Primary thermal degradation processes of poly(ether/ketone) and poly(ether ketone)/poly(ether-sulfone) copolymers investigated by direct pyrolysis-mass spectrometry

The mechanisms of thermal degradation of poly(ether-ketone) (PEK) and four poly(ether-ketone)/poly(ether-sulfone) copolymers (PEK/PES) have been investigated by direct pyrolysis-mass spectrometry (DPMS). Several families of pyrolysis compounds with H, OH and CHO end-groups have been identified in the pyrolysis mass spectra of PEK. All these pyrolysis compounds can arise from degradation mechanisms involving cleavages of the bridged groups (diphenyl ether and dibenzophenone units). Our data show that the main degradation products of PEK are aldehydes, most likely formed by an intramolecular thermal cleavage of benzophenone units. Compounds containing dibenzofuran units have also been observed in the DCI mass spectrum of PEK. The thermal decomposition of a low molecular weight PEK sample occurs in two stages with the maxima of decomposition at 390°C and 490°C, respectively. This fact indicates the occurrence of an end-group initiated thermal decomposition in the early degradation stage which is not present in the case of the high molecular weight PEK sample. The pyrolysis of PEK does not produce compounds containing biphenyl units, indicating that extrusion of carbonyls or recominbation processes are not involved. The thermal degradation compounds of the PEK/PES copolymers originate from the thermal cleavage of the bridge groups (diphenyl ether, benzophenone and diphenyl sulfone). The pyrolysis mass spectra of 1:1 (alt.), 1:1 (random), 3:1 and 1:3 PEK/PES copolymers appear essentially identical (apart for obvious differences in peak intensities), indicating that the molecular rearrangements (SO₂ extrusion, transesterification, cleavage of bridges) which occur at higher temperatures and/or in the pyrolysis processes are able to randomize the distribution of comonomer units originally present in the copolymers. Differences in peak intensities have been found to reflect almost quantitatively the molar composition of the copolymers.     

Synthesis and characterization of poly(ether ketone)/poly(ether sulfone) alternating and sequential copolymers by electrophilic reactions

The synthesis and NMR characterization of some poly(ether ketone)/poly(ether sulfone) (PEK/PES) alternating copolymers together with a series of sequential homopolymers containing CO, O, S and SO₂ bridging groups, all obtained by electrophilic condensation reactions using phosphorus pentoxide/methanesulfonic acid as dehydrating agent, is here reported. Properties of such polymers are compared with those of their model compounds from which it can be inferred that both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, S, CO and SO₂ bridges. Differential scanning calorimetry indicates that our polymers are essentially amorphous irrespective of the bridging sequence. From viscosity measurements the molecular weights of these copolymers are judged to be very low.     

Sequence distribution and glass transition of vinyl alcohol/n-alkyl vinyl carbonate copolymers

¹³C NMR spectroscopy was used for the determination of the sequence distribution in vinyl alcohol-ethyl vinyl carbonate copolymers prepared by reaction of poly(vinyl alcohol) with ethyl chloroformate. The ¹³C NMR spectra of the methylene carbons in the main chain show three split peaks whose intensities change with copolymer composition. These peaks can be assigned to the three dyad sequences. The obtained results show that ethyl vinyl carbonate units have an alternating tendency in the copolymer chain. The T_g values of the vinyl alcohol-ethyl vinyl carbonate and vinyl alcohol-butyl vinyl carbonate copolymers are influenced by both the overall copolymer composition and the monomer sequence distribution.     

