Über den thermischen Abbau des Polypivalolactons in cyclische Oligomere

Pyrolysis-mass spectra have indicated that polypivalolactone degrades thermally into cyclic oligomers. To confirm this degradation behaviour polypivalolactone was pyrolyzed in a glass apparatus and the degradation products trapped at 0°C. After separation by preparative gel chromatography the isolated fractions could be identified as cyclic trimers to undecamers of pivalolactone and characterized by independent analytical methods. With the exception of the cyclic heptamer all odd oligomers have a lower melting point and enthalpy than the next bigger and smaller even cyclics.     

Strukturuntersuchung von polyestern durch direkten abbau im massenspektrometer, 3. Poly-β-propiolacton,poly-β-pivalolacton und poly-δ-valerolacton

Poly(oxycarbonylethylene) (poly-β-propiolactone), poly(oxycarbonyl-1,1-dimeothylethylene) (poly-β-pivalolactone), and poly(oxycarbonyltetramethylene) (poly-δ-valerolactone) were pyrolyzed directly in the ion source of a mass spectrometer and their thermal and electron impact induced degradation mechanisms are established. Poly-β-propiolactone is thermally degraded by rupture of the O? CH₂-bond by a cis elimination to give carboxyl and acryloyl endgroups, whereas poly-δ-valerolactone depolymerizes to δ-valerolactone. Poly-β-pivalolactone degrades thermally to cyclic oligomers of pivalolactone, which could be proved by a separated pyrolysis and IR-spectroscopy and gel chromatography.     

Ring-closing depolymerization of poly(ε-caprolactone)

Ring-closing depolymerization of poly(ε-caprolactone) in toluene solution with catalytic amounts of Bu₂Sn(OMe)₂ results in a mixture of cyclic oligomers, the equilibrium concentration of which corresponds to the concentration predicted according to the Jacobson-Stockmayer theory. ε-Caprolactone, however, is absent from this reaction mixture. When poly(ε-caprolactone) is depolymerized in the melt at 260°C in the presence of a catalyst, beside ε-caprolactone its cyclic dimer and trimer are distilled off. The composition is dependent on the catalyst used, e.g., Bu₂Sn(OMe)₂ produces 95,4 wt.-% of ε-caprolactone and 3,7 wt.-% of its dimer while with Ti(OiPr)₄ (iPr: isopropyl) 51,4 wt.-% ε-caprolactone and 49,6 wt.-% of its dimer are obtained. Block copolymers containing poly(ε-caprolactone) result in a similar product distribution, however, the second block may influence the rate of decomposition. The activation energy of the catalysed (0,5 mol-% Bu₂Sn(OMe)₂) and uncatalysed ring-closing depolymerization were determined to be 63 kJ/mol, and 87 kJ/mol, respectively.     

Cyclization Routes for Formation of Cyclic Oligomers in Poly(ethylene terephthalate)

The effect of cyclization routes, alcoholysis, acidolysis and ester‐interchange reaction, on the contents of cyclic poly(ethylene terephthalate) (PET) oligomers and their distribution were investigated by regenerating cyclic oligomers from PET (p‐PET), carboxyl group end‐capped PET (c‐PET) and hydroxyl end group blocked PET (b‐PET). It was found that the possible cyclization routes in p‐PET are alcoholysis, acidolysis and ester‐interchange reaction, whereas the routes in c‐PET and b‐PET are acidolysis and ester‐interchange reaction, respectively. By comparing the contents of cyclic oligomers and their possible cyclization routes in the three PETs from one to another, it is concluded that alcoholysis is the most feasible route, while acidolysis is more effective than ester‐interchange reaction in the cyclic PET formation.     

Catalysis of olefin transformation by tungsten complexes, 6. Equilibrium oligomer concentration in the polymerization of 1,5-cyclooctadiene

Depending on the concentration, the ring-opening polymerization of 1,5-cyclooctadiene, or the metathesis of poly(2-butynylene), affords either cyclic oligomers or a mixture of cyclic oligomers and high molecular weight polymer, the 1,5-cyclooctadiene being not involved in the equilibrium. The concentration of oligomers at the equilibrium depends only on the nature of the solvent, and in the case of an aromatic solvent also on the total concentration of the reactants. The thermodynamic and kinetic pathways of the reaction are discussed.     

Development of Structure and Morphology during Crystallization and Solid State Polymerization of Polyester Oligomers

Low molecular weight oligomers of poly‐ (ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were synthesized and the crystallization behavior were examined. The crystallized oligomers underwent solid state polymerization (SSP) when subjected to temperatures close to melting temperature under nitrogen. The crystallites did not exhibit reorganization during SSP but the structure and morphology changed due to SSP. It was found that the catalyst used for the synthesis of the oligomers had an influence on both the crystallization and the SSP of the oligomer. Titanium isopropoxide (Ti(OⁱPr)₄) reduces the crystallization rate of the oligomers but enhances the SSP rate, whereas, antimony trioxide (Sb₂O₃) increases the crystallization rate but reduces the SSP rate.     

