: 200
Bakelite was the first fully synthetic polymer (Leo Baekeland, 1907). Formation is a multi-step process. Stage 1 — Novolac: Phenol (excess) + HCHO with ACID catalyst → linear polymer. HCHO (electrophile) undergoes electrophilic substitution at ortho/para positions of phenol. With excess phenol and limited HCHO, mostly linear chains form with methylene (-CH2-) bridges between phenol rings. Novolac is THERMOPLASTIC — can be melted and shaped. Stage 2 — Resole: Phenol + HCHO (excess) with BASE catalyst → methylol phenols (phenol with -CH2OH groups). Partially cross-linked prepolymer. Stage 3 — Bakelite: Novolac heated with hexamethylenetetramine (cross-linking agent, releases HCHO + NH3) under heat and pressure → all three reactive positions (2 ortho + 1 para) of each phenol ring participate → extensive 3D cross-linked THERMOSETTING network. Properties: Hard, rigid, excellent electrical insulator, heat-resistant, chemically inert. Cannot be remolded — decomposition occurs before softening. Uses: Electrical switches/plugs/sockets, pot handles, billiard balls. JEE tests: monomers, acid vs base catalyst role, novolac vs Bakelite (thermoplastic vs thermosetting), cross-linking mechanism.