湘大高分子专业英语Charpter-3-2

Charpter3-23.2.PolymerStructure3.2.1IntroductionThesizeandshapeofpolymersareintimatelyconnectedtotheirproperties.Theshapeofpolymersisalsointimatelyconnectedtothesizeofthevariousunitsthatmakeupthemacromoleculesandthevariousprimaryandsecondarybondingforcesthatarepresentwithinthechainandbetweenchains.Thischaptercoversthebasiccomponentsthatinfluencepolymershapeormorphology.Wegenerallydescribethestructureofbothsyntheticandnaturalpolymersintermsoffourlevelsofstructure.Theprimarystructuredescribestheprecisesequenceoftheindividualatomsthatcomposethepolymerchain.Forpolymerswherethereisonlyanaveragestructure,suchasproteins,polysaccharides,andnucleicacids,arepresentativechainstructureisoftengiven.Thestructurecanbegivenasasinglerepeatunitsuchthatthefullpolymerstructurecanbeobtainedbysimplyrepeatingtherepeatunit100,500,or1,000times,dependingontheprecisenumberofrepeatunitsinthepolymerchain.Forpoly(vinylchloride),PVC,thisis3.2.聚合物结构3.2.1介绍聚合物的尺寸和形状紧密地连接到它们的属性。聚合物的形状也是紧密相连的各单位组成的大分子和各种原发性和继发结合力是内链与链之间目前的大小。本章介绍了影响聚合物的形状或形态的基本组成部分。我们一般描述的四个层次结构方面包括合成和天然聚合物的结构。一级结构描述构成聚合物链中的单个原子的精确序列。用于聚合物如只有一个平均结构，如蛋白质，多糖和核酸，有代表性的链结构是经常考虑。该结构可作为一个单一的重复结构单元，使得全聚合物结构可以通过简单地重复，重复单元100，500，或1000倍，这取决于重复单元在聚合物链中的确切数目来获得。用于聚（氯乙烯），PVC，这是OrsomefullerdescriptionoftheprimarystructuremaybegivensuchasthatbelowforthreerepeatunitsofPVCwheretheparticulargeometryabouteachchiralcarbonisgiven.Theendsmayormaynotbegivendependingonwhethertheyareimportanttotheparticularpointbeingmade.Thus,forthesinglePVCrepeatunitgivenabovetheendgroupsmaygivenasfollows:或一级结构的一些更详细的描述可被用于PVC的3个重复单元，其中对于每个手性碳上的特定几何形状给定的给定如下面。的端部可以或不可以根据它们是否是重要的而作出的特定的点给出。因此，对于上面的端基中给出的单PVC重复单元可以给出如下：Thesecondarystructuredescribesthemolecularshapeorconformationofthepolymerchain.Formostlinearpolymersthisshapeapproachesahelicalor“pleatedskirt”(orsheet)arrangementdependingonthenatureofthepolymer,treatment,andfunction.ExamplesofsecondarystructuresappearinFiga.Thetertiarystructuredescribestheshapingorfoldingofthepolymer.ExamplesofthisarefoundinFigb.Finally,thequaternarystructurerepresentstheoverallshapeofgroupsofthetertiarystructureswherethetertiarystructuresmaybesimilarordifferent.ExamplesarefoundinFigc.(a)(b)(c)二级结构描述了分子形状的聚合物链的或构象。对大多数线性聚合物此形状接近螺旋形或“百褶裙”（或片）安排取决于聚合物，治疗和函数的性质。二级结构的例子出现在图一。三级结构描述了聚合物的成形或折叠。这方面的例子可见于图b。最后，四级结构表示的基团的整体形状三级结构，其中三级结构可为相同或不同。实例见于图C中。(a)(b)(c)Wecangetanideaoftheinfluenceofsizeinlookingattheseriesofmethylenehydrocarbonsasthenumberofcarbonatomsincreases.Forlownumbersofcarbons,methane,ethane,propane,butane,thematerialsaregasesatroomtemperature.Forthenextgroupings(Table)thematerialsareliquids.Theindividualhydrocarbonchainsareheldtogetherbydispersionforcesthatareasumoftheindividualmethyleneandendgroupforces.3.2.2StereochemistryofpolymersTableTypicalPropertiesofStraightChainHydrocarbons我们可以得到尺寸在着眼于系列亚甲基烃的碳原子数的增加的影响的想法。低数值碳，甲烷，乙烷，丙烷，丁烷，这些材料在室温下是气体。在接下来的分组（表）的材料是液体。个人烃链是由分散的力量是个别亚甲基和端基的力量的总和在一起。3.2.2聚合物的立体化学表的直链烃的典型性质Thereisagradualincreaseinboilingpointandtotaldispersionforcesfortheindividualchainsuntilthematerialsbecomewaxysolidssuchasfoundinbees’waxesandfinallywherethetotaldispersionforcesaresufficienttobegreaterthanindividualcarbon–carbonbondstrengths,sothatthechainsdecomposepriortotheirevaporation.Finally,thechainlengthsaresufficienttogivethetoughandbrittlesolidswecallpolyethylene.Itisinterestingtonotethattheselongchainstraightchainhydrocarbonsbecomeverystrongbutbrittle.Theyarecrystalline—andaswithmostothercrystallinematerials,suchasrocksanddiamonds,theyarestrongbutbrittle.Fortunately,syntheticpolyethylenecontainsbothcrystallineregionswherethepolymerchainsarearrangedinorderedlinesandregionswherethechainsarenotarrangedinorderedlines.Theselatterarrangementsareimposedonthepolyethylenebecauseofthepresenceofbranchinginthelinearpolymerbackbone.Theyarereferredtoasamorphousregionsandareresponsibleforallowingthepolyethylenetohavesomeflexibility.Thus,manypolymerscontainbothamorphousandcrystallineregionsthatprovidebothflexibilityandstrength.有和逐渐增加沸点总色散力为各个链，直到材料成为蜜蜂蜡，最后当总色散力足够大于单个碳-碳键的长处发现蜡状固体，例如，使该链之前，他们的蒸发分解。最后，链长足以使韧而脆的固体我们称之为聚乙烯。有趣的是要注意，这些长链直链烃变得非常强，但脆。它们是结晶的，并与大多数其他的晶体材料，如岩石和钻石，它们是强的，但是脆性的。幸运的是，合成的聚乙烯含有其中聚合物链被布置成有序的行和区域，进行链不是布置在有序线都结晶区域。因为支化的线性聚合物主链的存在而后者的安排施加在聚乙烯。它们被称作无定形区域，并负责使聚乙烯具有一定的灵活性。因此，许多聚合物包含同时提供灵活性和强度二者的无定形和结晶区。Thepolyethylenechainsdescribedintheprevioustableexhibitirreversibleand,whenappropriatecrosslinkingispresent,reversiblememory.Asasidenote,low-molecular-weightpolyethylenewithappreciablesidebranchinghasameltingrangegenerallybelow100oC,whereashigh-molecular-weightpolyethylenewithfewbrancheshasameltingrangeapproachingthetheoreticalvalueofabout145oC.High-densitypolyethylene(HDPE),formerlycalledlow-pressurepolyethylene[H(CH2CH2)nH],likeotheralkanes[H(CH2)nH],maybeusedtoillustratealotofpolymerstructure.Asinintroductoryorganicchemistry,wecancomprehendalmostallofthecomplexorganiccompoundsifweunderstandthebasicchemistryandgeometry.High-densitypolyethylene,likedecane[H(CH2)10H]orparaffin[H(CH2)~50H],isalargelylinearchain-likemoleculeconsistingofcatenatedcarbonatomsbondedcoval