Aliphatic poly(propylene dicarboxylate)s: Effect of chain length on thermal properties and crystallization kinetics

Polyesters based on 1,3-propanediol glycol and aliphatic dicarboxylic acids with different chain length were synthesized by melt polycondensation, obtaining samples characterized by high and comparable M_n. The polymers were subjected to molecular and thermal characterization. All polymers showed a good thermal stability, even though depending on the chain length. At room temperature all the polymers appeared as semicrystalline materials; the effect of the chain length was a lowering in the T_g value, an odd-even fluctuation for T_m and an increase of the crystallization rate. A comparison of the X-ray data revealed that the polymers with odd carbon number per repeat unit, show similar patterns, different from those of samples with even carbon atoms number. Multiple endotherms were evidenced in melt isothermally crystallized samples, due to melting and recrystallization processes. By applying the Hoffman-Weeks' method, the of the samples was derived. Lastly, the presence of an interphase was not evidenced.     

Epoxy/polyhedral oligomeric silsesquioxane (POSS) hybrid networks cured with an anhydride: Cure kinetics and thermal properties

A new class of organic-inorganic hybrid networks was prepared via copolymerization of octakis(dimethylsiloxybutyl epoxide)octasilsesquioxane (OB), N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and hexahydrophthalic anhydride (HHPA). Kinetic studies show that even with 1H-imidazole as the catalyst, the rate for the curing of OB/HHPA is still significantly higher than that for TGDDM/HHPA in the temperature range studied. Two-stage reactions were thus carried out to allow OB to react with HHPA first (Stage I). The glass transition temperature (T_g) of the networks was found to be strongly dependent on Stage I reaction since too short a reaction time caused poor bonding of OB to the networks while too long a reaction time led to the formation of OB oligomers that de-homogenized the networks. With 5 mol.% OB, the hybrid prepared via the optimized two-stage reaction displayed a large jump of ∼20 °C in T_g, which was accompanied by slight improvements in thermal degradation temperature and storage modulus, as compared to TGDDM/HHPA.     

Role of chain length in degradation process (chain breakdown)

The role of molecular weight of a chain in the chain breakdown in diluted solution at a constant concentration of chain molecules and constant temperature is discussed theoretically using the methods of the theory of the activated complex and kinetics of cooperative processes. The reaction starts at the certain molecular weight of the chain. The chain breakdown is the flat increasing function of the chain molecular weight. This function has a limit when chain molecular weight approaches infinity. Such dependence is explained by the increase of flexibility (following two theories) and increase of extra entropy of molecules of different sizes (following kinetics of cooperative processes. Unequal reactivity of chemically identical active centers links to the dependence of chain flexibility on the location of the more flexible part (place of reaction) of the chain. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1810–1817, 2002; DOI 10.1002/app.10356     

Effect of alkyl chain length grafted to graphene nanoplatelets on the characteristics of polypropylene nanocomposites

To improve the compatibility of graphene nanoplatelets (GNPs) to polypropylene (PP), alkyl chains were grafted to the GNPs’ surfaces by chemical reactions between alkyl amines and the corresponding functional groups of the GNPs. Hexylamine, dodecylamine, and octadecylamine were used respectively to prepare three different alkyl‐grafted GNPs (alkyl‐GNPs) with different alkyl chain lengths. Functional group analysis of the alkyl‐GNPs by Fourier transform infrared confirmed the alkyl‐grafting reaction. PP/alkyl‐GNP nanocomposites with 0.5 phr of hexyl‐, dodecyl‐, or octadecyl‐GNPs were prepared respectively by melt‐blending and compression molding and their mechanical and thermal properties and fracture surfaces morphology were investigated. With increasing alkyl chain length the flexural strength and melting temperature increased marginally but the flexural modulus, impact strength and storage modulus of the nanocomposites increased to a large extent. POLYM. ENG. SCI., 59:752–756, 2019. © 2018 Society of Plastics Engineers     

Uniaxial extension of poly(diethylsiloxane) networks: Mesophase formation under stress

The mesophase formation in chemically well-defined poly(diethylsiloxane) [PDES] networks has been investigated upon uniaxial extension by means of stress-strain and birefringence measurements. Variation of the temperature range of the mesomorphic state was shown to depend on the molecular weight between crosslinks, M c , and the applied stress. Formation and behavior of mesocrystals under stress can be described qualitatively within the framework of the crystallization thermodynamics and kinetics in stretched rubber. A particular feature of the mesophase formation in PDES networks under stress is that, at the initial stage of extension, metastable mesocrystals form with sizes smaller than M c that can reorganize on further extension into larger crystallites with a longitudinal size and isotropization temperature that is determined by M c . This transformation process is the cause of a peculiar stress-strain behavior of PDES networks on extension and subsequent contraction.     

