Thermal Stability Of Polymers Research Articles

Thermal stability and high glass transition temperature of 4-chloromethyl styrene polymers bearing carbazolyl moieties

A new styrene derivative monomer, 4-( N-carbazolyl)methyl styrene (CzMS), was synthesized by reacting 4-chloromethyl styrene with carbazole in the presence of sodium hydride. Then, CzMS was homopolymerized and copolymerized with different monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA) and n-butyl acrylate (BA) by free radical polymerization method in N, N-di-methylformamide (DMF) solution at 70 ± 1 °C using azobisisobutyronitrile initiator to give the copolymers I– V in good yields. The structure of all the resulted polymers was characterized and confirmed by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. The average molecular weight and glass transition temperature of polymers were determined using gel permeation chromatograph (GPC) and differential scanning calorimeter (DSC) instruments, respectively. It was found that these polymers with carbazole moieties have high thermal stability and the presence of bulk carbazole groups in polymer side chains leads to an increase in the rigidity and glass transition temperature of polymers.

Softening and melting mechanisms of polyamides interfering with sliding stability under adhesive conditions

The thermal stability of polymers is a main issue when used as friction elements under dry sliding. Cast polyamide grades processed with either natrium or magnesium catalysors are slid on a small-scale and a large-scale test configuration to reveal the effect of softening or degradation on the sliding stability and to investigate possibilities for extrapolation of friction and wear rates between both testing scales. The combination of softening and afterwards transition into the glassy state is detrimental for the sliding stability of natrium catalysed polyamides, characterised by heavy noise during sliding. A transfer film formed under continuous softening also provides high friction. Melting during initial sliding is necessary for stabilisation in both friction and wear, and eventual softening of a molten film near the end of the test then not deteriorates the sliding stability. Softening of magnesium catalysed polyamides is favourable for the formation of a coherent transfer film resulting in more stable sliding than natrium catalysed polyamides. The differences in softening mechanisms of both polyamide grades is correlated to structural changes investigated by thermal analysis and Raman spectroscopy: the γ crystalline structure prevails in magnesium catalysed samples and the α crystalline structure is predominant in natrium catalysed samples. For internal oil lubricated polyamides, a time dependent degradation of the polyamide bulk deteriorates the supply of internal oil lubricant to the sliding interface, resulting in high friction and wear under overload conditions. As the degradation mechanisms during sliding are strongly correlated to the test set-up, extrapolation is only possible for friction in a limited application range, while wear rates cannot be extrapolated.

An experimental investigation of heat transfer in thermally unstable polymer systems

An experimental study is made into the process of heat transfer from a pulse-superheated probe to a solidified polymer system at probe temperatures above the temperature Td∞ of the beginning of thermal destruction of matter in a quasi-static process. Use is made of the procedures of thermal stabilization of the pulse-superheated probe (with the characteristic time of constancy of superheated probe temperature of 1 ms) and of shock heating (with the characteristic time of increasing the probe temperature of 1 µs and that of monitoring its cooling-down of 1 ms). The effect of short-term thermal stability of polymers in the region of T > Td∞ is revealed. A procedure is developed for identifying the signs of thermal destruction of polymers in the pulsed process. The maximal values are estimated of the density of heat flux through samples without their thermal destruction.

Radiation-induced degradation of hydroxyapatite/poly L-lactide composite biomaterial

The effects of gamma irradiation on the structure and properties of hydroxyapatite/poly L-lactide (HAp/PLLA) biomaterial have been investigated. Effects of radiation on microstructure, degradation of polymer part and thermal stability of composite were determined by scanning electronic microscopy (SEM), gel permeation chromatography (GPC) and thermogravimetric analysis (TGA), respectively. Mechanical properties were obtained through mechanical strength and elasticity modulus. Presented results show that properties of HAp/PLLA decay with irradiation dose, but for doses required for sterilization, changes and damaging effects are acceptable.

