Step Growth Polymers: Polycarbonates and Polyurethanes

Flashcards covering key terms, concepts, chemical reactions, mechanisms, and applications related to step-growth polymers, specifically polycarbonates and polyurethanes.

Polycarbonates

Thermoplastic polymers containing main-chain carbonate groups ($\text{-O-C(=O)-O-}$), characterized by high transparency, a $T_g$ of $147\,^\circ\text{C}$, and solubility in chloroform.

Carbonate Group

The functional group ($\text{-O-C(=O)-O-}$) present in the main chain of polycarbonates.

Bisphenol A (BPA)

A bifunctional monomer reacted with phosgene in the presence of $\text{NaOH}$ to form commercial polycarbonate.

Phosgene

A toxic bifunctional monomer used alongside bisphenol A to synthesize polycarbonates.

Interfacial Polymerization

A two-phase synthesis technique ($0\text{--}50\,^\circ\text{C}$) combining aqueous bisphenol A with $\text{NaOH}$ and phosgene in 1,2-dichloroethane to prevent hydrolysis and early polymer precipitation.

Phase-Transfer Catalyst

A compound (such as quaternary ammonium salts or crown ethers) that transfers reactants across interfacial boundaries during reaction.

Polyurethanes

Polymers containing main-chain urethane linkages, synthesized by reacting diisocyanates with diols without forming by-products.

Urethane Linkage

The chemical linkage ($\text{-N(H)-C(=O)-O-}$) formed when an isocyanate ($\text{R-N=C=O}$) reacts with an alcohol ($\text{R'-OH}$).

DABCO

Diazabicyclo[2.2.2]octane; a tertiary amine catalyst that activates alcohol hydroxyl groups toward isocyanates via hydrogen bonding.

Toluene Diisocyanate (TDI)

An aromatic diisocyanate monomer consisting of 2,4- and 2,6-isomers used in polyurethane synthesis.

Methylene Diphenyl Diisocyanate (MDI)

An aromatic diisocyanate monomer reacted with diols like ethylene glycol to produce polyurethanes.

Reaction Injection Molding (RIM)

A molding technique where low-viscosity monomer mixtures are injected into a cavity to polymerize and crosslink into large components.

Blowing Agent (Polyurethane Foam)

In situ $\text{CO}_2$ gas generated by reacting water with isocyanate groups ($2\,\text{NCO} + \text{H}_2\text{O} \rightarrow \text{NH-CO-NH} + \text{CO}_2$) to expand flexible foam.