Hydrolytic degradation of copolymers based on l-lactic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has led to the use of novel degradable copolyesters. A series of copolyesters based on bis-2-hydroxyethyl terephthalate and l-lactic acid oligomers were synthesized by melt polycondensation [Olewnik E, Czerwiński W, Nowaczyk J, Sepulchre M-O, Tessier M, Salhi S, et al. Synthesis and structural study of copolymers of l-lactic acid and bis(2-hydroxyethyl terephthalate). Eur Polym J, in press]. Hydrolytic degradation of copolymers containing 16.8-52.9 mole ratio of l-lactic acid units was carried out in two buffered solutions at two different temperatures: phosphate buffer solution (pH 7.40) at 45 °C and phosphate-citric buffer solution (pH 7.35) at 60 °C. Degradation of copolyesters was studied by incubating samples in powder form in a concentrated solution from 30 to 180 days.The copolymers were characterized by various analytical techniques. The thermal properties, morphology and structural changes during controlled hydrolysis were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for determining melting points, heats of melting and decomposition temperatures of investigated copolyesters. ¹H NMR spectroscopy was used to observe the decomposition of the polyesters.     

Influence of structure on the properties of polypropylene copolymers and terpolymers

Several Ziegler-Natta copolymers of iPP with ethylene or 1-butene, and terpolymers with both counits have been characterized, devoting special attention to the effect of composition and processing conditions on the crystal structure and final properties. DSC and X-ray diffraction were used to study the polymorphism of copolymers and terpolymers. Comonomer insertion interrupts the isotactic sequences, acting as a structural defect, and the formation of γ form is enhanced. Moreover, crystallinity decreases and crystal structure is modified. Comonomer type and concentration determine the extent of these modifications, resulting in important changes in macroscopic properties. In particular, the excellent optical properties of the analyzed terpolymers make them very attractive for applications such as transparent film or packaging.     

Thermal degradation of copolymers of 2-hydroxyethyl methacrylate and alkyl methacrylates

Thermal degradation of homopolymers of ethyl methacrylate (I), n-butyl methacrylate (II), 2-hydroxyethyl methacrylate (III), and copolymers of III with I and II were carried out by thermal volatilization analysis (TVA) up to 440°C with subsequent subambient thermal volatilization analysis (SATVA). An on-line mass spectrometry coupled with TVA and SATVA was employed to identify the products of thermal degradations. Isothermal pyrolyses of the polymers were carried out separately at 400°C in vacuum for 30 min and the liquid products of decomposition were collected and analysed by gas chromatography. The relationship between the amounts of I and II obtained from pyrolysis and the amounts of these components actually present in the copolymer samples was determined. Also the amount of III and ethyleneglycol dimethacrylate obtained from pyrolysis increases with the amount of III in the copolymer. The polymers were also characterized by differential thermal analysis.     

Synthesis and thermal properties of crosslinkable phosphazene copolymers

Polyphosphazenes of formula [NP(OC₆H₄CN)_x(OCH₂CF₃)_2?x] (x = 0.04–2) were prepared. The copolymers were crosslinked via cyclotrimerization of the nitrilic function, using acid catalysts (chlorosulfonic acid, aluminum chloride) at elevated temperatures. The thermal properties of the crosslinked cyclomatrix polymer were compared to the linear polymer by thermogravimetric analysis and differential scanning calorimetry. When the 4-cyanophenoxy-2,2,2-trifluoroethoxy ratios were less than 0.2, the crosslinked polymers were soluble in polar organic solvents.     

Effects of ozone in surface modification and thermal stability of SEBS block copolymers

SEBS block copolymers were treated under mild conditions in an ozone atmosphere, producing very slightly chemically-modified surfaces. The thermal stability was analysed by chemiluminescence and related to morphological changes observed by AFM. The intrinsic thermal stability was diminished by ozone exposure, but the oxidation induction times were delayed which indicates an enhancement of thermal stability under oxidative conditions. Also, chemiluminescence analysis showed the presence of a typical order-disorder transition at temperatures around 120 °C. Two different sets of samples which showed different morphological patterns were imaged by AFM. The effects of micro-domain separation and inter-domain structure on thermal properties are discussed and explained by a coarsening of the internal interface induced by ozone. A detailed 2D Fourier transformed analysis of AFM images allowed us to identify a regular wrinkled nano-pattern induced by uniaxial strain combined with ozone treatment, offering new opportunities in applications ranging from organic electronics to bio-patterning.     

