Microstructure and rheological properties of thermo-responsive poly(N-isopropylacrylamide) microgels

The microstructure and rheological properties of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels cross-linked with methylenebis-acrylamide (BA) were examined by dynamic light scattering and rheological techniques. As the temperature was increased from 10 to 50 °C, the particles diameter decreased by approximately two times near the volume phase transition temperature, T_v of between 30 and 35 °C. The addition of salt to the microgel dispersion provides competition for the water molecules hydrating the PNIPAM chains thus weakening the PNIPAM-H₂O hydrogen bonds and the microgel progressively deswelled. The validity and limitation of the semi-empirical approach to model charged soft microgel particles developed previously were tested on this thermo-responsive system. A variable specific volume, k was introduced to convert the mass concentration to effective volume fraction. With increasing concentration, inter-particle repulsive force was enhanced, which overcame the osmotic force inside the soft particle, resulting in the expulsion of solvent from the swollen particles, and the particle shrank. The viscosity data for PNIPAM microgels at varying solution temperatures and ionic strength showed excellent agreement with the modified Krieger-Dougherty (K-D) model.     

Lateral flexible linking of polyurethane copolymer and the effect on shape recovery and tensile mechanical properties

Shape memory polyurethane (SMPU), flexibly crosslinked via a polyethyleneglycol (PEG) spacer attached to its side through an allophanate group, was tested for shape memory and compared with a linear SMPU. The new SMPU was composed of 4,4′‐methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG‐2000), and 1,4‐butanediol (BD), and included polyethyleneglycol (PEG‐200) as a spacer. A second MDI, linked to the carbamate group of the first MDI, served as the connecting point for the PEG‐200. Two types of SMPU, differing according to their soft segment (PTMG‐2000) and linker (PEG‐200) contents, were compared in mechanical and shape memory properties. In the best case, a 780% increase in maximum stress was attained without any sacrifice in strain for the new material compared with the linear polymer. In particular, the stress–strain curve showed that the PEG‐crosslinked SMPU had superior tensile mechanical properties. Its shape recovery was as high as 99%, which is the best value we have measured for an SMPU. After four cyclic tests, shape recovery remained greater than 95%. Shape retention of the best SMPU remained above 93% even after four cyclic tests. Here, results demonstrating the extraordinary shape memory properties of these types of SMPU, together with differential scanning calorimetry (DSC) and infrared spectroscopy data, are analyzed and discussed. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

压力温度双敏性聚氨酯中空纤维膜通透性研究

以聚氨基甲酸酯(PU)为基质相,添加成孔剂及二氧化硅粒子,采用熔融纺丝法制得了具有对压力、温度刺激双重敏感的PU中空纤维膜;研究了膜的水通量随压力、温度的变化,对膜表面形貌进行了表征;并考察了中空纤维膜的截留性能。结果表明:制得的PU中空纤维膜为均质膜;膜孔径分布较窄,87.17%的孔集中在0.15～0.20μm。随着压力、温度上升或下降,膜的水通量相应增大或减小,水通量与压力、温度变化有着明显的相关性。经一次过滤,无机粒子清除率达98.52%～99.78%。     

The effect of soft segment content and linker length on shape recovery and mechanical properties of laterally linked polyurethane copolymer

Lateral flexible linking of shape memory polyurethane (SMPU) by a polyethyleneglycol (PEG) linker through the allophanate linking method was studied, while adjusting the soft segment content and PEG length. The SMPU was composed of 4,4′‐methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG), 1,4‐butanediol (BD), and PEG‐200 as a linker. A second MDI was used to connect the carbamate group of the SMPU chain and PEG. The impact of soft segment content and PEG length on the mechanical properties and shape recovery of two series of SMPU were compared. In the best case, a 545% increase in maximum stress compared to a linear polymer was attained. The flexibly crosslinked SMPUs behave similarly to natural rubber in their stress–strain curve, but their tensile mechanical properties surpassed those of natural rubber. Shape recovery went up to 96%, which is among the best SMPUs tested so far, and shape recovery remained above 90% after four cyclic tests. The extraordinary shape memory results are analyzed and discussed together with DSC and IR data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Temperature effect on the permeation through poly(2-hydroxyethyl methacrylate) membrane

The temperature dependence of permeability through highly syndiotactic poly(2-hydroxyethyl methacrylate) [P(HEMA)] membrane is reported for highly polar organic solutes such as ureas, methyl substituted ureas and amides, and for NaCl and Na₂SO₄. The membranes used were equilibrated in distilled water at each temperature before measurements. From the linear correlationship between the excess heat capacities, ?C_p^o(excess) in aqueous solution at infinite dilution and the permeability parameter PM^1/3, it is found that the water structure perturbing capability of the polar organic solutes is a controlling factor in the permeation mechanism at relatively low temperature, where P(HEMA) membrane has higher water content and more structured water. In addition, it is found that the poor separation for urea of cellulose acetate membrane in the reverse osmosis practice is due to the higher water structure-breaking capability of urea.     

