DOCSLIB.ORG

Polymer Chemistry Sem-6, Dse-B3 Part-12, Ppt-12

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Polymer Chemistry Sem-6, Dse-B3 Part-12, Ppt-12 POLYMER CHEMISTRY SEM-6, DSE-B3 PART-12, PPT-12 Dr. Kalyan Kumar Mandal Associate Professor St. Paul’s C. M. College Kolkata Polymer Chemistry Part-12 Contents • Isomerism in Polymers • Sequence Isomerism • Constitutional Isomerism • Stereoisomerism Isomerism in Polymers • Two molecules are said to be isomers if they are made up of the same number and types of atoms, but differ in the arrangement of these atoms. Though a polymer is synthesized from a pure monomer where all the molecules are initially identical, it does not mean that the final product consists of chains of regularly arranged units. However branching can occur in a polymer such as polyethylene and it turns out that from an asymmetric monomer a variety of microstructures is obtained consisting of various geometric- and stereo-isomers. • It is a general rule that for a polymer to crystallize, it must have highly regular polymer chains. Highly irregular polymers are almost inevitably amorphous. Polymer chains can have isomeric forms that decrease the regularity of the chains. There are three important forms of isomerism in polymers. The most important types are sequence isomerism, structural isomerism and stereoisomerism. Sequence Isomerism (Head-to-Tail or Head-to-Head) • In chain polymerization, monomers with pendant groups can attach in two ways. The usual arrangement is head-to-tail with the pendant groups on every other carbon atom in the chain. Except in monomers like ethylene (H2C=CH2) and tetrafluoroethylene (F2C=CF2) where the substituents on the two carbons are identical, the two carbons of the double bond in a vinyl (H2C=CH-X, where X is an atom/group other than hydrogen) type monomer are distinguishable. One of them can be arbitrarily labeled the head and the other the tail of the monomer, as shown for vinyl chloride (A; Figure 1). Sequence Isomerism (Head-to-Tail or Head-to-Head) • When a monomer unit adds to a growing chain it usually does so in a preferred direction. Polystyrene, poly(methyl methacrylate) and poly(vinyl chloride) are only a few examples of common polymers where addition is almost exclusively head-to-tail (the arrangement is shown in Figure 2). • However, for several specific polymers there are significant numbers of structural units that are incorporated “backwards” into the chain leading to head-to-head and tail-to-tail placements. This is referred to as sequence isomerism. Classic examples include poly(vinyl fluoride), poly(vinylidene fluoride), polyisoprene, polychloroprene (the arrangement is shown in Figure 3). Problems on Isomerism • Problem 1: Explain the fact that in all polymerizations the head-to-tail addition is usually the predominant mode of propagation. • Answer: Vinyl monomers polymerize by attack of an active centre (A; Figure 4) on the double bond. Equation I (Figure 4) shows the propagation step in head-to-tail enchainment and Equation 2 that in head-to-head or tail-to-tail enchainment. Problems on Isomerism • The active centre involved in the propagation reaction may be a free-radical, ion, or metal- carbon bond. A propagating species will be more stable if the unpaired electron or ionic charge at the end of the chain can be delocalized across either or both substituents X and Y. Such resonance stabilization is possible in species (B) but not in (C) shown in Figure 4. • Moreover when X and/or Y is bulky there will be more steric hindrance in reaction of Equation 1 than in the reaction of Equation 2. So, in general, head-to-tail addition as in Equation 1 is considered to be the predominant mode of propagation in all polymerizations. • Answer the following questions: 1. Polyethylenes are often characterized as being of high density (HDPE) or low density (LDPE). What causes the difference in density between these polyethylenes? 2. What is “linear low density” polyethylene (LLDPE) and how does it get its name? 3. Different polypropylenes may be described as atactic or isotactic. What does this mean ? 4. What configurational isomers are possible following the polymerization of butadiene, CH2=CH-CH=CH2 ? Problems on Isomerism • Problem 2: A chemical method of determining head-to-head structures in poly(vinyl alcohol) is by means of the following difference in diol reactions: • Poly(vinyl acetate) of number-average molecular weight 250,000 is hydrolyzed by base- catalyzed transesterification with methanol to yield poly(vinyl alcohol). Oxidation of the latter with periodic acid yields the resulting poly(vinyl alcohol) with number-average degree of polymerization 485. Calculate the percentages of head-to-tail and head-to-head linkages in poly(vinyl acetate). Problems on Isomerism Answer: Repeat unit of poly(vinyl acetate): –[–CH2–CH(OCOCH3)–]– Molar mass of repeat unit = 86 g mol-1 -1 -1 푋n= 250,000 g mol /86 g mol = 2907 let us assume that poly(vinyl acetate) is completely hydrolyzed, so that 푋n of the