Thermal stability of poly(styrene) containing no head-to-head units

General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer. This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques. A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.     

Determination of residual levels of unsaturation in partially hydrogenated poly(2,3-diphenyl-1,3-butadiene) using TG

The thermal degradation characteristics of head-to-head poly(styrene) [HHPS] should provide insight with respect to the impact of head-to-head placement on the thermal stability of traditional atactic head-to-tail polymer [HTPS]. The synthesis of head-to-head poly(styrene) must be accomplished indirectly. The head-to-head polymer is most satisfactorily obtained by dissolving metal reduction of poly(2,3-diphenyl-1,3-butadiene) [PDBD] generated by radical polymerization of the corresponding diene monomer. Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of poly(2,3-diphenyl-1,3-butadiene) is prominent at 374°C and that for head-to-head poly(styrene) is similarly facile at 406°C, it seemed feasible that TG of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent of hydrogenation. This has been demonstrated for various levels of unsaturation remaining - from approximately 90 to less than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected by the asymmetry of the decomposition peak for the polymer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic Parameters of Polymer Degradation by SAPO-37

High density poly(ethylene) has been submitted to thermal degradation alone, and in the presence of silicoaluminophosphate SAPO-37. The processes were carried out in a reactor connected on line to a gas chromatograph/mass spectrometer in order to analyze the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature until 800°C, under nitrogen dynamic atmosphere, with multiple heating rates. From TG curves, the activation energy related to degradation process was calculated using the Flynn and Wall multiple heating rate kinetic model for pure polymer (PE) and for polymer in the presence of catalyst (PE/S37). SAPO-37 showed good selectivity for low molecular mass hydrocarbons in PE catalytic degradation. This revised version was published online in July 2006 with corrections to the Cover Date.     

高分子量DL-丙交酯的合成及热降解

研究了聚ＤＬ－丙交酯（ＰＤＬＬＡ）的合成及热降解性能。发现影响聚合物分子量的关键因素是单体的重结晶、引发剂的浓度以及安瓿瓶在封管时的干燥和真空度。采用ＤＳＣ、ＴＧＡ分析了ＰＤＬＬＡ的玻璃化转变和热分解。ＰＤＬＬＡ是热不稳定聚合物,影响其热稳定性的主要因素是残留单体、催化剂和低聚物的含量,将聚合物溶解沉淀处理可以延缓其热解速度,提高它的热稳定性。     

Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis–mass spectrometry

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.     

Studies on CSA-induced processability of conducting poly(o-toluidine) and its polyblend with ABS

Poly(o-toluidine) emeraldine base (EB) has been protonated with d,l -camphor sulfonic acid (HCSA). The CSA-doped poly(o-toluidine) (POT-CSA) is completely soluble in m-cresol, and the electrical conductivity is ∼ 28 S/cm. The incorporation of CSA has been proved by means of UV-Vis and IR spectroscopy. Thermogravimetric (TG)/mass (MS) analysis shows that POT-CSA is stable up to 180°C indicating the processability with other insulating polymers upto this temperature. TG curve of POT-CSA yields a four step decomposition pattern, and the degradation of the polymer backbone starts at 430°C. The thermal elimination of CSA occurs in the temperature range of 180 to 430°C. The viscometric and spectroscopic results suggest the change in molecular conformation from the compact coil to the expanded coil type which is enhanced by increasing the protonation level of EB by the addition of HCSA. The conductivity data were well equivalent to the viscometric data. Furthermore, POT-CSA-ABS (acrylonitrile/butadiene/styrene) blends were successfully fabricated with an extremely low percolation threshold of 2.66%. The scanning tunneling microscopic (STM) results reveal that the low percolation threshold reflects the formation of interconnecting path of conducting particles in ABS matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2657–2665, 1999     

Kinetics of the complex process of thermo-oxidative degradation of poly(vinyl alcohol)

The thermo-oxidative degradation of poly(vinyl alcohol) (PVA) has been investigated by TG+DTG+DTA simultaneous analysis performed in static air atmosphere, at four heating rates, namely 3, 5, 10 and 15 K min⁻¹. TG, DTG and DTA curves showed that, in the temperature range 25–700°C, four successive processes occur. The first process consisting in the loss of physical adsorbed water is followed by three processes of thermal and/or thermo-oxidative degradations. The processing of the non-isothermal data corresponding to the second process (the first process of thermo-oxidation) was performed by using Netzsch Thermokinetics — A Software Module for Kinetic Analysis. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the investigated process is complex one. The mechanism of this process and the corresponding kinetic parameters were determined by Multivariate Non-linear Regression Program and checked for quasi-isothermal experimental data. It was pointed out that the first process of thermo-oxidation of PVA consists in three consecutive steps having Avrami-Erofeev kinetic model. The obtained results can be used for prediction of the thermal lifetime of PVA corresponding to a certain temperature of use and an endpoint criterion.     

The thermal degradation of poly(diethyl fumarate)

The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 °C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P₀, calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA).     

