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08 A - POLYMERS


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Polymer
A compound comprised of long-chain molecules that consist of repeating units, called mers, connected end to end. Can be separated into plastics and rubbers: [1] Thermoplastcs [2] thermosets [3] Elastomers >>> POLLY EATS MERIC SPAGHETTI BEADS
Properties of polymers
Polymers have lower strength, hardness, stiffness, density, and temperature resistance compared to metals. In addition, polymers have low electrical and thermal conductivity.
Thermoplastic polymers
Plastics that you can melt and recast as much as you want, since they consist of linear or branched molecules that don't cross-link when heated, a property ensuring their financial importance: 70% of produced synthetic polymers are thermoplastics - polyethelen, nylon >>> SMART GIRL RECASTS THERMOPLASTIC DILDO INTO A STURUDY BUTT-PLUG.
Thermosetting polymers
Can't be recast after molding since they char and degrade instead of softening, since they become one big macromolecule due to cross-linking - epoxies, vulcanized rubber. >>> TRANSPARENT EPOXY ENCASES SIMMERING FIREBUGS
Elastomers
Stretchable and elastic polymers, , that derive their flexibility from long and tightly kinked molecules with low levels of cross-linking, such as rubber bands and natural, vulcanized rubber. >>> STRETCHY RUBBER CATCHES SNEAKY PROTEINS.
Structure of polymers
Consist of a mass of long, chain like macro-molecules, each link in the chain held fast by primary atomic bonds, and the macromolecules attract each other with secondary and much weaker bonds >>> PLASTIC SPAGHETTI BRUTALLY CHOKES INNOCENT WILD-LIFE
Polymerization
Synthesis of polymers by either addition or step polymerization. [1] Addition polymerization: adding monomer molecules to other molecules to form chains. [2] Step polymerization: adding molecules to chains and chains to chains. >>> ADDITIVE STEPS SLOWLY CREATE A PLASTIC CHAIN.
Degree of polymerization
Indicates the average number of mers or repeating units in the polymer molecule.
Polymer structures
Structures of polymers can vary between different polymers and and even in the molecules of the same polymer. Structures can classified in the following manner: [1] Stereoregularity - arrangement of atoms in each repeating group of polymer. [2] Branching and cross-linking. [3] Copolymers - polymers with molecules of different types. >>> STEREOREGULAR, CROSS-LINKED BRANCHES CREATE MUTANT COPOLYMERS.
Stereoregularity
Spatial arrangement of atoms in the repeating unit of a polymer molecule. Has three options: [1] ISOTACTIC - odd atom groups are all on the same side. [2] SYNDIOTACTIC - atom groups alternate sides. [3] ATACTIC - random arrangement of groups. -- Tactic arrangement influences properties: atactic polypropylene is soft and melts at 75C, isotactic polypropylene is strong and melts at 175C. >>> TACTIC ORDER BRINGS FORTH PLASTIC STRENGTH.
Branching and crosslinking
FORMATION OF CONNECTIONS BETWEEN THE LONG-CHAIN MOLECULES IN A POLYMER. It causes the polymer structure to be permanently altered. If the amount of cross-linking is low, the polymer is transformed into an elastomer; if cross-linking is significant, the polymer is transformed into a thermoset; if there is no crosslinking (linear strucutre), the polimer is a thremoplastic one. >>> CRUEL BRANCHES DETERMINE LINEAR POLYMER'S FATE
Linear polymer
Polymer without any branches
Copolymer
A POLYMER MADE UP OF TWO DIFFERENT TYPES OF MERS, such as ethylene and propylene - similar to alloying with metals. It's also possible to produce a polymer from 3 different kinds of mers, a ternary polymer, terpolymer >>> ALLOYED PLASTICS MAKE STRONG TOY SWORDS.
Arrangements of copolymers
The four possible arrangements of the mers along the chain are (1) ALTERNATING - the mers repeat every other position; (2) RANDOM - the mers are in random order; (3) BLOCK - mers of each type group themselves into long segments along the chain; and (4) GRAFT, - mers of one type are attached as branches to a main backbone of mers of the other type. >>> ALTERNATING, RANDOM BLOCK GRAFTS ALIEN BRANCHES.
Crystallinity
Partial forming of ordered, crystall like state by folding of the long chain, a structure that increases density, strength, toughness, heat resistance while reducing transparancy, if the polymer was transparent in a noncrystalline state. >>> STRONG, STIFF FOLDED CHAIN BREAKS MURKY WINDOWS.
Polymer crystallization factors
(1) only linear polymers can form crystals; (2) copolymers do not form crystals; (3) stereoregularity - isotactic polymers always form crystals, atactic polymers never form crystals, and syndiotactic polymers sometimes form crystals; (4) slow cooling from the molten states promotes crystal formation; (5) plasticizers inhibit crystal formation; and (6) stretching the polymer tends to promote crystallization by aligning the structure >>> LINEAR, ISOTACTIC, SLOW-COOLED AND OVER-STRETCHED CRYSTALS DROWN IN ATACTIC, FAST COOLING PLASTICIZERS.
