Coupling of microphase separation and dewetting in weakly segregated diblock co-polymer ultrathin films

We have studied the coupling behavior of microphase separation and autophobic dewetting in weakly segregated poly(ε-caprolactone)-block-poly(L-lactide) (PCL-b-PLLA) diblock co-polymer ultrathin films on carbon-coated mica substrates. At temperatures higher than the melting point of the PLLA block, the co-polymer forms a lamellar structure in bulk with a long period of L ～ 20 nm, as determined using small-angle X-ray scattering. The relaxation procedure of ultrathin films with an initial film thickness of h = 10 nm during annealing has been followed by atomic force microscopy (AFM). In the experimental temperature range (100-140 °C), the co-polymer dewets to an ultrathin film of itself at about 5 nm because of the strong attraction of both blocks with the substrate. Moreover, the dewetting velocity increases with decreasing annealing temperatures. This novel dewetting kinetics can be explained by a competition effect of the composition fluctuation driven by the microphase separation with the dominated dewetting process during the early stage of the annealing process. While dewetting dominates the relaxation procedure and leads to the rupture of the ultrathin films, the composition fluctuation induced by the microphase separation attempts to stabilize them because of the matching of h to the long period (h ～ 1/2L). The temperature dependence of these two processes leads to this novel relaxation kinetics of co-polymer thin films.     

Effect of annealing on the microphase separated behavior and properties of PDMS–MDI–PEG multiblock copolymer films

A model multiblock copolymer based on (Poly dimethylsiloxane) (PDMS),–4, 4′‐diphenylmethanediisocyanate (MDI)–(poly ethylene glycol) (PEG) was synthesized by employing two step growth polymerization technique. The effect of annealing on microphase separation of the copolymer surface and bulk, surface composition, hydrogen‐bonding and some properties was investigated by AFM, SAXS, XPS, FTIR, contact angle measurement, and protein adsorption experiment, respectively. It was found that increasing the annealing temperature availed formation of microphase separation and surface enrichment of PDMS, which was accompanied by increase in average interdomain spacing, long period, and the crystallizing degree in the hard domains. But the best microphase separated structure seemed to occur at the annealing temperature of 140 °C; exorbitant annealing temperature might demolish the ordered structure. The annealing temperature dependence of microphase separation was further confirmed by the changes in urea hydrogen‐bonding and melting points characterized by FTIR and DSC, respectively. Protein adsorption experiments revealed that all annealed copolymer films possessed the low protein adsorption. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 208–217, 2007     

Structure-property relationships in polycaprolactone-polyurethanes

The structure-property relationships of polycaprolactone-based segmented polyurethanes were studied using differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), wide-angle x-ray diffraction (WAXD), dynamic mechanical, and stress-strain testing. The materials studied varied in hard-segment type [4,4′-diphenylmethane diisocyanate/butanediol (MDI/BD) or 4,4′-dicyclohexyl methane diisocyanate/butanediol (H₁₂MDI/BD)], soft-segment molecular weight (830 or 2000 MW polycaprolactone), hard-segment content (23–77% by weight), and thermal history. The materials with aromatic (MDI/BD) hard segments had semicrystalline hard-segment domains, while the materials with aliphatic (H₁₂MDI/BD) hard segment had mostly amorphous domains. Materials with the shorter polycaprolactone soft segment (830 MW) exhibited thermal and mechanical behavior which indicated a considerable degree of hard- and soft-segment compatibility. The materials which contained a 2000-MW polycaprolactone soft segment exhibited better-defined microphase separation. SAXS was used to characterize the microphase structure of each system. The effects of hard-segment content and soft-segment molecular weight were similar for the aromatic (MDI) and aliphatic (H₁₂MDI) hard-segment-based block copolymers. Changing the hard segment from aromatic to aliphatic gave materials with larger interfacial area and slightly higher tensile strength. A range of morphologies between isolated hard domains in a rubbery matrix and isolated rubbery domains in a hard matrix was observed.     