resulting poly (vinyl alcohol) is also 2907. The fact that 푋n is reduced from 2907 to 485 upon treatment with periodic acid means that each poly(vinyl alcohol) molecule is, on the average, cleaved to yield 2907/485 or 6 smaller molecules each of 푋n = 485 and so the number of cleavages 6 - 1 = 5. Therefore, the average polymer molecule has 5 head-to-head linkages out of a total of 2907 - 1 = 2906 linkages in the polymer chain. % head-to-head = (5 x 100) / 2906 = 0.172 % % head-to-tail = 100 - 0.172 = 99.828 %. Constitutional (or Structural) Isomerism • The type of isomerism, which involves constitutional variations of a molecule is referred to as constitutional isomerism. Polymers of dienes, such as buta-1,3-diene, isoprene and chloroprene, etc., have the potential for head-to-tail and head-to-head (or tail-to-tail) isomerism and variations in double bond position as well. Many constitutional isomers can thus be resulted from the polymerization of these dienes. • The conjugated diene, e.g., buta-1,3-diene can polymerize to produce 1,4 and 1,2 polymers. The so-called 1,4 polymers are formed by linking carbon atom 4 of one monomer to carbon atom 1 of the next, and so on. The arrangement of the substituent carbon atoms relative to the double bond in 1,4 polymers can be in either the cis or trans configuration. The 1,2 or 3,4 polymers are formed when incorporation into the polymer chain occurs through either the first or second double bond, respectively. Constitutional (or Structural) Isomerism • There are three possible constitutional isomers viz., 1,2 polymer (head-to-tail linkage), 1,2- polymer (head-to-head or tail-to-tail linkage) and 1,4 polymer from buta-1,3-diene. In addition, there is the possibility of mixed structures. The constitutional isomers are shown in Figure 5. • Isoprene may be polymerized to polyisoprene by a variety of techniques including free radical, ionic and Ziegler-Natta catalysis. Mother Nature also synthesizes “natural” polyisoprenes, Heavea (Natural Rubber) and Gutta Percha, but uses trees instead of round bottom flasks as polymerization vessels. Constitutional (or Structural) Isomerism • The number of constitutional isomers with 2-substituted buta- 1,3-dienes like isoprene and chloroprene are different from that of butadiene. In this case, there are six possible constitutional isomers of isoprene or chloroprene as shown in Figure 6. • Elastomeric behavior is shown by 1,4-polymer, particularly if the polymer structure is cis about the residual double bond. The corresponding trans isomer is much more rigid. Stereoisomerism in Polymer • When a chiral centre is present in a polymer molecule, different configurations or optical isomers are possible. Stereochemistry can have an important effect on chain packing. Isotactic polypropylene (PP), for instance, is highly crystalline because the regular chains can pack closely together. Isotactic PP has a melting point of 160 oC. Atactic PP, on the other hand is a soft noncrystalline polymer with a melting point of only 75 oC. • Polymerization of a vinyl monomer, H2C=CHX, X may be a halogen, alkyl or other chemical moiety except hydrogen, leads to polymers with microstructures that are described in terms of tacticity. The substituent placed on every other carbon atom has two possible arrangements relative to the chain and the next X group along the chain. At one extreme, the monomer unit, which contains an asymmetric carbon atom, may be incorporated into the polymer chain in a manner such that each X group is meso to the preceding X group (i.e., on the same side of the extended chain; Figure 7A). This polymer is described as isotactic. Stereoisomerism in Polymer • Conversely, at the other extreme, addition of a monomer unit to the growing polymer chain may be directed to yield a polymer in which each successive X group is racemic to the preceding one (i.e., on the opposite side of the stretched out chain; Figure 7B). This is called a syndiotactic polymer. • Polypropylene (X=CH3), for example, may be synthesized to yield an essentially isotactic or syndiotactic polypropylene by varying the polymerization conditions. These structures are illustrated in Figure 8 for an extended polypropylene chain. Because of steric repulsions the isotactic chain does not like this zig-zag shape, but would prefer to fold into a helix. • Between these two extremes there is an enormous number of polymer chain microstructures based on different distributions of meso and racemic placements of structural repeating units. Stereoisomerism in Polymer • If there is no preferred direction to the addition of a monomer to the growing chain, i.e., the monomers are incorporated randomly with respect to the stereochemistry of the preceding unit, an atactic polymer is formed. Geometrical Isomerism • Since rotation cannot take place between two carbon atoms about a double bond, two nonsuperimposable configurations (geometrical isomers) are possible in polymeric chain if the two substituents on each carbon of a double bond differ from each other.
