Stepwise surface modification of mesoporous silica and its use in poly(urethane-urea) composite films

The compatibility between polymer matrix and filler is a vital issue in the fabrication of composites with desirable properties. To enhance the interfacial adhesion between matrix and filler, various surface modification treatments are applied. The objective of this study was to increase the affinity of silica and poly(urethane-urea)s (PUUs), thereby improving the mechanical properties of the resulting composites. Stepwise surface modification of mesoporous silica with amine-containing dendrimers was done. Various techniques were used to confirm the surface-modified structure during the stepwise reaction. Additionally, the N₂ adsorption–desorption method indicated a gradual reduction in surface area, pore diameter and pore volume of the particles, which warrants the gradual propagation of the dendrimers on the surface and also inside the pores. A type IV isotherm was obtained in this analysis. Two types of pre-synthesized PUUs were chosen for composite preparation containing the surface-modified silica with 0.5, 1, 2.5 and 5 wt% concentrations. Due to the high affinity of the dendrimers containing amine moieties on the particles with polyurethane, a proper dispersion of particles in the matrix was achieved based on scanning electron micrographs. Tensile measurements showed an increased Young's modulus and strength of polyurethane films as a result of addition of the particles. However, no significant improvement in the tensile performance of the composites was seen above 2.5 wt% particle loading due to some particle aggregations. © 2021 Society of Industrial Chemistry.     

Biodegradable and thermostable synthetic hyperbranched poly(urethane-urea)s as advanced surface coating materials

Aliphatic hyperbranched poly(urethane-urea)s with different weight percentages of branch generating moiety were synthesized by a one pot A₂ + BC₂ approach. Isophorone diisocyanate was used as the A₂ type monomer, while a tri-functional dihydroxyamine compound synthesized from ?-caprolactam and diethanol amine acted as the BC₂ monomer. Evidence supporting the hyperbranched structure of the synthesized poly(urethane-urea) was obtained from ¹H NMR spectra. FTIR study confirmed the nature and extent of hydrogen bonding present in this novel macromolecule. A Gaussian band fitting procedure of the IR band at amide-I region showed that the extent of hydrogen bonding increases with the increase of weight percentage of the tri-functional compound. The tensile strength, elongation at break, impact resistance, scratch hardness and gloss followed an increasing trend with the same. The thermal degradation of the hyperbranched poly(urethane-urea) was found to be dependent on the weight percentage of the BC₂ type moiety. The kinetics of thermal degradation studied by the Ozawa method showed that the activation energy required for thermal degradation of hyperbranched polymer is higher than its linear polyurethane analog. The synthesized polymer was found to be biodegradable by Pseudomonas aeruginosa bacteria. The study showed superiority of the hyperbranched structure over the linear one. Thus the results indicated the potential usage of the studied hyperbranched poly(urethane-urea) as an advanced surface coating material.     

Effect of chain extender on microphase structure and performance of self-healing polyurethane and poly(urethane-urea)

In this work, four aliphatic chain extenders, hexanediol (HDO), hexane diamine (HDA), cystamine (CY), and cystine dimethyl ester (CDE), were chosen to synthesize four kinds of polyurethane and poly(urethane-urea)s (PUs), respectively. HDO extended polyurethanes, HDA extended poly(urethane-urea), CY extended poly(urethane-urea), and CDE extended poly(urethane-urea) were denoted as OPU, APU, CPU, and SPU, respectively. The effect of chain extender type on microphase structure and performance of four PUs was investigated. Our research showed that mechanical strength increased in the following order: OPU < SPU < CPU < APU, and self-healing performance increased in the opposite direction. This result is attributed to the increasing degree of microphase separation: OPU < SPU < CPU < APU. The optimal sample SPU has not only excellent mechanical properties (tensile strength of 27.1 MPa and elongation at break of 397.7%), but also exhibits superior self-healing performance (self-healing efficiencies of 95.3% and 93.5% based on tensile strength and elongation at break). The moderate degree of microphase separation between the soft segments and the hard segments, the introduction of disulfide bonds and low degree of hydrogen bonding are responsible for preparing a polyurethane or poly(urethane-urea) system with high mechanical strength and excellent self-healing performance simultaneously. This work provides useful information for us to develop self-healing polyurethane or poly(urethane-urea) materials in the future.     

