Thermal degradation of styrene-butadiene diblock copolymer: Part 2—Characteristics and mechanism of degradation of the copolymer

The degradation behaviour of the copolymer has been studied under programmed heating conditions and isothermally at 380°C and compared with the characteristics of the degradation of polystyrene (PS), polybutadiene (PB) and a 1:1 by weight blend of the homopolymers, under the same conditions. The degradation shows many similarities to that of the blend. Evolution of styrene from the PS sections is at first inhibited by early volatile products from the PB parts of the chains and is subsequently retarded by other products. The extent of these stabilisation effects is greater in the copolymer than in the blend. In consequence, greater amounts of PS and PB chain structures can persist to higher degradation temperatures than in the case of homopolymer or blend: this explains the considerably higher proportion of toluene in the volatile products and the greater extent of aromatisation of the PB chain fragments.     

Thermal degradation of blends of polystyrene and poly-4-methoxystyrene with bisphenol A polycarbonate

Blends of polystyrene (PS) and poly-4-methoxystyrene (PMeS) with bisphenol A polycarbonate (PC) (1:1 by weight) have been studied using thermogravimetry (TG) and thermal volatilisation analysis (TVA). The condensable volatile products obtained in the TVA experiments were separated by subambient TVA and the less-volatile liquids were examined by GC-MS. The cold ring fraction of products was characterised by IR spectroscopy.

On degradation, both PS-PC and PMeS-PC blends show an interaction which is observed as a destabilisation. It is suggested that in the degrading blends, the PC component is destabilised as a result of transport of small radical species from the other polymer phase. These radicals may abstract hydrogen atoms, leading to an increase in backbone scission reactions and consequently a lower degradation temperature than when the polymer is degraded alone.     

Chromatographic pattern in recycled high-impact polystyrene (HIPS) - Occurrence of low molecular weight compounds during the life cycle

The analysis of the chromatographic pattern of virgin, reprocessed, thermo-oxidised, and recycled high-impact polystyrene (HIPS) proves to be a suitable and sensitive tool to assess the degree of degradation of HIPS during its first life and subsequent recycling. Different low molecular weight compounds, such as residues of polymerisation, degradation products, and additives have been identified and relatively quantified in HIPS, using microwave-assisted extraction and further analysis by gas chromatography-mass spectrometry (GC-MS). The release of residues of polymerisation has been proven to occur during reprocessing, thermo-oxidation, and in recycled samples, which may show the emissions of volatile and semi-volatile organic compounds during the life cycle of HIPS. A wide range of oxidised degradation products are formed during reprocessing and thermo-oxidation; these products can be identified as oxidised fragments of polystyrene (PS), oxidised fragments from polybutadiene (PB) phase, and oxidised fragments from the grafting points between the PS and PB phase. Real recycled HIPS samples may also contain contaminations and fragments from additives included in their original formulations; the presence of brominated fragments from flame retardants in electronic waste is here observed.     

New high impact polystyrene: Use of poly(1‐hexene) and poly(1‐hexene‐co‐hexadiene) as impact modifiers

In this study, polystyrene (PS) was melt blended with different amounts of poly1‐hexene (PH) and poly(1‐hexene‐co‐hexadiene) (COPOLY) and the blends were compared with conventional PS/polybutadiene (PS/PB) one. Scanning electron microscope revealed that the dispersion of PH and COPOLY in PS matrix was more uniform with the appearance of small particles in PS matrix; however, in the case of PS/PB blends, the fracture surface showed nonhomogenous morphology with the appearance of bigger rubber particles. Based on Differential Scanning Calorimetry (DSC) and dynamic mechanical thermal analysis results, T_g of the blends decreased in comparison with it in neat PS. Impact strength of PS/PH and PS/COPOLY blends was considerably higher than that in PS/PB and significantly higher than the value for neat PS. Tensile test showed substantial improvement in stress at yield and better elongation at break for COPOLY containing blend than the samples containing PH and PB rubbers. Also, blending of PS with 10% of the rubbers was considered in the presence of dicumylperoxide as a probable grafting/cross‐linking agent to produce XPS/COPOLY10 and XPS/PB10 samples, respectively. IR results of the nonsoluble solvent extracted gel showed that COPOLY and PB were grafted to PS matrix during melt blending, which caused higher impact strength in the related samples.     

