1.2 Basic concepts of polymer structure and bonding
2 min read•july 23, 2024
Polymers are built from chemical bonds that shape their structure and properties. Covalent bonds form the backbone, while secondary bonds influence behavior. Understanding these connections is key to grasping how polymers function in various applications.
Polymer chains come in different shapes and sizes, affecting their characteristics. From linear to branched to cross-linked structures, each type has unique properties. also plays a crucial role, impacting strength, flexibility, and processing capabilities.
Polymer Structure and Bonding
Chemical bonding in polymers
Top images from around the web for Chemical bonding in polymers
Condensation Reactions | Introduction to Chemistry View original
Is this image relevant?
1 of 3
Strong intramolecular bonds between monomers formed by sharing electrons between atoms
Holds polymer chains together and provides high tensile strength (nylon, polyethylene)
Weaker intermolecular forces between polymer chains influence properties like melting point and solubility
Van der Waals forces result from temporary dipoles induced by electron fluctuations (polyethylene)
occurs between electronegative atoms and hydrogen atoms (nylon, proteins)
Dipole-dipole interactions arise from permanent dipoles in polar molecules (polyvinyl chloride)
Types of polymer structures
Monomers connected in a single, continuous chain resulting in high tensile strength and crystallinity (high-density polyethylene)
Monomers form side chains or branches off the main polymer backbone leading to lower crystallinity and density but improved processability (low-density polyethylene)
Polymer chains connected by covalent bonds forming a three-dimensional network with improved mechanical strength, , and solvent resistance (vulcanized rubber)
Polymer Molecular Weight and Chain Conformation
Molecular weight in polymers
Polymers consist of chains with varying lengths and molecular weights
(MWD) describes the range and distribution of molecular weights within a polymer sample characterized by:
(Mn): Mn=∑Ni∑NiMi
(Mw): Mw=∑NiMi∑NiMi2
(PDI): PDI=MnMw
MWD influences mechanical strength, viscosity, and processability (high Mw polyethylene has increased strength and viscosity compared to low Mw polyethylene)
Factors of polymer chain properties
determined by ease of rotation around single bonds in the polymer backbone
Bulky side groups, double bonds, or ring structures reduce flexibility (polystyrene)
caused by restricted rotation due to steric hindrance or electronic effects
Aromatic rings in the polymer backbone increase chain stiffness (Kevlar)
refers to the stereochemical arrangement of side groups along the polymer chain
Types: (all side groups on the same side), (alternating side groups), and (random arrangement)
Affects crystallinity, mechanical properties, and thermal behavior (isotactic polypropylene has higher crystallinity and melting point than atactic polypropylene)
Intermolecular forces between polymer chains
Stronger secondary bonding leads to reduced chain flexibility and increased chain stiffness (polyamides)