二氧化碳-氧化苯乙烯的共聚反应

由ＣＯ２－氧化苯乙烯（ＳｔＯ）配位催化共聚制得脂肪族聚碳酸苯亚乙酯,并用 ＩＲ、１ＨＮＭＲ和 ＤＳＣ等进行表征,用 ＴＧ对聚合物的热稳定性进行了分析。     

Thermal degradation of poly(p-phenylene-graft-?-caprolactone) copolymer

The thermal degradation of poly(p-phenylene-graft-?-caprolactone) (PPP), synthesized by Suzuki polycondensation of poly(?-caprolactone) (PCL) with a central 2,5-dibromo-1,4-benzene on the chain with 1,4-phenylene-diboronic acid, has been studied via direct pyrolysis mass spectrometry. The thermal degradation occurred mainly in two steps. In the first step, decomposition of PCL chains occurred. A slight increase in thermal stability of PCL chains was noted. In the second stage of pyrolysis, the decomposition of the polyphenylene backbone takes place. The evolution of CL monomer or small CL segments left on the phenyl ring continued also in the temperature region where degradation of PPP backbone started.     

Anionic dispersion polymerization. I. control of particle size

Studies on the mechanism for the formation of the stable dispersion polystyrene prepared by anionic dispersion polymerization of styrene in n-hexane using poly(t-butylstyrene) as the stabilizing moiety in steric stabilizer have been performed by a combination of size exclusion chromatographic (SEC) and transmission electron microscopic (TEM) analyses. When the molecular weight of poly(t-butylstyrene) as the stabilizing moiety exceeded 1.76 X 10⁴ g/mol, the formed polymer particles successfully retained a steric stability. Block copolymerization of t-butylstyrene and styrene in n-hexane has also provided the dispersion polymer particles with a relatively narrow size distribution. The stable dispersion polystyrenes have been produced in n-hexane by polymerization of styrene using the mixture of sec-butyllithium and poly(t-butylstyryl)lithium. The polymerization is called living dispersion polymerization (LDP), in which poly(t-butylstyrene-b-styrene) as the steric stabilizer and polystyrene can be formed simultaneously. The particle size was readily controlled by a combination of the concentration of monomer and the molar ratio of poly(t-butylstyryl)lithium to sec-butyllithium, for instance, [stabilizing moiety]/[RLi]. © 1996 John Wiley & Sons, Inc.     

Effect of inert diluent segment on the miscibility behavior of poly(vinylphenol) with poly(acetoxystyrene) blends

Polymer blends of poly(vinylphenol) (PVPh) and poly(styrene‐co‐vinylphenol) with poly(p‐acetoxystyrene) (PAS) were prepared by solution casting from tetrahydrofuran solution. The thermal properties and hydrogen bonding of the blends were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy. Although hydrogen bonding existed between the PVPh and PAS segments, the experimental results indicated that PVPh is immiscible with PAS as shown by the existence of two glass‐transition temperatures over the entire composition range by DSC. This phenomenon is attributed to the strong self‐association of PVPh, intramolecular screening, and functional group accessibility effects of the PVPh/PAS blend system. However, the incorporation of an inert diluent moiety such as styrene into the PVPh chain renders the modified polymer to be miscible with PAS. Copolymers containing between 16 and 51 mol % vinylphenol were fully miscible with PAS according to DSC studies. These observed results were caused by the reduction of the strong self‐association of PVPh and the increase of the interassociation between PVPh and PAS segments with the incorporation of styrene on the PVPh chain. According to the Painter‐Coleman association model, the interassociation equilibrium constant of PVPh/PAS blends was determined by a model compound and polymer blend. Good correlation between these two methods was obtained after considering the intramolecular screening and functional group accessibility effect in the polymer blend. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1661–1672, 2002     

The non-oxidative thermal degradation of poly (Di-2-chloroethyl itaconate)

The non-oxidative thermal degradation of poly (di-2-chloroethyl itaconate) (PD2CEI) was studied by TG and by analysing the thermal products. The major processes occurring during thermal analysis are crosslinking, depolymerisation and carbonisation. The thermal degradation activation energy increased with increasing sample mass loss. The thermal degradation of PD2CEI was compared to that of the structurally similar poly(2-chloroethyl methacrylate) (P2CMA).     

Synthesis of Poly(styrene sulfonyl chloride) via reversible addition-fragmentation chain transfer polymerization and characterization thereof for membrane applications

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been examined for the synthesis of poly (styrene sulfonyl chloride) (PSSC) of high molecular weight and narrow polydispersity index (PDI). PSSC, contains reactive sulfonyl chloride that can allow use of organic solvent for membrane casting, and chemical modification through reactive sulfonyl groups. For PSSC preparation, end-capped styrene i.e. styrene sulfonyl chloride (SSC) is used as a monomer, which is derived from sodium 4-vinylbenzenesulfonate by chlorination with thionyl chloride. Fourier transform infrared spectroscopy, Raman spectroscopy and Proton nuclear magnetic resonance spectroscopy, have been successfully used to confirm the polymer architecture. End-group of PSSC containing RAFT agent (Cyanomethyl N-methyl-N-phenylcarbamodithioate), is also confirmed by fragmentation analysis using Gas chromatography-mass spectroscopy. Evaluation of PSSC by X-ray diffraction and differential scanning calorimetry showed that resulting polymer is predominantly amorphous in nature and has a glass transition temperature of 119 ​°C. Gel permeation chromatography data reveals formation of high molecular weight (84 ​kDa) PSSC with and low PDI (1.4). Moreover, PSSC can be converted to polyelectrolyte and can be crosslinked by interfacial polymerization concept; hence, it would have considerable prospective for membrane preparation for fuel cell and water purification.     

