Polymers

StudyBlue printing of Polymers html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td { margin: 0; padding: 0; border: 0; outline: 0; font-size: 100%; background: transparent; } body { line-height: 1; } blockquote, q { quotes: none; } blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; } /* remember to define focus styles! */ :focus { outline: 0; } /* remember to highlight inserts somehow! */ ins { text-decoration: none; } del { text-decoration: line-through; } /* tables still need 'cellspacing="0"' in the markup */ table { border-collapse: collapse; border-spacing: 0; } /* end RESET */ .header { min-width:800px; } .logo { padding:6px 20px 2px 20px; margin:0; font-size:25px; font-weight:bold; color:#808285; position:relative; border-bottom: 1px solid #c5c5c5; } .logo-blue { color:#70adc4; } .logo-desc { font-weight:normal; font-size:19px; color:#cccccc; margin-top:50px; position:absolute; display: none; } .back-button { position:absolute; top:20px; right:20px; font-size:13px; line-height:25px; color:rgb(0,175,225); font-weight:normal; } .back-button a { color:rgb(0,175,225); } .instructions { padding:0; margin:0; width:100%; position:relative; color:rgb(100,100,100); } .step-holder { border-left:1px solid #ededed; margin-left:20px; } .steps { padding:15px 0; float:left; width:24%; border-right:1px solid #ededed; text-align:center; } .steps-01 { } .steps-02 { } .steps-03 { } .steps-04 { } .label { padding:5px 10px; } .print-button { } .print-button a { background-color:rgb(0,175,225); color:white; line-height: 19px; padding:9px 8px 5px 30px; font-size:14px; text-decoration:none; background-image: url(images/printer.png); background-repeat: no-repeat; background-position: 7px 50%; -moz-border-radius: 5px; -webkit-border-radius: 5px; } .print-button a:hover { background-color:black; } .theNote .content { width: 8.0in !important; margin: 5px auto; padding:20px; background-color:white; } .theNote .header { border-bottom: 1px dashed #C8C8C8; font-size: 17px; padding: 0 0 10px; line-height: 19px; color: #00ADE1; min-width:500px; } .theNote .body { font-size: 14px; line-height: 19px; padding: 10px 0; } .theNote{ padding:6px 0; clear:both; background-color: rgb(200,200,200); } .theNote h3{ color: rgb(100,100,100); } .theNote h1, .theNote h3{ background-color:white; padding:2px 20px; width:8.0in !important; margin: 0 auto; font-size: 15px; } .theNote h1{ padding-top: 10px; font-size: 15px; } .theNote h1:first-child{ font-size: 20px; } .theNote h3 { font-size: 14px; font-weight: normal; } #options { border: 3px double #ccc; padding: 5px 12px; margin: 10px 50px 10px 20px; float: left; } #info { border-top: 1px solid #ccc; padding-top: 5px; font-style: italic; } li { margin: 5px 10px 5px 25px; } ul li { list-style: disc; } ol li { list-style: decimal; } img { border: 0; } table { clear: both; width: 100%; border: 1px solid #c5c5c5; border-width: 1px 0; margin: 0; page-break-after: always; } table#page { page-break-after: auto; } td { text-align: center; font-size: 12px; border-bottom: 1px dashed #c5c5c5; height: 1.75in; width: 50%; padding-left: 15px; } .leftside { border-right: 1px solid #cccccc; padding: 0 15px 0 0; } .bottom td { border-bottom: none; } .clearfix { clear:both; line-height:1px; height:1px; } img { max-width:80%; max-height:150px; margin:20px; } @media print {.header { display: none; } .content .header{ display:inherit; } table { border: 1px dashed #bbb; border-width: 1px 0; } .theNote{ background-color:white; } } Polymers includes plastics and rubbers organic materials, meaning they are chemically based on Carbon, Hydrogen, and other non-metallic elements long chanins, thus have high molecular weights generally insulative to heat and electricity relatively low densities may be quite flexible Composites combinations of two or more materials designed for a combination of the best properties of each of the component materials example: fiber glass has strength from the glass fibers but flexibility from the polymer wood and human bones are also both examples of composites Polymers II naturally occuring polymers are derived from plants, such as wood, rubber, cotton, wool, leather, silk polymers such as proteins, enzymes, starches, and cellulose are important to biological processes synthetic polymers can be made from small organic molecules Hydrocarbon Molecules & Polymer Molecules many organic materials are hydrocarbons, composed of hydrogen and carbon molecules in polymers are gigantic compared to hydrocarbon molecules polymers are often referred to as macromolecules atoms are bound together by covalent bonds for most molecules, bonds are in the form of long flexible chains with a long string of carbon atoms as the backbone polymer molecules are composed of structural entities called mer units, which are repeated successively along the chain monomer refers to a stable molecule from which a polymer is synthesized the conversion of a monomer to a polymer is called polymerization the degree of polymerization is the number of monomer units in a chain this is expressed as DP = M polymer /M monomer unit Molecular Weight Distribution average molecular weight Mw average sized based on weight of chains Mw = Σw i M i , where w i is the fraction of the total number of chains within a size interval, M i is the mean molecular weight within a size range i molecular weight distribution Mn average size based on the number of chains Mn = Σx i M i where x i is the fraction of the total number of the chains within a size interval and M i is the mean molecular weight within a size interval hypothetical polymer molecule size distribution on the basis of number and weight fractons of molecules the physical characteristics of a polymer depend on its molecular weight and shape and differences in the structure of the molecular chain structures can be linear, branched, crosslinked, and network Linear Polymers mer units are joined together end to end in single chains these long chains are flexible there may be extensive van der Waals and hydrogen bonding between the chain Branched and Crosslinked Polymers polymers with side-branch chains connected to the main ones are called branched polymers chain packing efficiency is reduced with the formation of side branches this lowers polymer density polymers that form linear structures may also be branched in crosslinked polymers, adjacent linear chains are joined to one another at various positions by covalent bonds process of crosslinking is achieved either during synthesis or by a nonreversible chemical reaction, usually carried out at an elevated temperature many rubber elastic materials are crosslinked (in rubbers it is called vulcanization Network Polymers trifunctional mer units having three active covalent bonds form 3-D networks a highly crosslinked polymer may be classified as a network polymer distinctive mechanical and thermal properties examples: epoxies and phenol-formaldehyde Thermoplastic and Thermosetting Polymers the response of a polymer to mechanical forces at elevated temperatures related to its dominant molecular structure often these are classified according to behavior with increasing temperature thermoplastics : soften when heated and eventually liquefy, harden when cooled. processes are reversible and may be repeated relatively soft most linear polymers and those having some branched structure with flexible chains materials normally fabricated by simultaneous application of heat and pressure thermosetting: become permanently hard when heat is applied and do not soften with subsequent heating during heat treatment, covalent crosslinks are formed between adjacent molecular chains (these bonds anchor the chains together to resist vibrational and rotational chain motions at high temperatures) crosslinking is usually extensive. 