SYNTHESIS AND CHARACTERIZATION OF MESOGEN-JACKETED LIQUID CRYSTALLINE POLYMER CONTAINING 1,3,4-OXADIAZOLE

A series of monomers {2,5-bis[(5-alkyl-phenyl)-1,3,4-oxadiazole] styrene}(BOXE) were designed and synthesized.By radical polymerization initiated BPO with a novel series of mesogen-jacketed polymers containing 1,3,4-oxadiazole were prepared.Molecular weight and molecular weight distribution of polymers were measured by GPC.The glass transition temperature (T_g) and thermal stability of polymers were studied by DSC and TGA.The results indicate that these polymers have good thermal stability.These liquid crystal polymers have well defined structure,and possess special photo-electronic properties.

Thermal studies on polythiophene containing mesogenic side chains

Series of thiophenes containing mesogenic side chains at the 3 rd position are synthesized. The thermal transitions and thermal stability of the synthesized monomers and polymers are studied. The polarizing microscopic studies of synthesized monomers showed nematic liquid crystalline phase and these mesophases further confirmed by differential scanning calorimetric study. The obtained melting and the isotropic temperatures decrease linearly with the increase of aliphatic chain length. The transition temperatures determined from DSC analysis, overlap well with the temperatures obtained from optical microscopy studies. Thermal stability of the compounds is analysed using thermogravimetric studies. Thermal stability of monomers and polymers has been determined by calculating IPDT values. Structural influence on thermal degradation patterns of monomers and polymers are also discussed.

Thermal characteristics and pyrolysis of methyl-di(phenylethynyl)silane resin

Thermal stability of a recently synthesized polymeric methyl-di(phenylethynyl)silane (MDPES) resin was studied using a number of thermal and spectrometric analytical techniques. The polymer exhibits extremely high thermal stability. Thermogravimetric analysis (TGA) shows that the temperature of 5% weight loss (Td5) was 615°C and total weight loss at 800°C was 8.9%, in nitrogen atmosphere, while in air, Td5 was found to be 562°C, and total weight loss at 800°C was found to be 55.8% of the initial weight. Differential thermal degradation (DTG) studies show that the thermal degradation of MDPES resin was single-stage in air and two-stage in nitrogen. The thermal degradation kinetics was studied using dynamic TGA, and the apparent activation energies were estimated to be 120.5 and 114.8 kJ/mol in air, respectively, by Kissinger and Coats–Redfern method. The white flaky pyrolysis residue was identified to be silicon dioxide by FTIR and EDS, indicating that the thermal stability of polymer may be enhanced by the formation of a thin silicon dioxide film on the material surface. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 605–610, 2007

Thermal analysis techniques for characterization of polymer materials

Routine DSC and TGA techniques, used to characterise polymer thermal stability, have been further used for assessment of comparative thermal stability of various polymer materials and for prediction of material lifetimes. The following materials were investigated: (1) commercial and experimental polymer materials – results for poly(vinyl chloride) (PVC) and bisphenol A polycarbonate (PC) are presented; (2) a polydimethylsiloxane–polytetrafluoroethylene (SIL–PTFE) coating system; and (3) commercially available linear low density polyethylene (PE-LLD), unmodified and modified chemically and physically. The plot of reciprocal temperature of initial decomposition 1/ T di vs log heating rate β has been recommended for assessment of comparative thermal stability. The lifetime of polymer materials was calculated from the plots of log time-to-failure, log t f, vs reciprocal temperature 1/ T, where t f values were obtained using T di from TGA measurements or directly from the oxidation induction time (OIT) data as criteria for initial deterioration of polymer thermal stability. The following sequences of increasing thermal stability were found for investigated materials: (1) PVC ≪ PC; (2) SIL < SIL–PTFE 20% < SIL–PTFE 50% ≪ PTFE; (3) (B) PE-LLD, grafted < (A) PE-LLD, unmodified < (C) PE-LLD, filled. The lifetime of polymer materials predicted from the plots of log t f vs 1/ T are in reasonable agreement with experimental data and users' observations, e.g. approximately 1 year for PC and unmodified PE-LLD both at 373 K (100 °C) and for PVC at temperature of outdoor conditions about 298 K (25 °C).

