Polymers & Environmental Chemistry: 5-Bullet Exam-Day Rapid Revision

HDPE vs LDPE: HDPE = Ziegler-Natta + LOW pressure → linear, dense, strong. LDPE = free radical + HIGH pressure (1000–2000 atm) → branched, flexible. (Traps always reverse this — memorize firmly.)
Nylon-6 vs Nylon-6,6: Nylon-6,6 = TWO monomers (hexamethylenediamine + adipic acid, 6C each); Nylon-6 = ONE monomer (caprolactam, ring-opening). Both are polyamides.
Rain pH / Acid Rain: Normal rain = pH 5.6 (CO2 + H2O → H2CO3). Acid rain = pH BELOW 5.6 (SO2/NOx → H2SO4/HNO3).
Heavy metal diseases: Hg → Minamata (neurological). Cd → Itai-Itai (bone pain). Clean BOD < 5 ppm; polluted BOD > 17 ppm.
Ozone + Smog: Cl• is catalytic — destroys ~100,000 O3 molecules without being consumed. London smog = SO2, reducing. Photochemical smog = O3 + PAN, oxidizing, eye irritation.