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Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl2 or ZnCl2 produces satisfactory molar masses. The number average molecular weights (Mn) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI-TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass-transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo-stabilities also followed this trend.
Polycondensations of 1,6-hexane diol and sebacic acid were conducted in bulk with addition of a lanthanide triflate as acidic catalyst. With exception of promethium triflate all lanthanide triflates were studied. A particularly low molecular weight was obtained with neodym triflate and the best results with samarium triflate. With Sm(OTf)3 weight average (Mw) values up to 65 kDa (uncorrected SEC data) were achieved after optimization of the reaction conditions. Comparison of these results with those obtained from bismuth, magnesium, and zinc triflates, on the one hand, and comparison with the acidities of all catalysts, on the other, indicates that the esterification mechanism involves complexation of monomer by metal ions. Preparation of multiblock copoly(ether ester)s failed due to insufficient incorporation of poly(tetrahydrofuran) diols.
The definition of the term “conversion” is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring–ring or chain–chain equilibration and chemical modification of polymers are considered.
Starting from dibutyltin oxide, four catalysts were synthesized, namely the dibutyltin bisphenoxides of Phenol (SnPh), 4-chlorophenol (SnCP), 4-hydroxybenzonitrile (SnCN) and pentafluorophenol (SnOPF). With the first three catalysts polymerizations of L-lactide at 160 °C in bulk yielded large fraction of linear chains having phenylester end groups at short reaction times. At longer times the fraction of cycles considerably increased at the expense of the linear chains, when SnCN was used as catalyst. With SnOPF only cyclic polylactides were obtained at low Lac/Cat ratios (< 400) with weight average molecular weights (Mw) up to 90 000 Da, whereas for high Lac/Cat ratios mixtures of cyclic and linear chains were found. Polymerizations in solution enabled variation of the molecular weight. Polymerizations of meso-lactide at temperatures down to 60 °C mainly yielded even-numbered linear chains supporting the postulated ROPPOC mechanism.
Polymerizations of L-lactide catalyzed either by neat SnCl2 or by SnCl2 + difunctional cocatalysts were conducted in bulk at 180, 160 and 140 °C with variation of the Lac/Cat ratio and time. With neat SnCl2 poly(L-lactide) having weight average molecular weights (uncorrected Mw’s) up to 190 000 g mol−1 were obtained mainly consisting of linear chains. Addition of salicylic acid or 1,1-bisphenol yielded a higher fraction of cyclic polylactides but lower molecular weights. Furthermore, SnCl2 was compared with Bu2SnCl2 and various other metal chlorides and the best results were obtained with SnCl2. With ethyl L-lactate as initiator SnCl2-catalyzed ROPs were performed at 120 °C and the lac/initiator ratio was varied. All these experiments were conducted under conditions allowing for comparison with ROPs catalyzed with neat Sn(II)-2-ethyhexanoate. Such a comparison was also performed with ε-caprolactone as monomer.
The polycondensations of adipic acid and 1,10-decanediol catalyzed by toluene sulfonic acid (TSA) were reinvestigated using MALDI TOF mass spectrometry and NMR spectroscopy. Unexpected reactions of TSA were detected along with incomplete conversion of the monomers. Furthermore, transesterification reactions of end-capped poly(1,10-decanediol adipate) and end-capped poly(ε-caprolactone) catalyzed by TSA were studied. Despite the quite different (ionic) reaction mechanisms, it was found that for polycondensations performed in bulk intermolecular transesterification is more efficient than the intramolecular “back-biting”; this scenario was not considered in the Jacobson–Stockmayer theory of reversible polycondensations.
These results also confirm that the Jacobson–Stockmayer explanation of reversible polycondensations solely on the basis of ring chain equilibration is not only devoid of any experimental evidence, but also in contradiction to the results elaborated in this work.
L-Lactide was polymerized with tin(II)acetate, tin(II)2-ethyl hexanoate, diphenyltin dichloride and dibutyltin bis(pentafluorophenoxide) at 130 °C in bulk. When an alcohol was added as initiator, linear chains free of cycles were formed having a degree of polymerization (DP) according to the lactide/initiator (LA/In) ratio.
Analogous polymerizations in the absence of an initiator yielded high molar mass cyclic polylactides.
Quite similar results were obtained when ε-caprolactone was polymerized with or without initiator.
Several transesterification experiments were conducted at 130 °C, either with polylactide or poly(ε-caprolactone) indicating that several transesterification mechanisms are operating under conditions that do not include formation of cycles by back-biting. Furthermore, reversible polycondensations (revPOCs) with low or moderate conversions were found that did not involve any kind of cyclization. Therefore, These results demonstrate the existence of revPOCs, which do neither obey the theory of irreversible polycondensation as defined by Flory nor the hypothesis of revPOCs as defined by Jacobson and Stockmayer. A new concept encompassing any kind of revPOCs is formulated in the form of a “polycondensation triangle”.
The Na salt of chloroacetic acid is condensed in suspension. Furthermore,glycolic acid is condensed in bulk or in concentrated solution by means of SnCl2 or 4-toluene sulfonic acid (TSA) as catalysts. The temperatures are varied from 160 to 200°C and the time from 1 to 5 days. Low molar mass cyclic poly(glycolic acid) (PGA) is detected by means of matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry in most PGAs. A predominance of certain cycles having an even number of repeat units is observed suggesting a thermodynamically favored formation of extended-ring crystals. Extremely high melting temperatures (up to 237.5°C)and high melting enthalpies are found for polycondensations with TSA in 1,2-dichlorobenzene.
Poly(ester urethane)s derived from lactide, isosorbide, terephthalic acidm abd various diisocyanates
(2014)
Isosorbide-initiated oligomerizations of ʟ-lactide were preformed in bulk using SnCl2 as catalyst. The resulting telechelic OH-terminated oligoesters were in situ subjected to simultaneous polycondensation and polyaddition with mixtures of terephthaloyl chloride and diisocyanates. Most polymerizations were conducted with 4,4'-diisocyanatodiphenyl methane and 2,4-diisocyanato toluene. The consequences of excess diisocyanate and four different catalysts were studied. The isosorbide/lactide ratio and the terephthalic acid/diisocyanate ratio were varied. Number average molecular weights up to 15 kDa with polydispersities around 3–5 were obtained. Depending on the chemical structure of the copolyester and on the feed ratio, incorporation of urethane groups may reduce or enhance the glass-transition temperature, but the thermal stability decreases dramatically regardless of composition.