[专业课]化学专业基础英语I 12章高分子化学术语 文本

[专业课]化学专业基础英语I 12章高分子化学术语 文本 高分子化学术语 Polymer Chemical Terms 12.1Polymers Polymers，or macromolecules，are produced when large number of smaller molecules (monomers) are bonded together. A thermoplastic polymer (or "plastic") softens when heated and resolidifies when cooled. The majority of common synthetic polymers have molecular masses between 1 X 104 and 1 X 106 a and contain several hundred to several thousand monomers. The physical properties of a polymer are determined by such factors as the flexibility of the macromolecules，the sizes of the groups attached to the polymer chains，and the magnitude of intermolecular forces. Polymers may be linear or branched;if the branches of one polymer chain are covalently bonded to other chains，the polymer is said to be cross一linked. Thermoset polymers are crosslinked polymers that are permanently rigid;they do not melt when heated. A homopolymer is formed by poiymerization of a single type of monomer，a copolymer by the polymerization of two or more different monomers. Most polymers are either amorphous or semicrystalline. At low temperatures an amorphous polymer is rigid and brittle. At the glass transition temperature，Tg， the flexibility of the polymer increases markedly. Rigid plastics are used at tempeatures below Tg， flexible plastics at temperatures above T',. To participate in polymerization，a molecule must be able to react at both ends. The principal types of polymerization reactions are chain reaction polymerization and step reaction polymerization. 12. 2 Natural Polymers The unique properties of living things are in many ways the result of the properties of polymers. We now know that many of the molecules of biochemistry are macromolecules. Two natural polymers-cellulose and rubber-were the first polymers to be put into commercial use. Each had to be structurally modified to achieve useful properties. 1. Cellulose The repeating unit in natural cellulose is a ring structure with numerous hydroxyl groups which provide strong hydrogen bonding between the chains. Microcrystalline regions also help to hold the chains together. Natural cellulose is not thermoplastic. Before the hydrogen bonds are broken and the microcrystals melted-a requirement for plastic flow-the molecule undergoes thermal decomposition. By converting some of the hydroxy1 groups to functional groups that do not form hydrogen bonds，it is possible to alter the properties of the natural polymer. The nitrate ester of cellulose was prepared and used commercially in lacquers and films in the 1809'。，before the nature of polymers was understood(Due to its high flammability，the use of cellulose nitrate in such applications is now obsolete.)Cellulose acetate and other cellulose esters are still used in fibers. (Garments made of such fibers are labeled "acetate.”) 2. Natural rubber Polymers that have elasticity，like rubber，are referred to as elastomers. Such polymers are utilized above their glass transition temperatures. The polymer chains in an elastomer must be flexible and they mast be joined by a moderate number of crosslinks. Inthe unexiended state，the molecules of an elastomer are tangled together. When a force is applied。the polymer chains move into an extended and more ordered arrangement.The crosslinks are necessary to prevent the chains from slipping past each other when force is applied. When the force is released the chains return to their less ordered state，largely because of the concomitant increase in entropy. Natural rubber is an unsaturated polymer in which the chain enters and leaves each covalent double bond in a cis orientation. (The trans isomer is not rubbery.)Note that there are no crosslinks between the polymer chains. Natural rubber becomes soft and sticky when heated and tends to become permanently deformed when stretched. However，when natural rubber is heated with sulfur and a catalyst，sulfur cross-links are formed between the chains. This process is called vulcanization;it was discovered accidentally by Charles Goodyear in 1839. Introduction of a moderate number of sulfur cross一links converts natural rubber into a useful elastomer. A large number of cross-links convert it into hard rubber，or ebonite，which is not an elastomer. 12. 3 Polymer Nomenclature Considering that a simple compound like C,H,UH is variously known as ethanol，ethyl alcohol，grain alcohol，or simply alcohol，it is not too surprising that the vastly more complicated polymer molecules are also often known by a variety of different names. The International Union of Pure and Applied Chemistry (IUPAC) has recommended a system of nomenclature based on the structure of the monomer or repeat unit. A semisystematic set of trivial names is also in widespread usage;these latter names seem even more resistant to replacement than is the case with low molecular weight compounds. Synthetic polymers of commercial importance are often widely known by trade names which seem to have more to do with marketing considerations than with scientific communication. Polymers of biological origin are often described in terms of some aspect of their function。