Synthesis and Characterization of Pyridine‐Based Polybenzimidazoles for High Temperature Polymer Electrolyte Membrane Fuel Cell Applications

AbstractA series of polybenzimidazoles (PBIs) incorporating main chain pyridine groups were synthesized from the pyridine dicarboxylic acids (2,4‐, 2,5‐, 2,6‐ and 3,5‐) and 3,3′,4,4′‐tetraaminobiphenyl, using polyphosphoric acid (PPA) as both solvent and polycondensation reagent. A novel process, termed the PPA process, has been developed to prepare phosphoric acid (PA) doped PBI membranes by direct‐casting of the PPA polymerization solution without isolation or re‐dissolution of the polymers. The subsequent hydrolysis of PPA to PA by moisture absorbed from the atmosphere usually induced a transition from the solution state to a gel‐like state and produced PA‐doped PBI membranes with a desirable suite of physiochemical properties. The polymer structure characterization included inherent viscosity (I.V.) determination as a measurement of polymer molecular weight and thermal stability assessment via thermogravimetric analysis. Physiochemical properties of the doped membrane were studied by measurements of the PA doping level, ionic conductivity and mechanical properties. The resulting pyridine‐based polybenzimidazole membranes displayed high PA doping levels, ranging from 15 to 25 mol of PA per PBI repeat unit, which contributed to their unprecedented high proton conductivities of 0.1 to 0.2 S cm–1 at 160 °C. The mechanical property measurements showed that the pyridine‐based PBI membranes were thermally stable and maintained mechanical integrity even at high PA doping levels. Preliminary fuel cell tests demonstrated the feasibility of the novel pyridine‐based PBI (PPBI) membranes from the PPA process for operating fuel cells at temperatures in excess of 120 °C without any external humidification.

Radiation Polymerization of 4-N-Acryloylamidobenzonitrile: Amidoximation, Complexation and Biological Activity

ABSTRACT A new polymer containing cyano groups was synthesized by γ-irradiation. The amidoximated polymer was prepared using hydroxylamine hydrochloride in basic medium. The characterization of monomer, polymer and amidoximation was confirmed by IR and NMR spectroscopy. The complex formation of the amidoxime salt towards AgI, CuII and AgI/CuII mixture in aqueous solution was studied by AAS, EDS, and ESR spectrometry. The binding capacity of these metal ions is selective in favor of silver(I) ion. The thermal stability of polymers and their complexes was investigated using TG analysis. The change in their morphology was observed by SEM. Potential biological activity of the polymer and its complexes towards some types of bacteria and fungi was tested under the same conditions. Silver (I) complexed polymer had a strong biocidal activity for all tested bacteria and fungi.

Thermal degradation and pyrolysis of mixtures based on poly(3-hydroxybutyrate-8%-3-hydroxyvalerate) and cellulose derivatives

Thermal degradation and pyrolysis behaviour of mixtures based on poly(3-hydroxybutyrate- co-8%-3-hydroxyvalerate) (P(HB-8%HV)) and cellulose derivatives has been studied. The effect of the formulation of mixtures in the thermal degradation of both co-components was evaluated. TG/DTG experiments and Py-GC–MS were used in this study. Solid–solid and gas–solid interactions between co-components were analyzed by using a simple mixture rule. Mixtures with microcrystalline cellulose (MC) resulted in an enhancement of thermal stability of both co-components due to strong hydrogen type interactions in the solid state and between gases evolved from polymer decomposition and solid MC. Crotonic acid seemed to induce a higher order in cellulose, causing disruption of some hydrogen bonds within it and promoting the formation of more stable cellulose structure. On the other hand, sisal fiber showed an unfavourable effect on polymer thermal stability. Acetic acid produced from hemicellulose thermal decomposition seemed to act as acid promoter for the random scission of ester linkages in P(HB-8%HV).

