Step polymerization self-catalyzed

Because TPA has a melting point of >300 °C and poor solubility in PDO, direct esterification is preferably carried out in the presence of a heel under a pressure of 70-150kPa and at 250-270 °C for 100-140min. A heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3 to 7, purposely left in the reaction vessel from a previous batch to improve TPA solubility and to serve as a reaction medium. The esterification step is self-catalyzed by TPA. 

Direct esterification of PDO with TPA is the preferred commercial route to polymerize PTT because it is more economical than using DMT. Figure 1 shows the reaction scheme. Because TPA has a melting point > 300°C and has poor solubility in PDO, esterification is carried out in the presence of a heel and imder a pressure of 70-150 kPa at 250-270°C for 100-140 min. Heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3-7 purposely left in the reaction vessel from a previous reaction to act as a reaction medium and to increase TPA solubility. The esterification step is self-catalyzed by TPA. After reaching a DP of about 3-7, 40-50% of the oligomers is transferred to the polymerization vessel. Titanium butoxide or dibutyl tin oxide catalyst (50-150 ppm) is added to initiate polymerization at 260-275°C. Vacuum (<0.15 kPa) is applied to remove the condensed water until the polymer reaches an intrinsic viscosity (IV) of 0.7-0.9 dL/g. 

Kinetics of Step Poiymerizations Step polymerizations can be divided into two broad categories, those catalyzed by some externally added chemical such as an acid, and those that are self-catalyzed. For simplicity, the self-catalyzed polyesterification reaction will be considered further. The reaction can be written. 

Block-Type Brushes by Sequential Polymerization The sequential hving polymerization of two macromonomers or a macromonomer with a conventional comonomer forms either block-block- or block-coil-type brush structures. For example, giant rod-coil amphiphilic block copolymer bmshes were prepared via a stepwise metallocene-catalyzed polymerization [58]. In the first step, a concentrated solution of methacryloyl end-functionalized PS macromonomer (DP = 18.3, MWD = 1.05) was polymerized by the organosamarium(iii) catalyst in THF. After PS macromonomer was completely consumed, the active center remained living, and tert-butyl methacrylate tert-butyl methacrylate (tBMA) as a comonomer was added to grow the second block. After termination by ethanol, the poly(tert-butyl methacrylate) (PtBMA) coil block was hydrolyzed into a hydrophihc block, poly(methacrylic acid) (PMAA). The final product consisted of a hydrophobic PS brush block and a hydrophihc PMAA coil. The hydrophilic PMAA coil collapsed in nonpolar solvents, which forced the block-coil CPBs to self-assembled into giant micelles with PMAA as the core component and the stiff PS brush block as the shell to stabihze the micelles. 

A-A/B-B monomers, polycondensations, 157 A-B monomers, polycondensations, 157 AB monomers, self-polymerization via benzimidazole-activated ether synthesis, 266--274 Acetophenones Ru-catalyzed addition, 67-69 Ru-catalyzed step-growth copolymerization with a,(0-dienes for high-molecular-weight polymer synthesis, 99-112 4-(Acryloxy)benzoic acid, ordered polymer synthesis, 442-450 Acyclic diene metathesis polymerization cycle, 116,118/... 

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