Crystallization behavior and morphological development of isotactic polypropylene blended with nanostructured polyhedral oligomeric silsesquioxane molecules

The thermal properties and morphological development of isothermally crystallized isotactic polypropylene (iPP) blended with nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules at very small loading of POSS were studied with differential scanning calorimeter (DSC), thermal gravimetric analysis, dynamic mechanical analysis, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The result of DSC indicated that the crystallization rate of iPP increases with the increase in POSS contents during crystallization; moreover, the melting temperature of iPP/POSS nanocomposites slightly decreases, while the heat of fusion increases with the addition of POSS molecules at melting and remelting traces. The storage modulus and thermal stability, respectively, remarkably decrease, while the glass transition temperature of isothermally crystallized iPP/POSS nanocomposites increases slightly with the increase in POSS contents. The morphologies results of WAXD and POM show that the POSS molecules form about 35 nm sized nanocrystals and aggregate to form thread‐like and network structure morphologies, respectively, in the molten state even when the POSS content is very small. These results, therefore, suggest that the interaction force between the POSS molecules should be larger than the force between POSS molecules and iPP matrix; however, those interactions depend on the chain length of functionalized substituents on the POSS cage. Therefore, the POSS molecules aggregate forming nanocrystals and act as an effective nucleating agent for iPP and influence the thermal properties of iPP/POSS nanocomposites due to the shorter chain length of functionalized substituents, methyl, on the POSS cage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2122–2134, 2006     

The effect of compatibilizers on the crystallisation, melting and polymorphic composition of β-nucleated isotactic polypropylene and polyamide 6 blends

Non-compatibilized and compatibilized blends of isotactic polypropylene (iPP) and polyamide 6 (iPP/PA6) as well as their β-nucleated versions were prepared using maleic anhydride functionalized iPP (MAPP) with different anhydride contents as compatibilizer. Ca-suberate, a highly efficient and selective β-nucleating agent was added to the blends in order to promote the formation of the β-modification of iPP. The melting and crystallisation characteristics, as well as the polymorphic composition of the blends were studied by differential scanning calorimetry (DSC). The supermolecular and phase structure of the blends were studied by polarised light microscopy (PLM). iPP and PA6 form blends with heterogeneous phase structure; the PA6 component is dispersed in the iPP matrix in the concentration range studied. The compatibilizer promotes the dispersion of PA6 resulting in smaller particles than without MAPP. In the non-compatibilized β-nucleated blends, an iPP matrix consisting mainly of the α-modification was formed already at low PA6 content. On the contrary, predominantly β-iPP matrix developed in the presence of MAPP compatibilizers. The formation of α-iPP matrix in the absence of compatibilizer is related to the selective encapsulation of the nucleating agent in the polar PA6 phase. The influence of the blending technique on the polymorphic composition of the matrix supports the hypothesis of selective encapsulation. Compatibilizers, besides their traditional benefits assist the distribution of the β-nucleating agent between both phases of the blends and promote the formation of a matrix rich in β-iPP. In the presence of β-nucleating agent MAPP with low anhydride content and blends of iPP containing maleated polypropylene crystallise predominantly in the β-form.     

Quantitative analysis of random scission and chain-end scission in the thermal degradation of polyethylene

The thermal degradation of polyethylene includes two different kinds of pathways. These are random and chain-end scissions which include β-scission on the chain end and radical transfer scission. We conducted a quantitative analysis on these pathways by Pyrolysis-GC/MS and computer simulation. Two different distributions of scission products of polyethylene were observed at different temperatures. They are determined by the relationship between rate of reaction and that of volatilisation. Furthermore, a characteristic distribution was observed in lower molecular weight. It could be explained by direct scission and one to five-step radical transfer scissions. The pathway possibilities calculated with the accumulated schemes showed that the direct scission and one-step-radical transfer increased with the temperature. This indicates that β-scission occurs on the chain end before the radical transfer because the rate of the β-scission becomes faster as the temperature rises.     

In-situ monitoring by fibre-optic NIR spectroscopy and rheometry of maleic anhydride grafting to polypropylene in a laboratory scale reactive extruder

The graft copolymerisation of maleic anhydride (MAH) onto polypropylene (PP) has been studied in situ by interfacing a laboratory scale mini-extruder/processor with a near-infrared (NIR) spectrometer via a fibre optic link. Apparent viscosity was measured simultaneously with the NIR spectra. The graft reaction was carried out at several temperatures with and without the initiator, dicumyl peroxide (DCP). Analysis of the NIR spectra showed the reaction to be first order with respect to MAH, and that the graft reaction rate was not affected by the presence of DCP. However, DCP caused a large increase in chain scission reactions leading to a dramatic drop in apparent viscosity. In the absence of DCP, scission reactions occurred at a slower rate and the apparent viscosity remained steady, after an initial drop, for about 15 min during the early part of the reaction. We suggest that a possible explanation for this might be a “repair mechanism” involving the reaction of two PP macro-radicals with a single MAH moiety, thus maintaining the molecular weight. Once the concentration of MAH drops, this reaction becomes less significant and scission reactions dominate.     