Primary thermal degradation processes of poly(ether-sulfone) and poly(phenylene oxide) investigated by direct pyrolysis-mass spectrometry

The thermal degradation processes which occur in poly(ether-sulfone) (PES) and poly(phenylene oxide) (PPO) have been studied by Direct Pyrolysis-Mass Spectrometry (DPMS). The pyrolysis mass spectra of PES and PPO contain molecular ions up to m/z 700, corresponding to pyrolysis compounds of sufficient size to allow the characterization of the primary processes which occur in the thermal cleavage of these polymers. The results obtained indicate that the thermal degradation of PES and PPO proceeds by thermal cleavage of the groups located at the bridges. In the case of PPO the bridges are all homogeneous, and therefore both an intramolecular thermal rearrangement or a radical cleavage process can account for the formation of the primary pyrolysis products. Formation of dibenzofuran units along the PPO chain is a parallel thermal process. In the case PES the simultaneous thermal cleavage of two different bridged units, diphenyl sulfone and diphenyl ether occurs. Extrusion of SO₂, with consequent formation of compounds containing biphenyl units, is observed in the thermal degradation of PES. This process is accompanied by formation of dibenzofuran units along the polymer chain, as expected from the thermal cleavage of diphenyl ether units, and by another rearrangement of the polymer backbone, yielding structures containing more oxygen atoms with respect to that of PES.     

Polymer conformation and NMR chemical shifts, 8. Monomer- and stereo-sequence dependences of 13C NMR spectrum of poly(methyl acrylate-co-styrene)

The ¹³C NMR spectra of poly(methyl acrylate-co-styrene) are interpreted by a theoretical procedure which consists of conformational analysis of the random copolymer chain and shielding calculation. The conformational probabilities of the diad sequences constituting poly(methyl acrylate-co-styrene) are calculated by a matrix method which is conducted by the statistical mechanics of polymer chains. All the elements of the matrices are determined by the force field method. As significant shielding factors for ¹³C nuclei, paramagnetic, diamagnetic, and anisotropic terms are taken into account. The calculation is used to assign the observed split peaks for the carbonyl carbon and methoxyl carbon in the copolymer. A good agreement between calculation and observation of the peak splittings due to the distribution of the monomer sequence as well as that of the stereo sequence was obtained by considering the feasibility of rotational isomerization at the side chain ester group in two successive MA units.     

Sequence analysis and comonomer interactions in poly[(4-chlorophenyl methacrylate)-co-(methyl methacrylate)]s

Copolymers of 4-chlorophenyl methacrylate and methyl methacrylate were prepared and investigated by ¹H and ¹³C NMR spectroscopy. The copolymer composition, determined by chlorine analysis, ¹H and ¹³C NMR, was found to be close to the initial composition of the monomer mixture. The sequence analysis was carried out by analyzing the methoxy signals of the ¹H NMR spectra. Six out of ten tactic and compositional triads could be resolved. It was found that the copolymers are predominantly syndiotactic and the compositional and tactic triad populations are given. The aromatic carbon atoms are sensitive towards compositional and tactic sequence effects, which results in a switch of the order of the tactic signals at different aromatic carbon atoms.     

The curing reaction of poly(ether-sulfone)-modified epoxy resin

One of the useful methods to improve the toughness of epoxy resin is by mixing the resin with poly(ether-sulfone) (PES). In the present work, two hydroxyl-terminated PESs with molecular weights M _n = 28 600 and 4 200 were used for blending with epoxy resin. The curing reaction of diglycidyl ether/bisphenol-A (DGEBA) with 4,4′-diaminodiphenyl sulfone (DDS) in the presence of hydroxyl-terminated PES was studied by means of differential scanning calorimetry (DSC) and gel-permeation chromatography (GPC). For the DGEBA-DDS-PES system with a stoichiometric ratio of epoxy and amino groups the DSC experimental results showed that at a fixed molecular weight of PES the curing reaction rate decreases with increasing PES concentration. At a fixed PES concentration (in the range of between 0 and 20 wt.-% of PES), the DGEBA-DDS system modified with hydroxyl-terminated PES with lower molecular weight had a faster curing reaction rate at low conversion and a slower curing reaction rate at high conversion. The GPC results showed the evidence of etherification between low-molecular-weight PES with epoxy resin. However, very little etherification of high-molecular-weight hydroxyl-terminated PES with epoxy resin was found. Based on the experimental results, a curing reaction mechanism of DGEBA with DDS in the presence of hydroxyl-terminated PES is proposed.     

