Polymeric Materials Chapter 3

Chapter 3: Polymeric Materials

• The presentation is about polymeric materials, specifically focusing on different types of polymers, their properties, and polymerization methods.
• The presenter is Dr. Nur Nabilah Shahidan, and the presentation room is BSP 2.18.

Outline

• 7.1 Polymerization and Properties of Polymers: This section discusses the process of polymerization and the resulting properties of polymers.
• 7.2 Effect of Structural Modification and Temperature on Properties of Polymers: This section examines how structural changes and temperature variations affect polymer properties.
• 7.3 High-Strength Thermoplastics: This section focuses on high-strength thermoplastic materials.

What is a Polymer?

• A polymer is a large molecule made up of repeating small building blocks called monomers.
• Monomers are the building blocks of polymers.
• The structure of the repeating unit in a polymer depends on the monomer used.

Definitions of Common Polymer Terms

• Repeating Unit: The fundamental repeating structural unit in a polymer chain, which depends on the monomer used in the synthesis process.

• Base Unit: The smallest possible repeating unit; independent of the synthetic route.

• Degree of Polymerization (DP): The average number of repeating units per chain, calculated as the ratio of the number-average molecular weight (Mn) to the molecular weight of a repeating unit (m).

• End Groups: Structural units terminating a polymer chain.

• Living Polymers/Telechelic Polymers: Macromonomers or oligomers with reactive end groups capable of undergoing polymerization (usually by heat), leading to network polymers.

Types of Atoms in Polymer Backbone

• Homochain Polymer: Polymer chain (backbone) consisting of a single atom type.
• Heterochain Polymer: Polymer chain (backbone) containing more than one atom type.

Order of Repeating Units in Backbone

• Homopolymer: Polymer made from a single monomer.
• Copolymer: Polymer made from more than one type of monomer.
• Different types of copolymers exist, including random, block, alternating and graft copolymers, each offering specific properties.

Classification of Polymers

• Polymers are classified by their origin (synthetic, bio, semi-synthetic), structure (linear, branch chain, cross-linked, network), types (thermosets, thermoplastics, elastomers), and polymerization types (addition, condensation).

Synthetic Polymers

• These are human-made polymers.
• They are categorized into thermoplastic, thermoset, elastomers, and synthetic fibers.
• Common examples include low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, and Teflon (PTFE).

Biopolymers

• These are polymers occurring naturally.
• Examples include natural rubber, natural silk, cellulose, starch, proteins.
• These polymers are biodegradable.

Semi-Synthetic Polymers

• Polymers obtained by treating natural polymers with simple chemical processes to alter their properties.
• Cellulose nitrate is an example.

Classification by Structure

• Linear: No branching aside from pendant groups.
• Branched: May have only a few side chains or many side chains per repeating unit.
• Network/Crosslinked: Crosslink density related to hardness; average of more than two crosslinks per chain forming an infinite network.
• Star polymers: Several linear polymer chains connected at one point.
• Dendrimers: Highly branched, near-spherical shapes.
• Comb polymers: High number of side chains all similar in length originating from macromonomers.

Classification Based on Polymerisation Types

• Polymerization: A chemical process creating polymers from monomers.
• Addition Polymerization: Monomers add one by one to an active site on the growing chain, with no byproducts (e.g., polyethylene from ethylene). The mechanism includes initiation, propagation, termination.
• Condensation Polymerization: Formation from monomers with the loss of small molecules like water, alcohol, or ammonia (e.g., nylon). This reaction differs from addition polymerization by the expulsion of small molecules like HCl gas.

Types of Polymers

• Thermoset: Cross-linked polymer, not meltable.
• Thermoplastic: Meltable plastic.
• Elastomer: Polymer that stretches and returns to its original shape and may be thermoplastic or thermoset.

Thermosetting and Thermoplastic Properties

• Thermoplastics: Melts and can be re-molded.
• Thermosets: Can't be re-melted and decompose when heated.

Examples of Thermoplastics

• Polyethylene (PE)
• Poly(vinyl chloride) (PVC)
• Polytetrafluoroethylene (PTFE)
• Polypropylene (PP)

Elastomers

• Elastomers are flexible polymers that can be deformed under force, but they return to their original shape once the stress is removed.
• Covalent bonds (cross-links) between polymer chains enable the elastic behavior

Effect of Temperature on Properties

• Glass Transition Temperature (Tg): The temperature at which a polymer transitions from a hard, brittle state to a softer, more flexible state.
• Melting Temperature (Tm): The temperature at which a polymer transitions from a solid to a liquid state (crystalline polymers only).

Polymer Crystallinity

• Polymers are rarely 100% crystalline.
• Crystalline regions are difficult to form with all chains aligned, leading to amorphous regions alongside crystalline regions in polymers.