End‐functionalization of isotactic polypropylene via consecutive chain transfer reaction to norbornadiene and hydrogen

Structurally well‐defined end functionalized isotactic polypropylene (iPP) is prepared by conducting a selective chain transfer reaction during the isospecific polymerization of propylene in the presence of norbornadiene (NBD) and hydrogen using rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ ZrCl₂/MAO as the catalyst. The production of NBD‐capped iPP involves a unique consecutive chain transfer reaction, first to NBD and then to hydrogen, for situating the incorporated NBD at the iPP chain end. The NBD end group of NBD‐capped iPP can be converted into other reactive functional group through functional group transformation reactions. The resulting functional group end‐capped iPP can be used for the construction of stereoregular block copolymers (e.g., iPP‐b‐PMMA and iPP‐b‐PS) through postpolymeriztion reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Physico-chemical aspects of polyethylene processing in an open mixer. Part 20: Additional product yields on bimolecular hydroperoxide decomposition with an alcohol group

Most products formed on polyethylene oxidation result from hydroperoxide decomposition. The product yields can be calculated for various mechanisms of hydroperoxide decomposition. This work concerns the reaction of a hydroperoxide with an alcohol group thought to be dominant in the advanced stages of polyethylene processing in the high temperature range (170-200 °C). Besides hydrogen abstraction by caged alkoxy radicals already envisaged previously, the possibility of β-scission is taken into account. This additional reaction introduces significant complexity into the reaction schemes. This is especially so because additional caged radical pairs must be included into the schemes and the calculations. It becomes possible to calculate the yields of aldehyde and vinyl groups that do not result from hydroperoxide decomposition in the absence of β-scission. The yields of the main oxidation products such as alcohols and ketones are not much affected by taking into account β-scission. The yield of aldehydes is important in the whole temperature range and increases considerably if the temperature is raised from 170 to 200 °C. It becomes more important than the ketone yield. The vinyl groups are formed in amounts corresponding roughly to 10-15% of the trans-vinylene groups in the temperature range of 170-200 °C.     

Intramolecular 1,8-hydrogen atom transfer reactions in disaccharide systems containing furanose units

A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4-C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric d-furanoses. d-xylo- and d-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas d-arabino- and d-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively.     

Monosaccharides as Versatile Units for Water‐Soluble Supramolecular Polymers

We introduce monosaccharides as versatile water‐soluble units to compatibilise supramolecular polymers based on the benzene‐1,3,5‐tricarboxamide (BTA) moiety with water. A library of monosaccharide‐based BTAs is evaluated, varying the length of the alkyl chain (hexyl, octyl, decyl and dodecyl) separating the BTA and saccharide units, as well as the saccharide units (α‐glucose, β‐glucose, α‐mannose and α‐galactose). In all cases, the monosaccharides impart excellent water compatibility. The length of the alkyl chain is the determining factor to obtain either long, one‐dimensional supramolecular polymers (dodecyl spacer), small aggregates (decyl spacer) or molecularly dissolved (octyl and hexyl) BTAs in water. For the BTAs comprising a dodecyl spacer, our results suggest that a cooperative self‐assembly process is operative and that the introduction of different monosaccharides does not significantly change the self‐ assembly behaviour. Finally, we investigate the potential of post‐assembly functionalisation of the formed supramolecular polymers by taking advantage of dynamic covalent bond formation between the monosaccharides and benzoxaboroles. We observe that the supramolecular polymers readily react with a fluorescent benzoxaborole derivative permitting imaging of these dynamic complexes by confocal fluorescence microscopy.     