preparation，or characterization. If a polymer is formed from a single monomer，as in addition and ring-opening polymerization，it is named by attaching the prefix poly to the name of the monomer. In the IUPAC system，the monomer is named according to the IUPAC recommendations for organic chemistry，arid the name of the monomer is set off from the prefix by enclosing the former in parentheses.Variations of this basic system often substitute a common name for the 1UPAC name in designating the monomer. Whether or not parentheses are used in the latter case is influenced by the complexity of the monomer name;they become more important as the number of words in the monomer name increases. The polymer is called poly(1-chloroethylene)according to the IUPAC system;it is more commonly called poly(vinyl chloride)or polyviny1chloride. Acronyms are not particularly helpful but are an almost irresistible aspect of polymer terminology，as evidenced by the initials PVC，which are so widely used to describe the polymer just named. The trio of names-poly(I-hydroxyethylene)，poly (vinyl alcohol)，and polyvinyl alcohol一emphasizes that the polymer need not actually be formed from the reaction of the monomer named;this polymer is formed by the hydrolysis of poly (1-acetoxyethylene)，otherwise known as poly (vinyl acetate);These name alternatives are used in naming polymers formed by ring-opening reactions;for example，poly(6-aminohexanoic acid)。poly (G-aminocaproic acid) and poly(:一 caprolactam) are all more or less acceptable names for the same polymer. Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example，the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly (oxyethylene oxyterephthaloyl) according to the IUPAC system，as well as poly (ethylene terephthalate)ox polyethylene terephthalate. The polyamides poly (hexarnethylene sebacarnide)and poly〔hexamethyiene adiparnide) are also widely known as nylon-6，10 and nylon-6，s，respectively. The numbers following the word nylon indicate the number of carbon atoms in the diamine and dicarboxylic acid，in that order. On the basis of this same system, poly (e-caprolactam) is also known as nylon-6. Most of the polymers to be given below are listed with more than one name. Also listed are some of the patented trade names by which these substances一or materials which are mostly of the indicated structure-are sold commercially. Some commercially important cross-linked polymers go virtually without names These are heavily and randomly cross-linked polymers which are insoluble and infusible and therefore widely used in the manufacture of such molded items as automobile and household appliance parts. These materials are called resins and，at best，are named by specifying the monomers which go into their production. Often even this information is sketchy. Examples of this situation are provided by phenol formaldehyde and ureaformaldehyde resins. e. g. 1 polyethylene;polystyrene;poly(vinyl chloride)，"vinyl";polyacrylonitrile， “acrylic";poly(vinylidene chloride);poly(methyl methacrylate)，plexiglass， Lucite;polyisobutylene;polytet.rafluoroethylene，teflon;poly (ethylene oxide)，carbowax;poly(:- caprolactani)，nylon-6. e. g. 2 Polyester:poly (ethylene tcrephthalate)，terylene，dacron-, mylar;Polyamide:poly (hexamethylene adiparnide》，nylon-6，6;Polyureiliane:poly (tetramethylene hexamethylene urethane)，spandex，perlon U:Polycarbonate:poly (4，4一isopropylidenediphyenylene carbonate)。 bisphenol A polycarhonate，Lexan;Inorganic polymer:poly (dimethyl siloxane). e. g. 3 Common narne-ILTPAC, name:。一(tribromomethyl )-wrchlor。一Poly(1，1.pl3enylene met.hylene);polyethylene一poly(rnethylene);polyacetylene-poly (vinytene); polypropene-poly (propylene);polyisohutylene --poly(1，1-dimethyl一ethylene);polybutadiene一poly(1一 butenylene);polyisoprene-poly(1一methyl一1-hutenylene);polystyrene一poly(1一 phenylethylene);poly (vinyl chloride)-poly( 1-chloroethylene);polytetrafluoroethylene一 poly(difluorornethylene);poly(methy-l-methacrylate)-poly(1-methoxycarbonyl-l-methyl-ethylene);poly(2，6，-dimethylphenylene oxide)一poly (oxy-2, 6-dimethyl一1，4-phenylene);poly(ethylene oxide)poly(oxyet hylene);polycyclopentene-poly(1，2-eyclopentylene)or polycyclopentane-1， 2-ylene. Basic Terms high (molecular weight)polymer，macromolecules (giant molecules)，polymer， nligomer (having 2一10 monomer units only，low molecular weight polymer)，synthetic plastics， synthetic rubber，synthetic fiber，monomer，regular polymer，irregular polymer，constitutional unit，constitutional repeating unit，configurational unit，degree of polymerization，tacticity， isotactic polymer，syndiotactic polymer.atactic polymer，stereoregular polymer，homopolymer， copolymer，alternating copolymer，random copolymer，block，block copolymer，graft copolymer， ionorner，interpenetrating polymer network (IPitl). 12.4 Historical Introduction The hypothesis that high polymers are composed of covalent structures many times greater in extent than those occurring in simple compounds，and that this feature alone accounts for the characteristic properties which set them apart from other forms of matter，is in large measure responsible for the rapid advances in the chemistry and physics of these substances witnessed in recent years (as of 1950's).This elementary concept did not gain widespread acceptance before 1930，and vestiges of contrary views remained for more than a decade thereafter. The older belief that colloidal aggregates，formed from smaller molecules through the action of intermolecular forces of mysterious origin，are responsible for the properties peculiar to high polymers I二 repudiated by this hypothesis Such characteristic properties。，high viscosity，long-range elasticity， and high strength are direct. consequences of the size and constitution of the covalent structures of highpoiy 。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。 。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。