Application of thermal methods in the characterisation of poly(urethane-urea)s formed by reaction injection moulding

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) have been used in conjunction with tensile testing and transmission electron microscopy (TEM) to characterise novel segmented poly(urethane-urea) (PUU) network materials formed by reaction injection moulding (RIM). Materials were based on a modified liquid 4,4′-diphenylmethane diisocyanate and a polyether triol in admixture with one of three hindered aromatic diamines: 3,5-diethyltoluene diamine (DETDA); methylene-bis-2,6-diisopropylaniline (MMIPA); methylene-bis-(2-methyl-6-isopropylaniline) (MMIPA). The materials ranged from tough translucent elastomers to opaque brittle plastics depending on the chemical nature and weight fraction of the hard segments (HS). DSC and DMTA studies showed the PUU materials to be phase-separated; this was confirmed by TEM and tensile testing. The soft-segment glass transition temperatures (DSC and DMTA) were independent of composition but varied with diamine structure. Hard-segment glass transition temperatures could only be evaluated by DMTA and no evidence of crystallinity was found by thermal methods or by wide angle x-ray diffraction. Heat capacity measurements and DMTA suggested that some degree of phase mixing had occurred, to a greater extent in the DETDA and MDIPA systems. Phase inversion was observed by DMTA and confirmed at ～55% hard-segment content for DETDA systems by tensile testing.     

Solid-state C NMR investigation of the structure and hydrogen bonding for stereoregular poly(vinyl alcohol) films in the hydrated state

The structure and hydrogen bonding of the hydrated stereoregular poly(vinyl alcohol) (PVA) films have been investigated by high-resolution solid-state ¹³C NMR spectroscopy. It is found by the ¹³C spin-lattice relaxation analysis that there exist three components with different T_1C values assigned to the crystalline, less mobile and mobile components for the hydrated syndiotactic PVA (S-PVA) and highly isotactic PVA (HI-PVA) films. The line shape analysis indicates that the probability of intramolecular hydrogen bonding is appreciably increased in the crystalline region for the S-PVA films by the hydration but a slightly helical structure, which is probably allowed by the formation of the successive intramolecular hydrogen bondings along the chains in the crystalline region, seems not to undergo any significant change by the hydration for HI-PVA. This fact indicates that intramolecular hydrogen bonding is more stable in the hydrated state in the crystalline region. As for the less mobile component, the line shape of the CH resonance line for the hydrated S-PVA or HI-PVA films is found to be very similar to that of the corresponding crystalline component, probably being due to the successive formation of intermolecular or intramolecular hydrogen bonding in the interfacial region, which mainly contributes to the less mobile component, for the S-PVA or HI-PVA films even in the hydrated state. The mole fractions of the mm, mr and rr sequences are also estimated for the mobile component that is produced in each stereoregular PVA sample by swelling with water and it is concluded that no prominent preferential partitioning of the mm, mr and rr sequences occurs in the crystalline and noncrystalline regions for the PVA films with different tacticities.     

Highly isotactic poly(vinyl alcohol) derived from tert-butyl vinyl ether. Part IV. Some physical properties, structure and hydrogen bonding of highly isotactic poly(vinyl alcohol) films

Some basic physical properties, structure and hydrogen bonding have been characterized for different stereoregular PVA films including highly isotactic PVAs (HI-PVAs), which were recently succeeded in synthesis, as functions of the mm fraction by using different analytical methods. The melting temperature, degree of crystallinity, and ¹³C spin-lattice relaxation time of the crystalline component are found to have their own clear minima at the mm fraction of about 0.4-0.5. This fact suggests that structural disordering associated with the decrease in crystallinity may be most strongly induced at this mm fraction. The formation of the new crystal form of PVA has been reconfirmed for HI-PVAs with the mm fractions higher than about 0.55 by FTIR spectroscopy and the structure and hydrogen bonding have been investigated in detail by solid-state ¹³C NMR spectroscopy. It is found that all OH groups are allowed to form successive intramolecular hydrogen bonding along the respective chains in the crystalline region for HI-PVAs with the mm fractions higher than about 0.7. Since these chains should contain some amount of r units even in the crystalline region, a slightly helical structure with a considerably long period may be adopted by them as an energetically stable state. On the basis of the line shape analysis of the CP/MAS ¹³C NMR spectra of the crystalline components, structural causes of the appearance of the minima of the physical values described above are also discussed in relation to the introduction of disordered units mainly associated with hydrogen bonding to the syndiotactic or isotactic sequences forming successive intermolecular or intramolecular hydrogen bonding, respectively.     