Poly(ether-sulfone)s with indan structure elements

Various poly(ether-sulfone)s with 1,1,3-trimethylindan units along the main chain were synthesized from different diphenols and activated dihalogen monomers containing the 1,1,3-trimethylindan moiety. The indan-containing monomers were derived from 1,1,3-trimethyl-3-phenylindan by sulfonylation with 4-halobenzenesulfonyl chloride in the presence of the Friedel-Crafts catalysts. The polymers are amorphous with glass transition temperatures between 206 and 247°C, and decomposition temperatures above 460°C in air. Due to their solubility in common organic solvents such as tetrahydrofuran and chloroform, the polymers could be fully characterized by gel-permeation chromatography as well as ¹H- and ¹³C NMR spectroscopy.     

Crystallization of the γ-form of isotactic poly(propylene)

The pure γ-form of isotactic poly(propylene) can be obtained by melt-crystallization starting from a fraction of a random ethylene-propene copolymer (ethylene content 4 wt.-%) soluble in p-xylene at 28°C. Some structural models previously reported are tested by comparing calculated wide-angle X-ray diffraction patterns with the experimental ones. A method for the quantitative determination of the γ-form crystallinity by X-ray line profiles is proposed. The original copolymer and its fractions are characterized by differential scanning calorimetry and ¹³C NMR techniques.     

13C NMR spectroscopical sequence analysis of poly(ethylene terephthalate-co-oxybenzoate)s

The sequence distribution of liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s was determined by ¹³C NMR spectroscopical investigations of samples with different compositions. All possible oxybenzoate- and terephthalate-centered triads could be identified and assigned. The analysis of NMR substituent effects confirms the assignment. The comparison of the calculated statistical with the experimentally determined triad distribution shows a tendency for the formation of oxybenzoate blocks in the polymer chain.     

Block poly(ester-urethane)s based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and poly(3-hydroxyhexanoate-co-3-hydroxyoctanoate)

A series of block poly(ester-urethane) poly(3/4HB-HHxHO) urethanes (abbreviated as PUHO) based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB-diol) and poly(3-hydroxyhexanoate-co-3-hydroxyoctanoate) (PHHxHO-diol) segments were synthesized by a facile way of melting polymerization using 1,6-hexamethylene diisocyanate (HDI) as the coupling agent, with different 3HB, 4HB, HHxHO compositions and segment lengths. The chemical structure, molecular weight and distribution were systematically characterized by ¹H, ¹³C nuclear magnetic resonance spectrum (NMR), two-dimensional correlation spectroscopy (COSY (¹H, ¹³C) NMR), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The thermal property was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The hydrophilicity was investigated by static contact angle of water and CH₂I₂. DSC revealed that the poly(3/4HB-HHxHO) urethanes are almost amorphous with a little crystallinity (less than 6%) and T_g from ?23 °C to ?3 °C. The polyurethanes are more hydrophobic (water contact angle 88°–117°) than the P3/4HB and PHHxHO raw materials. The lactate dehydrogenase (LDH) assay and platelet adhesion determination showed that the obtained polyurethanes have much higher platelet adhesion property than raw materials and common biodegradable polymers polylactic acid (PLA) and poly(3-hydroxybutyrate) (PHB). Hydrophobicity and crystallinity degree are important factors to affect the platelet adhesion. All the properties can be tailored by changing the composition and segment length of prepolymers P3/4HB-diol and PHHxHO-diol.     

