31.7 Polymer Structure and Physical
2 min read•may 7, 2024
Polymers come in various categories, each with unique properties. can be reshaped, are permanently set, are stretchy, and are strong and thin. These differences stem from their molecular structure and processing methods.
The structure of polymers greatly influences their properties. Factors like , , , and affect characteristics such as strength, flexibility, and melting point. Understanding these relationships is key to designing polymers for specific applications.
Polymer Categories and Physical Properties
Categories of polymers
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- Thermoplastics soften and melt when heated, harden when cooled allowing them to be reshaped and remolded multiple times (, , )
- Thermosets undergo irreversible chemical cross-linking during molding preventing them from being reshaped or remolded once set (, , )
- Elastomers are highly elastic and flexible materials that can be stretched and return to their original shape (, , )
- Fibers are long, thin, and strong polymers with high tensile strength and orientation (, , )
Polymer Structure and Properties
Structure vs properties of polymers
- Crystallinity refers to the degree of ordered molecular arrangement where higher crystallinity leads to increased hardness and higher melting points while amorphous regions contribute to elasticity and flexibility
- Cross-linking involves chemical bonds formed between polymer chains that increase hardness, strength, and resistance to heat and solvents but reduce elasticity and ability to be reshaped
- Molecular weight represents the average length of polymer chains where higher molecular weight increases strength, viscosity, and melting point
- Tacticity describes the regularity of side group arrangement along the where and polymers have higher crystallinity than polymers
- of the polymer chain influences properties such as crystallinity, melting point, and mechanical strength
Polymer Chain Characteristics
- Polymer chains are long molecules composed of repeating units called monomers
- The refers to the number of units in a polymer chain, affecting properties like strength and viscosity
- Copolymers are formed from two or more different types of monomers, allowing for tailored properties
- is the temperature at which an amorphous polymer transitions from a hard, glassy state to a soft, rubbery state
- is a property of polymers that exhibit both viscous and elastic characteristics when undergoing deformation
Fiber formation and polymer strength
- involves extruding a polymer melt or solution through small holes () followed by rapid cooling or solvent evaporation to solidify the polymer into filaments
- stretches the filaments to several times their original length aligning polymer chains along the axis and increasing crystallinity and orientation
- Heat treatment further increases crystallinity and strength by heating the fibers under tension
The resulting fibers have:
- High tensile strength along the fiber axis
- properties meaning different properties in different directions
- Increased modulus and reduced elasticity compared to the bulk polymer
Key Terms to Review (43)
Anisotropic: Anisotropic refers to a material or system that exhibits different properties or behaviors in different directions. This term is particularly relevant in the context of polymer structure and physical properties, where the orientation and arrangement of polymer chains can lead to anisotropic characteristics.
Anti stereochemistry: Anti stereochemistry describes the spatial arrangement in a chemical reaction where two substituents are positioned on opposite sides of a double bond or ring structure after the reaction. It is particularly relevant in the halogenation of alkenes, resulting in products where the added atoms are located across from each other.
Atactic: Atactic is a term used in polymer chemistry to describe a specific arrangement of substituents or side groups along the polymer backbone. In an atactic polymer, the substituents are randomly oriented, without any specific pattern or regularity.
Copolymer: A copolymer is a type of polymer that is composed of two or more different monomer units chemically bonded together in the same polymer chain. Copolymers exhibit properties that are a combination of the individual monomers, allowing for the tailoring of material characteristics to specific applications.
Cross-linking: Cross-linking is a chemical process in which polymer chains are connected to each other, forming a three-dimensional network structure. This process is crucial in the context of diene polymers, such as natural and synthetic rubbers, as well as in determining the overall physical properties of polymers.
Crystallinity: Crystallinity refers to the degree of structural order and organization within a solid material, particularly in the context of polymers. It describes the extent to which the polymer chains are arranged in a highly ordered, three-dimensional crystalline structure versus a more amorphous, disordered arrangement.
Crystallites: Crystallites are small, ordered regions within a polymer where the molecular chains exhibit a highly organized structure. They contrast with amorphous areas where the chains are arranged in a random, disordered fashion.
Degree of Polymerization: The degree of polymerization (DP) refers to the average number of monomer units that make up a polymer chain. It is a crucial parameter that determines the physical and chemical properties of polymeric materials, particularly in the context of step-growth polymers like polyamides, polyesters, and other macromolecular structures.
