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聚氨酯弹性体(polyurethane elastomer,简称PUE)的大分子主链是由低聚物多元醇柔性链段构成软段,二异氰酸酯及扩链剂构成硬段,硬段和软段交替排列,并形成重复的氨基甲酸酯基团结构单元的嵌段聚合物。聚氨酯弹性体具有较高的强度和弹性、优异的耐磨性、耐疲劳性及减振性能等。要制备具有优异防振缓冲性能的聚氨酯弹性体,则要求高分子链的硬段中具有柔性结构,在软段中又嵌有刚性链段。 相似文献
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采用一步法、以不同分子量的聚醚、二异氰酸酯、扩链剂为原料,通过调整原材料的比例来控制弹性体的硬段含量,得到不同硬段含量的综合性能较好的聚氨酯热塑性弹性体。采用GPC法对所制备的部分热塑性弹性体进行表征,经过数据处理得到所制备的热塑性弹性体的数均分子量及分散指数在文献报道的范围内。所得的GPC谱图峰形基本对称,并且没有杂质峰出现,说明体系的反应比较完全。 相似文献
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聚氨酯/聚丙烯酸酯复合乳液的紫外光谱研究 总被引:1,自引:1,他引:0
以水性聚氨酯(PU)分散液为种子,采用无皂乳液聚合技术合成出了聚氨酯/聚丙烯酸酯(PUA)复合乳液。紫外光谱研究发现,PU乳液的,n-π迁紫外吸收峰的λmax随溶液浓度增加明显红移。对于PU分散液,随着亲水性扩链剂用量增加,紫外光谱吸光度值变小;随着NCO/OH摩尔比增大,吸光度增大。对于PUA复合乳液,亲水性扩链剂用量取7.5%时,吸光度值最小;而第二阶段聚合引发剂种类对紫外光谱影响不大。紫外光谱的吸光度值反映了乳液粒子平均粒径的大小;随着NCO/OH摩尔比增大,吸光度增大。对于PUA复合浮液,亲水性扩链剂用量取7.5%时,吸光度值最小;而第二阶段聚合引发剂种类对紫外光谱影响不大。紫外光谱的吸光度值反映了乳液粒子平均粒径的大小。 相似文献
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用13C及29Si核磁共振研究了苯乙烯(S)及二甲基硅氧烷(Si)嵌段共聚物中硅氧烷软段的固体及溶液谱的自旋-晶格弛豫时间T1。固态嵌段共聚物主链29Si及侧甲基13C的T1都与均聚物的T1相近,但在CdCl3溶液中各种嵌段共聚物的T1与均聚硅氧烷相差颇大。用偶极-偶极相互作用来解释高聚物的自旋-晶格弛豫。苯乙烯-二甲基硅氧烷嵌段共聚物具两相结构,所以嵌段共聚物中软段及硬段微区中链段的运动与在均聚物分子中链段的运动模式基本相同。而CdCl3对聚苯乙烯或聚硅氧烷都是良溶剂,软段硬段之间有相互影响。所以其链段运动与均聚物不同,从而导致链段运动的相关时间τc变短和T1的增长。 相似文献
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以聚醚二元醇、甲苯二异氰酸酯为原料,合成了聚醚型聚氨酯预聚体(PUP)。采用该预聚体、扩链剂1,4-丁二醇、交联剂三羟甲基丙烷对TDE-85/甲基四氢邻苯二甲酸酐(MeTHPA)环氧树脂体系进行改性,通过示差扫描量热法与红外光谱法分析,探讨了聚氨酯(PU)改性环氧树脂体系固化反应机理及固化反应动力学特征。固化反应机理研究表明,TDE-85与MeTHPA之间的固化反应形成环氧聚合物网络Ⅰ,1,4-丁二醇及三羟甲基丙烷同PUP进行了扩链、交联反应形成了PU聚合物Ⅱ。异氰酸酯基同环氧基反应,使得聚合物Ⅰ与聚合物Ⅱ形成了接枝化学键。固化反应动力学研究表明,PU的加入可明显降低环氧树脂固化反应的表观活化能,活化能由TDE-85/MeTHPA树脂体系时的83.14 kJ/mol降至PU改性后的67.91 kJ/mol。 相似文献
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以聚醚二元醇、甲苯二异氰酸酯为原料,合成了聚醚型聚氨酯预聚体(PUP)。采用该预聚体、扩链剂1,4-丁二醇、交联剂三羟甲基丙烷对TDE-85/甲基四氢邻苯二甲酸酐(MeTHPA)环氧树脂体系进行改性,通过示差扫描量热法与红外光谱法分析,探讨了聚氨酯(PU)改性环氧树脂体系固化反应机理及固化反应动力学特征。固化反应机理研究表明,TDE-85与MeTHPA之间的固化反应形成环氧聚合物网络Ⅰ,1,4-丁二醇及三羟甲基丙烷同PUP进行了扩链、交联反应形成了PU聚合物Ⅱ。异氰酸酯基同环氧基反应,使得聚合物Ⅰ与聚合物Ⅱ形成了接枝化学键。固化反应动力学研究表明,PU的加入可明显降低环氧树脂固化反应的表观活化能,活化能由TDE-85/MeTHPA树脂体系时的83.14 kJ/mol降至PU改性后的67.91 kJ/mol。 相似文献
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《物理学报》2017,(1)
高分子链在纳米管道内的静态和动态特性与许多生物技术和生命过程相关.采用Monte Carlo方法模拟研究了两嵌段高分子链(ANABNB)在周期管道内的扩散过程.管道由长度相等的α和β两部分周期排列而成,其中α部分与高分子链A嵌段间存在吸引相互作用,而其他情形均为纯排斥作用.模拟结果表明,高分子链的扩散过程显著依赖于A嵌段长度,且扩散系数随A嵌段长度呈周期变化.通过对链与管道间的吸引作用能图像分析发现,在扩散系数峰位置,A嵌段的投影长度为管道周期长度的整数倍,同时高分子链的扩散规律与均质链在均质管道内的扩散规律一致;在扩散系数谷附近,A嵌段的投影长度为管道周期长度的半整数倍,同时扩散过程存在一系列明显的受限阶段,高分子链在不同的受限位置间跳跃转移.研究结果有助于嵌段高分子链的序列分离和可控输运. 相似文献
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取样平均法提高CCD多道探测器信噪比 总被引:1,自引:0,他引:1
应用取样平均法有效地提高了CCD光学多道探测器信噪比,当采样次数为m时,信噪比提高m~(1/2)倍,应用于实验得到了高信噪比的各种光谱谱图。 相似文献
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基于多源卫星多光谱遥感数据的过火面积估算研究 总被引:3,自引:0,他引:3