Chemical reactions occurring in the thermal treatment of PC/PMMA blends

The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu₂), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl₃, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1873–1884, 1998     

A novel route to poly(2-hydroxyethyl methacrylate) and its amphiphilic block copolymers

The vinyl of the ester group of 2-vinyloxyethyl methacrylate was first selectively reacted with acetic acid to obtain 2-[1-(acetoxy)ethoxy]ethyl methacrylate ( 2 ). This protected monomer was subjected to anionic polymerization in tetrahydrofuran at −60°C in the presence of LiCl, using 1,1-diphenylhexyllithium as initiator. The molecular weight of the polymer could thus be controlled and a narrow molecular weight distribution obtained. The protecting group, 1-(acetoxy)ethyl, could be easily eliminated (by quenching the polymerization reaction with methanol and water) to generate poly(2-hydroxyethyl methacrylate) (poly(HEMA)). Block copolymers were also prepared by the sequential anionic polymerization of MMA and 2 or styrene and 2 . They possess narrow molecular weight distributions, and controlled molecular weights and compositions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1865–1872, 1998     

Dynamic birefringence in solutions of poly (naphthoyleneimide benzimidazole) in different stages of hydrolytic thermal degradation

Flow birefringence (FB) has been investigated in solutions of products of hydrolytic degradation of poly(naphthoyleneimide benzimidazole) (PNIB) in 96% sulphuric acid PNIB solutions have previously been subjected to heating at various temperatures from 65 to 120°C and then investigated at 22°C by FB and viscometry. A monotonic decrease in intrinsic viscosity and the molecular weightM of thermal degradation products with increasing degradation temperature was detected. At the same time, the shear optical coefficients in series of products with decreasingM first increases and then, at treatment temperatures exceeding 90°C, decreases with decreasing [ν] in accordance with decreasingM of the product. Possible reasons for the detected anomaly have been discussed.     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure

A styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure, 4‐vinylbenzyl 1,3‐oxathiolane‐2‐thione‐5‐ylmethyl ether (VBTE), was synthesized from 4‐vinylbenzyl glycidyl ether (VBGE) and carbon disulfide in the presence of lithium bromide in 86% yield. Radical polymerization of VBTE in dimethyl sulfoxide by 2,2′‐azobisisobutyronitrile was carried out at 60 °C to afford the corresponding the polymer, polyVBTE, in 64% yield. PolyVBTE with number‐averaged molecular weight higher than 31,000 was obtained. The glass transition temperature (T_g) and 5 wt % decomposition temperature (T_d5) of the polyVBTE were evaluated to be 66 and 264 °C under nitrogen atmosphere by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBTE repeating unit could also be obtained via polymer reaction, that is, a lithium bromide‐catalyzed addition of carbon disulfide to a polyVBGE prepared from a radical polymerization of VBGE. Copolymerization of VBTE and styrene with various compositions efficiently gave copolymers of VBTE and styrene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Thermo‐mechanical Properties of PEO‐PU/PAN Semi‐Interpenetrating Polymer Networks and their LiClO4 Salt‐Complexes

This paper is an investigation on the thermo‐mechanical properties of a new class of materials, which holds promise for its potential use as solid polymer electrolytes, i.e., SPE material. A series of poly(ethylene oxide)‐polyurethane/poly(acrylonitrile) (PEO‐PU/PAN) semi‐IPNs, along with their LiClO₄ salt complexes, were characterized for their thermal, mechanical and dimensional stability using DSC, TG‐DTA, UTM and DMTA. The glass transition temperature (T_g) of both the undoped and doped semi‐IPNs, obtained by DSC, remained well below room temperature (～?50°C to ?35°C), satisfying one of the essential requirements to serve as a SPE host matrix. The crystallization process in the PEO segments of the PEO‐PU/PAN semi‐IPNs was prevented at higher salt concentrations, which is attributed to the Li⁺ ion mediated pseudo‐crosslinks. Good thermal stability of the semi‐IPNs was evident from the degradation onset temperature (T₀～240°C) with a three‐stage degradation process, which is independent of the PAN content as observed from differential thermogravimetric studies. The incorporation of PAN in the PEO‐PU networks results in improved mechanical properties, such as tensile strength and modulus while retaining the flexibility of the semi‐IPNs. The peak temperatures and storage modulus obtained from DMTA correlates well with the observations of DSC and tensile measurements.