Über die polykondensation von diäthylphosphit mit aliphastischen diolen

The transesterification of diethyl phosphite with diols of type HO–(CH₂)_x–OH (x = 2 to 6 and 8) was investigated. A balance of the reaction showed that besides the desired transesterification ether structures are formed to a more or less extent. This reaction, not yet described in this connection, proceeds very probably as a direct alkylation of the alcoholic OH-groups by the phosphite ester because it does not need a catalyst. In the course of this reaction, the ester groups change to acidic P–OH-groups which are not able to condense with diols under the applied conditions. The ratio of undesired ether formation and polycondensation depends on the number of CH₂-groups in the diol. Polyesters of considerably higher molecular weights are obtained only if x ≥ 6. With 1.5-pentanediol and 1.4-butanediol the cyclic ethers tetrahydropyran and tetrahydrofuran are the main products. With 1.3-propanediol the cyclic ester 2-hydro-2-oxo-1.3.2-dioxaphosphorinane is formed, besides small amounts of ether structures and of low molecular oligomers. Ethylene glycol leads to a complex mixture of oligomers of the desired structure and of oligoethylene glycols. All the reaction phenomena obey the following rule: The main products of reactions between diethyl phosphite and diols are always obtained via 5- or 6-membered transition states. Polycondensation is a slow process, which is observed only if reactions with such cyclic transition states are impossible.     

Über die stabilität von copolymeren aus 1,3,5-trioxan mit verschiedenen lactonen

The thermal degradation of the copolymers of 1,3,5-trioxane and the lactones β-propiolactone (3-propanolide), pivalolactone (2,2-dimethyl-3-propanolide) and ε-caprolactone (6-hexanolide) has been investigated. The reaction was characterized by a slow but complete degradation by the following steps:

• 1 Random chain scission catalyzed by acidic chain ends;
• 2 Cleavage of acrylic acid from the acidic chain end;
• 2 Random chain scission by the pyrolysis of ester bonds especially in sequences of β-propiplactone units.

The addition of butanediol glycidylether (1,4-bis(2,3-epoxypropoxy)butane) or N-(2-naphthyl)aniline reduced the effects of steps (1) and (2) on the degradation. However, the copolymer of 1,3,5-trioxane and β-propiolactone was essentially less thermally stable than that of 1,3,5-trioxane and ethylene oxide or 1,3-dioxolane. Step (3) was examined by the model reaction: pyrolysis of ethyl β-ethoxypropionate; the rate constant was found to be k=3,5·10^?6 min^?1 at 180°C. Copolymers of 1,3,5-trioxane and pivalolactone showed much better stability against heat and alkali than those of 1,3,5-trioxane and β-propiolactone. The copolymers of 1,3,5-trioxane and ε-caprolactone degradated thermally a little faster than those of 1,3,5-trioxane and pivalolactone.     

Oxydativer Abbau von Dibenzylsulfid

Dibenzylsulfid (DBS) as a model of the organic sulfur compounds in crude oil was converted by a mixed culture (containing Pseudomonas aeruginosa) into several water soluble organic substances. Whereas these compounds are detectable with DC- and IR-spectroscopi°C techniques, benzylmercaptoacetic acid (BMA) was the only isolated product of DBS utilization. Efficiency of degradation, respectively, accumulation of BMA were dependent on aeration and pH-regulation.     

Isolierung und charakterisierung von cyclischen oligomeren des formaldehyds

Residues from the polymerization of trioxane were analysed. Besides trioxane and tetroxane higher cyclic oligomers of formaldehyde could be isolated. The cyclic pentamer was obtained using preparative gaschromatography. The zone melting technique was suitable to isolate a ring containing 15 formaldehyde units. The acid-catalyzed pyrolysis of polytrioxane also leads to higher oligomers of formaldehyde. Gaschromatographic investigations indicate the formation of pentoxane, and Probably also of hexoxane. The cyclic acetals are characterized on the basis of their IR, NMR, and mass spectra.     