The effect of flexible chain length on thermal and mechanical properties of poly(m-methylene 2,6-naphthalate)s

The effect of flexible chain length on the thermal and mechanical properties such as melting temperature, glass transition temperature, dynamic mechanical relaxation behavior, and uniaxial tensile deformation for melt-quenched poly(m-methylene 2,6-naphthalate) (PmN) films was investigated using differential scanning calorimeter (DSC), dynamic mechanical thermal analyzer, and universal tensile machine. It was found from DSC thermograms that PmNs with even number of methylene group have higher melting temperatures and faster crystallization rates than PmNs with odd number of methylene group, showing an odd-even fluctuation. The plots of versus temperature show that all PmN samples have three relaxation processes (β, β^∗, and α) regardless of the number of methylene group in their backbone. It was found that both β^∗- and α-relaxations are cooperative processes and that the activation energies of both relaxations as well as the glass transition temperature associated with the α-relaxation show odd-even fluctuations as a function of the number of methylene group. The initial tensile modulus at the low drawing rate of 0.15 cm/min also shows an odd-even fluctuation. In summary, the macroscopic thermal and mechanical properties of PmN such as melting temperature, glass transition temperature, crystallization rate, activation energies of α- and β^∗-relaxations, and initial modulus measured under a slow drawing rate exhibit odd-even fluctuations as the number of methylene group in PmN increases.     

Effect of side‐chain length of succinic anhydride on coefficient of thermal expansion behavior of epoxy resins

The effect of an alkenyl side‐chain of succinic anhydride (SA) on the thermal behavior and the coefficient of thermal expansion (CTE) of diglycidylether of bisphenol A (DGEBA) epoxy resins was studied. The number of carbons in the side‐chain of SA was varied from 6 to 14 and N,N‐Dimethylbenzylamine was used as an accelerator. As a result, the reactivity of SA with epoxide groups was decreased on increasing the length of the alkenyl side‐chain of SA. The thermal stabilities of cured DGEBA/SA samples were approximately constant with varying alkenyl side‐chain of SA. Also, the CTE of the systems was increased as the length of the alkenyl side‐chain of SA increased. This could be attributed to the increased motion of the chain segments in the epoxy network structure induced by the longer alkenyl side‐chain of SA. The effect of amount anhydride, thermoplastics, and fillers on the CTE of the epoxy resins was also discussed. Copyright © 2006 Society of Chemical Industry     

聚四氢呋喃的生产技术及国内外市场分析(下)

介绍了聚四氢呋喃的生产方法，分析了国内外聚四氢呋喃的生产消费现状及发展前景，提出了发展我国聚四氢呋喃生产的建议。     

Effects of epoxy resin on mechanical and thermal characteristics of poly(propylene oxide)/poly(butyl acrylate) networks

We report mechanical and thermal characteristics of a network composed of poly(propylene oxide) (PPG) and poly(butyl acrylate) crosslinked with tolylene diisocyanate. It was found that addition of about 4 wt % of an epoxy resin resulted in a higher mechanical toughness and less discoloration. Furthermore, it was found that the epoxy has a self‐restoration function against thermal degradation of the network. The reaction mechanism between the network and the epoxy was investigated with infrared spectroscopy and ¹³C‐NMR and the effect of the epoxy resin on the thermal stability and physical properties is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1886–1893, 2000     

Effect of cross-linker length on the thermal and volumetric properties of cross-linked epoxy networks: A molecular simulation study

Volumetric and thermal properties of cross-linked epoxy systems consisting of diglycidyl ether of bisphenol A (DGEBA) and poly(oxypropylene) (POP) diamines of four different lengths ranging from 3 to 68 units were investigated by molecular dynamics (MD) simulations. The cross-linked structures were built by using the simulated annealing polymerization approach. The density, coefficients of volume thermal expansion and glass transition temperature (T_g) of each of the four cross-linked epoxy systems were obtained from their volume–temperature behavior. The density obtained in the simulations agreed well with the experimental value, whereas the coefficients of volume thermal expansion were at least 30% lower than their corresponding experimental results. The predicted T_g values were higher than the experimental values due to the considerably faster cooling rates that are used in the simulations. It was observed that an increase in the chain length of the cross-linker POP-diamines led to a larger difference between the predicted and experimental values of T_g. Three different approaches were used to estimate the expected shift in the experimental T_g to higher values had these measurements been made at cooling rates comparable to those used in MD simulations. It is shown that, in general, the T_g values obtained in MD simulations are consistent with such shifted T_g values that account for the difference in the cooling rates, although no one particular shift approach worked well for all four epoxy systems studied.     