Effect of the composition ratio of copolymerized poly(carbonate) glycol on the microphase‐separated structures and mechanical properties of polyurethane elastomers

Randomly copolymerized poly(carbonate) glycols were employed as starting materials for the synthesis of polyurethane elastomers (PUEs). The poly(carbonate) glycols had hexamethylene (C₆) and tetramethylene (C₄) units between carbonate groups in various composition ratios (C₄/C₆ = 0/100, 50/50, 70/30, and 90/10), and the number‐average molecular weights of these poly(carbonate) glycols were 1000 and 2000. The PUEs were synthesized with these poly(carbonate) glycols, 4,4′‐diphenylmethane diisocyanate, and 1,4‐butanediol by a prepolymer method. Differential scanning calorimetry measurements revealed that the difference between the glass‐transition temperature of the soft segment in the PUEs and the glass‐transition temperature of the original glycol polymer decreased and the melting point of the hard‐segment domain increased with an increasing C₄ composition ratio. The microphase separation of the poly(carbonate) glycol‐based PUEs likely became stronger with an increasing C₄ composition ratio. Young's modulus of these PUEs increased with an increasing C₄ composition ratio. This was due to increases in the degree of microphase separation and stiffness of the soft segment with an increase in the C₄ composition ratio. The molecular weight of poly(carbonate) glycol also influenced the microphase‐separated structure and mechanical properties of the PUEs. The addition of different methylene chain units to poly(carbonate) glycol was quite effective in controlling the microphase‐separated structure and mechanical properties of the PUEs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4448–4458, 2004     

Effect of side groups of polymer glycol on microphase‐separated structure and mechanical properties of polyurethane elastomers

The effect of side methyl and dimethyl groups of the soft segment component on the microphase‐separated structure and mechanical properties of polyurethane elastomers (PUEs) was investigated. Poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG‐X) and methyl side groups (PTG‐L) were used as a polymer glycol, which forms a soft segment in the PUEs. The PUEs were synthesized with 4,4′‐dipheylmethane diisocyanate [1,1′‐methylenebis(4‐isocyanatobenzene)], 1,4‐butane diol, and 1,1,1‐trimethylol propane by a prepolymer method. The degree of microphase separation of the PUEs became weaker with increasing side group content in polymer glycols. Dynamic viscoelastic properties measurement showed reorganized‐crystallization and melting of the soft segment for the PUEs based on PTMG, PTG‐L, and PTG‐X with a lower content of the side groups, but not for a PTG‐L and PTG‐X with higher content of the side groups. Tensile testing revealed that increasing methyl group concentration made the PUEs soften and weaken. The PTMG‐based PUEs obviously exhibited strain‐induced crystallization of the soft segment chains during elongation process. In contrast, for the PTG‐L and PTG‐X‐based PUEs, crystallinity decreased with increasing side group content, and the PUEs with PTG‐L and PTG‐X with highest methyl group content did not crystallize even at a large strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2054–2063, 2008     

硬链段浓度对RIM交联聚氨酯结构和性能的影响

用l-MDI/1,4-BDO/PPO-EO快反应体系,考察硬段浓度对聚氨酯结构与性能的影响。发现样品的交联度、模量和抗张强度随硬段浓度增加而提高,交联趋向均匀,断裂伸长率在浓度30％处出现最大值。ATR-FTIR和DSC分析表明,微相分离程度随硬段浓度增大而降低。     

Mesoscopic simulation of the self-organization of a binary mixture of copolymers in the vicinity of a selective adsorbing surface

A new strategy for the construction of ultrathin structured films with cylindrical microdomains oriented primarily perpendicularly to the surface of a solid substrate is proposed. This approach is based on the phase separation of a binary mixture of incompatible compositionally asymmetric block copolymers, microphase separation of their blocks, and selective adsorption of one of the copolymers on the surface. Preferentially adsorbed copolymer forms a regular pattern on the surface, which serves as an orienting support for another component that dominates in the system and forms the hexagonal mesophase in the bulk of the film. This approach has been verified by the mesoscopic simulation based on the dynamic version of the density functional theory. As a result of the self-organization of macromolecules, the morphology with perpendicularly oriented domains can be thermodynamically stable for the films with a thickness of ∼100 nm. The commensurability of the parameters of the surface pattern and volume mesophase is shown to be the key factor controlling the orientation of cylindrical microdomains.     

Single-step synthesis of layered double hydroxides ultrathin nanosheets

A novel single-step approach was developed to prepare large-scale MgAl-LDHs ultrathin nanosheets. The key point of the successful realization was that we employed a high concentration of H(2)O(2). Oxygen molecules, derived from in situ decomposition of H(2)O(2), were speculated to be the decisive factor leading to complete separation of LDHs layers. The ultrathin nanosheets were characterized by XRD, TEM, AFM, FT-IR, and TG-DSC. The results indicated that the thickness of these nanosheets was about 1.44 nm, which was almost in perfect agreement with the theoretical thickness of two LDHs layers. From the TG-DSC curves, the weight loss of these exfoliated MgAl-LDHs ultrathin nanosheets at 500°C was 18.5%, which was much smaller compared to the 32.3% weight loss of unexfoliated MgAl-LDHs.     

