2022年2022年化学专业英语文献 .pdf
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1、Aliphatic acid estersof (2-hydroxypropyl) cellulosed Effect of sidechain length on properties of cholesteric liquid crystalsBin Huanga, JasonJ. Geb,1, Yonghong Lia, Haoqing Houa,*aCollege of Chemistry and Chemical Engineering, Jiangxi Normal University, 99 Ziyang Street, Nanchang, Jiangxi 330022, Ch
2、inabMaurice Morton Institute and Department of Polymer Science, University of Akron, Akron, OH 44325-3909, USAReceived 13 August 2006; received in revised form 12 November 2006; accepted 15 November 2006Availableonline 4 December 2006AbstractA series of aliphatic acid estersof (2-hydroxypropyl)cellu
3、lose (CnPC) were synthesized via the esteri?cation of aliphatic acid chloride and(2-hydroxypropyl) cellulose (HPC). The liquid crystalline (LC) phasesand transitions were investigated using differential scanning calorimetry,wide-angle X-ray diffraction (WAXD), andpolarized light microscope (PLM) tec
4、hniques. This seriesof CnPC polymers exhibited characteristicfeaturesof cholesteric LC phasesbetween their glasstransition and isotropization temperatures.The cholesteric LC characteristics were studiedutilizingan ultraviolet/visible/nearinfrared spectrometer in a re?ection mode. It was con?rmed tha
5、t, with an increase in the number ofmethylene units in the side chains of this seriesof CnPC polymers, there wasan increase,on the scale of nanometers,in the layer spacingvaluesfor the cholesteric LC phasesmeasured by WAXD. This periodic layer spacing representsthe thickness of the neighboring twist
6、ed layers ina helical structure. Basedon a unique signi?cant red shift of the maximum re?ection peakfor the LC phasesin this seriesof CnPCs, it is evidentthat the pitch distance in the helical structure also increaseswith an increasein the length of methylene units in the side chains. 2006 Elsevier
7、Ltd. All rights reserved.Keywords: Cholesteric liquidcrystal; Cellulose derivative; Side chain1. IntroductionCholesteric liquidcrystals (ChLCs) are of great scienti?cand technological interest due to their unique selective re?ec-tion of light at characteristic wavelengths with a speci?c pitchdistanc
8、e. Importantapplications of ChLCs have been identi-?ed, including rigid or ?exible re?ective liquid crystal displaysand re?ective polarization ?lms for usein ?at panel displays toimprovebrightness1e 4.Theselectivere?ection(l ?nPocosq) is caused by the molecularhelical structure witha pitch distance
9、(Po) in cholesteric liquid crystalline(ChLC)phaseswhere the average refractive index (n) is equal to (nk2t2nt2)/30.5and the incident angle is q 1 . Interestingly, mostof the cellulosederivatives formcholesteric LC phases insolutions withincertain concentration regions (lyotropic)orin the bulk within
10、 certain temperature regions (thermotropic)5e 18. Generallyspeaking, it is understood that physicalpacking (chiral arrangement) schemes of stiff cellulose chainscould be considered playing important roles in inducing theformationof cholesteric LC phases. In particular, when the?exibleside chains are
11、 connected onto the cellulose back-bones, the resulting hairy-rod cellulose polymers start formingthese cholesteric LC phases.It is believed that the attachmentof ?exible side chains onto the rigid cellulose molecules canfacilitatethe orientationalorder of the semi-rigidhairy-rodbackbones with side
12、chains with increasing the chain mobilityand enhancing the solubility. Among the cellulose derivatives,(2-hydroxypropyl)cellulose (HPC) derivatives are of speci?cinterest because they can form either cholesteric lyotropic orthermotropicLC phases 18e 24. A particularlyinterestingproperty of the cellu
