聚酯类生物基聚合物的扩链改性

以丙二醇、丁二醇、癸二酸、丁二酸及衣康酸为原料合成了端羟基与端羧基并存的聚酯类生物基预聚物,以亚磷酸三苯酯(TPP)为扩链剂,研究了扩链温度、TPP添加量及数均分子量不同的预聚物等对扩链反应的影响。结果表明,在扩链温度为180℃、预聚体数均分子量为1.0×104左右的条件下,加入质量分数为15%的TPP,经扩链反应后,产物的数均分子量可达到4.8×104。红外光谱分析证实了扩链反应的发生;差示扫描量热分析结果显示扩链后产物的玻璃化转变温度有所上升,熔点有所下降;热重分析表明扩链后产物的热稳定性有所提高。     

Completely amorphous high thermal resistant copolyesters from bio-based 2,5-furandicarboxylic acid

Polyesters from renewable resources with glass transition temperature (T_g) higher than 100°C are crucial in broadening their application range. In this work, a series of high molecular weight copolyesters, poly(butylene bis[4-(2-hydroxyethoxy) phenyl] sulfone 2,5-furandicarboxylate) (PBSF), was synthesized from bis[4-(2-hydroxyethoxy) phenyl] sulfone (BHEPS), bio-based 1,4-butanediol (BDO), and 2,5-furandicarboxylic acid (FDCA) via transesterification. Nuclear magnetic resonance spectroscopy (¹H-NMR and ¹³C-NMR) was used to confirm their chemical structures, composition, and sequence distribution. Characterizations demonstrated that with the increasing content of BHEPS unit, T_g of synthesized polyesters was increased from 38.2°C for PBF to 122°C for PBSF-95, in which the content of BHEPS unit was 95%. However, the weight average molecular weight (M_w) of PBSF was dramatically decreased after the addition of BHEPS, from 95,300 g/mol for PBF to only 9600 g/mol for PBSF-95, which was too low for practical application. Taking molecular weight, T_g, and mechanical properties into account, PBSF-65 was considered to be a promising polyester with M_w of 28,500 g/mol, T_g of 104.7°C, tensile strength of 82 MPa, and elongation-at-break of 98%. Besides, it was a completely amorphous polyester with a transmittance of 89.9% by cutoff at 700 nm. Summarily, PBSF-65 showed great potential to be used as raw material for the manufacture of baby bottles, children's toys, kitchen appliances, and beverage packaging, especially in the case when high transparency and heat resistance are required.     

Interaction-structure-property relationships in amorphous polymer blends

Summary Miscibility, structure and property relationships were studied by different techniques for various polymer pairs. Four blends of polystyrene (PS), styrene-acrylonitrile copolymer (SAN), polycarbonate (PC) and polyphenylene oxide (PPO) [PS/PPO, PS/PC, PS/SAN and PPO/SAN] were investigated in the entire composition range. Glass transition temperatures were measured by DSC, mechanical properties were characterized by tensile test, methanol absorption was determined at 50 °C. The Flory-Huggins interaction parameter (χ) was derived from Hildebrand solubility parameters, and compared to χ-related quantities calculated from the experimental results. Good correlation was obtained between parameters derived from different methods used for the characterization of polymer/polymer interaction. Received: 5 August 1999/Revised version: 20 March 2000/Accepted: 27 March 2000     

The retarding effects and structural evolution of a bio-based high-performance polyimide during thermal imidization

