It seems that after gunpowder weapons became more commonplace, the armours of the medieval era fell out of favour and then personal armour seems to disappear until relatively recently. Were there any attempts to develop bulletproof armour, and when was the first effective bulletproof armour developed?
Pretty much immediately; while gunpowder weapons were an advantage against armored opponents, within decades of their introduction armorers would test their work by firing a pistol against the breastplate to 'proof' it; this is the source of the word 'bulletproof'. Armor and gunpowder weapons existed side by side for about 300 years; the arquebus was introduced in the mid 15th century, and infantry were wearing mass produced metal armor 200 years later in the 30 Years War, and heavy cavalry continued to wear cuirasses after the Napoleonic Wars.