1、Thermosetting plastics Thermosetting plastics (thermosets) are polymer materials that irreversibly cure. The cure may be done through heat (generally above 200oC), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. Most often, the cure process
2、 involves cross-linking which strengthens the polymer (setting). Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circui
3、ts.Thermosetting plasticsCross-linked molecules CooledHeatedsoftensPermanently hardThermosetting means the plastic softens when initially heated , but sets permanently rigid once it has cooled or has been chemically crosslinked.It is similar to the relationship between a raw and a cooked egg.Prepara
4、tion Strategy of thermosets+Multi functional monomer to crosslinked polymerMelamine resinPolyester resinPrepolymerto crosslinked polymerPhenolic resinUrea resinPhenolic resin 酚醛树脂酚醛树脂n Dr. Leo Baekelandn First totally synthetic plastic (1907)n Patented in 1909n By controlling the pressure and temper
5、ature applied to phenol and formaldehyde, he found he could produce his dreamed-of hard moldable plastic: bakeliten Replaced rubber for insulation in electrics Dr. Leo H. BaekelandIn 1872， the famous Germany chemist, Adolf von Bayer had already observed the residue at the bottom of the test tube usi
6、ng for the reaction of Phenol and formaldehyde, which was very hard to get rid of. However, his interesting was focused on the organic dye, he didnt research this reaction在酸性介质中，酚与醛的反应过程如下： 式中的 n一般为 4 12，其数值的大小与反应物中苯酚的过量程度有关。固化时，利用树脂中酚基上未反应的对位活泼氢与甲醛或六甲基四胺作用，形成不溶不熔的热固性酚醛树脂。 OHOH CH2O CH2OHOH CH2OH OHH2O CH2OHOH CH2OH OH CH2OHnn二羟二苯基甲烷热塑性酚醛树脂
