Question

Thermosets tend to be stronger than thermoplastics due to their network structures. Name and describe one way of controlling the structure of thermoplastics to make them stronger.

Answer 1

Thermoset polymer are cross linked or heavily branched molecules which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. eg, bakelite, urea formaldehyde resin

Thermoplastic polymer are linear or slightly branched long chain molecules capable of repeatedly sofetning on heating and hardening on cooling.eg, polyethyene, polystrene, polyviniyls

Thermoplatic are made stronger by coordination polymerization. eg, high density polythene are made from ethene by coordination polymerization. In this process, ethene is heated to 333-343 K under a pressure of 6-7 atm in presence of catalyst consisting of triethyl aluminium and titanium trichloridr or tetrachloride(Ziegler-Natta catalyst). The polymer thus produced consist of linear chain of polymer molecule. These polymer molecule pack well and hence this type of polymer has higher density and higher melting point.

Coordination polymerization occur through intermediate formation of coordination complexes. Ethylene first form coordination complex with transtition metal titanium by donating its pi-electrons. The complex thus formed react stepwise with lagrge number of ethlene molecules ultimately leading to formation of polymer.