Neopenthyl glycol containing poly(propylene azelate)s: Synthesis and thermal properties

Poly(neopenthyl azelate) (PNAz) and poly(propylene/neopenthyl azelate) random copolymers (PPAz-PNAz) (NAz unit content from 5 to 20 mol%) were synthesized and characterized in terms of chemical structure and molecular weight. Afterwards, the polyesters were examined by TGA, DSC and X-ray diffractometry. Good thermal stability was found for each sample. The thermal analysis showed that the T_m of the copolymers decreased with the increment in NAz unit content, differently from T_g, which on the contrary increased. X-ray diffraction measurements allowed the identification of the PPAz crystalline structure in all the copolymers. Multiple endotherms were shown in the PPAz-PNAz samples, due to melting and recrystallization processes, similarly to PPAz. The of the copolymers was derived from the application of the Hoffman-Weeks’ method. Baur’s equation described well the T_m-composition data. The isothermal crystallization kinetics were analyzed according to Avrami’s treatment. The introduction of NAz units decreased the crystallization rate compared to pure PPAz. Values of the Avrami’s exponent n close to 3 were obtained in all cases, regardless of T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by a three dimensional spherulitic growth.     

Thermal decomposition of poly(propylene sebacate) and poly(propylene azelate) biodegradable polyesters: Evaluation of mechanisms using TGA, FTIR and GC/MS

The synthesis, characterization and thermal behavior of two biodegradable aliphatic polyesters poly(propylene azelate) (PPAz) and poly(propylene sebacate) (PPSeb) are described in the present work. The thermal degradation of both polyesters was studied using thermogravimetric analysis (TG) by the determination of their mass losses during heating. From the thermogravimetric curves it can be seen that both polyesters are thermally stable materials since PPAz has its highest decomposition rate at 411.3 while PPSeb at 413.6 °C. From the variation of activation energy (E) with increasing degree of conversion it is found that the polyester's decomposition proceeds with a complex reaction mechanism with the participation of at least two different mechanisms. To evaluate these mechanisms the TG, FTIR and a combination of TG-gas chromatography-mass spectrometry (TG/GC-MS) methods were used. From mass ions detection of formed decomposition compounds, it was found that the decomposition of both polymers takes place, mainly, through β-hydrogen bond scission and secondarily through α-hydrogen bond scission. The main decomposition products are aldehydes, alcohols, allyl, diallyl, and carboxylic acids.     

Transcrystallinity of thin films of isotactic poly(propylene)

The isothermal crystallization behavior of thin films of isotactic poly(propylene) between plates coated with chromium, Teflon® or gold is studied by polarized light microscopy. At all contact surfaces between poly(propylene) and the other materials, transcrystallinity can be observed and competes with the growth of entities which originate in the bulk phase. The shape of these entities can be described by two intersecting paraboloids.     

Morphological studies of spin-coated films of poly(styrene-block-methyl methacrylate) copolymers by atomic force microscopy

The surface structure of very thin (15–20 nm) spin-coated films of a symmetrical poly(styrene-b-methyl-methacrylate) block copolymer on silicon and mica is analyzed by atomic force microscopy (AFM). The films show a surface corrugation of a very regular 100 nm lateral periodicity and 6–8 nm amplitude. Film thickness is measured by AFM at induced film defects and checked by ellipsometry. XPS shows that both blocks are at the film surface. Selective degradation of the methyl methacrylate block is used for contrast enhancement and allows to assign poly(styrene) to the elevated surface regions and poly(methyl methacrylate) to the substrate/film interface.Friction interactions of the AFM tip with the film surface may be used to induce high orientational ordering of the morphological pattern perpendicular to the fast scan direction.     

聚碳酸丙烯酯中碳酸丙烯酯含量的测定

建立了气相色谱分析聚碳酸丙烯酯中碳酸丙烯酯含量的方法,该方法操作简单,准确度高,可满足工业检测需求.     

Thermal decomposition behavior of poly(propylene carbonate) in poly(propylene carbonate)/poly(vinyl alcohol) blend

Journal of Thermal Analysis and Calorimetry - To provide guidance for the practical thermal processing and applications of poly(propylene carbonate)/poly(vinyl alcohol) (PPC/PVA) blend, an...     

Nanostructured latex films from poly(butyl methacrylate) latex cross-linked with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock macro-cross-linker

Biphasic polymer latexes were synthesized by a seeded swelling and polymerization method. The latexes were composed of a poly(butyl methacrylate) core and a poly(ethylene oxide) rich shell cross-linked with poly(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock diol diacrylate macro-cross-linker. Nanostructured films were obtained by annealing the biphasic polymer latexes at a temperature between the glass-transition temperatures of the core latex and the cross-linked poly(ethylene oxide) based shell. Atomic force microscope images of the latex film revealed that the poly(butyl methacrylate) core phase is confined in the poly(ethylene oxide)-rich continuous phase with the form of separate nanosized spheres.     

Radiation chemistry of poly(propylene oxide)

Atactic, isotactic, and optically active poly(propylene oxides), PPOx, were irradiated with both γ-rays and electron beams. Up to a dose of 37 Mrad no change could be detected in the optical activity. G values for hydrogen evolution decreased as compared to polypropylene in about the same ratio as G(H₂) of polyoxymethylene decreased as compared to polyethylene. G values for crosslinking and scission, estimated by means of gelation theories of Saito and Inokuti, were found to be greater for isotactic than for atactic PPOx. The behavior of transient infrared and ultraviolet absorption bands is discussed. Intrinsic viscosity data indicate a rapid initial chain degradation whereas CO gas and OH group production is linear with dose. Evidence for the conversion of one type of free radical to another on heating an irradiated sample from 77°K to room temperature is based on the behavior of transient infrared and ultraviolet absorption bands.     

