Gal) on the complex film was 2- and 4-fold faster than those by the enzyme immobilized on single-component it-PMMA and atactic (at) PMMA films, respectively. Quartz crystal microbalance (QCM) analysis revealed that greater amounts of β-Gal were immobilized on the complex film through physical adsorption than those on the single-component films. Michaelis constants (Km) of the enzyme were independent of film components; however, catalytic efficiencies (kcat/Km) were increased by regulation of PMMA conformation at film surfaces. Attenuated total reflection infrared (ATR-IR) analysis revealed that structural denaturation...

A Stereocomplex Platform Efficiently Detecting Antigen−Antibody Interactions

Ultrathin poly(methyl methacrylate) (PMMA) stereocomplex films with macromolecularly double-stranded regular nanostructures were prepared by layer-by-layer assembly of isotactic and syndiotactic PMMAs on solid surfaces. Antibodies were immobilized through the Fc region-capturing protein A, which had been physically adsorbed on the complex film, and the binding of antigens to immobilized antibodies was quantitatively investigated by the quartz crystal microbalance technique. Greater amounts of protein A with native forms were adsorbed on the complex film than those on conventional single-component PMMA films. Antibodies with high target-binding activities were also immobilized on the complex film. A greater amount of antigens could be detected on the complex film. The activity of protein A was maintained on the complex for a long time even within a dried state. The mechanism for the preservation of protein native forms on the complex surface was speculated by analyzing the physical adsorption of proteins with various secondary structures. Stereocomplex films can be utilized as novel coating nanomaterials for efficiently detecting protein-protein interactions.