Load more

Recommended publications
  • Pd Nanoparticles-Loaded Vinyl Polymer Gels: Preparation, Structure and Catalysis
    catalysts Article Pd Nanoparticles-Loaded Vinyl Polymer Gels: Preparation, Structure and Catalysis Elsayed Elbayoumy 1,2 , Yuting Wang 1, Jamil Rahman 1,3, Claudio Trombini 3, Masayoshi Bando 1, Zhiyi Song 1, Mostafa A. Diab 2, Farid S. Mohamed 2, Naofumi Naga 4 and Tamaki Nakano 1,5,* 1 Institute for Catalysis and Graduate School of Chemical Sciences and Engineering, Hokkaido University, N21 W10, Kita-ku, Sapporo 001-0021, Japan; [email protected] (E.E.); [email protected] (Y.W.); [email protected] (J.R.); [email protected] (M.B.); [email protected] (Z.S.) 2 Department of Chemistry, Faculty of Science, Damietta University, New Damietta 34517, Egypt; [email protected] (M.A.D.); [email protected] (F.S.M.) 3 Dipartimento di Chimica “G. Ciamician”, Università degli Studi di Bologna, via Selmi 2, 40126 Bologna, Italy; [email protected] 4 Department of Applied Chemistry, Shibaura Institute of Technology, College of Engineering, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan; [email protected] 5 Integrated Research Consortium on Chemical Sciences (IRCCS), Institute for Catalysis, Hokkaido University, N21 W10, Kita-ku, Sapporo 001-0021, Japan * Correspondence: [email protected]; Tel.: +81-11-706-9155 Abstract: Four vinyl polymer gels (VPGs) were synthesized by free radical polymerization of divinyl- benzene, ethane-1,2-diyl dimethacrylate, and copolymerization of divinylbenzene with styrene, and ethane-1,2-diyl dimethacrylate with methyl methacrylate, as supports for palladium nanoparticles. VPGs obtained from divinylbenzene and from divinylbenzene with styrene had spherical shapes while those obtained from ethane-1,2-diyl dimethacrylate and from ethane-1,2-diyl dimethacry- late with methyl methacrylate did not have any specific shapes.
    [Show full text]
  • United States Patent Office Patented Jan
    3,019,208 United States Patent Office Patented Jan. 30, 1962 2 3,019,208 has of itself properties which were obtained by copoly METHOD OF MAKING GRAFT COPOLYMERS OF merizing comonomers with vinyl chloride. Certain spe WNYEL CHORDE AND POLYACRYLATE cial properties are obtained by using various copoly Robert J. Reid, Canal Fulton, and Chris E. Best, Franklin merizable monoethylenically unsaturated comonomers Township, Summit County, Ohio, assignors to The with the vinyl chloride, and in producing the graft co Firestone Tire & Rubber Company, Akron, Ohio, a polymer up to 10 or 15 percent of such comonomers corporation of Ohio may be used, such as for example vinyl acetate, vinylidene No Drawing. Filled Jan. 18, 1954, Ser. No. 404,806 chloride, trichlorethylene, etc. The term “vinyl chlo 6 Claims. (C. 260-45.5) ride resin' will be used herein generally to include poly 0. vinylchloride and copolymers of vinyl chloride with This invention relates to the production of graft co small amounts of comonomers which are often employed polymers by grafting a vinyl resin (composed of either in making copolymers with vinyl chloride. vinyl chloride or a mixture of vinyl chloride and a The graft copolymerization process is carried out in comonomer) onto an acrylate polymer. The polyacryl latex. Vinyl chloride with or without a small amount of ate is first polymerized in an emulsion, and then without 5 other suitable monomer is added to a previously pre Separation of the polyacrylate from the emulsion the pared latex of polyacrylate. Additional catalyst and vinyl resin is polymerized onto it. emulsifying agent, such as soap, etc., may be added but Acrylate polymer and vinyl polymer or copolymer are are not required.