The thermal imidization evolution of a bio-based high-performance polyimide, namely adenine-containing polyimide (API), was investigated by thermogravimetric analysis (TGA), in situ Fourier transform infrared spectroscopy (in situ FTIR), and wide-angle X-ray diffraction (WAXD), in contrast to an adenine-free 4,4′-oxydiphthalic anhydride (ODPA)/4,4′-oxydianiline (ODA) PI. The influence derived from adenine was focused. At precursor stage of API (polyamic acid, PAA), the H-bonding interaction of PAA–PAA type as well as the especial interaction between the secondary amine of adenine and solvent (dimethylacetamide, DMAc) was discovered. Structural evolution of API was traced by in situ FTIR and multistage WAXD from PAA stage to PI stage. Compared with OPI, the retarding effects were found in the process of thermal imidization of API, partly due to the formation of H-bonding derived from the extra secondary amine of adenine moieties, which complicated the H-bonding form in API. Finally, a hypothesis of evolution of thermal imidization process about API molecule was proposed in contrast with adenine-free ODPA ODA PI. Compared with the consistency of both API and ODPA ODA PI in PAA stage, API possessed a more delicate thermal imidization process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46953.     

Electrospun porous carbon nanofibers derived from bio-based phenolic resins as free-standing electrodes for high-performance supercapacitors

Phenolic resins were employed to prepare electrospun porous carbon nanofibers with a high specific surface area as free-standing electrodes for high-performance supercapacitors. However, the sustainable development of conventional phenolic resin has been challenged by petroleum-based phenol and formaldehyde. Lignin with abundant phenolic hydroxyl groups is the main non-petroleum resource that can provide renewable aromatic compounds. Hence, lignin, phenol, and furfural were used to synthesize bio-based phenolic resins, and the activated carbon nanofibers were obtained by electrospinning and one-step carbonization activation. Fourier transform infrared and differential scanning calorimetry were used to characterize the structural and thermal properties. The results reveal that the apparent activation energy of the curing reaction is 89.21 kJ·mol^–1 and the reaction order is 0.78. The activated carbon nanofibers show a uniform diameter, specific surface area up to 1100 m²·g^–1, and total pore volume of 0.62 cm³·g^–1. The electrode demonstrates a specific capacitance of 238 F·g^–1 (0.1 A·g^–1) and good rate capability. The symmetric supercapacitor yields a high energy density of 26.39 W·h·kg^–1 at 100 W·kg^–1 and an excellent capacitance retention of 98% after 10000 cycles. These results confirm that the activated carbon nanofiber from bio-based phenolic resins can be applied as electrode material for high-performance supercapacitors.     

Dielectric properties of amorphous cellulose acetate-butyrate polymer films

The dielectric constant, loss tangent and AC conductivity of solution grown cellulose acetate-butyrate films of 5μm thickness were studied as a function of temperature (300-450 K) in the frequency range 10 Hz-10 MHz. The decrease in dielectric constant was observed with the increase in frequency as well as with temperature. A loss peak was observed in the dielectric loss spectra and was identified as the β-relaxation peak. The frequency-dependent conductivity was also studied. The results were interpreted in terms of electronic conduction via hopping processes.     

高性能环氧高分子材料的制备及应用

通过特殊的分子设计和配方设计,采用改性固化剂对环氧树脂进行改性,得到一种高性能环氧高分子材料。该材料具有优异的耐候性、耐水耐碱性、耐低温开裂、突出的防滑性,附着力等性能。UV老化测试15周,拉伸强度仅从14 MPa降低至13 MPa,断裂伸长率仅从40%降低至30%,明显强于国外同类型竞品(拉伸强度下降了10 MPa,断裂伸长率下降幅度更大,从42%降低至15%),性能稳定。耐水耐碱耐低温涂膜均无异常;附着力(划圈法)1级;抗滑值(BPN)达到70,属于高防滑型。该高性能环氧高分子材料对填料以及固化剂用量容纳度高,配方设计性强;在很宽的范围内均具有稳定的性能(拉伸强度稳定在14～15 MPa波动,断裂伸长率保持在36%～40%)。该高性能环氧高分子材料性能特点明显,作为全民健身场地地面材料,具有传统聚氨酯和丙烯酸材料不具备的特点,应用前景广阔。     

Relaxation of amorphous multichain polymer systems using inverse kinematics

Atomic scale simulations of polymer materials is a topic of interest since it permits to reduce costly experiments to determine their physicochemical properties. In this context, modeling heterogeneously ordered multichain systems such as amorphous polymers, remains a challenging problem. A recently proposed two-step method consists of iteratively generating the structures using a simplified energy model, and subsequently relaxing the system, considering a more accurate model, in order to reduce its potential energy. This work proposes an improvement of this method by integrating a novel relaxation technique, which applies analytical rebridging moves inspired by robotics. A comparative analysis using models of amorphous polyethylene with different sizes and densities shows that the rebridging scheme described here is very effective for the simulation of long alkanes.     