Molecular design of multicomponent polymer systems. VII. Emulsifying effect of poly(ethylene–b–styrene) copolymer in high-density polyethylene/polystyrene blends

Poly(butadiene–b–styrene) copolymers containing a pure, 1,4-PB block have been synthesized by a “living” coordination process. The complete hydrogenation of the PB chain leads accordingly to a high-density polyethylene (HDPE) block. The emulsifying efficiency of such a copolymer (H-7) in HDPE/PS blends is compared with that of a previously reported poly(ethylene–butene–b–styrene) copolymer (SE-7) obtained by the PB hydrogenation of an anionically prepared PB–b–PS. Microscopy examinations demonstrate unambiguously the interfacial activity of both copolymers in HDPE/PS blends. The tensile mechanical properties of the blends are significantly but also differently modified by the two emulsifiers. The copolymer H-7 gives rise to the highest strengths, but, contrary to the copolymer SE-7, provides a poor ductility to the blends. This different behavior is assumed to result in part from the different characteristics of the hydrogenated PB blocks. The elastomeric HPB chain of SE-7 should form at the interface a more or less extended soft zone whereas a rigid interface would result from the cocrystallization of the HPB chain of H-7 with the HDPE homopolymer.     

Degradation of polymer blends—Part XI. Blends of polystyrene with polyisoprene

The degradation behaviour of polystyrene and cis-1,4-polyisoprene when both are present in the same film as a 1:1 blend has been compared with that when the polymers are degraded separately. Degradations have been studied under programmed heating conditions using TG, TVA, DTA and DSC and also under isothermal conditions at 340 and 360°C. Volatile products of degradation have been studied and separated by sub-ambient TVA and also identified by spectroscopic methods. The volatile products from the blend are the same as those from the constituent polymers. Volatile production occurs less readily for each polymer than when it is degraded alone. Stabilisation of PS is especially marked and under isothermal conditions at the above temperatures, PS does not evolve volatiles until PI degradation is completed. Chain scission in PS, prior to volatilisation, is increased, however, in the presence of PI. It is concluded that the increased scission results from attack on PS by PI radicals of short chain length and that the stabilisation effect on the PS is due to an inhibiting action of dipentene evolved by the PI. Both these reactions follow diffusion of mobile species of rather low volatility from the PI phase into the PS phase.     

Morphology, morphology development and mechanical properties of polystyrene/polybutadiene blends

Polystyrene/polybutadiene (PS/PB) blends with different plastic/rubber ratios were prepared by melt mixing. A detailed investigation on phase morphology development of 30/70 wt.% PS/PB blends as a function of processing conditions was quantitatively analyzed. Morphology is developed at the initial stages of mixing. Suitable blending conditions resulting in optimum phase morphology were obtained at 180 °C, 60 rpm and at 8 min mixing time. Phase morphologies of the blends were also studied as a function of composition. Mechanical properties of the blends were measured. Attempts were made to correlate the morphologies with the properties. Parallel-Voids model has been applied to characterize phase morphology of these blends.     

Thermal analysis of blends of low density polyethylene, poly(ethyl acrylate) and ethylene ethyl acrylate copolymer with polydimethylsiloxane

The thermal stability of blends of polyethylene, poly(ethyl acrylate) and ethylene ethyl acrylate (EEA) copolymer with polydimethylsiloxane has been investigated in inert atmosphere using TG-DTC and TVA. The condensable volatile degradation products from the TVA experiments were separated by subambient TVA and investigated by FT-IR spectroscopy, GC., MS and GCMS techniques. The cold ring fraction was characterised by FT-IR spectroscopy and GC. Most of the degradation products from the blends were similar to the degradation products from polydimethylsiloxane and the corresponding polyolefin when degraded alone, but the presence of some additional products indicated interactions during degradation as a result of blending. The mechanisms of formation of degradation products from the blends are discussed in detail.     