Synthesis, structural study and hydrolytic degradation of copolymer based on glycolic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has initiated the use of novel degradable copolyesters. One of them is a copolyester based on poly(ethylene terephthalate-co-glycolic acid) (PET-GLA). The copolymer was synthesized by the melt reaction of bis-2-hydroxyethyl terephthalate (BHET) with glycolic acid (GLA) oligomers in the presence of Sb₂O₃ as a catalyst.Hydrolytic degradation of the copolymer was carried out in two buffered solutions at 45 °C: degradation was studied by incubating samples in powder form, in a concentrated solution from 30 to 150 days.The copolymer before and after degradation was characterized by means of different analytical techniques. ¹H and ¹³C NMR spectroscopy was used to confirm the incorporation of glycolide units in PET chains and to observe the structure and decomposition of the novel polyester. The thermal properties and morphology before and during the degradation were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis for determining melting points as well as melting and decomposition temperatures of investigated copolyester.     

Dielectric study of polyacrylonitrile,poly-2-hydroxyethyl methacrylate and their copolymers

A dielectric study on polyacrylonitrile (PAN), poly-2-hydroxyethyl methacrylate (P-HEMA) and copolymers of acrylonitrile and HEMA in the temperature range 30–150° is reported. The loss peaks occur in the frequency region 0.1–100 kHz at temperatures between 110° and 140 for PAN. In copolymers of acrylonitrile with HEMA, these loss peaks were present although their positions on temperature scale and their peak heights depended on the HEMA content. For P-HEMA no relaxation peak was observed in this range of frequency and temperature. The results for copolymers compared with those for the homopolymers suggest that the loss peaks in PAN are due to molecular motion in amorphous regions.     

Influence of changes in fine structure on thermal properties of cotton fibres

Examinations of the structural changes of mercerized cottons in sodium hydroxide or liquid ammonia were followed by determination of the degree of polymerization, sorption ratio and X-ray percentage crystallinity. Comparisons were made of the thermal stability, as indicated by differential thermal analysis and thermogravimetric analysis of the mercerized cottons. A decrease in the percentage crystallinity was found to lower then onset and peak temperatures of the major decomposition reaction. It was also found that the temperature where the major weight loss began increased in the sequence: cellulose III, cellulose II, and cellulose I. Samples in cellulose III crystals form were less thermally stable than samples of cellulose I and cellulose II. It will be noted however that the difference between cellulose II and cellulose III was small. Cotton cellulose II gave a lower yield of levoglucosan than either cotton cellulose I or II.

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Zusammenfassung Strukturelle Veränderungen von merzerisierter Baumwolle in Natriumhydroxid oder flüssigem Ammoniak wurden durch Bestimmung des Polymerisationsgrades, des Sorptionsverhältnisses und der röntgen-Kristallinität verfolgt. Die differentialthermoanalytisch und thermogravimetrisch bestimmte thermische Stabilität der merzerisierten Baumwollen wird verglichen. Eine Verminderung der Kristallinität hat eine Abnahme der Temperaturen zur Folge, bei der die Hauptzersetzungsreaktion einsetzt bzw. mit maximaler Geschwindigkeit verläuft. Es wurde ebenfalls festgestellt, daß die Temperatur, bei der der Hauptgewichtsverlust einsetzt, in der Reihenfolge Cellulose III-Cellulose II-Cellulose I ansteigt. Proben in der Kristallform Cellulose III sind thermisch weniger stabil als die in der Celluloseform I und II. Baumwollcellulose II ergab geringere Ausbeuten an Levoglucosan als Baumwollcellulose I oder III.

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, , , , . . , . , : III, II I. , III , I II. II , 1 III.

     

Influence of substituents in chloropolystyrenes and styrene copolymers on their thermal stability

The thermal properties of chloropolystyrenes and styrene copolymers were investigated by using TG and DTA methods. The chloropolystyrenes were obtained by chlorination of polystyrene (PS) with sulfuryl chloride in two ways: a) radical-initiation (products PR1-PR4, containing 15.7–48 wt. % of chlorine), b) ionic catalysis (product PI, containing 64 wt. % of chlorine). Thus, their structures were different. Three styrene copolymers were investigated too: poly(costyrene-phenyl maleimide) — PF, poly(co-styrene-o-chlorophenylmaleimide) —PCl, poly(co-styrene-p-hydroxyphenylmaleimide)-POH. The thermal stability of the polymers was higher when chlorine atoms were present on the aromatic ring.