Modeling shape memory effect in uncrosslinked amorphous biodegradable polymer

Shape memory effect (SME) is critical for minimally invasive surgical procedures in medicine. In this paper, the shape memory behavior of amorphous biodegradable polymer, poly(d,l-lactide-co-glycolide), is experimentally investigated. Based on the experimental observations and the understanding of the underlying mechanism of SME, a one-dimensional constitutive model is derived to describe the shape memory behavior in the context of (1) the stress-strain behavior in deformation, (2) the isothermal recovery and (3) the recovery at constant heating rate, by using a set of model constants. By fine tuning the model constants, a good agreement between the experimental results and computer predictions was achievable.     

Thermal and mechanical properties of injection molded liquid crystalline polymer/amorphous polymer blends

Injection molded samples of binary blends of Vectra (LCP) and the three amorphous polymers polyethersulfone (PES), polycarbonate (PC), and aromatic poly(ester carbonate) (APEC) have been subjected to morphological and rheological characterization, and coefficients of linear thermal expansion and Young's moduli have been determined. The Young's modulus of the PES/LCP blends exhibited a near lower-bound behavior that could be predicted by the one-adjustable-parameter equations of Halpin-Tsai (ζ = 0.18) and Takayanaga (b = 0.23), whereas the coefficients of linear thermal expansion followed the Takayanaga equation with a value of b = 0.50. The chain orientation of the LCP component was essentially constant in all PES/LCP blends with a Herman's orientation parameter of 0.39 ± 0.03. Transesterification reactions led to randomization of the constituents of the PC/LCP and APEC/LCP blends. The effect was more pronounced in the PC/LCP blends. The introduction of the LCP into the PC/LCP blends led to no reduction in melt viscosity and no self-reinforcement. APEC/LCP exhibited self-reinforcement in blends with a content greater than 27 vol% LCP, and especially the blend with 67 vol% LCP. The self-reinforcement was caused by the presence of an oriented LCP phase, confirmed by X-ray diffraction, and by improved interfacial bonding, presumably resulting from the transesterification reactions occurring at the phase boundaries.     

Water‐based amorphous carbon nanotubes filled polymer nanocomposites

A novel method of making water‐based amorphous carbon nanotubes (ACNTs) for advanced polymer nanocomposites is presented. In this approach, sodium dodecyl sulfate (SDS) is introduced onto the amorphous carbon nanotubes to improve the solubility in water and the dispersion in polyvinyl alcohol [PVA] matrix. As a result, the addition of 0.6 wt % ACNTs in the polymer resulted in the significant improvement (167.5 and 175.8%) in the tensile strength and modulus of the polymer, respectively. The improved mechanical property could be ascribed to the load transfer to the nanotubes in the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

The amorphous contribution to the modulus of a semi-crystalline polymer

The amorphous contribution to the Young's modulus of a semi-crystalline polymer is calculated for two morphologies: the spherulite and the stacked lamellae structure. Four types of amorphous chains are considered: bridges (or tie molecules); cilia; loops; and floating, unattached chains. The statistics of a polymer chain between two, infinite, impenetrable, parallel walls are used in the modulus calculation. It is found that for each type of amorphous chain, the Young's modulus is greater in the stacked lamellae structure than in the spherulite. The Young's modulus of a cilium, loop and floating chain all increase with increasing chain contour length while the Young's modulus of a bridge passes through a minimum value. The behavior of the Young's modulus as a function of temperature is analogous. These results are discussed in terms of the relative importance of crystalline lamellar impenetrability and the inherent elastic nature of the amorphous chains, in the Young's modulus behavior.