13、lose derivatives is that, based on differentchemical structures, the materials can re?ect light at a speci?clightwavelength and in a speci?c temperature region. For* Correspondingauthor. Tel.: t 86 791 8120389; fax: t 86 791 8120536.E-mail address: (H. Hou).1Present address: AltuglasInternational,Ar
14、kema, 900 1st Avenue, King ofPrussia, PA 19403, USA.0032-3861/$ - see front matter 2006 Elsevier Ltd. Allrights reserved.doi:10.1016/j.polymer.2006.11.033Polymer 48 (2007) 264e - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 1 页,共 6 页 - - - - - - - - - example, (2-ethoxyprop
15、yl)cellulose (EPC) 15 re?ects visi-ble lightat 130e 160 C, while (2-acetoxy-propyl)cellulose(C2PC) 18, (2-propionyloxy)-propylcellulose (C3PC) 19and (2-butyrionyloxy)propylcellulose (C4PC) 24 displayiridescent color at ambient temperature due to the selectivere?ections of light from the cholesteric
16、LC phases.One of the most importantapproaches towards obtainingcellulose derivatives exhibitingcholesteric LC phase transi-tions is via the esteri?cation of HPC 19,24 . These cellulosederivatives can possess different side chain lengths based ondifferent numbers of methylene units. The motivationof
17、thiswork is to design a series of HPC derivatives (CnPC, n ? 5,6, 7 and 10) to further improve the systematic understandingof the side chain effect on the formation of thermotropic cho-lesteric LC phasesand phase transitions aswell astheir uniqueselectivityfor color re?ections and the pitch distance
18、 in thecholesteric LC phases.2. Experimentalpart2.1. Materials2-Hydroxylpropylcellulose (HPC) (Aldrich,weight aver-age molecularweight,Mw? 100,000 g/mol)was driedat50C(30 mbar)priortouse.Aliphaticacidchloride(CH3(CH2)n2COCl, n? 2, 3, 4, 5, 6, 7, 10, purchased fromAldrich)was used as received. Aceton
19、e (Aldrich)was driedover CaCl2for 2 days and was distilledin an N2atmospherebefore use.The synthetic procedure of CnPC is described here usingC5PCas anexample.HPCof5.0 g(correspondingto41.71 mmol of hydroxyl groups) was added to 30 mL acetoneunder a dry nitrogen atmosphere and was dissolved by heati
20、ngthesolution.Then15.1 mL(125.13 mmol)valericacidchloride was swiftlyadded to the solution of HPC by usinga syringe. After 2 h of re?ux, the reaction mixture was pouredinto 200 mL distilledwater. After removing the liquid phase,a cream-colored, sticky material was obtained and then dis-solved in 80
21、mL acetone and precipitated by adding 5 mL ofwater to the solution. The pasty product was liberated fromthe acetone/water by decantation. The second solution precip-itation was repeated for 5 times. Finally, the product was driedat 60C (30 mbar, 48 h). The amount of 6.57 g of the ?nalpolymer materia
22、l was obtained with a yield of 76.8%.Gel permeation chromatographic (GPC) results showed thatMw? 6.83? 104. The degreeof substitution (DS) 23 was de-termined as 2.67 by1H nuclear magnetic resonance(NMR) andas 2.79 by saponi?cation. Infrared (IR) spectroscopic resultsshowed absorption at 3300e 3600 c
23、m1for e OH stretching,2850e 3000 cm1for the CeH stretching, and 1731.2 cm1for the CO stretching. The results obtained in1H NMR (inCDCl3) analysisare2.8e 4.5ppm for the protons of the anhydro-glucose ring; 4.95 ppm for -OCH2CH(CH3)OCH2CH(CH3)-(OOC(CH2)3CH3); 3.48 ppm for -OCH2CH(CH3)OC H2CH-(CH3)(OOC
24、(CH2)3CH3);1.08ppmfor-OCH2CH(CH3)-OCH2CH(CH3)(OOC(CH2)3CH3); 2.23 ppm for -OCH2CH-(CH3)OCH2CH(CH3)(OOCCH2CH2CH2CH3);1.63 ppmfor-OCH2CH(CH3)OCH2CH(CH3)(OOCCH2CH2CH2CH3);1.29 ppm for -OCH2CH(CH3)OCH2CH(CH3)(OOCCH2CH2-CH2CH3); 0.92 ppm for -OCH2CH(CH3)OCH2CH(CH3)-(OOCCH2CH2CH2CH3);1.17 ppm for-OCH2CH(C
25、H3)-OCH2CH(C H3)(OOCCH2CH2CH2CH3) ( stands forthestructure of cellulosic chain).The rest of the CnPC polymers with different lengths in theside chains were synthesized using the same procedure asdescribed for C5PC,similar to Refs. 18,24 . Molecular weightvalues and yields are given in Table 1.2.2. E
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