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Understanding Different Classes of Polymers
Polymers are a crucial component in various industries like automotive, packaging, electronics, and healthcare. The term "polymer" derives from the Greek words for 'many parts'. They are large molecules comprised of repeating sub-units called monomers. There are different types of polymers categorised based on their source, structure, and mode of polymerisation. Recognising the diverse classes of polymers is not just crucial to material scientists and engineers but also to those interested in exploring advanced science.Importance of studying Classes of Polymers in Materials Engineering
Materials Engineering is a field that deals with the design and discovery of new materials, which includes polymers. The study of different classes of polymers uncovers the vast diversity and capabilities of these materials.
- Molecular weight
- Chemical structure
- Level of polymerisation
- Thermal characteristics
For example, understanding the difference between thermosetting and thermoplastic polymers impacts how a product will be manufactured and its end use. Thermosetting polymers become permanently hard when heated and cannot be reshaped without breaking. On the other hand, thermoplastic polymers can be heated and reshaped repeatedly, making them ideal for applications such as food containers or toys.
Getting to know the basic Classes of Polymers
There are three basic classes of polymers:Addition Polymers | Condensation Polymers | Copolymers |
Did you know that polystyrene, a common type of polymer, was discovered way back in 1839? Fascinatingly, this versatile polymer made its way from being initially used for insulating homes in the 19th century to being used in manufacturing safety equipment and toys in the 20th century!
Classification of Polymers based on their Structure
Another pivotal classification of polymers lies in their structural attributes. The structure of a polymer is dictated by the arrangement of its monomeric units and provides essential information about its properties.Defining Structure-based Classes of Polymers
At a fundamental level, polymers can be allocated into three structure-based classes: 1. Linear Polymers 2. Branched Polymers 3. Cross-linked or Network Polymers Linear Polymers: These are the simplest polymers where monomers connect end-to-end in single file, forming long, straight chains. Their intermolecular forces are weak, giving them lower melting points. They are simple to process and have a high degree of crystallinity. The chemical formula of a linear polymer with monomers \( x \) and polymer units \( n \) can be represented as: \((x)_n\). Branched Polymers: These have additional chains attached onto the principal chain. Branched polymers bear the same chemical formula as linear ones but differ in spatial organisation, leading to different physical properties. The branches hinder the close packing of chains causing them to have less crystallinity and, therefore, less density than their linear counterparts. Cross-linked or Network Polymers: These are built of monomeric units forming three-dimensional networks. Here, strong covalent links connect the polymer chains. Cross-linked polymers, due to their molecular structure, exhibit high melting points, superior strength and good chemical resistance.Examples and characteristics of Structure-based Polymers
To clarify, let's consider some examples of polymers belonging to each structural class:Class | Examples | Characteristics |
Linear Polymers | Polyethylene, Polyvinyl chloride | Moderate strength, flexibility, easy to process |
Branched Polymers | Low-density polyethylene (LDPE) | Lower density and strength, more flexibility |
Cross-linked Polymers | Vulcanised Rubber, Bakelite | High strength, rigidity and temperature resistance |
Diving into Classification of Polymers based on Source
Another important criterion classifying polymers is their source. Polymers can be primarily categorised as either natural or synthetic, depending on whether they are obtained naturally or artificially synthesised.Natural vs Synthetic: Understanding source-based Polymers
Natural Polymers: These are a class of polymers that are naturally produced in plants and animals. They play an essential part in their structures and biological functions. Some common examples of natural polymers include:- Proteins (such as silk and wool)
- Nucleic acids (such as DNA and RNA)
- Polysaccharides (like cellulose and starch)
- Rubber
For instance, proteins are natural polymers made of amino acid monomers connected by peptide linkages. The sequence of amino acids and the configuration of these linkages result in the three-dimensional conformation of proteins, defining their biological function.
- Polystyrene
- Acrylonitrile butadiene styrene (ABS)
- Polyvinyl chloride (PVC)
- Polypropylene
- Polyethylene
For instance, polystyrene, an addition polymer, is synthesised from the monomer styrene. Because of its lightweight, insulating, and transparent properties, it finds extensive use in packaging, insulation, and household products.
