Synthesis Technology Of Bisphenol A Polycarbonate Solid-state Postpolycondensation

Polycarbonate(PC) is an important engineering plastics, and bisphenol Apolycarbonate(BAPC) is conmmonly used for good physical characteristics.The synthesis of the BAPC has traditionally pollution and needs much energyand precision equipment. A novel green process for synthesis of the BAPCwas developed in this paper. Firstly, the prepolymer of the BAPC wasprepared using diphenyl carbonate(DPC) and bisphenol A(BPA). Theprepolymer was then induced crystallization by supercritical CO₂. Finally, theBAPC with higher molecular weight was synthesized using the prepolymerinduced crystallization by N₂ sweeping under normal pressure and lowertemperature. The main conclusions are as follows:1. It has been found a novel method to analyze the content of phenol, theDPC and the BPA in the prepolymer by HPLC.2. It has been determined molecular weight of the prepolymer preparedin different conditions which include raw materials proportion, catalystconcentration, reaction temperature and time. According to the experimentresults, the better synthesis conditions are: catalyst concentration, first stepreaction temperature and time, second step reaction temperature and time andraw materials proportion are 2.5×10^-4 mol/mol BPA, 160℃～180℃, 35min;200℃～240℃, 25min and 1.08, respectively. The prepolymer molecularweight ranges from 2000 to 9000g/mol and molecular weight distributionranges from 1.95 to 2.69.3. A polycarbonate containing 38.9% of crystallinity degree can beobtained by supercritical CO₂ induced crystallization when molecular weightof the prepolymer, reaction temperature and pressure are 2373g/mol, 100℃and 36Mpa, respectively. The BAPC prepared at different conditions whichinclude temperature, pressure, cosolvent and molecular weight of theprepolymer, was characterized by DSC, WAXD, SEM and IR. The resultsshow the better induced crystallization conditions are: molecular weight of theprepolymer, reaction temperature, reaction pressure, cosolvent and reactiontime are 2373g/mol, 140℃, 36Mpa, acetone and 6h, respectively.4. Both the supercritical CO₂ induced crystallization and solvent induced crystallization make the amorphous prepolymer form the lamellar crystals, butthe supercritical CO₂ induced crystallization is better. After inducedcrystallization, the BAPC forms two lamellar crystals. They have the samecrystal configuration which is monoclinic crystal, though they have differentsizes.5. Under normal pressure, the molecular weight of the prepolymerchanges from 2373g/mol to 4.6×10⁴g/mol after the prepolymers polymerizedat 220℃for 2.5h by N₂ sweeping. The polymer obtained is the amorphousand its Tg is 150℃.6. The BAPC prepared at different conditions which include temperature,N₂, crystallinity degree and molecular weight of the prepolymer, wascharacterized by DSC, GPC, SEM and IR. The results show that the polymermolecular weight increases with temperature, N₂, crystallinity degree and timeincreasing. The polymer molecular weight ranges from 3.6×10⁴ to 4.9×10⁴g/mol and molecular weight distribution ranges from 1.02 to 1.07.