    [Show full text]
  • Arxiv:1805.10147V1 [Cond-Mat.Soft] 25 May 2018
    Polymorphism of syndiotactic polystyrene crystals from multiscale simulations Chan Liu,1 Kurt Kremer,1 and Tristan Bereau1, a) Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany (Dated: 4 May 2019) Syndiotactic polystyrene (sPS) exhibits complex polymorphic behavior upon crystallization. Computational modeling of polymer crystallization has remained a challenging task because the relevant processes are slow on the molecular time scale. We report herein a detailed characterization of sPS-crystal polymorphism by means of coarse-grained (CG) and atomistic (AA) modeling. The CG model, parametrized in the melt, shows remarkable transferability properties in the crystalline phase. Not only is the transition temperature in good agreement with atomistic simulations, it stabilizes the main α and β polymorphs, observed experimentally. We compare in detail the propensity of polymorphs at the CG and AA level and discuss finite-size as well as box-geometry effects. All in all, we demontrate the appeal of CG modeling to efficiently characterize polymer-crystal polymorphism at large scale. I. INTRODUCTION bead B The crystallization of molecular assemblies often in- volves the stabilization of a variety of distinct conform- ers, denoted polymorphism.1 The impact of polymorphs, may it be thermodynamic, structural, or physiological, makes their understanding and prediction essential for (a) a broad area of research, from hard condensed mat- bead A ter to organic materials. The computational modeling of crystalline materials has rapidly developed in recent years, from crystallization2,3 to predicting polymorphs and their relative stability4{7. These developments are remarkable given the complexity of the system: from the (b) (c) (d) molecular architecture to sampling challenges at low tem- peratures to the significant timescales involved.
    [Show full text]
  • AN F V O N (M Ny // | VN 5C N I Ya 5 Loool \ - H F N O V\ | // T VV I M 5OO W - 1
    July 16, 1968 G. H. POTTER ETA 3,393,174 HOT MELT ADHESIVE COMPOSITION Filed Sept. 17, 1965 LAP SHEAR AND PEEL STRENGTH WS. PER CENT MgO INETHYLENE/WINYLACETATE (72.28) - -T M 2OOOH- |- - / N 2O O tap SAAAA S7APAWG7A/ I A. AEA/ 57 AAWG7A/ 5OO |- H ea | 5 / | V AN f V o N (m Ny // | VN 5C N I Ya 5 loool \ - H f N O V\ | // t VV I M 5OO w - 1. - - |- 5 -----1 : \/ O O 2O 3O 4O so 68 % BY WT. MgO NVENTORS GEOAPGA. A1 AO77 Ap CA1ADA M/A/7M/OAP7Ay VA By6.waufMA7HAW L. ZV77 ATTORNEY 3,393,174 United States Patent Office Patented July 16, 1968 1. 2 3,393,74 The a-olefin content of the olefin polymers is at least HOT MELT ADHESIVE COMPOSITION 60% of the total copolymer. Where vinyl esters are utilized George H. Potter, St. Albans, and Clyde J. Whitworth, as comonomers with a-olefins they constitute at least Jr., Charleston, W. Va., and Nathan L. Zutty, West 10% by weight of the total copolymer and preferably field, N.J., assignors to Union Carbide Corporation, a about 18% to 40% by weight. Where acrylic acids or corporation of New York alkyl esters are utilized as the comonomers with ox-olefins Filed Sept. 17, 1965, Ser. No. 488,086 they are preferably present in an amount constituting at 8 Claims. (CI. 260-41) least about 5% by weight and preferably about 10% to 30% by weight of the total copolymer. ABSTRACT OF THE DISCLOSURE 10 Among the fillers that are useful in these hot melt The lap shear and peel strengths of the vinyl polymers, adhesive compositions can be mentioned zinc oxide, such as, polyvinyl acetate, ethylene/vinyl acetate copoly barium oxide, magnesium oxide, calcium oxide, lead mers, ethylene/acrylic acid copolymers and ethylene/ethyl Oxide (PbO4), ferric oxide, carbon black, hydrated silica, acrylate copolymers were enhanced by blending these hydrated magnesium aluminum silicate and the like.