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Zusammenfassung Mittels TG- und DTA-Verfahren wurden die thermischen Eigenschaften von Chlorpolystyrolen und Styrolkopolymeren untersucht. Chlorpolystyrole wurden durch die Chlorierung von Styrol mittels Sulfurylchlorid auf zwei Wegen erhalten: a) durch radikalischen Kettenstart (Produkte PR1-PR4 mit 15.7–48 Massenprozent Chlor), b) durch ionische Katalyse (Produkt PI mit 64 Massenprozent Chlor). Die Strukturen sind somit verschieden. Es wurden auch drei Styrolkopolymere untersucht: Poly(co-styrolphenylmaleinsÄureimid) - PF, Poly(co-Styrol-o-ChlorphenylmaleinsÄureimid) PCl, Poly(co-Styrol-p-HydroxyphenylmaleinsÄureimid)- OH. Durch die Einführung von Chloratomen am aromatischen Ring wÄchst die thermische StabilitÄt der Polymere.

     

Influence of transesterification reactions on the miscibility and thermal properties of poly(butylene/diethylene succinate) copolymers

Poly(butylene/diethylene succinate) block copolymers (PBSPDGS), prepared by reactive blending of the parent homopolymers (PBS and PDGS) in the presence of Ti(OBu)₄, were analyzed by ¹H-NMR, TGA and DSC, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. ¹H-NMR analysis evidenced the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis of the melt-quenched samples showed that the melting peak, due to the crystalline phase of PBS, tends to disappear with increasing mixing time and therefore with decreasing the block length in the copolymers. As concern miscibility, a single homogeneous amorphous phase always occurred, independently on block length. Nevertheless, a phase separation, due to the tendency of the PBS blocks to crystallize, was evidenced in the copolymers with long butylene succinate sequences. The results obtained indicated that the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the block copolymers.     

Influence of chemical composition of amide block on the thermal properties and structure of terpolymers

Multiblock terpolymers -(PBT-b-PTMO-b-PA12.10)_n- comprising the polymer systems in which one of the three blocks (PBT) is not soluble in the hard phase of PA12.10 blocks but is slightly soluble in the soft phase of PTMO blocks have been obtained. The DSC and DMTA method was applied to investigate the thermal properties of these polymers and it was found that the PBT block acts as an element that produce stiffness of -(PBT-b-PTMO-b-PA12.10)_n- structure. The terpolymers were compared with the previously described [5] -(PBT-b-PTMO-b-PA12)_n- elastomers, in which the rigid PBT block (DP > 7) dissolves in the hard phase of PA12 blocks and partly dissolves in the soft phase. It was found that even a small change in the chemical structure of the amide block influences significantly on the structure, phase separation and the properties of terpolymers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and thermal properties of diblock copolymers utilizing non-covalent interactions

Diblock copolymers of poly(styrene) and poly(ethylene oxide) were prepared utilizing a bisterpyridine ruthenium complex as non-covalent interaction for the connection of the two blocks. Apart from the synthesis and characterization of four metallo-supramolecular block copolymers, first studies on the thermal properties of the block copolymers have been performed. A complex crystallization behavior was observed and is described in a qualitative fashion. The influence of the metal complex on the thermal stability of the metallo-supramolecular block copolymers remains a question for further investigation.     

Structural effects on the thermal properties of PDPS/PDMS copolymers

A series of PDPS/PDMS copolymers were synthesized through living anionic polymerization withn-butyllithium as an initiator. The changes of thermal property as a function of PDPS content were compared with respect to different types of monomer sequence using differential scanning calorimetry and thermogravimtery. The results indicated that the related variations of the thermal propertiesvs. the PDPS content and the monomer sequence provided independent operative control for preparing materials with desired thermal properties. The thermal stability of these copolymers was dramatically improved with introducing PDPS segment. However, the degree of these improvement pedended greatly on the monomer sequence in the copolymers.     

