PBT cyclic oligomers

Scheme 3.2 Preparation of cyclic PBT oligomers via high-dilution condensation of oligomers [13]...

Figure 3.1 HPLC traces of (a) cyclic PBT oligomers from the reaction of butane diol with terephthaloyl chloride (cyclic dimer at 3.6 min), and (b) linear oligomers from butane diol and dimethyl terephthalate...

Figure 5.7 (a) GPC of cyclic PBT oligomers extracted from chip mixed with xylene isomers, (h) GPC of cyclic PBT oligomers from a solution ring-chain reaction in 1,2-dichlorobenzene with dibutyl tin as catalyst. Reproduced with permission from J.J.L. Bryant and J.A. Semiyen, Polymer, 1997, 38, 4531. 1997, Elsevier... 

Table 5.3 Fragment structures and corresponding m/z values present in FAB-MS (of cyclic PBT, oligomers from a solution ring-chain reaction in 1,2-dichlorobenzene) and the product-ion mass spectra of the cyclic trimer of PBT ...

It seems reasonable that polyester cyclics could be prepared by an extension of the /wendo-high-dilution [17] chemistry used for the preparation of cyclic carbonate oligomers [18, 19] however, such proved not to be the case. Brunelle et al. showed that the reaction of terephthaloyl chloride (TPC) with diols such as 1,4-butanediol did not occur quickly enough to prevent concentration of acid chlorides from building up during condensation [14]. Even slow addition of equimolar amounts of TPC and butanediol to an amine base (triethylamine, pyridine or dimethylaminopyridine) under anhydrous conditions did not form cyclic oligomers. (The products were identified by comparison to authentic materials isolated from commercial PBT by the method of Wick and Zeitler [9].)... 

Figure 3.4 HPLC trace showing the formation of 5 % PET/PBT cyclic oligomers from the depolymerization of 5% PET/PBT. Cyclic dimers are indicated at 3.0 and 4.0 min, with trimers appearing at 5.0 and 6.0min, etc. the small peaks represent mixed co-cyclics...

Reports of depolymerization studies carried out by Semiyen and co-workers at the University of York, UK, typically used much longer reaction times (24-72 h) for the depolymerization of PET [27], This group also reported that the titanates were ineffective catalysts for depolymerization, but it is not known whether measures to prevent titanate hydrolysis were taken. The York group also reported that the relative proportions of cyclic oligomers (trimer, tetramer, etc.) altered as the dilution ratio was changed. Similar results were seen with PBT. They have also reported fast-atom bombardment mass spectrometry (FAB-MS), LC-MS, GPC and X-ray crystallography data. The most recent work reports characterization of the cyclic oligomers from six ester and ether ester systems [29],... 

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... 

Table 3.2 Polymerization of PET/PBT (5% molar ratio) co-cyclic oligomers ...

---