Toughening of poly(propylene carbonate) by hyperbranched poly(ester‐amide) via hydrogen bonding interaction

Poly(propylene carbonate) (PPC) is a biodegradable alternative copolymer of propylene oxide and carbon dioxide. As an amorphous polymer with lower glass transition temperature around 35 °C, PPC shows poor mechanical performance in that it becomes brittle below 20 °C and its dimensional stability deteriorates above 40 °C; thus toughening of PPC is urgently needed. Here we describe a biodegradable hyperbranched poly(ester‐amide) (HBP) that is suitable for this purpose. Compared with pure PPC, the PPC/HBP blend with 2.5 wt% HBP loading showed a 51 °C increase in thermal decomposition temperature and a 100% increase in elongation at break, whilst the corresponding tensile strength remained as high as 45 MPa and tensile modulus showed no obvious decrease. Crazing as well as cavitation was observed in the scanning electron microscopy images of the blends, which provided good evidence for the toughening mechanism of PPC. The intermolecular hydrogen bonding interaction confirmed by Fourier transform infrared spectral analysis proved to be the reason for the toughening phenomenon. Copyright © 2011 Society of Chemical Industry     

Synthesis and properties of hydrogen‐bonded poly(amide‐imide) hybrid films

Poly(amide‐imide), PI, hybrid films are prepared by using sol–gel techniques. First, the poly(amide amic acid) with controlled block chain length of 5000 and 10,000 g/mol and uncontrolled chain length are synthesized by condensation reaction with 4,4′‐diaminodiphenyl ether (ODA), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), trimellitic anhydride chloride (TMAC) and terminated with p‐aminopropyltrimethoxysilane (APrTMOS). And then the imidization reactions of poly (amide amic acid) are proceeded to obtain the poly (amide‐imide) hybrid film. Hybrid films with 5000 g/mol block chain length possess higher storage modulus, lower glass transition temperature and damping intensity comparing to films with 10,000 g/mol block chain length. The addition of TMAC to the poly(amide‐imide) hybrids is due to the increase of toughness and intermolecular hydrogen bonding, which is the average strength of intermolecular bonding and studied by the hydrogen‐bonded fraction (f_bonded), frequency difference (Δν) and shiftment. Meanwhile, PI hybrid films containing more APrTMOS and TMAC content possess higher thermal and mechanical properties. On the other hand, hybrid films with 10,000 g/mol block chain length and more TMAC content have higher gas permeabilities than other films. The degradation temperatures of 5 wt % loss of all hybrid films are all higher than 540°C and increased as the increase of TMAC content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Interpolymer complexes of poly(acrylamide) and poly(N-isopropylacrylamide) with poly(acrylic acid): a comparative study

The interpolymer complexation, through successive hydrogen bonding, between poly(acrylamide) (PAAm) and poly(N-isopropylacrylamide) (PNiPAAm) with poly(acrylic acid) (PAA) in aqueous solution has been viscometrically and potentiometrically investigated. The stoichiometry of the complexes formed was determined. By comparing the strength of the two complexes the very important contribution of the hydrophobic interaction in their formation has been indicated.     

Comparative studies of electrochemically deposited poly(o-toluidine) and poly(m-toluidine) films

Under galvanostatic deposition conditions poly(o-toluidine) exhibits a higher rate of polymerization than poly(m-toluidine). This observation is supported by results obtained by different characterization techniques such as spectrophotometry, scanning electron microscopy and thermogravimetric analysis. The monomer concentration was found to be the predominant parameter in obtaining selectively a conducting salt phase in both cases. However, the morphology of these polymeric films does not reveal any particular relationship with monomer concentration; instead a mixed morphology, i.e. a combination of granules and fibres, is observed. Finally, the thermal stability of poly(m-toluidine) is lower than that of poly(o-toluidine) with a shift of 190°C in the final decomposition temperature.     

萘酰亚胺树枝状聚（胺-酯）荧光材料的合成及性能

以乙二胺(EDA)、三羟甲基丙烷三丙烯酸酯(TMPTA)和1,8-萘二甲酸酐为原料,合成了萘酰亚胺树枝状聚(胺-酯)(PAE-1,8-NL),产率为32.79%。用IR和1HNMR表征了它的结构。通过紫外-可见吸收光谱、荧光光谱等手段对PAE-1,8-NL及加入稀土金属离子(La3+、Nd3+、Dy3+、Gd3+、Eu3+)或质子的各种溶液的光物理性能进行研究。结果表明,PAE-1,8-NL在氯仿-乙醇(体积比1∶1)稀溶液中在激发波长为335 nm激发下产生两处荧光峰370 nm和386 nm,分别归属为萘单体荧光峰和分子内萘基-萘基激基缔合物荧光峰;稀土金属离子或质子与PAE-1,8-NL内部的胺络合后,对萘单体荧光峰影响不大,而对激基缔合物荧光强度产生规律性的变化。PAE-1,8-NL溶液的荧光强度随稀土金属离子浓度的增大先增强后减弱;随H+浓度的增大而增强;随稀土金属离子和H+浓度的增大先增强后减弱。     