Drawing: Drawing is the act of representing an object or idea on a surface by means of lines. It is a fundamental skill in the visual arts, used to capture and convey information, express emotions, and communicate concepts. Drawing is a versatile technique that can be applied in various contexts, including polymer structure and physical properties.
Elastomer: An elastomer is a type of polymer with the property of elasticity, meaning it can stretch significantly under force and return to its original shape once the force is removed. These materials are viscoelastic, combining both viscosity and elasticity characteristics.
Elastomers: Elastomers are a class of polymeric materials that exhibit high elasticity, allowing them to undergo large deformations under stress and then return to their original shape and size when the stress is removed. They are the key components in the production of natural and synthetic rubbers, which have widespread applications in various industries.
Epoxy Resins: Epoxy resins are a class of thermosetting polymers known for their exceptional adhesive properties, chemical resistance, and high strength. They are widely used in a variety of applications, including coatings, adhesives, and composite materials, due to their versatility and ability to form strong, durable bonds.
Fiber: In the context of organic chemistry, particularly within the chapter on synthetic polymers, a fiber is a long, chain-like molecule consisting of many repeating units (monomers) that exhibit high strength and flexibility. Fibers can be natural like cotton or synthetic like nylon, and are characterized by their ability to form filaments suitable for textiles.
Fibers: Fibers in the context of organic chemistry and synthetic polymers are long, continuous strands made from polymerization, where small monomer units join to form a large molecule with repeating structural units. These materials are characterized by their high strength, flexibility, and resistance to chemicals and environmental conditions.
Glass Transition Temperature: The glass transition temperature (Tg) is a critical characteristic of polymeric materials that marks the temperature at which the amorphous regions of a polymer transition from a rigid, glassy state to a more flexible, rubbery state. This temperature is a crucial factor in determining the physical and mechanical properties of polymers.
Glass transition temperature, Tg: Glass transition temperature, Tg, is the temperature at which a polymer transitions from a hard and relatively brittle "glassy" state to a soft and pliable "rubbery" state. It marks a significant change in the physical properties of the material without a phase change like melting.
Isotactic: Isotactic is a term used to describe the configuration of polymer chains, where the substituent groups (such as methyl or chlorine) are all oriented in the same direction relative to the polymer backbone. This arrangement results in a highly regular and symmetrical structure of the polymer.
Kevlar: Kevlar is a synthetic, high-strength, and heat-resistant aramid fiber that is used in a variety of applications, including bulletproof vests, protective clothing, and reinforced composite materials. It is known for its exceptional tensile strength, durability, and resistance to abrasion, making it a versatile and widely used material in the fields of polymer structure and physical properties.
Melt transition temperature, Tm: Melt transition temperature, Tm, is the temperature at which a polymer transitions from a solid to a liquid state. It is a critical physical property that indicates the thermal stability and usability of polymeric materials in various applications.
Molecular Weight: Molecular weight, also known as molar mass, is the mass of a single molecule of a substance. It is a fundamental property that describes the size and composition of a molecule and is an important factor in understanding the physical and chemical properties of polymers.
Monomer: A monomer is a small molecule that can react with other monomer molecules to form a polymer through chemical reactions. In the context of alkenes, it often contains carbon-carbon double bonds that are reactive sites for polymerization.
Monomer: A monomer is a small, repeating molecular unit that can be chemically bonded to other identical molecules to form a larger polymer structure. Monomers are the fundamental building blocks of polymers, which are macromolecules composed of many repeating monomer units.
Natural Rubber: Natural rubber is a naturally occurring, elastic polymer derived from the sap of certain tropical plants, particularly the Hevea brasiliensis tree. It is a diene polymer that exhibits unique physical properties, making it a valuable material in various applications.
Nylon: Nylon is a synthetic polymer that belongs to the class of step-growth polymers. It is a versatile material widely used in various applications due to its exceptional mechanical properties and chemical resistance. Nylon's unique structure and physical characteristics make it a valuable material in the field of polymer science.
Plasticizers: Plasticizers are additive chemicals used in the production of plastics to increase their flexibility, transparency, durability, and longevity. They work by embedding themselves between the polymer chains, making the material less rigid and more pliable.