Polyurethane microcellular elastomers: 1. Effect of chemical composition on tensile strength and elongation at break of poly(ethylene-butylene adipate) based systems

The relationships between tensile strength and elongation at break and the chemical composition of a microcellular elastomer used in shoe sole technology have been calculated using multiple linear regression analysis. Using the statistical Student's test, the importance of the factors that influence the above characteristics have been established. It has been found that the moulded density has the major influence on the tensile strength while the elongation at break depends to a great extent on the hard-segment dispersion into the soft matrix, as indicated by the influence of the water contents and the quasi-prepolymer index (I_NCO). Hydroxyl number in the usual range of 52–61 mg PKOH/g has no influence on the above characteristics.     

Effect of hygroscopic materials on water vapor permeation and dehumidification performance of poly(vinyl alcohol) membranes

In this study, two hygroscopic materials, inorganic lithium chloride (LiCl) and organic triethylene glycol (TEG) were separately added to poly(vinyl alcohol) (PVA) to form blend membranes for air dehumidification. Water vapor permeation, dehumidification performance and long‐term durability of the membranes were studied systematically. Membrane hydrophilicity and water vapor sorbability increased significantly with higher the hygroscopic material contents. Water vapor permeance of the membranes increased with both added hygroscopic material and absorbed water. Water permeation energy varied from positive to negative with higher hygroscopic content. This observation is attributed to a lower diffusion energy and a relatively constant sorption energy when hygroscopic content increases. Comparatively, PVA/TEG has less corrosive problems and is more environmentally friendly than PVA/LiCl. A membrane with PVA/TEG is observed to be highly durable and is suitable for dehumidification applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44765.     

Blocking of soft segments with different chain lengths and its impact on the shape memory property of polyurethane copolymer

The arrangements, whether block or random type, of the soft segments of polyurethane block copolymers prepared with MDI and two kinds of poly(tetramethylene glycol) (PTMG; MW of 1000 or 2000) in various ratios were compared for possible effects on the physical properties of the copolymers. A long soft segment, PTMG‐2000, was superior in all mechanical properties (strain, stress, and modulus) because a long chain length could provide more motional freedom than a short one (PTMG‐1000) could and therefore was helpful in forming strong interchain attractions among hard segments. Inclusion of more PTMG‐2000 led to a lower T_g and a peak shift in infrared spectra. The arrangement of two soft segments in a block‐type copolymer, a key finding in this study, was controlled by separately synthesizing two prepolymers, each with a different chain length, and connecting two prepolymers in a second step. Random‐type copolymers prepared for purposes of comparison were allowed to react with two PTMGs in one step. Two types of copolymers were compared, and the reason for the differences in the shape memory property are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1435–1441, 2007     

The effect of graphene on the lower critical solution temperature of poly(N-isopropylacrylamide)

N-isopropylacrylamide is grafted on graphene by free radical polymerization to produce a series of graphene–poly(N-isopropylacrylamide) (PNIPAM) hybrid materials with different contents of graphene. The lower critical solution temperatures of the resulting materials have been investigated by ultraviolet–visible transmission spectroscopy. The result shows that the lower critical solution temperature of the resulting materials increases with the content of graphene increasing, and can be tuned to the human body temperature (37 °C) when the content of graphene is in the range of 10–30%, which is very important for application of the hybrid materials in biomedical field. The result is ascribed to the high surface area of graphene that could graft a large amount of PNIPAM molecules and the immobilization of one end of PNIPAM chain on the surface of graphene. To further understand the effect of graphene on the lower critical solution temperature of PNIPAM, atomic force microscopy has been used to trace the morphology change of the hybrid materials in solid state with the temperature increasing from 33 to 40 °C.     