露天生物质燃烧是重要的大气污染物排放源,导致空气质量恶化并引起气候变化。卫星遥感数据能够提供大尺度、多时相的监测信息,然而燃烧火点监测和火烧迹地监测两种方式都存在着局限性。以美国东南部地区为研究区域,通过结合卫星遥感获取的高分辨率燃烧面积数据及多时相的燃烧火点数据,建立时空匹配模型估算露天生物质燃烧过火面积。通过分析植被燃烧前后的光谱变化特征,基于高分辨率的Landsat-5 TM4波段(0.84 μm)与7波段(2.22 μm)数据, 利用差分归一化燃烧比(dNBR: the differential normalized burn ratio)提取燃烧面积数据;而燃烧火点数据则通过分析燃烧植被的热红外光谱特征利用MODIS 4与11 μm波段数据提取。结果显示,该地区燃烧面积与燃烧火点数量之间相关系数达0.63,并且二者之间的比例关系随植被类型而发生变化,林地、草地、灌木、耕地和沼泽五种植被类型对应的像元燃烧面积分别为0.69,1.27,0.86,0.72和0.94 km2。通过与美国火灾中心(national interagency fire center, NIFC)地面调查数据比对,模型估算的美国东南部过火面积数据较为精确,而同期的MODIS燃烧面积产品(MCD45)及燃烧源清单产品(global fire emissions database, GFED)遗漏了该区域大量的小面积燃烧事件。因此,本研究建立的过火面积估算模型能够提供更为精确的排放源参数信息,有利于区域空气质量模式准确地模拟露天生物质燃烧排放状况。 相似文献
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The isoscaling and the isobaric yield ratio difference (IBD) probes, both of which are constructed by yield ratio of fragment, provide cancelation of parameters. The information entropy theory is introduced to explain the physical meaning of the isoscaling and IBD probes. The similarity between the isoscaling and IBD results is found, i.e., the information uncertainty determined by the IBD method equals to β-α determined by the isoscaling (α (β) is the parameter fitted from the isotopic (isotonic) yield ratio). 相似文献
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Chih-Wei Chiang Subrata Kumar Das Huang-Shih Liao 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(2):197-203
We report the first inter-comparison of vertical profiles of aerosols and clouds derived from space (CALIPSO) and ground based lidar over Chung-Li, Taiwan. Results show that inter-comparison is closer in case of aerosols than clouds. The strength/shortcoming of the comparison has been also discussed. An iterative calculation to retrieve extinction-to-backscatter ratio (lidar ratio) by using sun-photometer and CALIPSO data is also documented. By using the mentioned method, a mean lidar ratio of 23.5±8.2 sr was found. The derived lidar ratios are lower than former studies. The possible reasons for the difference have been discussed in this paper. The discussed methodology will be helpful to reduce the uncertainty of optical parameters derived from lidar data especially near the surface where the atmosphere is inhomogeneous. 相似文献
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We investigate the impact of extinction ratio of single arm sin2 LiNbO3 Mach-Zehnder (MZ) amplitude modulator on the performance of 10 and 20 Gb/s single-channel optical communication system. For different fiber lengths, the system performance has been analyzed with the increase in the extinction ratio. The effect of variation in dispersion parameter has also been illustrated. The impact of extinction ratio (ζ), dispersion parameter and length of the fiber has been further optimized with minimum bit error rate (BER) at optimal decision threshold (10−9) for 10 and 20 Gb/s bit rate. It is found that the system gives optimum performance at extinction ratio (ζ) value 20 dB. The increase in the transmission distance from 468 km for 10 Gb/s to 532 km for 20 Gb/s has been reported, and 8 dB improvement in the Q value has been observed as the value of ζ is increased from 10 to 20 dB. At 20 Gb/s, the system gives optimum performance for dispersion parameter value only up to 4 ps/nm km; however, at 10 Gb/s the system can operate for dispersion values up to 14.3 ps/nm km. Further we investigate the self-phase modulation (SPM) effect for the increase in the input power. It is observed that the SPM effect is negligible below 3 dB m input power and it increases at higher power levels. 相似文献