Effect of thermal aging on the crystal structural characteristics of poly(tetra fluoro ethylene)

The residual effects of cumulative thermal aging on the crystal structural characteristics of the fluoro carbon poly(tetra fluoro ethylene) (PTFE) have been studied by X‐ray diffraction methods. The initial hexagonal arrangement of the PTFE chains in a 15₇ helical conformation is left unaffected by the exposures to temperatures (T), up to and beyond its melting point, T_m. The unit cell registers a residual anisotropic volume expansion. The anisotropy arises from the enhanced enlargement of the basal plane dimension a compared with the axial dimension c. Conformational changes contributing to the observed increase in the chain length have been examined. Enhancement of residual crystallinity of samples aged at T's < T_m suggests that the selective thermal aging could be used as an effective tool to improve the initial crystallinity of commercially available PTFE. The activation energy for 50% enhancement in initial crystallinity has been estimated as 53.9 kJ mol^?1. Aging at 400°C, a temperature above T_m, is accompanied by markedly different features viz., deterioration in crystallinity and other structural characteristics. The overall behavior of thermally aged PTFE bears a marked similarity to many polyamides. POLYM. ENG. SCI., 47:1724–1729, 2007. © 2007 Society of Plastics Engineers     

Effect of thermal treatments on the chemical characteristics of mora crab meat (Homalaspis plana)

Marine species muscles present non-proteins nitrogenated compounds, used as quality index. They are total volatile basis (NBVT), trimethylamine oxide (TMAO) and trimethylamine (TMA). pH is considered too as a quality index. The aim of this work was to evaluate these parameters in a fresh and canned marine product from the V region, corresponding to mora crab (Homalaspis plana). Fresh pincer meat from mora crab was extracted and kept in ice until theits analysis and thermal process of the canned product. A 3(2) statistical design was applied, considering two variables with 3 levels: 15, 30 y 45 minutes time levels: 80 degrees, 100 degrees y 121 degrees C temperature levels. Nine conditions of time-temperature were obtained. The thermal treatment caused an increase in pH and BVT. The TMA was increased since reduction of TMAO.     

Aliphatic urethanes. Effect of chain length on some physical properties

During a study of the thixotropic behavior of certain fatty materials a series of alkyl esters of substituted carbamic acids was prepared, and some of the physical properties were examined. Highly purified fatty aleohols and fatty isocyanates were reacted to give urethanes with from 8 to 22 carbon atoms in both the O-alkyl and N-alkyl groups. The melting points of the urethanes were dependent not only on the number of carbon atoms in the molecule but also on the symmetry of the moiety. In an homologous series the melting point increases with the number of carbon atoms. When symmetry is reached, there is a sharp increase in the melting point. After this the increase is less pronounced. The urethanes give thixotropic gels with ethyl alcohol, soybean oil, solvent-thinned resins, and other similar materials at concentrations as low as 0.5%. In general, better-defined crystal structure and poorer thixotropic properties were observed with an increase in symmetry. Technical Paper No. 177, Archer-Daniels-Midland Company.     

Influence of chain length on conformations of poly(ethylene glycol) chains grafted on silica

Electron spin resonance (e.s.r.) spectroscopy of labelled grafted poly(ethylene glycol) chains has been used to estimate the ratio of the population of end segments free in solution to that of ones adsorbed on the silica surface, as a function of temperature. In particular, the influence of chain length is investigated. The grafted molecules have the following molecular weights, 44, 88, 132, 176, 400, 600, 2000, and are in contact with benzene. Taking the random walk models as reference, two different behaviours are distinguished, one for the oligomers and one for the polymers. The measured values are consistent with an overall picture of ‘brush bristles’ for oligomers and of weakly overlapping partly collapsed coils for polymers.     

Dynamic relaxation characteristics of crosslinked poly(ethylene oxide) copolymer networks: Influence of short chain pendant groups

The dynamic relaxation characteristics of short-branch rubbery amorphous networks prepared by the photopolymerization of poly(ethylene glycol) diacrylate [PEGDA] crosslinker have been investigated using dynamic mechanical analysis and broadband dielectric spectroscopy. Copolymerization with low molecular weight acrylates was used to control effective crosslink density in the networks and led to the insertion of ethylene oxide pendant groups along the network backbone. Substantial differences in the sub-glass and glass-rubber relaxation properties of the copolymers were observed as a function of pendant length and the nature of the pendant terminal group (e.g., -OH vs. -OCH₃); the results are compared with prior studies on model copolymers containing longer, more flexible side branches.     