HIPS／PP熔融反应共混及其动态力学性质

研究了高抗冲聚苯乙烯（HIPS）／聚丙烯（PP）共混物在过氧化二异丙苯（DCP）存在下的熔融反应过程及其动态力学性质．HIPS在DCP存在下以聚苯乙烯（PS）的降解为主，伴随着聚丁二烯（PB）的交联和接枝，PP在DCP存在下以降解为主，HIPS／PP在DCP存在下以PP同HIPS的反应接枝为主，这种原位生成的增容剂显著地改善了HIPS／PP两组份间的相容性，其分子运动特征较前两者发生明显变化，PS的Tg下降，PB和PP的Tg升高．     

Morphology, thermal stability and visco-elastic properties of polystyrene-poly(vinyl chloride) blends

The morphology, thermal and mechanical properties of polystyrene (PS) blends with 2.5-20 wt% of poly(vinyl chloride) (PVC) have been studied. The measurement of the glass transition temperature (T_g) from the maxima of tan δ data using dynamic mechanical thermal analysis showed that the blends were incompatible and homogenously distributed only within a limited range of PVC contents in PS. The value of the storage modulus was found to increase initially but then decreased with further addition of PVC in the matrix. Distribution of the phases in the virgin and degraded blends was also studied through scanning electron microscopy. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of blends were found higher than that of pure PS which indicated the stabilizing effects of PVC on PS. The effect varies with the heating rates and the composition of the blends and the phenomenon has been explained due to changing morphology of the blends with composition and the degradation time which affect the interfacial interaction between the degrading products from the polymer components. The kinetic parameters of the degradation process calculated from a method described by Ozawa have been reported for these blends.     

Degradation of polymer mixtures. VII. Blends of poly(vinyl acetate) with polystyrene

The degradation of films containing both PVA and PS has been investigated for comparison with the behavior already reported for PVC/PS blends. The presence of PS had little, if any, effect on the behavior of PVA, but PVA had an effect similar to that of PVC on the degradation of PS. Styrene production was retarded in the blend, compared to PS alone, and an increase in the rate of chain scission was observed for a high molecular weight sample. The molecular weight effect, however, was much smaller than in corresponding experiments with PVC/PS blends. Interference with intermolecular transfer in PS is again advanced as the probable explanation of the stabilization of PS.     

Microphase separation in poly(acrylonitrile–butadiene–styrene) (ABS) studied with paramagnetic spin probes. II. Simulation of electron spin resonance spectra

We recently presented electron spin resonance spectra of poly(acrylonitrile–butadiene–styrene) (ABS) doped with 10‐doxylnonadecane (10DND) and 5‐doxyldecane (5DD) as spin probes. The spectra were measured in three types of ABS that differed in their butadiene contents and methods of preparation. Results for the ABS polymers were evaluated by comparison with similar studies on the homopolymers polybutadiene (PB) and polystyrene (PS) and the copolymers poly(styrene‐co‐acrylonitrile) (SAN) and poly(styrene‐co‐butadiene) (SB). Only one spectral component was detected for 10DND in PB, PS, SAN, and SB. In contrast, two spectral components differing in their dynamic properties were detected in the ABS samples and were assigned to spin probes located in butadiene‐rich domains (the fast component) and SAN‐rich domains (the slow component). The presence of two spectral components was taken as an indication of microphase separation. In this study, we present details on the dynamics and microphase separation by simulating spectra of 10DND in ABS, PB, PS, and SAN. The simulations are based on a dynamic model defined by the components of the rotational diffusion tensor and the diffusion tilt angle between the symmetry axis of the rotational diffusion tensor and the direction of the nitrogen 2p_z atomic orbital. The jump diffusion model led to good agreement with experimental spectra. In this model, the spin probe has a fixed orientation for a given time and then jumps instantaneously to a new orientation. The temperature variation of the rotational correlation time in PB and PS consisted of two dynamic regimes, with different activation energies. The transition temperature at which the change in dynamics occurs (T_tr) is 380 K for PS and 205 K for PB, essentially the same as the corresponding glass‐transition temperatures measured by differential scanning calorimetry. We suggest that T_tr is a better indicator of the glass transition than the temperature at which the total spectral width is 50 G, especially for large probes. The simulation program allowed the determination of the relative intensities of the fast and slow spectral components as a function of temperature; this information was used to clarify the redistribution of the probe above the glass transition of the SAN‐rich component in ABS systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 424–433, 2002; DOI 10.1002/polb.10110     