10-50% of chain mer units are crosslinked heating to excessive temperatures will cause severance of crosslinked bonds and polymer degradation thermoset polymers are generally harder and stronger than thermoplastics thermoset polymers usually have better dimensional stability than thermoplastics most crosslinked and network polymers, including vulcanized rubbers, epoxies, phenolic and some polysester resins, are thermosetting Crystallinity in Polymers crystalline state may exist in polymeric materials we think of polymer crystallinity as the packing of molecular chains so as to produce an ordered atomic array density of a crystalline polymer will be greater than an amorphous one of the same material and molecular weight because the chains are more closely packed together crystallization is not favored in polymers that are made up of chemically complex mer structures crystallization is not easily prevented in chemically simple polymers, even for very rapid cooling rates there are models of how polymers crystallize fringed-micelle model: semicrystalline polmer consists of small crystalline regions called crystallites or micelles, each having a precise alignment and embedded within the amorphous matrix composed of randomly oriented molecules in this model, a single chain molecule might pass through several crystallites as well as intervening amorphous regions analysis of polymers shows a characteristic maltese-cross appearance for each spherulite Mechanical Properties of Polymers modulus of elasticity E, Yield Strength, Tensile Strength mechanical characteristics are highly sensitive to rate of deformation (strain rate), temperature, chemical nature of the environment, such as the presence of water, oxygen, organic solvents three different types of stress-strain behaivor for polymeric materials britle - mainly thermosets plastic - mainly thermoplastics highly elastic - mainly elastomers Necking in Polymers when necking occurs in many thermoplastics, there is localized strengthening in the region of the neck differs from metals: all plastic deformation is confined to the reck region once necking has initated Strain Mechanisms in Polymers Low energy = chain unfolding, unwinding, unwrapping, uncoupling, chain sliding High energy = bond stretching, side-group ordering, bond breaking Polymerization Reactions large macromolecules of commercially useful polymers must be synthesized from substance with smaller molecules this is called polymerization it is the process by which monomer units are joined over and over to create a giant molecule Most generally, the raw materials for synthetic polymers are derived from coal and petroleum products these are composed of molecules having low molecular weights reactions by which polymerization occurs can be either addition or condensation addition is sometimes referred to as chain reaction polymerization it is the process by which bifunctional bonomer units are attached one at a time in a chainlike fashion to form a linear macromolecule this happens in three distinct stages: initiation, propagation, termination condesation polymerization is also known as a step reaction it is the formation of polymers by stepwise intermolecular chemical reactions that normally involve more than one monomer species there is usually a small molecular weight by-product that is eliminated (ex: water) no reactant species has the chemical formula of the mer repeat unit and the intermolecular reaction occurs every time a mer repeat unit is formed this could happen head to tail or head to head Isomerism polymers that have more than one side group bonded to the main chain have properties highly effected by the symmetry and regularity there are two classes: stereoisomerism and geometrical isomerism stereoisomerism can be isotactic, syndiotactic, and atactic geometrical isomerism can be cis or trans The Glass Transition Temperature T g occurs in all amorphous materials including amorphous polymers and inorganic glasses a polymer will go from a rubbery state to a glassy state on cooling through T g presence of double bonds and aromatic side groups lowers chain flexibility this increases Tg and T m . size and type of side group bulky or large side groups restrict molecular rotation this increases T g and T m . M w increases T g and T m . Composite Materials composite is considered to be any multiphase material that exhibits a significant proportion of the properties of both constituent phases such that a better combination of properites is realized accroding to the principle of combined action better property combinations are fashioned by judicious combination of two or more distinct materials a composite is a multiphase material which is artifically made constituent phases must also be chemically dissimilar and separated by a distinct interface most metallic alloys and many ceramics do not count as composites because their multiple phases are formed as a conseqence of natural phenomena many composites are composed of just 2 phases, matrix and dispersed matrix is contineous and surrounds the other phase dispersed or reinforcement phase the properties of composites are a function of the properties of the constituent phases, their relative amounts, and the geometry of the dispersed phase the dispersed phase may be a fiber, a whisker, a particle, or a layer both the matrix and the dispersed phases may be metals, polymers, or ceramics strengths of continuous and unidirectional fibrous composites are highly anisotropic these composites are normally designed to be loaded along the high-strength, longitudinal direction transverse tensile loads may also be present under these circumstance, premature failure may result inasmuch as transverse strenth is usually extremely low (it lies below the tensile strength of the matrix, thus, the reinforcing effect of the fibers is negative)