Toughening of poly(propylene carbonate) using rubbery non-isocyanate polyurethane: Transition from brittle to marginally tough

To overcome the brittleness of poly(propylene carbonate) (PPC), rubbery non-isocyanate polyurethane (NIPU) with rich hydrogen bonding moiety was synthesized for toughening PPC. Debonding phenomenon of NIPU was observed during the impact process of PPC/NIPU blends, which was beneficial for toughening PPC. When the NIPU loading increased to 10 wt%, the unnotched impact strength increased 3 times compared with neat PPC. The NIPU dispersed uniformly and a transition from brittle to marginally tough occurred when L/d reached a critical value, 1.74, where L and d were center-to-center distance and the diameter of the particle, respectively. The debonding of NIPU accounted for the increase of toughness, and shear yielding of the matrix was limited around the microvoids. When the NIPU loading reached 13 wt%, NIPU flocculated in the matrix leading to decline in toughness. The equilibrium between self-associating hydrogen bonding and intermolecular one formed between PPC and NIPU affected their miscibility and thereby the morphology of the blends.     

The effect of preparation temperature on the swelling behavior of poly (N-isopropylacrylamide) gels

Summary The role of the preparation temperature of poly(N-isopropylacrylamide) (PNIPA) gels on their swelling behavior in water and in aqueous solutions of sodium dodecylbenzenesulfonate was investigated. PNIPA gels were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis) acrylamide in water at fixed monomer and crosslinker concentrations. The equilibrium swelling ratio of the gels increases first slightly up to about 20°C then rapidly with increasing gel preparation temperature. Magnitude of the collapse transition in water at 34°C becomes larger as the gel preparation temperature increases. Calculations indicate a decrease in the effective crosslink density of PNIPA gels with increasing preparation temperature. The gels prepared at temperatures higher then 20°C were heterogeneous consisting of highly crosslinked regions interconnected by the PNIPA chains. Received: 3 May 2000/Revised version: 3 July 2000/Accepted: 17 July 2000     

Temperature sensitive water vapour permeability and shape memory effect of polyurethane with crystalline reversible phase and hydrophilic segments

Polyurethanes based on poly(caprolactone) (PCL) diol, hexamethylene diisocyanate, 4,4′‐diphenylmethane diisocyanate and hexamethylene diamine were modified by hydrophilic segments, diol‐terminated poly(ethylene oxide) or dimethylol propionic acid (DMPA). Differential scanning calorimetry, dynamic mechanical tests, tensile tests, and measurement of water vapour permeability were carried out to characterize these polyurethanes. Temperature sensitive water vapour permeability, that is, the abrupt increase of water vapour permeability at the melting temperature of the PCL phase, was enhanced by modification with hydrophilic segments. Fatigue in shape memory effects was minimized by introducing some amount of DMPA units into the polyurethane chain. © 2000 Society of Chemical Industry     

Collagen immobilization on poly(ethylene terephthalate) and polyurethane films after UV functionalization

An attractive alternative method to add new functionalities such as biocompatibility due to the micro- and nanoscaled modification of surfaces is offered by UV-modified polymers. The aim of this study was to evaluate the effect of the UV light functionalization on two polymers, poly(ethylene terephthalate) (PET) and polyurethane (PU) films, by means of atomic force microscopy (AFM), Fourier transform infrared–attenuated total reflectance (FTIR–ATR), and contact angle measurements. Thus, the UV-irradiation activates the polymers surface by breaking some chemical bonds and generation of new functional groups on the surface. This process can be controlled by the irradiation time. The topography provides the formation of superposed ‘nap’ and ‘wall-type’ structures on both untreated and treated samples. The surface parameters were found to depend on the polymer films before and after irradiation. The immobilization of collagen on PET surface was confirmed by X-ray photoelectron spectroscopy measurements and for PU surface was proved by FTIR–ATR. First technique suggests an increase of the nitrogen content at longer UV exposure time, and the second one reveals the appearance of the protein Amide I band. Supplementary, AFM measurements clearly revealed the presence of collagen attached on the polymer surface. Thus, these new UV-irradiated polymers are promising materials in our further attempts to obtain new biofunctionalized surfaces.     

PBA型超支化水性聚氨酯的合成与表征

以2,4-甲苯二异氰酸酯（TDI）、聚己二酸丁二醇酯二醇（PBA）、二羟甲基丙酸（DMPA）和二乙醇胺（DEOA）为原料,采用（A2＋bB2）共聚合路线合成了具有超支化结构的水性聚氨酯（HBAPU）。采用红外光谱（FT—IR）和核磁共振（^13C NMR）对产物结构进行了表征,证实了产物具有超支化结构,其支化度为0．33。用PCS、TG、电子拉力机对产物性能进行了测试,结果表明,胶膜的耐水性优异,由于引入了超支化结构,当DMPA的用量为0．20mmol／g时,就能得到稳定的聚氨酯水分散液,且得到的HBAPU膜具有较好的热学性能和力学性能。     

Effects of the recycled poly(ethylene terephthalate) fibers on the rigid polyurethane foam

Recycled poly(ethylene terephthalate) (PET), subjected to the treatment with the flame retardant first, was used to reinforce the rigid polyurethane foams (RPUFs). Different loadings of PET fibers (3–12 wt %) of different lengths (5, 10, 15, and 20 mm) were added into RPUF. The mechanical properties of composites were studied by compressive strength test and shear stress test. The flame-retardant properties were evaluated by cone calorimeter and limited oxygen index test. The results showed that the proper addition of PET fibers could improve the mechanical and flame-retardant properties of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47758.     