Amino acids attached to poly(alkylene phosphate)s, 1. Synthesis

The synthesis of poly(alkylene phosphate)s with attached amino acids was elaborated. Two methods of coupling through P—NH bond were used. They were based on the direct reaction of amino acid esters or N,O-bis(trimethylsilyl) substituted amino acids with poly(alkylene chlorophosphate)s. The assumed microstructure of the resulting polymers was confirmed by analysis of the ¹H, ¹³C and ³¹P NMR spectra. Preliminary data on the hydrolytic stability of amino acids modified poly(alkylene phosphate)s are also given.     

Thermotropic elastomers with poly(oxy-1,4-butanediyl) units in the main chain

The paper describes the synthesis of thermotropic elastomers from trimellitimide-terminated poly(oxy-1,4-butanediyl) [synonyms: poly(tetramethylene ether glycol), PTMG; poly(tetrahydrofuran), poly(THF)] and acetoxy group-terminated rigid blocks. Copolyester imides are formed by transesterification polycondensation in the melt. According to ¹³C NMR investigations, their chain sequence distribution is characterized by a block-like structure in which the preformed rigid units are partially exchanged by transesterification reactions during the melt polycondensation. The degree of transesterification depends on the reaction time. The influence of the length of the flexible PTMG units and of the concentration of rigid units on the phase behaviour as well as on the thermal behaviour and the dynamic-mechanical behaviour of the block copolymers is discussed with respect to aromatic model compounds.     

13C NMR sequence analysis, 15. Copolymerization of alanine-NCA with other α-amino acid NCAs

Alanine-N-carboxylic acid anhydride (Ala-NCA) was copolymerized with glycine-NCA, phenylalanine-NCA, valine-NCA, leucine-NCA, and sarcosine-NCA in various solvents and with various catalysts; 22,6 MHz ¹³C NMR spectra and 90 MHz ¹H NMR spectra of the resulting copolypeptides were measured in trifluoroacetic acid and from the signal intensities the rate of incorporation was estimated. The copolypeptides poly(Ala/Gly) and poly(Ala/Phe) contained both monomeric units in an almost equal concentration, while the low reactivity of Val-NCA and Leu-NCA resulted in a lower concentration of these residues compared with Ala in poly(Ala/Val) and poly(Ala/Leu). The ¹³C NMR spectra of poly(Ala/Gly) exhibit four CO-signals which could be assigned by comparison with the corresponding homopolypeptides and with the sequence polypeptides (Ala-Ala-Gly-Gly)_n, and (Ala-Gly-Gly)_n. From the intensities of these CO-signals the average length of the homogeneous blocks was calculated. Both block lengths and rate of incorporation proved to be almost independent of solvent, catalyst, and reaction temperature. Poly(Ala/Phe) and poly(Ala/Sar) show also four CO-signals, but poly(Ala/Val) only two and poly(Ala/Leu) one. The number and shape of the CO-signals allow one to decide whether random copolypeptides were obtained or not.     

Investigation of γ-irradiated syndiotactic poly(2-methylheptyl methacrylate) using NMR spectroscopy

Syndiotactic poly(2-methylheptyl methacrylate) which was γ-irradiated at room temperature to a dose of 1600 kGy was investigated by NMR spectroscopy. The ¹H and ¹³C resonances for the macromolecular chain were assigned by using the 2D and the DEPT (distortionless enhancement by polarization transfer) technique. The spin-echo modified 2D NMR pulse sequence was used to investigate the small molecules and new structures which were formed during γ-irradiation. The radiation mechanisms for cleavage of the side chain from the main chain and formation of double bonds from both the main chain and the side chain have been formulated based upon the NMR analysis.     