TG-FTIR study of the thermal degradation of polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends

A series of blends of polyoxymethylene (POM)/thermoplastic polyesterurethane (TPU) has been obtained by mechanical processing using a double screw extruder. The thermal stability and the thermal degradation profiles of POM/TPU blends were investigated by thermogravimetric analysis (TG) coupled on-line with Fourier transform infrared spectroscopy (FTIR). It was found that incorporation of TPU into POM matrix resulted in increase of thermal stability of blends in comparison with pristine materials. The thermal degradation of TPU in inert gas atmosphere proceeds in two steps while the thermal degradation of POM is basically a one step process with a substage in a higher temperature range. The most abundant volatile products of the thermal degradation were identified; the possibly routes of their formation have been presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric study of blends of poly(butylene terephthalate) and a liquid crystalline polyester

The thermal properties of solution-prepared blends of poly(butylene terephthalate) (PBT) and liquid crystalline poly(biphenyl-4,4′-ylene sebacate) (PB8) have been studied by differential scanning calorimetry (DSC). The smectic-to-isotropic (s → i) transition of the mesomorphic component is observed at temperatures slightly increasing with the PB8 content, in the 270–280°C range; on cooling, the mesophase formation (i → s transition) takes place at temperatures that decrease markedly with decreasing PB8 content. The temperatures of the crystal-to-smectic and smectic-to-crystal transitions of PB8 are almost invariant with blend composition. The melting and crystallization temperatures of the PBT phase decrease on increasing the content of the liquid crystalline component. These results, together with those of isothermal calorimetry of both the crystallization of the PBT component and the mesophase formation of the PB8 component of the blends, indicate that the two polymers are not immiscible in the isotropic state. In this latter state, however, the two polyesters undergo transesterification, which can be followed through changes in the DSC scans. The effect of the thermal history on the properties of the blends has been studied with particular attention. Both the dynamic and the isothermal calorimetric measurements provide evidence of an increase of the degree of crystallinity of PBT on addition of the liquid crystalline component up to about 35–50% by weight.     

Degradation of polymer mixtures. VI. Blends of poly(vinyl chloride) with polystyrene

The degradation of films containing both PS and PVC has been examined by TVA and TG. Stabilization of both polymers, more notably PS, is observed, but the degradation products are the same as when the polymers are degraded alone. Molecular weight measurements indicate a more rapid decrease in the molecular weight of PS when PVC is present. The possibility of grafting or other processes leading to chlorine incorporation in PS has been excluded by the results of experiments using ³⁶Cl-labeled PVC. The mechanisms of possible interactions between the degrading polymers are discussed. Processes involving reaction of chlorine radicals with PS at lower temperatures and reaction of PS radicals with the residue of PVC dehydrochlorination or its decomposition products at higher temperatures appear probable.     