Formation of ordered microphase-separated pattern during spin coating of ABC triblock copolymer

In this paper, the authors have systematically studied the microphase separation and crystallization during spin coating of an ABC triblock copolymer, polystyrene-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO). The microphase separation of PS-b-P2VP-b-PEO and the crystallization of PEO blocks can be modulated by the types of the solvent and the substrate, the spinning speed, and the copolymer concentration. Ordered microphase-separated pattern, where PEO and P2VP blocks adsorbed to the substrate and PS blocks protrusions formed hexagonal dots above the P2VP domains, can only be obtained when PS-b-P2VP-b-PEO is dissolved in N,N-dimethylformamide and the films are spin coated onto the polar substrate, silicon wafers or mica. The mechanism of the formation of regular pattern by microphase separation is found to be mainly related to the inducement of the substrate (middle block P2VP wetting the polar substrate), the quick vanishment of the solvent during the early stage of the spin coating, and the slow evaporation of the remaining solvent during the subsequent stage. On the other hand, the probability of the crystallization of PEO blocks during spin coating decreases with the reduced film thickness. When the film thickness reaches a certain value (3.0 nm), the extensive crystallization of PEO is effectively prohibited and ordered microphase-separated pattern over large areas can be routinely prepared. When the film thickness exceeds another definite value (12.0 nm), the crystallization of PEO dominates the surface morphology. For films with thickness between these two values, microphase separation and crystallization can simultaneously occur.     

EFFECTS OF SOLVENT TREATMENT ON SURFACE MORPHOLOGY AND COMPOSITION OF POLY(METHYL METHACRYLATE)-g-POLY(ETHYLENE OXIDE)

Surface morphology and composition of solution-cast films of poly(methyl methacrylate)-g-poly(ethylene oxide)(PMMA-g-PEO) were investigated by using XPS, DSC, SEM and contact angle measurement. The microphase separatedstructure of the copolymers was studied by TEM. Generally, for the same graft copolymer, the surface content of PEO orhydrophilicity can be as follows: Surface treated with petroleum ether or cyclohexane>surface untreated with solvent>surface treated with water or ethyl alcohol. Graft copolymer having longer PEO side chains and higher PEO content shows aseparated PEO phase with even a certain degree of crystallinity on the surface. PEO crystallinity was destroyed by water orethyl alcohol treatment, however, surface treatment with petroleum ether or cyclohexane favors the growth of PEO crystal.TEM shows that graft copolymers with longer PEO side chains (M_n of PEO, 3200) may readily undergo microphase separation and the shape and size of domains depend on the copolymer's composition.     

Structures and electrical properties of ferroelectric copolymer ultrathin films

Ultrathin films of ferroelectric copolymer vinylidenefluoride and trifluoroethylene, P(VDF-TrFE), were successfully obtained by spin-coating and their nanoscale structures and electrical properties were studied utilizing atomic force microscopy (AFM). We succeeded in obtaining ultrathin copolymer films on graphite whose thickness ranged from 1 nm to several tens of nanometers by controlling concentration of copolymer solutions in methylethylketone. We found that ultrathin films thinner than 4 nm showed layered structures whose layer thickness was about 0.5 nm. On the other hand, films thicker than 4 nm formed typical edge-on lamellar crystal structures. Furthermore, we investigated surface potential distribution and piezoelectric property by AFM-based techniques and discussed interaction between electrical dipoles in the molecular chains and graphite substrate.     

A Non-isocyanate Route to Poly(ester urethane) with High Molecular Weight: Synthesis and Effect of Chemical Structures of Polyester-diol

A series of non-isocyanate linear high molecular weight poly(ester urethane)s(PETUs)were prepared through an environmentallyfriendly route based on dimethyl carbonate,1,6-hexanediol and 1,6-hexanediamine.In this route,the polyurethane diol was first prepared by the reaction between bis-1,6-hexamethylencarbamate(BHC)and 1,6-hexanediol.A series of polyester soft segments of polyurethane have been synthesized from the polycondensation of adipic acid and different diols,including butanediol,hexanediol,octanediol and decanediol.The subsequent polycondensation of polyurethane diol and polyester diol led to linear PETUs.The resultant polymers were characterized by GPC,FTIR,¹H-NMR,¹³C-NMR,DSC,WAXD,TGA and tensile test.The results indicated that PETUs possess weight-average molecular weights higher than 1×10⁵ and the tensile strength as high as 10 MPa.The thermal properties,crystallization behavior,microphase separation behavior and morphology were studied by DSC and AFM,and the results indicated that the degree of phase separation was affected by two factors,the crystallization and hydrogen bonding interaction between soft segment and hard segment.     