    [Show full text]
  • Characterization of High Molecular Weight Poly(Vinyl Chloride) – Lithium Tetraborate Electrolyte Plasticized by Propylene Carbonate
    9 Characterization of High Molecular Weight Poly(vinyl chloride) – Lithium Tetraborate Electrolyte Plasticized by Propylene Carbonate Ramesh T. Subramaniam1,*, Liew Chiam-Wen1, Lau Pui Yee2 and Ezra Morris2 1Centre for Ionics University Malaya, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 2Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Kuala Lumpur Malaysia 1. Introduction An electrolyte is a substance consisting of free ions and acts as a medium channel for transferring the charges between a pair of electrodes. Sometimes, they are also referred as “lytes” which is derived from the Greek word, “lytos”, which means “it may be dissolved”. Electrolyte is comprised of positively charged species which is called as cation and negatively charged species, anion. The properties of an electrolyte can be exploited via electrolysis process: separation of chemically bonded element or compounds by applying the electrical current. In the early stage, liquid electrolytes have been discovered and investigated. Liquid electrolyte is a substance that conducts the electricity in an aqueous solution by migrating both cations and anions to the opposite electrodes through an electrically conducting path as a useful electric current. However, it faces problem of leakage of hazardous liquids or gases. Other drawbacks are formation of lithium dendrite, electrolytic degradation of electrolyte and uses of flammable organic solvent (Ramesh et al., 2011a). Apart from that, it exhibits poor long–term stability due to the evaporation of the liquid phase in the cells (Yang et al., 2008). Therefore, solid polymer electrolytes (SPEs) were synthesized to prevail over the limitations of conventional liquid electrolytes. 1.1 Solid polymer electrolytes The development on SPEs was initiated by the pioneering work of Wright et al.
    [Show full text]
  • Lecture1541230922.Pdf
    MODULE-1 Introduction: -The macromolecules are divided between biological and non-biological materials. The biological polymers form the very foundation of life and intelligence, and provide much of the food on which man exists. The non-biological polymers are primarily the synthetic materials used for plastics, fibers and elastomers but a few naturally occurring polymers such as rubber wool and cellulose are included in this class. Today these substances are truly indispensable to mankind because these are essential to his clothing,shelter, transportation, communication as well as the conveniences of modern living. Polymer Biological Non- biological Proteins, starch, wool plastics, fibers easterners Note: Polymer is not said to be as macromolecule, because polymer is composedof repeating units whereas the macromolecules may not be composed of repeating units. Definition: A polymer is a large molecule built up by the repetition of small, simple chemical units known as repeating units which are held together by chemical covalent bonds. These repeating units are called monomer Polymer – ---- poly + meres Many parts In some cases, the repetition is linear but in other cases the chains are branched on interconnected to form three dimensional networks. The repeating units of the polymer are usually equivalent on nearly equivalent to the monomer on the starting material from which the polymer is formed. A higher polymer is one in which the number of repeating units is in excess of about 1000 Degree of polymerization (DP): - The no of repeating units or monomer units in the chain of a polymer is called degree of polymerization (DP) . The molecular weight of an addition polymer is the product of the molecular weight of the repeating unit and the degree of polymerization (DP).