Graft copolymerization of maleic anhydride/styrene onto isotactic polypropylene using supercritical CO2

The free‐radical grafting of maleic anhydride (MAH) and styrene (St) onto isotactic polypropylene (iPP) was studied by thermal decomposition of dicumyl peroxide (DCP) using supercritical CO₂ as a solvent and swelling agent. Several effects of molar ratio of monomer, soaking temperature and time, reaction time, and reaction pressure on the graft degree were discussed. It was found that the addition of St to the grafting system as a comonomer could significantly enhance the graft degree of the grafted PP. Under the optimal reaction condition, the maximum of iPP grafting MAH and St in supercritical CO₂ medium was 10.58%. The chemical structures and properties of grafting copolymers were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The results showed that the supercritical CO₂ method had noticeable advantages over the existed method when compared, such as a lower temperature, a higher graft degree, easy separation, and environmentally benign. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthese et reactivite des perfluoroalkyl-3 alkylthio-3 propenoates d'ethyle: thiophenes et β-thioxoesters perfluoroalkyles

The action of thiols with perfluoroalkylated α,β,-unsaturated compounds (ethyl 3-F-alkyl propynoates 1 and ethyl 3-F-alkyl propenoates 2) was investigated and the reactivity of the adducts reported. The mono-adducts Z and E formed by the action of thiols with 1 were unambiguously identified by ¹⁹F-NMR. In addition to the expected alkenes Z and E, the reaction of 1 with ethyl mercaptoacetate led to ethyl 2-F-alkyl-4-hydroxy-3-thiophenecarboxylate 7. The cyclisation of ethyl 3-F-alkyl-3-(methoxycarbonylmethylthio) propenoate Z in basic medium afforded methyl 5-F-alkyl-3-hydroxy-2-thiophenecar-boxylate 8, whereas in similar conditions ethyl 3-F-alkyl-3-(methoxycarbonylethylthio)propenoate led to ethyl 3-F-alkyl-3-mercaptopropenoate as a first example of β-thioxoesters bearing a sulfur atom on the α-carbon of the perfluoroalkylated chain.     

Degradation of poly(vinyl chloride) by u.v. radiation—II: Mechanism

The mechanism of the light-induced degradation of solid poly(vinyl chloride) (PVC) has been investigated, and an overall reaction scheme has been developed, based on values of the quantum yields for the primary photoproducts. Only a very small fraction (0.2%) of the excited polyenes induces the degradation of PVC, primarily by photocleavage of the allylic CCl bond. The high instability of β-chloroalkyl radicals is responsible for the chain dehydrochlorination that leads to formation of polyenes. In the absence of O₂, chain scissions and crosslinking are postulated to originate mainly from α-chloroalkyl radicals through β-cleavage of CC bonds and radical coupling, respectively. In the presence of O₂, the chain dehydrochlorination still proceeds, together with an oxidative chain process which yields, via peroxy and alkoxy radicals, hydroperoxides, ketones and peroxide crosslinks. Cleavage of the polymer backbone results most probably from the decomposition of tertiary alkoxy radicals by a carbon-carbon β-scission process.     

2D supramolecular assemblies of benzene-1,3,5-triyl-tribenzoic acid: temperature-induced phase transformations and hierarchical organization with macrocyclic molecules

Two-dimensional supramolecular honeycomb networks with cavities of an internal diameter of 2.95 nm were formed by the self-assembly of 4,4',4' '-benzene-1,3,5-triyl-tribenzoic acid (BTA) on a Ag(111) surface at room temperature. Annealing to higher temperatures resulted in two sequential phase transformations into closer-packed supramolecular arrangements. The phase transformations are associated with stepwise deprotonation of the carboxylic acid groups. The voids of the honeycomb network of BTA have a suitable size for the construction of hierarchical structures with guest molecules. Single molecules of the macrocyclic compound mt-33 were successfully confined inside 2D nanocavities of the honeycomb networks and released when the phase was transformed to the close-packed structure.     

稀土化合物参与的聚丙烯反应挤出接枝马来酸酐

将多种稀土化合物用于等规聚丙烯(iPP)与马来酸酐(MAH)的接枝反应, 对接枝共聚物的结构、 接枝率和加工行为等进行了表征和研究. 结果表明, 稀土氧化物CeO2和Nd2O3的加入促进了iPP熔体接枝MAH的反应, 与未加入稀土化合物的接枝体系相比, MAH单体接枝率最大值分别提高了14%和25%, 同时接枝共聚物的熔体流动速率(MFR)也分别增大了34%和56%. 根据实验条件下接枝共聚物的MFR与MAH单体接枝率间的关系, 并结合熔体接枝反应机理, 提出了采用MFR来表征接枝率的方法, 并建立了工作曲线. 同时, 对不同稀土化合物抑制或促进熔体接枝反应发生的机理进行了初步探讨.     