Investigations of a series of PPDI-based polyurethane block copolymers. I. General morphology

The morphology of a series of segmented polyurethane block copolymers is characterized by x-ray scattering, differential scanning calorimetry (DSC), density measurements, and tensile studies. The materials contain hard segments formed from paraphenylene diisocyanate (PPDI) and flexible segments formed from poly(oxytetramethylene) (POTM) ranging in molecular weight from 650 to 2000. Four different molecular weight compositions were investigated, with the weight fraction of the hard segment (w_h) ranging from 0.14 to 0.33. The microphase structure has been examined using small-angle x-ray scattering, and the microphase transition zone thickness is estimated to be on the order of 1 nm. Oriented samples have been characterized with wide-angle x-ray scattering, and the flexible segment is shown to undergo stress-induced crystallization. DSC thermograms show flexible segment melting in the compositions containing the highest two molecular weights of the flexible segments. The hard segment thermal transitions were complex with a broad melting peak that varied with weight fraction and with a high temperature transition attributed to regions with hard segment lengths longer than the bulk of the hard segment component. There is an increase in tensile strength and initial modulus and decrease in elongation with increasing w_h. Density data suggest the existence of a multiphase system.     

Micromorphology and phase behavior of cationic polyurethane segmented copolymer modified with hydroxysilane

A series of cationic waterborne polyurethane dispersions (SiPU) modified with hydroxysilane (HPMS) were successfully synthesized based on poly(oxytetramethylene) glycols (PTMG) and isophorone isocyanate (IPDI), and the films were obtained by casting the dispersions on tetrafluoroethylene (TFE) plates. Effects of HPMS content on micromorphology, particle size of the dispersions were studied, as well as thermal properties, phase behavior and surface structure of the films. The particles had the morphology of a solid sphere, with particle size varying from 17.1 nm to 114.4 nm corresponding to the increase of HPMS concentration, which can be attributed to the increase of interfacial tension. XPS spectra indicated the surface migration of Si element in the process of film forming, and the SiPU surface was mainly composed of soft segments. DSC analysis, together with TG-DTG-DTA results demonstrated the HPMS soft segment merged with the transition region of PU matrix, forming part of polyurethane backbone, but an improved microphase separation was observed when HPMS concentration greater than 15%. It was also found that incorporation of flexible HPMS prevented the degradation of polyurethane backbone, resulting in the increase of thermal stability in ultimate copolymer.     

Microcrystalline domains of monolayer and multilayer BDN-SA Langmuir–Blodgett films

Monolayer and multilayer BDN(Bis(4-diethyannodithiobenzil)nickel)-SA(stearyl alcohol) LB (Langmuir–Blodgett) films were prepared and the characteristics of microcrystalline domains were studied using UV–vis.–NIR and AFM. The results indicate that BDN-SA LB films consist of numerous ball-like microcrystalline domains at size scales from a few tens to a few hundreds of nm. AFM images of a multilayer LB film show that well-ordered molecular arrangements exist on the surface of domains which resemble a mosaic structure. The relationship between the mean size of the domain of a BDN-SA LB film with the thickness of the film was also shown.     

Investigations of a series of PPDI-based polyurethane block copolymers. II. Annealing effects

In a previous study, the morphologies of a group of paraphenylene diisocyanate (PPDI)-based polyurethane block copolymers were examined. These polyurethanes exhibited a multiphase structure with an interfacial boundary thickness estimated to be on the order of 1 nm and crystallization of the polyoxytetramethylene (POTM) flexible segment. Further studies involving annealing of these polyurethanes are reported here. An annealing time of 4 h was used, and the annealing temperature varied from 125 to 200°C. The samples have been characterized using differential scanning calorimetry (DSC) and with wide- and small-angle x-ray scattering (WAXS, SAXS) in order to determine the effects of annealing on the microphase structure. Annealing increases the phase separation of the two phases as evidenced by sharper endotherms in DSC thermograms and increased intensities in WAXS diffractometer traces. Annealing also slightly increases the transition zone thickness and long-period spacing. At the highest annealing temperature in this study, the long-period spacing increases dramatically due to hard segment domain aggregation.     