Key Differences between natural and synthetic Polymers
Apart from their derivation sources, natural and synthetic polymers demonstrate significant differences in their properties and applications.Polymer Type | Properties | Applications |
Natural polymers | Biodegradable, highly complex and diverse structure | Biomedical applications, textiles, food industry |
Synthetic polymers | Non-biodegradable, adaptable properties, large-scale production | Packaging, automotive, electronics, construction |
Delving into Classification of Polymers based on Molecular Forces
An often overlooked but crucial criterion for classifying polymers is the type and strength of the molecular forces operating between the polymer chains. These forces, arising due to the chemical nature of the constituent monomers, dictate the physical properties exhibited by these polymers, like toughness, flexibility, melting point, solubility, and others.The Role of Molecular Forces in the Properties of Polymers
Polymers, with their complex 3-D structure arising from long chains of monomers, display a labyrinth of intermolecular forces interacting between the chains. These forces, although specific to the chemical nature of the monomers, can be broadly classified into four categories: 1. Van der Waals Forces: These are the weakest among intermolecular forces, yet play a significant role in polymers. Arising due to temporary polarization of electron clouds, these forces contribute to the flexibility and low melting points of non-polar polymer materials like polyethylene and polystyrene. 2. Dipole-Dipole Interactions: In polymers with polar monomers, the permanent dipole from the polar bonds can induce attractions with other dipoles. A classic example would be Polyvinyl Chloride (PVC), where polar \(\text{C-Cl}\) bonds lend to stronger interactions, resulting in higher strength and thermal stability compared to non-polar polymers. 3. Hydrogen Bonds: Despite being classed as a type of dipole-dipole interaction, hydrogen bonds deserve special mention due to their significantly higher strength. These forces exist in polymers containing \(\text{N-H}\) or \(\text{O-H}\) groups, such as Nylon and Polyvinyl Alcohol (PVA). The strong hydrogen bonds dramatically enhance the rigidity, melting point, and solvent resistance of such polymers. 4. Covalent Bonds or Cross-links: In certain polymers, covalent bonding between the polymer chains can produce an immensely strong, infusible, and insoluble structure. The rigorous cross-linking observed in vulcanised rubber or bakelite enhances these materials' toughness and durability. The kind and extent of these forces present dramatically influence the polymer's properties. For instance, polymers with dominantly weak intermolecular forces like Van der Waals are soft and flexible, ideal for packaging or insulation. Conversely, polymers exposed to hydrogen bonding or cross-linking display rigidity and toughness, qualifying them for engineering and heavy-duty applications.Notable Classes of Polymers defined by Molecular Forces
Polymers can be classified into three distinct categories based on the molecular forces: Elastomers, Fibres, and Thermoplastics. 1. Elastomers: These materials are highly elastic, able to resume their original shape after significant deformation. This flexibility arises due to the weak Van der Waals forces holding their loosely packed chains. Notable examples include natural rubber and neoprene. 2. Fibres: Characterised by stiffness, strength, and durability, fibres are composed of linear polymer chains tied by strong intermolecular forces, including hydrogen bonding. Prominent examples are silk, wool, and nylon. 3. Thermoplastics: These materials soften upon heating and harden on cooling, a property conferred by moderate strength forces like dipole-dipole interactions and Van der Waals forces. Examples include polyethylene, polypropylene and PVC. Below is how the molecular forces categorise these classes of polymers:Class | Molecular Forces | Examples |
Elastomers | Weak Van der Waals forces | Natural Rubber, Neoprene |
Fibres | Strong Hydrogen Bonds+ | Silk, Wool, Nylon |
Thermoplastics | Moderate Strength Forces (Dipole-Dipole, Van der Waals) | Polyethylene, Polypropylene, PVC |
Practical Uses of Different Polymer Classes
Understanding the practical application of different polymer classes is crucial in choosing the right material for relative applications, as the properties of polymers greatly dictate their functionality. Let's study the everyday applications of various polymer classes, and how their unique properties play an essential role in defining their industrial use.Everyday Applications of Different Classes of Polymers
When it comes to everyday applications, the different classes of polymers cater to diverse sectors and necessities owing to their distinct chemical structures and properties. 1. Elastomers: Owing to the property of high flexibility and elasticity, elastomers such as natural and synthetic rubber find their way in numerous daily applications. From the manufacture of tyres, hoses, and belts in the automotive industry to clothing materials such as gloves and bands, elastomers are an indispensable part of our lifestyle. 2. Fibres: The major application of polymers such as silk, wool, and nylon lies in the textile industry due to their robustness and resistance. Nylon, being highly durable, is also used in the production of fishing nets, ropes, tents, and parachutes. Furthermore, they are utilised in manufacturing surgical threads due to their biocompatibility. 3. Thermoplastics: Given their adaptability and ease of moulding upon heating, thermoplastics like polyethylene, polypropylene, and PVC are abundantly used in the packaging industry, from cling film to beverage bottles and plastic bags. They are implemented in the construction industry for pipe and insulation applications as well. Polyvinyl Chloride, with high corrosion resistance, is commonly employed in window frames and plumbing pipes.Notably, the electronics industry extensively exploits the insulating properties of thermoplastics. They’re used in coating electricity cables and forming circuits boards, shielding the components from environmental factors.
Influence of Polymer Class on its Use
The influence of the polymer's class, based on source and intermolecular forces, has a profound impact on its industrial applications. Natural vs Synthetic Polymers: The biodegradable and non-toxic nature of natural polymers like cellulose and proteins makes them suitable for food packaging applications, agriculture, and textiles. Additionally, they are popular for medical applications due to their biocompatibility, with collagen used in wound dressings and gelatin in drug capsules. By contrast, synthetic polymers, like PVC and polystyrene, with their tailored properties, dominate in robust applications such as construction, electronics, and automotive parts. With respect to the strength of intermolecular forces: Elastomers being rubbery and flexible due to weak intermolecular forces, find use in applications that demand resilience. This includes tyres, seals, shock absorbers, and more. Fibres due to the strength provided by the strong intermolecular forces, are employed in the manufacture of strong and durable materials like ropes, nets, and clothing material. Thermoplastics are perfect for applications that require the polymer to be moulded into various shapes and sizes due to their flowy nature upon heating. This makes them ideal for packaging, electrical insulation, and component manufacturing in the electronics industry.Polyethylene, a thermoplastic, has two broad types – High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE). HDPEs are utilised in rigid applications like piping systems, gas cans, and cutting boards due to their toughness. On the other hand, LDPEs, being flexible, are preferred for films, bags, and wires’ insulation due to their good tear resistance and transparency.
Classes of Polymers - Key takeaways
- Condensation polymers are formed by repetitive condensation reactions and examples include Polyethylene terephthalate (PET) and Polyurethanes.
- Copolymers consist of two or more types of monomers, allowing their properties to be fine-tuned for specific applications.
- Polymers can be classified into three structure-based classes: Linear Polymers, Branched Polymers, and Cross-linked or Network Polymers.
- Polymers can be classified based on source as either natural or synthetic, these include proteins (natural) and Polyethylene (synthetic).
- Classification of polymers can also be based on molecular forces, including Van der Waals Forces, Dipole-Dipole Interactions, Hydrogen Bonds, and Covalent Bonds or Cross-links.
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