Aliphatic acid esters of (2-hydroxypropyl) cellulose—Effect of side chain length on properties of cholesteric liquid crystals

A series of aliphatic acid esters of (2-hydroxypropyl) cellulose (C_nPC) were synthesized via the esterification of aliphatic acid chloride and (2-hydroxypropyl) cellulose (HPC). The liquid crystalline (LC) phases and transitions were investigated using differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized light microscope (PLM) techniques. This series of C_nPC polymers exhibited characteristic features of cholesteric LC phases between their glass transition and isotropization temperatures. The cholesteric LC characteristics were studied utilizing an ultraviolet/visible/near infrared spectrometer in a reflection mode. It was confirmed that, with an increase in the number of methylene units in the side chains of this series of C_nPC polymers, there was an increase, on the scale of nanometers, in the layer spacing values for the cholesteric LC phases measured by WAXD. This periodic layer spacing represents the thickness of the neighboring twisted layers in a helical structure. Based on a unique significant red shift of the maximum reflection peak for the LC phases in this series of C_nPCs, it is evident that the pitch distance in the helical structure also increases with an increase in the length of methylene units in the side chains.     

Effect of alkyl chain length on the thermophysical properties of pyridinium carboxylates

In the present study,new series of pyridinium carboxylate protic ionic liquids (PILs) were synthesized by pairing pyridinium cation with carboxylate anion from C1-C3 forming pyridinium formate ([CsH6N+][HCOO-]),pyridinium acetate ([CsH6N+][CH3COO-]) and pyridinium propionate ([C5H6N+][CH3CH2COO-]) respectively.The physical properties namely,density,viscosity,surface tension (298.15-343.15) K,and refractive index (293.15-323.15) K were measured.Thermal properties namely,glass transition temperature,molar heat capacity,and thermal decomposition temperatures were also determined.The thermal expansivity was calculated using the experimental density data.The effect of increasing the alkyl chain length on the thermophysical properties of the pyridinium carboxylate PILs has been evaluated.As expected the physical properties i.e.density,viscosity,surface tension and refractive index of the investigated pyridinium carboxylates decreased with increasing temperature.In general pyridinium carboxylate PILs possessed low viscosity,high thermal stability and excellent hydrogen bonding capability,and these properties lead them to outperform conventional solvents employed for lignin dissolution.     

Effect of chain length on the rate of quaternization of alkyl amines

Trialkyl amines from triethyl to tristearylamine were quaternized with benzyl chloride and compared for the effect of chain length on the rate of quaternization. Triethylamine reacted about twice as fast as tripropylamine with virtually no chain-length effect from propyl to stearyl. Results are compared to previous rate studies on steric hindrance and chain-length dependence.     

Effect of FA chain length on normal- and reversed-phase HPLC of phospholipids

Forty-seven saturated synthetic diacyl PA, PC, PE, PG, and PS and five unsaturated diacyl phospholipids (PL) underwent normal- and reversed-phase (RP) HPLC with isocratic isopropanol/hexane/water (5∶4∶1) and methanol/chloroform/acetonitrile/water (79.5∶9∶8∶3.5) mobile phases, respectively. For normal-phase HPLC, capacity factors (k′ _i ) decrease with chain length (n) of the two identical PL FA residues, whereas the opposite occurs with RP (C₁₈)-HPLC. Plots of In k′ _i vs. n for individual PL classes are in general curved, violating the linear free-energy relationship. For PL of the same n but with different head groups, k′ _i with normal-phase HPLC varies as PE<PG<PA<PS<PC, except when n≥16, when the order is PE<PS≈PA≈PG<PC. For RP-HPLC, the order of k′ _i values is PG<_A≈PS≤PC≈PE until n≥16, when it is PA≈PG<PS≪PC≈PE. With normal-phase HPLC, k′ _i values of PL with unsaturated FA of n=18 are ordered as PE<PA<PC. Increasing degrees of unsaturation lead to increasing k′ _i .     

Synthesis and thermal characteristics of poly(thioarylene)s by thermal polymerization

Thermal polymerization of bis[4-(4-bromophenylthio)phenyl] disulfide (I), bis[4-(4-bromophenyloxy)phenyl] disulfide (II) and bis[(4-(4-bromophenylsulfony)phenyloxy)phenyl] disulfide (III) was carried out at 250°C in diphenyl ether. The resulting poly(thioarylene)s show high crystallinity and high thermal stability. The blends and copolymers of poly(thioarylene) were also prepared, whose thermal properties were investigated by DSC measurements.