Synthesis and characterization of α-hydroxy, α-thiol and α-chloroformyl oligomers of poly(butylene terephthalate)

α-Hydroxy and α-chloroformyl oligomers of poly(butylene terephthalate) (PBT) were prepared in 1,1,2,2-tetrachloroethane by condensing terephthaloyl chloride and 1,4-butanediol and using benzoyl chloride and 4-hydroxybutyl benzoate as chain limitator. The average molecular weight was determined by ¹H NMR analysis, and thermal properties were assessed by differential scanning calorimetry (DSC). Preparation of α-thiol oligomers of PBT was also investigated by esterification of α-hydroxy oligomers with thioglycolic acid and using p-toluenesulfonic acid as catalyst. The DSC and TGA analyses pointed out that the introduction of a thiol group by esterification has no influence on the thermal properties of the PBT oligomers.     

Thermischer Abbau von linearen polymeren unter nicht isothermen bedingungen

During the study of the thermogravimetric behaviour of linear polymers under anisothermic conditions in air, we found that it is not possible to make accurate statements about the thermal degradation only by a simple comparison of the TG and DTG curves from dynamic thermogravimetry. But an attempt to estimate the kinetics of these curves, particularly by consideration of the influences of the degree of conversion and of the heating rate evidenced remarkable differences. Accordingly, anionic poly(methyl methacrylate) degradates under the applid conditions by a chain mechanism, while anionic polystyrene shows two parallel reactions. The degradation of linear polyethylene seems to be so complicated, that it is not possible to give any more detailed informations.     

Creep-resistant elastomeric networks prepared by photocrosslinking fumaric acid monoethyl ester-functionalized poly(trimethylene carbonate) oligomers

Biodegradable elastomeric networks were prepared from ethyl fumarate-functionalized poly(trimethylene carbonate) oligomers. Photocrosslinkable macromers were synthesized by reacting three-armed, hydroxyl group-terminated poly(trimethylene carbonate) oligomers with fumaric acid monoethyl ester at room temperature using N,N-dicyclohexylcarbodiimide as a coupling agent and 4-dimethylamino pyridine as a catalyst. Poly(trimethylene carbonate) macromers with molecular weights ranging between 4500 and 13,900 were prepared and crosslinked by ultraviolet-initiated radical polymerization. The gel contents of the resulting transparent networks varied between 74% and 80%. All obtained networks had low glass transition temperatures, which varied between ?18 and ?13 °C. They showed rubber-like behavior and excellent mechanical properties, with tensile strengths and elongations at break of up to 17.5 MPa and 750%, respectively. Moreover, static- and dynamic creep experiments showed that these amorphous networks were highly elastic and resistant to creep. In cyclic tensile testing to 50% strain, the permanent deformation after 20 cycles was 0%, while static creep tests at 35% of the yield stress did not indicate creep or permanent deformation after removal of the load. Porous structures were prepared by photopolymerizing the macromers in the presence of salt particles, and subsequent leaching of the salt. Such networks, built up of non-toxic compounds and designed to release benign degradation products, may find application as tissue engineering scaffolds for dynamic cell culture.     

Mass spectrometric characterization and thermal decomposition mechanism of some poly(organophosphazenes)

This work is concerned with the mass spectrometric characterization of polyaryloxy- and polyaminophosphazenes 1a–e . The mass spectral data show that the pyrolytic breakdown of poly(di-β-naphthoxyphosphazene) ( 1a ) leads to the formation of cyclic oligomers. The poly(di-arylaminophosphazenes) 1b–d decompose at low temperatures by a two-stage process involving amine evolution. Finally, in the case of poly(dipiperidinophosphazene) ( 1e ) the thermal decomposition leads to the complete destruction of the polymer backbone, with formation of ammonia and elemental phosphorus. The wide range of thermal decomposition pathways observed are peculiar of the phosphazene structure and represent a remarkable difference between this class of inorganic polymers and the organic ones.     

Über Polyarylenalkenylene und Polyheteroarylenalkenylene, 4. Synthesen und Charakterisierung von Poly(2,7-fluorenylenvinylenarylenvinylen)en und einigen dazugehörigen Oligomeren

Some poly(2,7-fluorenylenevinylenarylenevinylene)s ( 3a–c ) and some of their corresponding oligomers were prepared via the Wittig-reaction starting from 2,7-fluorenedicarbaldehyde ( 1 ) and “mono- and bis-Wittig-salts” of the benzene and thiophene series. 2-Fluorenecarbaldehyde ( 6 ) submitted to the same reaction with “mono- and bis-Wittig-salts” gave an additional series of oligomers. These polymers and oligomers were characterized by elemental analyses and by their IR- and electronic spectra–the oligomers in addition by their mass spectra. The electrical conductivities of the polymers and oligomers were investigated as well as the thermooxidative degradation of the polymers and of some oligomers.     