Synthesis and Crystal Structure of a Cu2+ Supra-molecular Complex [Na2Cu(BTA)2(H2O)8]·H2Owith a Three-dimensional Network Structure

A three-dimensional Cu2+ supramolecular complex [Na2Cu(BTA)2(H2O)8]·H2O 1 (H2BTA = bistetrazolylamine) was synthesized by reacting the aqueous solution of CuSO4·5H2O and H2BTA under stirring. The crystal structure of 1 was determined by single-crystal X-ray diffraction. The result indicates that 1 crystallizes in triclinic,space group P1,with a = 7.0518(2),b = 12.2692(2),c = 13.8583(3) ,α = 115.7260(10),β = 93.2440(10),γ = 98.3610(10)o,Mr = 573.90,V = 1059.01(4) 3,Z = 2,Dc = 1.800 g·cm-3,μ(MoKα) = 1.155 mm-1,F(000) = 586.0,S = 1.074,the final R = 0.0273 and wR = 0.0744 for 4334 observed reflections with Ⅰ > 2σ(Ⅰ). The Cu2+ ion is five-coordinated with a N4O1 donor set with τ = 0.153 according to the method of Addison et al. And the Na+ ions form an infinite main chain through bridging O atoms from coordinated water molecules. In 1,a three-dimensional supramolecular network is formed by O-H···O,O-H···N,N-H···O and N-H···N hydrogen bonds.     

Photoaddition of maleic anhydride to unsaturated polymers in homogeneous solution,solid polymer–solution,and solid polymer–vapor systems

Photoreactions of maleic anhydride (MAH) with unsaturated olefinic polymers such as 1,2-polybutadiene, 1,4-polybutadiene, block copolymer of styrene and butadiene, polystyrene, poly(styrene-co-isoprene), and poly(styrene-alt-methyl methacrylate) were investigated in air. When the polymers have olefinic unsaturation, the addition of MAH to the polymers in homogeneous solutions proceeded efficiently by a chain mechanism, and the quantum yield of the photoaddition of MAH was greater than unity under irradiation at λ > 310 nm. From the effects of solvent and photosensitizer, a radical chain mechanism involving crosslinking of the polymers by MAH molecules was suggested. Together with the spectroscopic results, the reaction mechanism was discussed. The photoaddition reaction was then applied to the surface photomodification of polymer films. Photoreactions were conducted at the interphase between solid polymer and acetone solution of MAH and also at the interphase between solid polymer and gaseous MAH. Irradiation by a 300-W high-pressure mercury lamp could bring about considerable modification of the surface properties of the polymers, which then show improved wettability and dyeability. From the oxygen permeation experiments, the present interfacial phototreatment was shown to provide a double-layered polymer film in which one side of the film is polar and hydrophilic while the other side is nonpolar and hydrophobic.     

Décomposition du percarbonate de O,O-t-butyle et O-isopropényle en solution dans des cyclanes

Thermolysis of O,O-t-butyl and O-isopropenyl percarbonate in cyclohexane involves free-radical acetonylation of solvent. Free radicals derived from solvent add to the percarbonate double bond and after a double β-scission reaction, cyclohexylacetone carbon dioxide and t-butoxy radicals are formed. Abstracting H atoms from the solvent, t-butoxy radicals regenerate free radicals from solvent, and the reaction becomes a chain process. Extending the study to other cycloalkanes it has been shown that the process is a general synthesis method for cycloalkylacetones. On the other hand, competitive reactions of pairs of solvents have shown that the reactivity of the substrates depends on H atom lability and on more complex phenomena like transfers between hydrocarbons and C-centered free-radicals.     

Vibration-dependent Crystal Form of Isotactic Polypropylene under Nonisothermal Crystallization

A study concerning the effect of vibration on the crystal structure and morphology for isotactic polypropylene(iPP) was conducted. The crystallite size. crystal structure and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry(DSC) and wideangle X-ray diffraction(WAXD). The results reveal that the crystallinity of the vibrated samples decreases at a high cooling rate, but it remains constant at a low cooling rate because of the chain relaxation of iPP. It has been found that vibration obviously increases the content of β-form of crystal phase and the amount of β-crystal mainly depends on the vibration amplitude.     

The synergistic effects of β-nucleating agent and ethylene–octene copolymer on toughening isotactic polypropylene

The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.     

Formation of β-crystal from nonisothermal crystallization of compression-molded isotactic polypropylene melt

The crystalline structures of isotactic polypropylene (iPP) subjected to compression-molding were studied by means of differential scanning calorimeter (DSC), optical microscope (OM) and wide-angle X-ray diffraction (WAXD). β-crystal can be formed from nonisothermal crystallization of the sample compression-molded at the molten state and the β-phase content increased with increasing pressure of molding. Thermal treatment of the molten sample at 200 °C could eliminate the effect of compression-molding on crystalline structure. It was suggested that the compression-molding of iPP melt plays an important role in improving the nucleation ability of β-crystal.     

Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.