Thermal stability and degradation products analysis of benzocyclobutene-terminated imide polymers

Benzocyclobutene-terminated imides were prepared and fully characterized with 1H NMR, MS, and FT-IR. The thermal degradation of polymers was investigated by using thermogravimetric analyzer (TGA) and high-resolution pyrolysis-gas chromatography–mass spectrometry (HR-Py-GC–MS). TGA showed that thermal degradation of the polymer was a single-stage process in N 2, whereas a three-stage degradation in air atmosphere. The major involved products were found to be CO 2, naphthalene and naphthalene derivatives. Degradation mechanism of the polymer was suggested and the relationship between structures of the polymer and degradation products was also discussed.

Effect of Nanoparticles on the Thermal Stability of Polymers

ABSTRACTThe thermal stability of polymethylmethacrylate loaded with silica nnaoparticles is investigated. The temperature dependence of the mass has been accurately fitted with a single Boltzmann-like dependence. The effect of surface functionalization, size of silica nanoparticles, and concentration of silica nanoparticles is analyzed. A weak increase of the thermal stability of polymethylmethacrylate has been obtained by loading the polymer matrix with nanoparticles. Surface functionalization produced a modest increase in the thermal stability (compared to composites with silica nanoparticles without surface modification).

Effect of Piezoceramic and Ferroelectric Ceramic Materials on the Thermal Stability of an Epoxy Polymer

Effect of Piezoceramic and Ferroelectric Ceramic Materials on the Thermal Stability of an Epoxy Polymer

Characterising the Response of Energetic materials and Polymer-Bonded Explosives (PBXs) to High-Rate Loading.

AbstractPolymer-bonded explosives (PBXs) are being increasingly used as energetic fillings and components in many systems. They are perceived as more chemically and mechanically stable than traditional fillings such as RDX/TNT. They are castable into predetermined shapes, machinable and can be used as structural components. However, along with all these undeniable advantages, as a class, these materials are now undergoing extensive characterisation to ensure they comply with both the legal and technical requirements in energetic systems.It is well-known that polymers display non-linear behaviour and are much more complex than, for example, simple metal systems at any rate of strain. The understanding of PBX systems involves areas as diverse as polymer chemistry, chemical compatibility, mechanical properties, impact tests, and thermal stability. In this paper, aspects of energetic material response are outlined which are relevant to the understanding of PBX sensitivity.

Pervaporation separation of aqueous alcohol solution through a carbazole-functionalized norbornene derivative membrane using living ring-opening metathesis polymerization

Living ring-opening metathesis polymerization (ROMP) of a norbornene derivative containing carbazole group, 5-( N-carbazolyl methylene)-2-norbornene (CbzNB), was carried out to prepare pervaporation membranes for aqueous alcohol solution separation. The linear dependence of the number average molecular weight ( Mn ¯ ) on the [M]/[I] ratio ([M], monomer concentration; [I], initiator concentration) and low polydispersity (PDI) demonstrated a living polymerization of CbzNB. Hydrogenation of poly(CbzNB), poly(H-CbzNB) increased the polymer thermal stability. The water molecules preferentially permeate through the poly(H-CbzNB) membranes. The feed compositions, degree of swelling and molecular size effects of the alcohols on the pervaporation performances were investigated. The separation factor and the permeation rate increase with increasing ethanol concentration in the feed.

Segmented Multifunctional Poly(ether ester) Polymers Containing H-Bonding Units. Preparation and Characterization

A series of poly(ether ester)s containing amide and carbamate groups as H-bonding units and 13-50 mol-% of poly(ethylene glycol) (PEG) segments were prepared by polycondensation in bulk using Ti(OBu)4 as a catalyst. The copolymers were obtained starting from PEG/1,4-butanediol mixtures and a synthetic monomer carrying H-bonding groups. These polymers were designed for biomedical applications, where material biodegradability is required. The influence of the nature of the H-bonding units, the length of the polymethylene spacer between the H-bonding groups and the PEG content on the thermal and solubility properties of the copolymers was investigated. Amide-containing copolymers were more thermally stable than those containing carbamate groups. The PEG content also slightly affected the polymer thermal stability. The DSC traces of all samples presented multiple transitions, whose shape and peak temperature were strongly dependent on the PEG content. Polymer hydrophilicity, surface free energy and equilibrium swelling in phosphate buffer solution (PBS) at 37 °C were mainly influenced by the PEG content, whereas the nature of the H-bonding groups had little effect.