Dissolution rates for thin films of miscible polymer blends

The dissolution rates of thin polymer films were measured and compared. Mixtures of various ratios of poly(methyl methacrylate), PMMA, and poly(p-hydroxystyrene), PPHS, were dissolved in methyl isobutyl ketone, MIBK. The polymer solutions were then spun into thin films on silicon wafers and dried. The coated wafers were immersed in an MIBK bath and the rate of dissolution was observed using laser interferometry. The results show that pure PPHS films have dissolution rates 1000 times greater than films of pure PMMA at comparable molecular weights. However, for films containing both PPHS and PMMA, a minimum dissolution rate occurs for a mixture with about 20% (by weight) PPHS. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2015–2020, 1997     

Poly(O‐methoxyaniline) thin films: Cyclic voltammetry study

Electrochemical polymerization of poly(O‐methoxyaniline) (POMA) thin films was carried out under cyclic voltammetric conditions. The cyclic voltammograms (CV) of the POMA films in the presence and absence of monomer in the aqueous solution of 1M H₂SO₄ were studied. The electrochemical degradation of the POMA films was investigated by cyclic voltammetry and UV‐visible spectroscopy. It was observed that the rate of degradation is strongly dependent on the applied potential. UV‐visible spectroscopy revealed no significant chemical modification or phase change from the degradation. The temperature dependence of the voltammetric response of the POMA films in the aqueous solution of 1M H₂SO₄ was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3009–3015, 1999     

树枝状聚（胺-酯）的功能化及其荧光性能研究

以乙二胺(EDA)、三羟甲基丙烷三丙烯酸酯(TMPTA)和苯甲醛(BZA)为原料,合成了聚(胺-酯)-苯甲醛树枝状大分子(PAE-BZA),产率为60.82%,色谱纯度为65.27%。用IR、1HNMR和13CNMR表征了它的结构;并测定了PAE-BZA的荧光性能;考察了不同浓度PAE-BZA、不同溶剂及n(Sn2+)/n(PAE-BZA)对其荧光性能的影响。结果表明,丙酮为溶剂时,0.5 mmol/L PAE-BZA荧光强度最强;以丙酮、甲醇、DMSO、DMF和乙醇等为溶剂,PAE-BZA在乙醇中的荧光强度最强。随着n(Sn2+)/n(PAE-BZA)增加,PAE-BZA的荧光强度先减弱后增强,且Sn2+与PAE-BZA络合顺序是由外围的N原子逐步向内部的N原子络合。     

Atmospheric flame vapor deposition of WO3 thin films for hydrogen detection with enhanced sensing characteristics

Nowadays, with the increasing demand for hydrogen, sensors that can detect low concentrations of this gas are essential for its safe use. In this paper, Pd/WO₃ film hydrogen sensors are developed using a solid-feed flame vapor deposition (SF-FVD), as an atmospheric, economical, and fast film fabrication method. The crystal structure and morphology of the samples were characterized by different means. The performance of the obtained sensors was investigated for different hydrogen concentrations (1–2500 ppm) and at different operating temperatures (100–250 °C). We attempted to determine the optimum deposition conditions, including feed and substrate to flame nozzle distances. In most of the sensing conditions, the response and recovery times were measured in the order of 20 to 30 s. The layer with a more open morphology showed sensitivity at ppb hydrogen level, good stability, and selectivity. The response behavior of the samples was explained according to the power-law in the metal oxide semiconductor (MOS) gas sensors.     

Electrochemical polymerization of poly(o-anisidine) thin films: effect of synthesis temperature studied by cyclic voltammetry

The effect of temperature on the electrochemical synthesis of poly(o-anisidine) (POA) thin films has been investigated. The POA films were synthesized electrochemically under cyclic voltammetric conditions in aqueous solutions of H₂SO₄ at various temperatures between -6°C and 40°C. These films were characterized by cyclic voltammetry (CV), UV–visible spectroscopy and scanning electron microscopy (SEM). It has been found that the rate of polymer formation depends on the synthesis temperature and is highest at 15°C. The optical absorption spectra indicate a major peak at about 800nm and a shoulder at about 440nm independent of the synthesis temperature. The peak at about 800nm corresponds to the presence of the emeraldine salt phase of POA, while the latter may be attributed to the formation of radical cations. The absorbance and width of the peak at about 800nm is observed to increase at low synthesis temperatures. The POA film synthesized at 15°C shows predominant formation of the emeraldine salt phase of POA. The surface morphology as revealed by SEM, is observed to depend on the synthesis temperature, and is caused by different rates of polymer formation at different temperatures. © 1998 SCI.     