    [Show full text]
  • Line Width of Nuclear Magnetic Resonance High Resolution Spectra of Vinyl Polymers
    VoI. I, No. I, Junuary-Februury I968 NhlR SPECTRA OF VINYL POLYMERS 93 are nine distinct branching possibilities (A, B, or C constants would be required for complete description branching from A,, B, or C), as many as nine additional of the system. kinetic constants would be required to specify the B. Two major simplifications were made in the system, not considering whatever constants are neces- derivation of eq 15-20. The first was that the effect of sary to describe the branching mechanism. penultimate and ante-penultimate units was negligible, 2. Nearest Neighbor Effects. In the model, the sta- the second assumed constant feed ratios of monomers bility of any link was assumed to be independent of the (fi). If the first assumption is invalid, alternate treat- presence and type of neighboring links. If, however, ments are available.18 If the second is invalid (as, for the effect of a given linkage extends beyond this linkage, example, in a batch or semibatch process), then eq then additional (constants are necessary. For a ter- 15-20 may be integrated numerically to give appropriate polymer, in the case of an A-A linkage, for example, values ofJi. the following scission constants need to be included: (18) E. Merz, T. Alfrey, and G. Goldfinger, J. Polymer Sci., 1, ka~~a,kaaab, k,,,,, kbaab, kbaac, k,,,,. A total of 36 75 (1946). Line Width of Nuclear Magnetic Resonance High Resolution Spectra of Vinyl Polymers A. L. Segre Centro Nazionale di Chiniica delle Macromolerole del C.N.R., Sezione I .Milan, Italy. Receiced Nofiember 21, 1967 ABSTRACT: The line widths of high resolution nmr spectra of vinyl polymers were studied with particular refer- ence to isotactic polypropylene.
    [Show full text]
  • Mesophases in Polyethylene, Polypropylene, and Poly(1-Butene)
    Polymer 51 (2010) 4639e4662 Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer Feature Article Mesophases in polyethylene, polypropylene, and poly(1-butene) René Androsch a, Maria Laura Di Lorenzo b, Christoph Schick c, Bernhard Wunderlich d,e,*,1 a Martin-Luther-University Halle-Wittenberg, Center of Engineering Sciences, D-06099 Halle/S., Germany b Istituto di Chimica e Tecnologia dei Polimeri (CNR), c/o Comprensorio Olivetti, Via Campi Flegrei 34, 80078 Pozzuoli (NA), Italy c University of Rostock, Institute of Physics, Wismarsche Straße 43-45, D-18051 Rostock, Germany d Department of Chemistry, University of Tennessee, Knoxville, USA e Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA article info abstract Article history: This paper contains new views about the amorphous and partially ordered phases of the three polymers Received 15 April 2010 listed in the title. The discussion is based on information on structure, thermodynamic stability, and Received in revised form large-amplitude molecular motion. Polyethylene is the basic backbone of all alkene polymers, and the 14 July 2010 other two are the first members of the vinyl polymers which have stereospecifically placed alkyl side Accepted 17 July 2010 chains. Their multiphase structures consist of metastable crystals, mesophases, and surrounding rigid Available online 4 August 2010 and mobile amorphous fractions. All these phases have sizes ranging from micrometer dimensions down to nanometers. Besides the phase structures, information about the molecular coupling between the Keywords: Equilibrium phases must be considered. Depending on temperature, the polymer phases can vary from solid (rigid) to Mesophase liquid (mobile).
    [Show full text]
  • The Effects of Shear Stress on the Crystallization Kinetics of Syndiotactic Polystyrene." (1995)
    Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1995 The ffecE ts of Shear Stress on the Crystallization Kinetics of Syndiotactic Polystyrene. Douglas Henry Krzystowczyk Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Krzystowczyk, Douglas Henry, "The Effects of Shear Stress on the Crystallization Kinetics of Syndiotactic Polystyrene." (1995). LSU Historical Dissertations and Theses. 5965. https://digitalcommons.lsu.edu/gradschool_disstheses/5965 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. Hie quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely, event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note wifi indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps.
