Hydroxyl Value: The milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl groups (-OH) present in one gram of polymer polyol, expressed as mgKOH/g.
Equivalent Weight: The average molecular weight corresponding to one functional group.
Isocyanate Content: The proportion of isocyanate groups within a molecule.
Isocyanate Index: Indicates the level of isocyanate excess in a polyurethane formulation, typically denoted as “R.”
Chain Extender: Low-molecular-weight alcohols or amines that elongate molecular chains or form spatially cross-linked networks.
Hard Segment: Chain segments in the polyurethane backbone formed by the reaction of isocyanates with chain extenders or cross-linkers, characterized by high cohesion energy, larger molecular volume, and greater rigidity.
Soft Segment: Polymer polyol segments with a carbon-carbon backbone that provide flexibility within the polyurethane main chain.
One-Shot Method: A production method where oligomeric polyols, diisocyanates, chain extenders, and catalysts are mixed and directly injected into a mold, where they cure at a specific temperature.
Prepolymer Method: Involves pre-reacting oligomeric polyols with diisocyanates to form NCO-terminated polyurethane prepolymers, which are later combined with chain extenders to produce polyurethane elastomers.
Semi-Prepolymer Method: Similar to the prepolymer method, but some polyesters or polyethers are mixed with chain extenders and catalysts before being added to the prepolymer.
Reaction Injection Molding (RIM): A process where low-molecular-weight oligomers in liquid form are rapidly mixed and injected into a mold, where they quickly react to form new high-molecular-weight polymers.
Foaming Index: Defined as the amount of water, expressed as parts per hundred polyether, that determines the foaming index (IF).
Foaming Reaction: Refers to the reaction of water with isocyanates, forming substituted urea and releasing CO₂.
Gel Reaction: Typically refers to the formation of urethane linkages.
Gel Time: The time required for a liquid substance to form a gel under specific conditions.
Cream Time: The time at which a polyurethane mixture begins to show a creamy or whitish appearance, indicating the onset of foam formation.
Chain Extension Ratio: The ratio of active hydrogen groups (amino or hydroxyl) in chain extenders to the NCO content in prepolymers, expressed in moles.
Low Unsaturation Polyether: Designed for PTMG (polytetramethylene ether glycol), with unsaturation reduced to 0.05 mol/kg to achieve properties close to PTMG. DMC catalysts are used, such as Bayer’s Acclaim series.
Urethane-Grade Solvent: Solvents used in polyurethane production must balance solvency and evaporation rates but avoid reacting with NCO groups. They must also be free from water, alcohols, and bases to prevent degradation.
Physical Blowing Agent: Creates foam by changing the physical state, such as gas expansion, liquid evaporation, or solid dissolution.
Chemical Blowing Agent: Compounds that release gases like CO₂ or N₂ upon decomposition to form foam cells within the polymer matrix.
Physical Crosslinking: The phenomenon where certain hard segments in the polymer maintain properties similar to chemically crosslinked rubber at temperatures below their softening or melting points.
Chemical Crosslinking: The formation of network or three-dimensional structures in polymers through chemical bonds induced by light, heat, radiation, mechanical force, or crosslinking agents.
Foaming Index: The water amount, equivalent to 100 parts of polyether, defines the foaming index (IF).