Thermal behavior of polymers
Crystalline polymers increase in size after melting point. Amorphous polymers change thermal expansion coefficient after glass-transition temperature. >>> HOT CRYSTALS GROW IN GLASSY GARDENS.
Polymer additives
[1] Fillers - can add strength, bulk up volume and reduce cost. [2] Plasticizers - softens, adds flexibility by reducing glass transition temperature below room temperature (polymer is softer above that temp). [3] Colorants - add color by pigments: fine, colored powders or by dies. [4] Flame retardants. [5] Cross-linking agents. [6] Ultraviolet light absorbers. [7] Antioxidants. >>> FPC_FUCA - FILLERS, PLASCTICISERS, COLORANTS;;; FLAME_RETARDANTS, UV_BLOCKERS, CROSSLINKING_AGENTS, ANTIOXIDANTS
Properties of thermoplastics
Thermoplastics can be heated and cooled down multiple times without degradation of polymer's quality due to it consisting of linear of branched polymers, yet in reality heating cooling cycles or prolonged exposure to high temperature can degrade the material >>> CRUEL HEAT DEGRADES CYCLYNG THERMOPLASTICS.
Thermal aging
Degradation of thermaplastics after long exposure to elevated temperatures below melting point
Mechanical properties of thermoplastics
Lower strength and stiffness than that of metals or ceramics, low tensile strength: about 10% of metals, a greater ductility. Mechanical properties also depend on temperature and structure: highly crystalline TP retains rigidity during heating until just before its T_m is reached. An amorphous TP shows a significant drop in deformation resistance as its T_g as temperature is reached; it becomes increasingly like a liquid as temperature continues to increase. >>> SOFT, WEAK PLASTIC SOFTENS UNDER GRUELING HEAT
Physical properties of thermoplastics
[1] Low density, [2] High coefficient of thermal expansion about 5 times that of metal and 10 times that of ceramics, [3] Lower melting temperatures. [4] Higher specific heat. [5] Low conductivity. [6] Insulating electrical properties.
Properties of thermosets
Due to thermosets being a one big, amorphous, cross linked macromolecule with a thermally stable, three-dimensional, covalently bonded structure, they are (1) more rigid—modulus of elasticity is 2 to 3 times greater; (2) brittle—they possess virtually no ductility; (3) less soluble in common solvents; (4) capable of higher service temperatures; and (5) not capable of being remelted—instead they degrade or burn. >>> RIGID, BRITTLE, GLASS LIKE THERMOSET RESISTS HIGH TEMPERATURES AND SOLVENTS.
Crosslinking activation
ACTIVATES DURING CURING OR SETTING. Activation of crosslinking in thermosets is done if three following manners: [1] Temperature - heating a linear polymer to produce cross-links. [2] Catalist activation. [3] Mixing activation - mixing two chemical produces a thermoset: epoxy. >>> HOT CATALIST MIXES NOXIOUS CONCOCTION
Properties of elastomers
Amorphous, brittle below glass transition temperature, tightly kincked and slightly cross-linked one macromolecule has a great deal of elasticity - when stretched the molecule is stretched, and then it's covalent bond come into play, thus giving the elastomers a non-linear stress-strain curve. >>> AMORPHOUS, CROSS-LINKED RUBBER CROOKEDLY DEFORMS ABOVE GLASS TRANSITION POINT.
Curing of elastomers
Elastomers can be cured by heat, vulcanized when speaking about natural rubber, or by adding a catalyst to initiate some cross-linking.
Thermoplastic elastomers
Elastomers conisting of two thermoplastics, a mix of two phases - one stiff, being above glass transition temperature, and the other one soft, below Tg, the mixture of hard and soft interlinking particles resulting in a soft and somewhat elastic material. Elasticity is lower than rubbers, yet it can be melted and formed in a cheaper manner than elastomers. used for shoe soles, rubber bands, exrtuded tubing, automotive parts >>> CHEAP THERMOPLASTIC MIXTURE FILLS ELASTIC MOLDS
Recycling
Plastics are hard to recycle, since there are a lot of different types with different additives and fillers. Recycled thermoplastics are remelted, thermosets and elastomers are ground up to particulate matter and used as fillers. Even with the standardization of recyclable plastics, recycling plastics is more labor intensive than recycling metals. >>> CHEAP PLASTICS COST MUCH IN GREEN RECYCLING.
Biodegradable polymers
Plastics that can be decomposed by nature, such as by bacteria and fungi. Two types exist: [1] Partially biodegradable - conventional polymer and a natural filler, a filler that will be eaten out by bacteria, leaving only a sponge like structure that might degrade. [2] Fully biodegradable - plastics with a natural polymer and filler that decompose fully in nature but can be expensive. >>> CRAZY GREEN SELLS FOR MUCH GOLD