    [Show full text]
  • Polymer Crystals
    Rep. Prog. Phys. 53 (1990) 549-604. Printed in the UK Polymer crystals Paul J Phillips Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200, USA Abstract In the twenty years since this subject was last reviewed for this journal by Andrew Keller there has been an almost explosive growth of research in the area of crystallisation of polymers. This growth has been almost exclusively in the area of crystallisation of polymers from the molten state, whereas when Keller wrote his review most of the work was on crystallisation from solution. At that time, the research was conducted exclusively on flexible chain polymers, but during the past ten years or so rigid and semi-rigid crystallisable polymers have been synthesised and become available in large enough quantities for physical measurements to be carried out. Our level of understand- ing of such systems at this time does not warrant an extensive review, so the major concerns of this area are simply summarised. The major developments in our understanding of polymer crystals and the kinetics of their formation have been many. It is now established that adjacent re-entry folding of the molecule occurs on crystallisation from solution, but when crystallised from the melt the molecular trajectory approximates a random coil when viewed from a distance. From a closer viewpoint, it appears that adjacent re-entry folding is only one contributor and that any given molecule exits and re-enters several crystals in a manner that is determined by the crystallisation temperature. In addition, it is now accepted that the interface between the crystal and the random melt may be macroscopic in nature.
    [Show full text]
  • Molecular Parameters of Hyperbranched Polymers Made by Self-Condensing Vinyl Polymerization
    7024 Macromolecules 1997, 30, 7024-7033 Molecular Parameters of Hyperbranched Polymers Made by Self-Condensing Vinyl Polymerization. 2. Degree of Branching† Deyue Yan‡ and Axel H. E. Mu1 ller* Institut fu¨ r Physikalische Chemie, Universita¨t Mainz, D-55099 Mainz, Germany Krzysztof Matyjaszewski Department of Chemistry, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213-3890 Received December 30, 1996; Revised Manuscript Received July 30, 1997X ABSTRACT: Using a modified definition, the average degree of branching, DB, the fraction of branchpoints, FB, as well as the fractions of various structural units are calculated as a function of conversion of double bonds for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (or “inimers”) with the general structure AB*, where A is a vinyl group and B* is an initiating group. The results are compared to those for the polycondensation of AB2-type monomers. At full conversion, DB is somewhat smaller for SCVP (DB∞ 0.465) than for AB2 systems (DB∞ ) 0.5). ≈ There are two kinds of linear groups in SCVP whereas there is only one kind in AB2 systems. Since there are two different active centers in SCVP, i.e., initiating B* and propagating A* centers, the effect of nonequal reactivities on DB is also discussed. At a reactivity ratio of the two kinds of active centers, r ) kA/kB 2.59, a maximum value of DB∞ ) 0.5 is reached. For the limiting case r << 1, a linear polymer resembling≈ a polycondensate will be formed whereas for r >> 1 a weakly branched vinyl polymer is expected. NMR experiments allow for the determination of reactivity ratio r.
    [Show full text]
  • Acrylic Copolymer) Ternary System Peelable Sealing Decontamination Material
    polymers Article Synthesis and Preparation of (Acrylic Copolymer) Ternary System Peelable Sealing Decontamination Material Zhiyu He 1,2, Yintao Li 1, Zhiqiang Xiao 3, Huan Jiang 1, Yuanlin Zhou 1,* and Deli Luo 4,* 1 State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China; [email protected] (Z.H.); [email protected] (Y.L.); [email protected] (H.J.) 2 Communist Youth League of Southwest University of Science and Technology, Mianyang 621010, China 3 Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621010, China; [email protected] 4 Institute of Fluid Physics, China Academy of Engineering Physics, Jiangyou 621908, China * Correspondence: [email protected] (Y.Z.); [email protected] (D.L.) Received: 16 June 2020; Accepted: 8 July 2020; Published: 14 July 2020 Abstract: Traditional methods that are used to deal with radioactive surface contamination, which are time-consuming and expensive. As one effective measure of radioactive material purification, strippable coating, which effectively coats the pollutant, and settles them on the surface of objects. However, there are some shortcomings in terms of film formation and peelability, such as a brittle coating and poor peelability. Therefore, in order to meet the treatment methods for radioactive contaminants needs, the strippable coating must have excellent sealing, corrosion resistance, weather resistance, low environmental pollution, short film formation time, and good mechanical properties; in addition, the spraying process should be simple, with moderate adhesion, and it should be capable of being quickly and completely peeled off.
    [Show full text]