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Donna S. Lundy Soham Roy Roy R. Casiano Jun W. Xue Joseph Evans 《Journal of voice》2000,14(4):490-493
The singing power ratio (SPR) is an objective means of quantifying the singer's formant. SPR has been shown to differentiate trained singers from nonsingers and sung from spoken tones. This study was designed to evaluate SPR and acoustic parameters in singing students to determine if the singer-intraining has an identifiable difference between sung and spoken voices. Digital audio recordings were made of both sung and spoken vowel sounds in 55 singing students for acoustic analysis. SPR values were not significantly different between the sung and spoken samples. Shimmer and noise-to-harmonic ratio were significantly higher in spoken samples. SPR analysis may provide an objective tool for monitoring the student's progress. 相似文献
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T. Matsuzaki K. Nagamine M. Tanase M. Kato K. Kurosawa K. Ishida S.N. Nakamura I. Watanabe G.H. Eaton 《Hyperfine Interactions》1999,119(1-4):361-363
For muon catalyzed fusion (μCF) experiments at RIKEN-RAL muon facility, a tritium gas handling system for a high purity D–T
target, free from 3 component, has been constructed to perform precise measurements of α-sticking probability in the μCF cycle. The system has
been constructed to enable us to purify the target D–T gas by removing 3He component, to adjust the D/T mixing ratio, and to measure the hydrogen isotope components at the experiment site. The whole
performance has been confirmed and a tritium gas with the inventory of 56 TBq (1500 Ci) has been operated in the system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Chih-Wei Chiang Subrata Kumar Das 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(7):1187-1195
The aerosol optical thickness (AOT) is an important parameter for understanding the radiative impact of aerosols. AOT based on lidar measurements is often limited by its finite detection range. In this paper, we have reported a method of fitting and iterative calculation to derive the extinction profile of background aerosols from 0 to 30 km at 532 nm, which is virtually the AOT of the entire atmosphere. The mean extinction derived from this method at the ground level tallies with visibility measurement and it is also consistent with the sun-photometer data, within experimental error. These data have been further treated to study the dust cases. For most of the cases, transmission losses were determined to estimate the extinction as well as lidar ratio. The result of the analysis shows that for background aerosols, a mean lidar ratio of 47±15 sr was found. For dust layers, a mean lidar ratio of 44±19 sr and an optical thickness of 0.53±0.49 were determined at 532 nm. 相似文献