Effect of hydrogen bonding on the crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/silica hybrid composites

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-HHx)/hydrophobically modified silica hybrid composites were prepared using simple melt compounding and the effect of hydrogen bonding on their crystallization behavior was observed. The intermolecular hydrogen bonding between PHB-HHx and silica increased gradually with the increase of silica content of the hybrid composites. However, the extent of intermolecular hydrogen bonding was not directly proportional to the silica content. Although, the crystallization rates of the PHB-HHx/silica hybrids decreased as the strength of intermolecular hydrogen bonding increased, the constant value of the Avrami exponent indicates that the presence of silica does not alter the nucleation mechanism or the geometry of the crystal growth of the PHB-HHx hybrids. The calculated crystallization activation energy increased with the addition of silica, suggesting that silica retards the overall crystallization rate of the PHB-HHx hybrid composites as a result of the existence of intermolecular hydrogen bonding. The relationship between the extent of intermolecular hydrogen bond and crystallization rate is described by the empirical second-order equation.     

萘酰亚胺树枝状聚（胺-酯）对染料的荧光增强作用研究

以乙二胺（EDA）、三羟甲基丙烷三丙烯酸酯（TMPTA）和l,8-萘二甲酸酐为原料,合成了萘酰亚胺树枝状聚（胺-酯） [PAE-1,8-NL]。研究PAE-1,8-NL与染料（曙红B、罗丹明B、达旦黄、亚甲基蓝和甲基橙）组成的能量转移体系中,染料荧光强度的变化。实验结果表明,PAE-1,8-NL作用于染料的DMF溶液,荧光强度增强;且随着PAE-1,8-NL浓度的增大,荧光强度先增强后减小。增强作用大小为：亚甲基蓝 > 罗丹明B > 甲基橙 > 曙红B > 达旦黄。在DMF、丙酮和乙腈溶剂中,PAE-1,8-NL对染料的荧光强度增强作用不同。     

Elastic behavior of flexible polyether(urethane-urea) foam materials

Polyether(urethane-urea) foams (PEUU) with varying urea contents and different polyether segments (PPO and PPO-co-PEO (93/7 w/w)) were compacted to transparent solid plaques via compression molding. The thermal, mechanical and elastic properties of the compacted PEUU materials were studied. With increasing urea content, the shear modulus was increased, while the glass transition temperature (T_g) remained low and unaffected. The T_g's of PEEU's with PPO segments were, however, lower than with PPO-co-PEO segments, indicating more mixing of urea segments with PPO-co-PEO. The flow temperatures of both PEUU's were high (∼300 °C) for all compositions. The compression sets, tensile sets and hysteresis energy of the PEUU's were low and increased with urea content. The use of PPO-co-PEO segments resulted in PEEU's with higher compression sets and tensile sets and also more hysteresis. The recovery of the PEUU's showed two relaxation regimes: a fast (elastic) recovery and a slower (viscoelastic) recovery. The recovery of these PEUU's is almost complete giving time.     

Orientation microstructure and properties of poly(propylene carbonate)/poly(butylene succinate) blend films

The blends of high molecular weight poly(propylene carbonate) (PPC) and poly(butylene succinate) (PBS) were melt blended using triphenylmethane triisocyanate (TTI) as a reactive coupling agent. TTI also serves as a compatibilizer for the blends of PPC and PBS. The blend containing 0.36 wt % TTI showed that the optimal mechanical properties were, therefore, calendared into films with different degrees of orientation. The calendering condition, degree of orientation, morphologies, mechanical properties, crystallization, and thermal behaviors of the films were investigated using wide‐angle X‐ray diffraction, scanning electron microscopy, tensile testing, and differential scanning calorimetry (DSC) techniques. The result showed that the as‐made films exhibited obvious orientation in machine direction (MD). Both tensile strength in MD and the tear strength in transverse direction (TD) increased with increasing the degree of orientation. The orientation of the film also increased the crystallinity and improved the thermal properties of the PPC/PBS blend films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013