Synthesis and properties of bio-based thermoplastic polyurethane based on poly (L-lactic acid) copolymer polydiol

The goal of this work is the synthesis of a new kind of bio-based thermoplastic polyurethane (BTPU) based on poly(L -lactic acid) (PLA) and poly(tetramethylene) glycol (PTMEG) segments via chain-extension reaction of dihydroxyl terminated (HO-PLA-PTMEG-PLA-OH) copolymer using hexamethylene diisocyanate (HDI) as a chain extender. Polydiols were synthesized through polycondensation of lactic acid and PTMEG in bulk. The chemical structures and molecular weights of polydiols and BTPUs containing different segment lengths and weight fractions of PLA, were characterized by ¹H-NMR and FTIR. The effects of the structures on the physical properties of BTPUs were studied by means of DSC, SEM, and tensile test; crystallization behavior was characterized by POM. The DSC and SEM results indicate that PLA segment is perfectly compatible with PTMEG segment and the crystallization of BTPU is predominantly caused by PLA segment. Polydiol with lower PLA content shows lower T_g and lower crystallinity. Tensile test shows that the elongation at break of BTPU is above 340% at the composition of PLA/PTMEG = 80/20 (w/w). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of annealing-induced phase separation on the shape memory effect of graphene-based thermoplastic polyurethane nanocomposites

Thermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long-chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase-separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene-based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene-based nanoparticles on the shape memory effect.     

羟基氯醋改性聚氨酯预聚体合成反应动力学研究

采用化学分析方法研究了羟基氯醋树脂微粉存在下的聚醚N-220、蓖麻油等聚醚多元醇混合物与甲苯二异氰酸酯（TDI-80）的预聚合反应动力学,获得了聚氨酯预聚体合成反应动力学参数及反应表观速率常数表达式k=0．049exp（-23．95／RT）,并通过反应初期的实验数据对反应级数进行了验证。结果表明,在该体系下的预聚体合成反应中,氨酯化反应的表观速率常数随反应温度的升高而增大,合成反应以氨酯化反应为主,总反应级数为1．74~1．88,为近二级反应。该合成反应机理具有一定的复杂性。实验结果对相关聚氨酯弹性体预聚物合成及改性反应具有一定的理论价值和指导意义。     

The influence of stretching on tensile strength and solubility of poly(vinyl alcohol) fibres

The strength of wet-spun poly(vinyl alcohol) ( ) fibres is given as function of bath-stretching, wet-stretching and hot-stretching. In the two equations derived for strength of wet-stretching and hot-stretching the complex influence of the bath-stretching and hot-stretching is demonstrated. The bath-stretching is connected with a pure orientation effect and the residence time in the coagulating bath which is a measure for the ‘freshness’ of the fibre. The hot-stretching can be separated in a pure orientation effect and a crystallization effect. Fibres of the , used in the experiments, were soluble in boiling water. After shrinkage of the fibres at temperatures near the temperature of hot-stretching, the dissolution temperature can be raised. Insoluble fibres were prepared after removing most of the bulky residual ester groups.     

Influence of crosslinking on the tensile strength and fractography of poly(methyl methacrylate)

Glassy crosslinked networks were prepared by copolymerization of methyl methacrylate with up to 4.7 mole-percent ethylene dimethacrylate. These networks were degraded by exposure to γ-rays and the solubilized fraction estimated by benzene extraction using the analysis of A. R. Schultz. The efficiency of the Crosslinking agent was found to be 0.5 and this value was used to calculate the molecular weight between crosslinks. The molecular weight of the primary molecules in the network, M, was estimatfrom the radiation dose using the known fact that one fracture requires an energy deposition of 59 ev. Crosslinking was found to have little influence on the tensile strength of networks of primary molecular weight > 10⁵. In contrast. crosslinking raised, the strength of polymers of M < 10⁵ to, a value approaching that of a high molecular weight linear polymer (ca. 70MN/m²). Crosslinking was found to have only a small influence on the gross morphology of fracture surfaces.