S2-Glass/Epoxy Polymer Nanocomposites: Manufacturing, Structures, Thermal and Mechanical Properties

This paper is primarily focused in studying the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials. Basic correlations between polymer morphology, strength, modulus, toughness, and thermal stability of thermoset nanocomposites were investigated as a function of layered silicate content. S2-glass/epoxy-clay nanocomposites were manufactured through an affordable vacuum assisted resin infusion method (VARIM). The nanocomposites are formed during polymerization when the adsorbing monomer separates the clay particles into nanometer scales. Transmission electron microscopy (TEM) and wide angle X-ray diffraction(WAXD) were used to characterize the morphology of the dispersed clay particles. The thermal properties such as onset of decomposition and glass transition temperatures were determined by Thermo Gravimetric Analysis (TGA) and Dynamic Modulus Analyzer (DMA). Mechanical properties such as interlaminar shear strength, flexural properties and fracture toughness are also determined for both conventional S2-glass/epoxy composites and S2-glass fiber reinforced nanocomposites. The results show significant improvements in mechanical and thermal properties of conventional fiber reinforced composites with low loading of organo silicate nanoparticles. By dispersing 1% by weight nanosilicates, S2-glass/epoxy-clay nanocomposites attributed to almost 44, 24 and 23% improvement in interlaminar shear strength, flexural strength and fracture toughness in comparison to conventional S2-glass/epoxy composites. Similarly, the nanocomposites exhibit approximately 26 C higher decomposition temperatures than that of conventional composites. This improved properties of fiber reinforced polymer nanocomposites are achieved mostly due to increased interfacial surface areas, improved bond characteristics and intercalated/exfoliated morphology of the epoxy-clay nanocomposites. The TEM observations provide evidence of detailed morphology of the polymer layered-clay nanocomposites.

Influence of the amination conditions on the textural properties and chromatographic behaviour of amino-functionalized glycidyl methacrylate-based particulate supports

Amino-functionalization of particulate macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate), obtained by “bulk” polymerization of a novel mixture of monomers, was carried out by reaction with concentrated ammonia, diethylamine (DEA) and the mixture DEA/THF (1:1). The influence of the amination conditions on the polymer mechanical and thermal stability, porous structure and degree of amination was analyzed; it was also found a narrow correlation between these properties and the chromatographic behaviour of the supports. The polymers functionalized with ammonia and DEA/THF were used for hen egg white proteins separation in column packed experiments; both resins carried out the separation of a mixture of lysozyme, ovalbumin and trypsin inhibitor. The DEA/THF functionalized resin showed better performance for egg white protein separation and very good retention capacity (38 mg ovalbumin/ml resin).

Epoxy-silica polymers as restoration materials. Part II

Room temperature reaction of the epoxy resin poly(bisphenolA-co-epichlorohydrin), glycidyl end-capped with the coupling agent (3-aminopropyl)triethoxysilane, in 1:2 (1), 1:1 (2) and 2:1 (3) molar ratios, leads, after curing for three months at room temperature, to glassy, transparent, crack-free solids which were investigated by SEM, TGA, DSC, NIR and Raman spectroscopy. SEM investigations show substantially a great homogeneity over the entire area with absence of cracks, veins and/or fissures and without formations of clusters and/or aggregates. The conversion of oxirane rings, as found by Raman spectroscopy, decreases by increasing the epoxy/amine ratio, with conversion percentages ranging from 95.3 to 81.3%. As a common feature, the presence in 1, 2 and 3 of Si–O–Si linkages increases the polymer degradation temperature and thermal oxidative stability relative to the parent epoxy resin by shifting the weight loss to higher temperatures. Differently from mixtures 2 and 3, which show the Tg at 90 °C, the mixture 1 does not exhibit any detectable glass transition.