Temperature-reversible ultrathin films of N-isopropylacrylamide terpolymer adsorbed at the solid-liquid interface

This article describes the stability and reversibility of ultrathin films of N-isopropylacrylamide (NIPA)-vinylimidazole (VI)-poly(ethylene glycol) (PEG) graft terpolymer adsorbed at the solid-liquid interface upon temperature cycling from below to above its phase transition temperature. The coil-to-globule and globule-to-coil phase transitions were captured by in situ fluid tapping atomic force microscopy (AFM). The film thickness of 1 nm was determined by AFM, X-ray photoelectron spectroscopy, and X-ray reflectivity. The concentration required to reach full coverage was found to be higher when adsorption occurred below the phase transition temperature. From 23 to 42 degrees C, the adsorbed NIPA terpolymer film was observed to be molecularly smooth, corresponding to the close-packed structure of flexible polymer coils. Particles containing between one and a few globules appeared abruptly at the interface at 42-43 degrees C, the same temperature as the solution phase transition temperature, which was determined by dynamic light scattering. The size of the particles did not change with temperature, whereas the number of particles increased with increasing temperature up to 60 degrees C. The particles correspond to the collapsed and associated state of the globules. The film morphological changes were found to be reversible upon temperature cycling. Subtle differences were observed between dip-coated and spin-coated films that are consistent with a higher degree of molecular freedom for spin-coated films. The study contributes to the fundamental understanding and applications of smart ultrathin films and coatings.     

Microstructure and properties of polyurethanes derived from castor oil

The goal of this work was the synthesis of novel segmented polyurethanes with a high percentage of components derived from renewable sources. The soft segment was a polyol derived from castor oil and the hard segment structure was varied by means of different chain extenders, petrochemical-based 1,4-butanediol (BD) and corn sugar-based 1,3-propanediol (PD). The synthesis was carried out in bulk and without catalyst via a two-step polymerization varying hard segment ratio. Physico-chemical, mechanical and morphological characterization was performed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscopy (AFM), mechanical testing and termogravimetric analysis (TGA). Properties have been discussed from the viewpoint of hard/soft microdomain phase separation and also the hard segment nature and formed structure. An increase in hard segment content was accompanied by an increase in hard domain order, crystallinity, and stiffness. The hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to impart properties ranging from elastomeric to rigid behaviour with the increase of hard segment content. Polyurethanes synthesized from bio-based chain extender showed a slightly lower crystallinity in the hard segment structure than that synthesized from BD as the chain extender. This lower crystallinity avoids strength concentrations at the soft/crystalline hard segment interface, thus improving the mechanical properties at high hard segment content. The slightly higher thermal stability observed for BD based polyurethanes is related with their more packed structures and crystallinity observed in the hard segment structure.     

纤维素硫酸盐与壳聚糖自组装有序超薄膜的制备和AFM研究

纤维素和壳聚糖作为两种来源最充足的天然聚合物 ,其潜在的应用前景吸引了众多的注意力 [1] ,特别是其半刚性高分子骨架和优良的成膜性能使其在膜技术领域中得到了广泛的应用 [2 ] .2 0世纪 90年代初 ,Decher[3] 提出将基片交替地浸入带相反电荷的聚电解质溶液中 ,依靠静电作用自组装成膜 .该法方便、快捷 ,近年来被广泛采用 [4 ,5] .本文将纤维素的一种新型离子型衍生物——甲苯磺酰纤维素硫酸盐 ,在处理过的石英基片和硅基片上自组装成膜 ,并在其上再自组装一层脱乙酰壳聚糖膜 .AFM观察证明 ,形成了结构致密、缺陷少、厚度在纳米范围内…     

The degradation and biocompatibility of waterborne biodegradable polyurethanes for tissue engineering

To better investigate the degradation and biocompatibility of waterborne biodegradable polyurethanes for tissue engineering, a series of new waterborne biodegradable polyurethanes (PEGPUs) with low degree of crosslinking was synthesized using IPDI, BDO and L-lysine as hard segments, PCL and PEG as soft segment. The bulk structures and properties of the prepared polyurethanes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), tensile mechanical tests and water contact angle (WCA) measurements. The degree of microphase separation was slightly improved because of the lowered crosslinking degree of these PEGPUs in comparison with the high cross-linking degree samples, leading to good mechanical properties, as indicated by DSC and stress-strain data. Moreover, biodegradability of the polyurethanes was evaluated in phosphate buffer solutions (PBS) under different pH values and enzymatic solution at pH 7.4 through weight loss monitoring. The results suggested that the degradation of these PEGPUs was closely related to their bulk and surface properties. And the degradation products didn’t show apparent inhibition effect against fibroblasts in vitro. These studies demonstrated that the waterborne biodegradable polyurethanes could find potential use in soft tissue engineering and tissue regeneration.