Le poly(α-acétoxystyrène) et les copolymères de l'α-acétoxystyrène avec le styrène et styrènes substitués obtenus par polymérisation thermique. Etude de la microstructure et de la stabilité thermique des polymères

The microstructure of poly(α-acetoxystyrene), prepared from α-acetoxystyrene by bulk thermal polymerization, was studied by ¹H and ¹³C NMR spectroscopy. Anomalies observed in the NMR spectra could be ascribed to fragmentations with formation of benzoxy and acetoxy radicals followed by re-initiation. The thermal degradation of the polymer, resulting in the formation of polyphenylacetylene, rules out certain types of transfer. α-Acetoxystyrene was copolymerized with styrene or substituted styrenes and the NMR study (¹H and ¹³C) was limited to α-acetoxystyrene. The composition of the copolymer could be ascertained by means of the resonances of the quaternary carbons of the aromatic cycle. The copolymers were characterized by viscometry, GPC, and thermal degradation. Their compositions, except that of poly(α-acetoxystyrene-co-styrene) were determined by elemental analysis.     

NMR evidence of the block structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization

The structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization was studied by ¹H and ¹³C 1 D and 2D NMR methods including SINEPT, COSY, LR H-H-C RELAY and COLOC using model homopolymers of methyl methacrylate (MMA) and ethyl acrylate (EA) of a length equal to that of the blocks and prepared under the same conditions. The ¹H and ¹³C spectra of the copolymer are shown to be a superposition of the respective spectra of the homopolymers, with the exception that the copolymer lacks the terminal group present in the MMA homopolymer and the initiating group of the EA polymer. Moreover, a new minor signal is found in the CH₂ region of the copolymer which is shown to belong to the link of the blocks. The existence of a direct link between the blocks is further supported by the results of 1D and 2D coherence transfer methods, especially, those using the newly modified DS INEPT and H-C-C RELAY pulse sequences.     

A modified synthesis of liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s with completely random chain structure

A new method for synthesis of liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s (PET/HBA) is proposed. In order to prevent formation of PET-rich phases, complex monomers were used instead of PET. In comparison tc copolyesters synthesized conventionally, the new products proved to be much more homogeneous. ¹³C NMR measurements evidenced that the chain segment distribution is almost random. In contrast to literature data for a copolyester composition of PET/HBA (50/50 mol/mol) only a single glass transition was detected by dynamic mechanical analysis. The influence of transesterification reactions on the homogeneity is discussed.     

Synthesis and characterisation of poly(arylene sulfides), 6. Synthesis of block copoly(arylene sulfides)

Novel ABA block copolymers of poly(1,4-phenylene sulfide) (PPS(A)) and poly-(2-methyl-1,4-phenylene sulfide) (PMPS(B)) were synthesised from bis(4-bromophenyl) sulfone (BBS) by sequential reaction with copper(I) 4-bromo-2-methylbenzenethiolate (CBMT) and copper(I) 4-bromobenzenethiolate (CBT). PPS, PMPS and PPS/PMPS random copolymers were also prepared to aid block copolymer characterisation. Polymer fractions were studied by hot-stage microscopy to evaluate melting ranges, and molar masses were computed from bromine end-group concentrations and from gel permeation chromatography studies. Compositional analyses were made by IR and ¹H NMR spectroscopy leading to confirmation of the block copolymer structure and to evaluation of the degrees of polymerisation of the individual blocks.     

Investigation of poly(arylenevinylene)s, 24. High-resolution solid-state 13C NMR spectroscopy of poly(1,4-phenylenevinylene)s

High-resolution ¹³C NMR spectra of solid poly(1,4-phenylenevinylene), poly(1,4-phenylene-1,2-diphenylvinylene) and of three related, substituted polymers (? CN, ? OCH₃, ? O? ) were obtained with a combined technique of heteronuclear decoupling, cross-polarization and magic angle spinning. The reported chemical shifts were assigned by means of solid model compounds (trans-stilbene, trans, trans-1,4-distyrylbenzene, tetraphenylethylene). Utilizing the high sensitivity of ¹³C NMR chemical shifts to chemical structure, this method is applied to structure confirmation, the determination of sp³-defects in poly(phenylenevinylene)s PPV, and the determination of sterical and electronical effects of phenyl and phenylene groups.