CHEMBIO 3BM3 Lecture Notes - Lecture 11: Cross-Link, Elastomer, Thermosetting Polymer
21 Apr 2019
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Document Summary
Polymers swell in good solvents gel. Reduces chain mobility increases tg of polymer. 3 branches functional, or tetra, star, etc: 2 leads only to chain extension. Physical: crystallization, phase separation, entanglement, fillers. Crosslinking: covalent, non-covalent (h-bonding, ionic bonds. Network polymer that is typically insoluble: thermoset (cannot be remolded, does not melt or flow) Physical association of (hard) styrene block give crosslinks that can be overcome thermally. At room temp, they co-crystallize and form block sites. Heated up, it melts and you get a flowable fluid. Chains are being polled out, and all the chains are organized. But there is still a restoring force that allows it to come back. Think of rubber tires: absorb lots of energy, butyl rubber, don"t want a bouncy car. More crosslinking (i. e. more branched) = harder plastic. Condensation polymers: silicones cap polymer with multifunctional agent: byproducts: ethanol, methanol, acetic acid or other alcohols/acids, residual: catalyst can be done in vivo.
