Polymers evs ppt (3)
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Polymers evs ppt (3)

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all about polymers

all about polymers

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Polymers evs ppt (3) Polymers evs ppt (3) Presentation Transcript

  • Introduction To Polymer
  • Introduction to Polymers Poly = many, mer = unit, many units Polymer science is relatively a new branch of science . It deals with chemistry physics and mechanical properties of macromolecule .
  • It consist of large no. of repeating units known as monomers The no. of repeating units in a chain of polymer is known as degree of polymerization
  • Classification schemes Classification by Origin Synthetic organic polymers  Biopolymers (proteins, polypeptides, polynucleotide, polysaccharides, natural rubber)  Semi-synthetic polymers (chemically modified synthetic polymers)  Inorganic polymers (siloxanes, silanes, phosphazenes)
  • Classification by Monomer Composition Homopolymer Copolymer Block Graft Alternating Statistical Homopolymer Consist of only one type of constitutional repeating unit (A) AAAAAAAAAAAAAAA Copolymer Consists of two or more constitutional repeating units (A.B )
  •  Statistical copolymer (Random) ABAABABBBAABAABB two or more different repeating unit are distributed randomly  Alternating copolymer ABABABABABABABAB are made of alternating sequences of the different monomers  Block copolymer AAAAAAAAABBBBBBBBB long sequences of a monomer are followed by long sequences of another monomer  Graft copolymer AAAAAAAAAAAAAAAAAA B B B B B B (d) Several classes of copolymer are possible
  • Classification by Chain structure (molecular architecture) Linear chains :a polymer consisting of a single continuous chain of repeat units Branched chains :a polymer that includes side chains of repeat units connecting onto the main chain of repeat units Hyper branched polymer :consist of a constitutional repeating unit including a branching groups Cross linked polymer :a polymer that includes interconnections between chains Net work polymer :a cross linked polymer that includes numerous interconnections between chains Linear Branched Cross-linked Network Direction of increasing strength
  • Classification by Thermal Behavior Thermoplastics - materials become fluid and processible upon heating, allowing them to be transformed into desired shapes that are stabilized by cooling. Thermosets - initial mixture of reactive, low molar mass compounds reacts upon heating in the mold to form an insoluble, infusible network Classification by Application  Plastics  Fibers  Elastomers  Coatings  Adhesives Classification Based on Kinetics or Mechanism Step-growth Chain-growth
  • Polymerization mechanisms - Step-growth polymerization
  • Stage 1 Consumption of monomer n n Stage 2 Combination of small fragments Stage 3 Reaction of oligomers to give high molecular weight polymer Step-Growth Polymerization
  • Polymerization mechanisms - Chain-growth polymerization
  • Chain polymerization Radical polym. The C=C is prefer the Polym. by R.P. and also can be used in the steric hindrance of the substituent Ionic polym. Anionic polym. Cationic polym. X X X radical cationic anionic Electron with drawing substituent decreasing the electron density on the double bond and facilitate the attack of anionic species such as cyano and carbonyl δ+ δ- CH2=CH Y Electron donating substituent increasing the electron density on the double bond and facilitate the attack of cationic species such as alkoxy, alkyl, alkenyl, and phenyl δ- δ+ CH2 =CH Y
  • Polymer Degradation  Polymer degradation is a change in the properties – tensile strength, colour, shape, etc of a polymer or polymer based product under the influence of one or more environmental factors such as heat, light or chemicals.  The term 'biodegradation' is limited to the description of chemical processes (chemical changes that alter either the molecular weight or solubility of the polymer)
  • Degradation:  CHEMICAL DEGRADATION  BIOLOGICAL DEGRADATION  MECHANICAL DEGRADATION  CHLORINE INDUCED CRACKING  THERMAL DEGRADATION  PHOTO DEGRADATION
  • Biological Degradation  Biodegradable plastics can be biologically degraded by microorganisms to give lower molecular weight molecules.
  • Chlorine induced cracking  Another highly reactive gas is chlorine, which will attack susceptible polymers such as acetal resin and polybutylene pipe work.  There have been many examples of such pipes and acetal fittings failing in properties in the US as a result of chlorine-induced cracking.
  • Chemical Degradation: Polymers can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or base. Polymers are susceptible to attack by atmospheric oxygen, especially at elevated temperatures encountered during processing to shape.
  • Thermal degradation  Thermal degradation of polymers is molecular deterioration as a result of overheating. At high temperatures the components of the long chain backbone of the polymer can begin to separate (molecular scission) and react with one another to change the properties of the polymer. The chemical reactions involved in thermal degradation lead to physical and optical property changes relative to the initially specified properties.
  • Photo degradation  One of the disadvantages of using polymers in high temperature conditions or in outdoor applications – degradation  environment negatively influences the service life.  This process is called weathering - ageing an irreversible chemical process,  undesired changes of properties of the polymers,  discoloration and loss of mechanical properties
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