Polymerization of Oligomeric Ester Cyclics

Many reports on the polymerization of PET cyclic oligomers, with various results, have appeared. Polymerization in the melt at 275-310 °C has been reported by Goodman and Nesbitt [8], The latter claimed that a linear polyester was formed when the macrocycles are heated with a catalyst, neat, or in 2-methylnaphthalene at 240 °C. They also stated that scrupulously dried material 

MacKnight and co-workers reported the preparation and polymerization of PET cyclics at about the same time [38,39], Polymerization to high Mw (Mn = 20 GOO-27 000) was achieved within 10-25 min at temperatures of 270-293 °C, using antimony oxide as the catalyst at 0.3 -1.0 %. Other catalysts were also investigated, including the cyclic stannoxanes reported earlier by Brunelle et al. [14], However, at the high temperatures required for PET polymerization, the tin catalysts proved to be unstable. 

Finally, Nagahata et al. have reported polymerization of PET cyclic dimer [16], The latter is a minor component in PET cyclics, normally present at less than 10 % of the total cyclics made either from acid chlorides or via depolymerization. Nagahata et al. report melt polymerization at 250-325 °C, leading to an Mw  

DSC analysis of a mixture of PBT cyclic oligomers containing the stannox-ane 3 showed only the melting endotherm (AH = 68 J/g), with no exotherm evident. Apparently, polymerization starts as the cyclics melt. Cooling showed the crystallization of the polymer, while the second heating stage displayed only the melting point of the PBT polymer at 213 °C (A H = 54 J/g) the polymer had an Mw of 117 000, and was 97 % polymerized (from GPC analysis). 

Data for examples of polymerization of PBT cyclic oligomers are shown in Table 3.2 [14], Polymerization under mild conditions (0.2-0.3mol% titanate initiator at 190 °C) for 6min led to Mws of 95000-115 000 (entries 2, 4 and 5). These results indicate that either the PBT cyclic polymerization is far more facile than observed for PET cyclics, or that the cyclics had higher purity, since the rates were faster and the final molecular weights significantly higher. As 

Conversion of cychc oligomers to composite structures via Resin Transfer Molding (RTM) and Reaction Injection Molding (RIM) techniques has been demonstrated, and will be the subject of subsequent publications. Glass loadings 

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