Packing mode and conformational transition of alkyl side chains in N-alkylated poly(p-benzamide) comb-like polymer

A series of rigid-rod poly(p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA(n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl (n=10) to octadecyl (n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA(n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA(n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all-trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.     

Order-disorder transition in eicosylated polyethyleneimine comblike polymers

Order-disorder transition (ODT) behavior in eicosylated polyethyleneimine (PEI20C) comblike polymer obtained by grafting n-eicosyl group on polyethyleneimine backbone was systematically investigated by the combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy as well as solid-state high resolution nuclear magnetic resonance (NMR) spectroscopy. DSC investigations showed two obvious transitions, assigned to the transitions (1) from orthorhombic to hexagonal and (2) from hexagonal to amorphous phase, respectively. These transitions are induced by the variations of alkyl side chain conformation and packing structure with temperature changing, which consequently lead to the destruction of original phase equilibrium. The ODT behavior can also be confirmed by spectroscopic methods like WAXD, FTIR and NMR. The ordered structure and the transition behavior of the alkyl side chains confined by the PEI backbone are obviously different from those of pristine normal alkanes. The transition mechanism of ODT and the origin of the phase transition behavior in PEI20C comblike polymer were discussed in detail in this paper.     

Side-chain crystallization and phase transition of poly[styrene-co-(maleic anhydride)]-g-alkylamine comb-like polymers

Taking ? NHCO? as the chemical spacer, poly[styrene-co-(maleic anhydride)]-g-alkylamine (SMACnN) comb-like polymers are prepared through grafting reaction between poly[styrene-co-(maleic anhydride)] and n-alkylamine with n changing from 12 to 18. SMACnN comb-like polymers present an obvious crystallization behavior owing to the introduced alkyl side chains, and the melting temperature and enthalpy of the side-chain crystallites increase from 9.2 to 41.6 °C and from 6.0 to 17.6 kJ mol^?1, respectively, showing a variation with the side-chain length. At least 12 side-chain carbon atoms are required to pack into a hexagonal crystal structure for SMACnN comb-like polymers. Fourier transform infrared and X-ray analysis results demonstrate the phase transition from hexagonal to an amorphous state, and the conformationally disordered alkyl chains affect the packing manner of side-chain crystallites. Including the side-chain length and polymer backbone, the chemical spacer between the side chain and the main chain influences the formation of side-chain crystallites and the phase transition process. So, the study of SMACnN further strengthens the understanding of the phase transition behavior and side-chain crystallization of comb-like polymers triggered by the side-chain length and the microstructure differences. © 2021 Society of Industrial Chemistry.     

Confined relaxation dynamics in long range ordered polyesters with comb-like architecture

The cooperative relaxation dynamics of methylene units in self-assembled amorphous alkyl nanodomains with typical dimensions in the range 5–20 Å is studied in a series of poly(1,4-phenylene-2,5-n-dialkyloxy terephthalate)s (PPAOTs) with C = 6–12 alkyl carbons per side chain. These comb-like polymers are long range ordered on the nanoscale since domains where main chains are stacked in a crystal-like manner alternate with alkyl nanodomains formed by aggregated side chains. Dynamic mechanical data for the investigated PPAOTs show polyethylene-like glass transitions α_PE which are similar to those for many other polymer series with comb-like architecture containing long alkyl side groups. Hence, self-assembled PPAOTs are excellent model systems for studies focusing on a detailed understanding of the influence of (i) alkyl nanodomain size, (ii) average volume per CH₂ unit and (iii) number of alkyl groups per interfacial area on the cooperative dynamics of methylene units seen as α_PE process. Structural parameters as obtained from X-ray diffraction experiments allow to deduce quantitative information about these influencing factors. The results are compared with those for regio-regular poly(3-alkyl thiophenes) with similar molecular architecture. The comparison shows that important features of the α_PE process within amorphous alkyl nanodomains are main chain independent even in case of long-range ordered polymers with quite different main chain packing. It is concluded that the alkyl nanodomain size is the most important factor determining the α_PE dynamics of the methylene units. Main chain dependent aspects like average volume per CH₂ unit and interfacial constraints do only weakly influence the relaxation behavior within the alkyl nanodomains.     

Reorganization of the chain packing between poly(ethylene isophthalate) chains via coalescence from their inclusion compound formed with γ‐cyclodextrin

Amorphous poly(ethylene isophthalate) (PEI) was synthesized, and was used for preparing an inclusion compound (IC) with γ‐cyclodextrin (γ‐CD). Coalesced polymer was produced by washing the PEI‐γ‐CD‐IC with hot water. Wide angle X‐ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses were employed to verify formation of PEI‐γ‐CD‐IC and to compare the as‐synthesized and coalesced PEI samples. These observations suggested that the conformations and morphology/chain‐packing of PEI were changed via coalescence from its γ‐CD inclusion compound. The glass‐transition temperature of the amorphous coalesced PEI is 15–20°C higher than the T_g observed for the as‐synthesized sample, even when observed in the second heat after cooling from well above T_g at 260°C. The amorphous as‐synthesized PEI retains its randomly‐coiling structure, while coalesced PEI has at least partially retained, the highly extended and parallel chains from the narrow channels of the inclusion compound, resulting in better/tighter packing among the PEI chains manifested by a higher T_g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6049–6053, 2006     