Degradation of polymer mixtures. VIII. Blends of poly(vinyl acetate) with poly(methyl methacrylate)

The degradation of blends of PVA and PMMA in the form of films cast from a common solution of the polymers has been studied by TVA, TG, and EGA (evolved gas analysis) for acetic acid. Volatile degradation products have been characterized by spectroscopic and GLC techniques. Molecular weight, spectral and thermal stability changes in PMMA extracted from partially degraded blends have been examined. These blends behave in a closely analogous manner to PVC-PMMA blends already investigated. The results suggest that the PMMA component of the heterogeneous blends is modified in two ways: (1) in a destabilization reaction series initiated by attack of acetate radicals generated in the PVA phase which migrate into the PMMA phase, and (2) in a stabilization reaction involving conversion of ester side groups to acid and subsequently to anhydride ring structures which act as blocking points for depolymerization. The rate of acetic acid production in the blend is less than in PVA degraded alone. The mechanism of degradation of PVA is reconsidered in the light of these results.     

The effect of zinc bromide on the thermal degradation of poly(methyl methacrylate): Part 1—Thermal analysis studies and general nature of the interaction

The degradation behaviour of several different blends of poly(methyl methacrylate) (PMMA) and zinc bromide, under programmed heating to 500°C, has been studied using thermal volatilisation analysis and spectroscopic investigation of the volatile degradation products. The samples were in the form of films cast from a common solution of the components in acetone; these films are found to be transparent, indicating compatibility of PMMA and ZnBr₂. From studies of the visible spectra of cobalt bromide, PMMA and blends of PMMA with CoBr₂, it has been argued that complex formation occurs between the polymer and the transition metal halides: structures are suggested.When degraded alone, PMMA gives only monomer as the degradation product. In the blends with ZnBr₂ (or with CoBr₂), the polymer becomes considerably less stable and the pattern of degradation becomes very complex, with a range of volatile products, of which methyl bromide, carbon dioxide and methanol are the major constituents; carbon monoxide and methane are also formed. It is proposed that complex formation facilitates the release of methyl bromide as the first stage of breakdown, with the formation of zinc methacrylate units in the polymer chain; depolymerisation is prevented or severely inhibited, depending on the amount of ZnBr₂ present.     

聚苯乙烯溶胀聚苯乙烯－聚丁二烯－聚苯乙烯三嵌段共聚物微区的研究

嵌段共聚物/均聚物共混体系,各嵌段会形成各自的相,并且嵌段间的连接点一定在两相之间的界面上,这一要求极大地影响了嵌段共聚物/均聚物共混体系的链构象和相行为.     

Morphologies, crystallinity and dynamic mechanical characterizations of polypropylene/polystyrene blends compatibilized with PP-g-PS copolymer: Effect of the side chain length

PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. ¹H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends.     

Novel block–comb/graft copolymers with the macromonomer strategy and anionic polymerization

The following block–comb/graft copolymers of styrene (S), isoprene (I), and butadiene (B)—PS‐b‐(PB‐g‐PB), PS‐b‐(PB‐g‐PB)‐b‐PS, (PB‐g‐PB)‐b‐P2VP, (PS‐g‐PB)‐b‐(PI‐g‐PS), (PS‐g‐PB)‐b‐(PI‐g‐PS)‐b‐(PB‐g‐PI), (PS‐g‐PB)‐b‐(PI‐g‐PS)‐b‐(PB‐g‐PI)‐b‐(PI‐g‐PS)‐b‐(PS‐g‐PB), and (PS)₂(PB‐g‐PB) [where PS is polystyrene, PB is polybutadiene, P2VP is poly(2‐vinylpyridine) (2VP), and PI is polyisoprene]—were synthesized with the macromonomer strategy and anionic polymerization high‐vacuum techniques. The synthetic approach involves the synthesis and block copolymerization of styrenic macromonomers in situ without isolation. The prepared samples were characterized by size exclusion chromatography with a differential refractometer detector, size exclusion chromatography with a two‐angle laser light scattering detector, and NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4040–4049, 2005