Drying of films formed by ordered poly(ethylene oxide)-poly(propylene oxide) block copolymer gels

The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.     

Glass transition in poly(propylene glycol) networks

Difficulty in controlling and determining the structural parameters of polymer networks has hindered experimental studies on the glass transition in crosslinked polymers. A series of wellcharacterized networks of poly(propylene glycol) having narrow network chain-length distributions and average molecular weight between crosslinks M _c in the range of 425–3000 has been prepared. The glass transition temperatures T_g of these networks were found to vary linearly with M , consistent with several theoretical treatments. Both the physical crosslinking and the incorporation of crosslinking agent into the system (a “copolymer” effect) are shown to be responsible for increase in T_g upon crosslinking in this system. Varying the network chain-length distribution without changing M _c did not affect the T_g of the system. The chemical nature of the crosslinking agent, however, does affect the T_g of the network, particularly at high crosslink densities.     

Radiation grafting of dimethylaminoethylmethacrylate onto poly(propylene)

Radiation-induced grafting of dimethylaminoethylmethacrylate onto poly(propylene) films by preirradiation method in presence of air was investigated. The effects of monomer concentration, preirradiation dose and temperature on grafting value as well as the effect of grafting value on crystallinity of the modified polymer were determined.     

Novel thermooxidatively stable poly(ether-imide-benzoxazole) and poly(ester-imide-benzoxazole)

4-Hydroxy-5-nitrophthalimides were produced via nucleophilic aromatic substitution (NAS) of 4,5-dichloro phthalimide substituents by potassium nitrite. The use of a N-phenyl-phthalimide having a protected 4′-hydroxyl group allows concurrent deprotection and nitro reduction to amine to give the 4-hydroxy-5-amino-N-(4′-hydroxyphenyl) phthalimide. This key intermediate is the precursor to a poly (ether-imide-benzoxazole), and is the condensable monomer for a poly (ester-imide-benzoxazole). Benzoxazole monomer formation via condensation with p-fluorobenzoyl chloride afforded 2-(4′-fluorophenyl)-5,6,-N-[4′(-hydroxyphenyl) imide]-benzoxazole, which was polymerized under NAS conditions to produce a poly(ether-imide-benzoxazole) having an endothermic transition at 454°C with weight retention of 90% at 500°C in both air and nitrogen. Solution polycondensation of the 4-hydroxy-5-amino-N-(4′-hydroxyphenyl) phthalimide monomer with isophthaloyl chloride afforded a poly(ester-amide-imide) which was isolated and thermally cyclodehydrated in the solid state under vacuum to give a poly(ester-imide-benzoxazole) having 95% weight retention at 500°C in both air and nitrogen, with no detectable DSC transitions up to 500°C. © 1994 John Wiley & Sons, Inc.     

Crystallization,thermal behavior,and compatibility of poly(ethylene oxide)/poly(propylene oxide) blends

Isothermal and nonisothermal crystallization kinetics of different poly(ethylene oxide)/poly(propylene oxide) blends were investigated by means of differential scanning calorimetry (DSC). Glass transition temperature of quenched samples have also been reported. Phase morphologies and poly(ethylene oxide) spherulite growth rates were analyzed by polarizing light transmission microscopy. Results show morphological changes along with regime transitions of poly(ethylene oxide) crystal growth. Kinetic analyses of the data suggest that, although the blend behaves as a noncompatible, phase-separated system, there exists a certain degree of interaction between polymer chains. © 1996 John Wiley & Sons, Inc.     

Miscibility of biodegradable poly(propylene succinate)/poly(propylene adipate) blends: Effect of the transesterification reactions

The miscibility of poly(propylene succinate)/poly(propylene adipate) blends was investigated by means of DSC, WAXS and NMR techniques. Poly(propylene succinate) and poly(propylene adipate) were found to be completely immiscible in as blended-state. The miscibility changes upon extended mixing at elevated temperature: for enough long mixing time, the original two phases gradually merged into a single one because of transesterification reactions. The NMR analysis showed that the transesterifications led to block copolymers whose average sequence length decreased as the mixing time is increased at a fixed temperature. Upon very long mixing time (150 min), all PPS and PPA chains are fully transformed into a random copolymer characterized by a single amorphous phase.     

Head-to-head units in poly(propylene oxide) by ozonation

By extensive ozonation and lithium aluminum hydride reduction, poly(propylene oxide) can be converted to material containing dipropylene glycol. Since the diprimary, disecondary, and primary-secondary isomers are readily separable by vapor-phase chromatography, it has been possible to show that some (but not all) noncrystalline PPO samples contain many head-to-head, tail-to-tail monomer units. Correlation of the fraction of head-to-head units with the optical rotation of noncrystalline fractions from optically active monomer, indicates that there is one asymmetric center inverted for every unit inserted head-to-head. The earlier suggestion that the noncrystalline fraction was due to atactic stereochemistry is thus shown to be generally incorrect in favor of an explanation due to positional isomerization.