Über den thermo-oxidativen Abbau von Polyvinylacetat unter thermogravimetrisch-dynamischen Bedingungen

The present work discusses the results of studies on the elimination of acetic acid from poly(vinyl acetate) in air under thermogravimetric-dynamic conditions. The dependence of the kinetic parameters on the degree of transformation, the heating rate and on the average molecular weight of the studied samples, as well as the presence of an exothermic process at the end of the first degradation step indicate a modification of the reaction mechanism, probably because of the superposition of an oxidation process at higher temperatures.     

Extrapolation of solubility data of monomeric,oligomeric and polymeric hydrocarbons

Solubility data of hydrocarbons in poly(propylene) were determined by means of inverse gas chromatography and vapour pressure measurements. For better extrapolation, these data were arranged in solubilities of monomers in monomers, in dimers, in oligomers and in polymers as well as in solubilities of monomers, dimers and oligomers in polymers. The results indicate that cyclic compounds are better solvents for polymers than linear ones, because both are more similar in terms of end-groups. From a theoretical point of view, the extrapolation of solubilities of monomers in polymers to polymers in polymers leads from the Bunsen solubility to the ideal rubber elasticity. The extrapolation of solubilities of monomers in monomers to monomers in their polymers conduces from the ideal gas law or the solubility in itself to the Henry law. The knowledge of solubility is important for the physical foaming process where very fine cell structures are promoted by supercritical gases. Solubility data of propene in hydrocarbons and in poly(propylene) support the thermodynamics of poly(propylene) manufacturing: the heat of solution for propane in poly(propylene) was determined to be 14,7 kJ/mol.     

Synthesis of biodegradable poly(L-lactic acid-co-D,L-mandelic acid) with relatively low molecular weight

A homopolymer of L -lactic acid (LA), which was synthesized by direct polycondensation in the absence of a catalyst at 200°C, is crystalline, in contrast to the homopolymer of D ,L -mandelic acid (MA) which is amorphous. Poly(LA-co-MA), obtained under the above conditions, is amorphous over a wide range of composition from 15 to 100 mol-% of monomeric units of MA. The in vitro degradation mechanism of these homopolymers shows a parabola-type degradation pattern for poly(LA) and no degradation throughout an experimental period of 15 weeks for poly(MA). In poly(LA-co-MA) the degradation mechanism leads to a typical S-type degradation pattern, which may be divided into two processes, initial swelling at the surface of the matrix without degradation (induction period), followed by the erosion of oligomers produced by degradation of the main chain in the swollen state.     

Synthesis,structure and ring‐opening polymerization of phenolphthalein macrocyclic polyarylates

Phenolphthalein based polyarylate macrocyclic oligomers were selectively synthesized by an interfacial polycondensation reaction of o‐phthaloyl dichloride with phenolphthalein. The high selectivity benefits from the role of phenolphthalein as a color indicator, an efficient phase transfer catalyst, and a preferred conformation of the starting materials as indicated by analyzing a single‐crystal X‐ray structure of an analogous macrocycle. The melt ROP of phenolphthalein polyarylate cyclic dimer was studied using nucleophilic initiators. The molecular weight of the resulting polymers builds up very rapidly at the very early stage of polymerization but decreases with time. During the ROP of cyclic dimer, analogous macrocycles with higher degree of polymerization (n ≥ 3) and linear oligomers were produced by backbiting reaction especially at later stage of polymerization. Conversion of cyclic dimer is very fast at the earlier stage of polymerization and then increases slowly with time as analyzed by gel permeation chromatography. However, the total amount of cyclic oligomers in the ROP system increases with time at the later stage of polymerization because of the formation of larger macrocycles. The resulting polymers are amorphous. Glass transition temperatures (T_gs) of these polymers are influenced by the polymerization time, type of initiator, and initiator concentration.     

Functional polymers and sequential copolymers by phase transfer catalysis, 2. Synthesis and characterization of aromatic poly(ether-sulfone)s containing vinylbenzyl and ethynylbenzyl chain ends

A simple method for the synthesis of α,ω-bis(vinylbenzyl) aromatic poly(ether-sulfone)s ( 2 ) and their transformation into α,ω-bis(ethynylbenzyl) aromatic poly(ether-sulfone)s ( 4 ) is presented. This method involves a fast and quantitative Williamson etherification of the α,ω-bis(hydroxyphenyl)polysulfone with a mixture of p- and m-chloromethylstyrenes in the presence of tetrabutylammonium hydrogen sulfate as phase transfer catalyst, a subsequent bromination, and then a dehydrobromination with potassium tert-butoxide. The DSC study of the thermal curing of these α,ω-bis(vinylbenzyl)polysulfones and α,ω-bis(ethynylbenzyl)polysulfones demonstrates high thermal reactivity for this new class of styrene-terminated oligomers.