ENB331 Materials and Manufacturing 2 Week 1.docx

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Prasad Yarlagadda

ENB331 Lecture Materials and Manufacturing 2 Basic Definitions Polymers Polymers are a high molecular weight molecules consisting of repeating subunits Dimer Two which are bound to each other. It is a substance which is built of such molecules in which one or more kinds of atoms or groups of atoms are repeatedly linked together. Monomer Repeating subunits; small molecules (mers) Trimer Three Oligomer Less repeating subunits and lower MW than a polymer Tetramer Four Plastics Plastikos: fit to be moulded Pentamer Five Hexamer Six Chemical Bonding Ionic Bonds Ionic bonds result from the electrostatic attraction of +ve and –ve ions This type Covalent Bonds Atoms are held together by sharing of electrons This type of bonding typically occurs between atoms of non-metals Molecular species usually contains covalent bonds Covalent bonds are indicated by a line in a structural formulae Metallic Bonds Van Der Waals Bonds Methods of adding monomers Step Growth Polymerization Addition Polymerization Each monomer has at least two functional groups and Growth only occurs at the end of the chain can, at any instant, form links with chains or other This is often achieved using iconic or free radical monomers polymerization. As growth only occurs at the ends of a This process leads to the simultaneous growth of many small number of chains, long chains can be grown while short chains. Long chains only achieved when all the there is still a lot of monomer remaining. monomer is consumed In order for addition to take place, there must be an Two different monomers (A-A and B-B) or one monomer unsaturated or double bond. Another molecule (may be with two different end groups (A-B) condense with loss the same, or different) is added across the double bond, of small molecule (water). forming two sigma bonds where the pi bond was. Polymers retain end groups at completion of polymerization. Three important steps Typical forms: 1. Initiation  Polyester (PETE) I. The generation of the activated species  Polycarbonate 2. Propagation  Polyurethane (Polycarbamate) I. The addition of repeat units of the  Polyamide (Nylon 6-6, Kevlar) starting monomer via addition reaction to form chains 3. Termination I. The active species on the polymer chain reacts with another active species in the system and the reaction ends. Typical forms of addition polymerization  Polystyrene  Polybutadiene  Poly(methyl)methacrylate Functionality of monomer will effect polymer properties. 1 Week 1 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2 Common monomer functionalities Family Representative Compound Alcohols Methyl Alchohol Ethers Dimethy Ether Acids Acetic Acid Aldehydes Formaldehyde Aromatic Hydrocarbons Phenol Characterizing polymers: molecular weight Polymers with long chains have large molecular weights (mass). This is a distribution of weights NOT a discrete number. Normally described in one of two ways  Number average molecular weight: M n  Weight average molecular weight: M w Number average molecular weight: Weight average molecular weight The number average molecular weight is the total weight The weight average is based on the fact that a bigger of all the polymer molecules in a sample, divided by themolecule contains more of the total mass of the total number of molecules in the sample. Add all the polymer sample than the smaller molecules do. chains together, divide by number of chains Therefore each molecule is ‘weighted’ by its concentration in the sample. Polydispersity: Degree of Polymerisation Average chain size of a polymer can be expressed using the degree of polymerisation, n (average number of monomer units in a chain).  Number Average degree of polymerization  Weight Average degree of polymerization Size Exclusion Chromatography (SEC) or Gel permeating Chromatog
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