Polyester: Polyester is a type of synthetic polymer that is widely used in various applications, including clothing, textiles, and plastics. It is formed through a step-growth polymerization process, where monomers are linked together to create long polymer chains. Polyester's unique physical and chemical properties make it a versatile material in the context of polymer structure and physical characteristics.
Polyethylene: Polyethylene is a thermoplastic polymer made from the polymerization of ethylene. It is one of the most widely used and versatile plastics, with applications ranging from packaging to construction materials.
Polymer Chain: A polymer chain refers to the long, repeating sequence of monomers that make up a polymer molecule. These monomers are covalently bonded together to form the backbone of the polymer, creating a macromolecular structure with unique physical and chemical properties.
Polypropylene: Polypropylene is a thermoplastic polymer derived from the monomer propylene. It is widely used in a variety of industrial and consumer applications due to its unique properties, making it an important material in the context of both the industrial preparation and use of alkenes, as well as the structure and physical characteristics of polymers.
Polyurethanes: Polyurethanes are a class of polymers formed through the reaction of diisocyanates and polyols. They are versatile materials used in a wide range of applications, from foams and coatings to adhesives and elastomers.
PVC: PVC, or polyvinyl chloride, is a widely used thermoplastic polymer that has become an essential material in a variety of applications due to its versatility, durability, and cost-effectiveness. PVC is a key player in the context of both radical additions to alkenes for chain-growth polymers and the structure and physical properties of polymers.
Silicone Rubber: Silicone rubber is a synthetic rubber material composed of silicon, oxygen, and other elements such as carbon and hydrogen. It is known for its unique physical and chemical properties, making it a versatile material with a wide range of applications, particularly in the context of polymer structure and physical properties.
Spandex: Spandex, also known as elastane, is a synthetic, elastic fiber that is widely used in the production of various textiles and garments. It is known for its exceptional stretch and recovery properties, making it a popular choice for clothing that requires flexibility and comfort.
Spinneret: A spinneret is a specialized structure found in many arthropods, particularly spiders and silkworms, that is used to extrude silk or other protein-based fibers. It serves as the outlet through which these animals produce their unique and versatile natural materials.
Spinning: Spinning refers to the process of imparting a rotational motion or twisting action to a material, often in the context of polymer structure and physical properties. This rotational force can influence the alignment, orientation, and overall structure of polymeric materials, which in turn affects their physical characteristics and performance.
Stereochemistry: Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and how this arrangement affects the chemical and physical properties of the substance. It examines the spatial orientation of atoms and their relationship to one another, which is crucial in understanding many organic chemistry concepts.
Syndiotactic: Syndiotactic is a term used in polymer chemistry to describe the stereochemical configuration of a polymer chain, where the substituents (e.g., side groups) are arranged in an alternating pattern along the backbone of the polymer. This specific arrangement of the substituents gives the polymer unique physical and chemical properties.
Tacticity: Tacticity refers to the spatial arrangement of substituents along the polymer backbone in a vinyl polymer. It describes the stereochemical configuration of the repeating units in a polymer chain and is a crucial factor in determining the physical and mechanical properties of the polymer.
Thermoplastics: Thermoplastics are a type of polymer that can be repeatedly softened and hardened by heating and cooling, respectively. This unique property allows them to be easily molded, extruded, or otherwise shaped into a variety of products and applications.
Thermosets: Thermosets are a class of polymeric materials that undergo an irreversible chemical reaction during the curing process, resulting in a rigid, cross-linked molecular structure. This unique property sets them apart from thermoplastics, which can be repeatedly softened and reshaped by the application of heat and pressure.
Thermosetting resins: Thermosetting resins are a class of polymers that irreversibly harden when heated, forming a rigid three-dimensional network. Unlike thermoplastics, they do not soften or melt upon reheating, making them ideal for high-heat applications.
Viscoelasticity: Viscoelasticity is a material property that describes the combined viscous and elastic behavior of a substance, such as polymers, under applied stress or strain. It reflects the ability of a material to both store energy like an elastic solid and dissipate energy like a viscous fluid.
Vulcanized Rubber: Vulcanized rubber is a type of processed rubber that has been chemically treated to improve its physical properties, making it more durable, resistant to heat and chemicals, and less prone to deformation. This process was a significant breakthrough in the development of modern rubber-based materials and products.