Effect of precipitation medium and thermal treatment on structure and textural properties of chromium orthophosphates

The effect of the precipitation agent on the structure and textural properties of CrPO₄ (Cr/P=1) catalysts has been studied. Catalysts obtained in propylene oxide-aqueous ammonia exhibited higher thermal stability and, hence, greater surface areas and pore volumes than catalysts obtained in propylene oxide or aqueous ammonia exclusively. The former also showed a small surface area decrease on increasing calcination temperature up to 1073 K. Nevertheless, calcination at 1273 K develops in all cases crystalline CrPO₄, showing the -structure. Moreover, CrPO₄ catalysts thermally treated below 1273 K only exhibited hydrogen bonded hydroxy groups .     

Effects of transesterification and degradation on properties and structure of polycaprolactone-polylactide copolymers

Ester bonds of biodegradable polymers, such as poly (α-hydroxy esters), synthesized by the coordinated anionic ring opening polymerization (CAROP), are subject to transesterification during synthesis. In this work, a series of poly(?-caprolactone)-poly(l-lactide) (PCL-PLA) block and random copolymers with targeted molar mass of 10,000 Da was synthesized to study the mechanism of transesterification reactions via NMR and MALDI-TOF.Polylactide segments are more vulnerable to transesterification compared to polycaprolactone. As a result, the actual quantity of l-lactide in the polymers was less than the target for all studied copolymers because of the decarboxylation and consequent CO elimination from fragments of macromolecules after transesterification. The presence of decarboxylation during transesterification was confirmed analytically and was reflected in the MALDI-TOF and ¹³C NMR spectra. An analysis of the polymer structure pointed to dehydration reactions that led to the formation of cyclic structures and double bonds with possible crosslinking.     

Peculiar temperature dependence on the binding of methyl orange and its homologs by 2-hydroxyethyl methacrylate-N-vinyl-2-pyrrolidone copolymers

2-Hydroxyethyl methacrylate (HEMA)-N-vinyl-2-pyrrolidone (VPy) copolymers of various compositions have been prepared. The copolymers obtained were examined for their ability to bind a homologous series of methyl orange derivatives, methyl orange, ethyl orange, propyl orange, and butyl orange, at 5, 15, 25, and 35°C, respectively, in an aqueous solution. The first binding constants and the thermodynamic parameters that accompanied the binding were evaluated. The binding ability of the copolymer for the small cosolute was enhanced with an increase of the HEMA content in the copolymer. Moreover, a bell-shaped curve appeared in the binding of butyl orange by the copolymers having higher HEMA residues when the first binding constant was plotted as a function of temperature, whereas no such phenomenon was detected for the copolymers with less HEMA content or for the less hydrophobic dye, methyl orange, ethyl orange, or propyl orange. This peculiar temperature dependence of the first binding constant shows that the enthalpy of the binding varies from a positive (unfavorable) value below ca. 15°C to a negative (favorable) one above this temperature. This behavior can be accounted for in terms of more hydrophobic effects involved in the binding process.     

Photocrosslinkable polynorbornene-based block copolymers with enhanced dielectric and thermal properties

Block copolymers poly(endo-N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine)-block-poly(exo-N-(cinnamoyloxyethyl)-7-oxanorborn-5-ene-2,3-dicarboximide) (endo-PTNP-b-exo-PCONBI) and poly(exo-N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine)-block-poly(exo-N-(cinnamoyloxyethyl)-7-oxanorborn-5-ene-2,3-dicarboximide) (exo-PTNP-b-exo-PCONBI) were synthesized by ring-opening metathesis polymerization. The endo- or exo-PTNP served as the high dielectric functional chain, and exo-PCONBI acted as the crosslinking segment. The endo-PTNP-b-exo-PCONBI, in which endo-PTNP has a high content of trans double bond and adopts isotactic configuration, shows a dielectric constant (ε) of 15.5, whereas exo-PTNP-b-exo-PCONBI, in which exo-PTNP has 67% trans double bonds and atactic microstructure, displays relatively low ε of 7.1. The cinnamate groups in exo-PCONBI were crosslinked to form three-dimensional network by cycloaddition reaction under UV irradiation. Exposed to UV-light for 10 min, the cinnamate group in polymer films has a crosslinking conversion of 36%, as determined by UV-Vis absorption measurements. By photocrosslinking, the polymer film has an increased ε of 16.6, a dielectric loss of 0.03, an elevated glass-transition temperature of 137 °C, and an enhanced decomposition temperature of 405 °C, compared to those of polymer films without irradiation.