Molecular dynamics and thermal analysis study of anomalous thermodynamic behavior of poly (ether imide)/polycarbonate blends

Molecular dynamics simulation used to study the binary polymer blend of poly (ether imide) (PEI) and polycarbonate (PC) showed that these polymer blends are immiscible. The Flory-Huggins interaction parameter, χ, calculated from simulation reached a minimum value at 80 wt% PEI. The simulation results showed that the concentration dependence of χ was mainly due to electrostatic interaction and van der Waals force. The simulation results were supported by differential scanning calorimetry (DSC) measurements. The DSC measurements showed that there are two distinct glass transition temperatures for all the blends' concentrations. However, at 80wt % PEI, the T_g of PEI-rich phase reached a minimum while that of the PC-rich phase was comparable to its pure form indicating that there is some partial miscibility of PC in the PEI rich phase, but no PEI is incorporated in the PC rich phase. From simulations, the χ versus concentration plot shows the same trend as the experimentally measured glass transition temperature versus concentration plot.     

Supramolecular complexes: lamellar structure and crystalline transformation

Interfacial reaction of highly-branched polyethyleneimine (PEI) with octadecanoic acid (OA) was performed to prepare a series of supramolecular complexes (PEI(OA)_x). The complexes at solid state have typical lamellar structure, and the interlamellar distance can be modulated by the OA content. The long period values of the supramolecular complexes measured by SAXS were found to be dependent on the compositions, which are in good consistency with those measured by TEM. For example, the long period values from SAXS for PEI(OA)_0.76, PEI(OA)_1.03, and PEI(OA)_1.67 were 46.5, 62.7, and 56.2 Å, respectively. The corresponding data from TEM were 45.7, 60.7, and 56.6 Å, respectively. A model was proposed for the construction mode of the side alkyl chains (crystallization region) associated with PEI backbone (amorphous region), in which the side alkyl chains were arranged to be ‘end-to-end’ packing for the x=1 complex, while an ‘interdigitated structure’ of the side alkyl chains was deduced for the x>1 and x<1 complexes. Temperature variable FT-IR combination investigation of the scissoring band, rocking band, and stretching band of methylene (CH₂) and vibrational band of carbonyl group (CO) indicated that the crystalline form of the crystallization region in the lamellae can be transformed from orthorhombic to hexagonal with the temperature increasing, and vice versa.     

Evaluation of local polarity of polymer solids by a rigid fluorescent probe of carbazole-terephthalate cyclophane

A novel rigid fluorescent probe, carbazole-terephthalate cyclophane (Cz-TP) was applied to evaluate local dielectric constants (ε) of various polymer solids in a wide range of temperatures. For poly(vinylidene fluoride), the ε increased above the glass transition temperature (T_g), due to relaxations of the polar segment -(CH₂CF₂)- of the main chain. For poly(alkyl methacrylate)s, the ε increased above the T_g or the melting temperature of the side chain, where motions of the polar ester groups are activated. For cyanoethylated polymers, the ε increased owing to motions of the polar cyano groups at the end of the side chain and the ε corresponded to the dielectric constant evaluated by dielectric relaxation measurement at a high frequency, because the Cz-TP exciplex has a lifetime of tens of nanoseconds. For a cyanoethylated polymer with a high content of cyano groups, the ε was larger at low temperatures than the dielectric constant obtained by the macroscopic dielectric relaxation measurement. These results show that the Cz-TP molecule is a useful probe for evaluation of the local polarity in polymer solids over a wide temperature range and can detect even a small change in ε at transition temperatures such as glass transition, side-chain melting, and side-chain relaxation.     

Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

Polymeric ionic liquids based on ether functionalized ammoniums and perfluorinated sulfonimides

A new family of polymeric ionic liquids (PILs) based on alkyl and alkyl ether substituted ammoniums and perfluorinated sulfonimides (i.e., bis(fluorosulfonyl)imide (FSI⁻), and bis(trifluoromethanesulfonyl)imide (TFSI⁻)) have been synthesized by polymerization of the corresponding ionic liquid monomers (ILMs). Their structures and compositions have been characterized by ¹H and ¹⁹F NMR, FTIR and viscosity-average molecular weight (M_v). The physicochemical properties of both the ILMs and the PILs have been studied in terms of thermal stability, phase transition, and ionic conductivity. All the prepared ILMs and PILs reveal excellent thermal stabilities to greater than 250 °C. The PILs containing alkyl ether side unit show significant decrease in glass transition temperature (T_g), the values of T_g of the alkyl ether based-PILs are all significantly lower by 10–77 °C in magnitude than those of the corresponding alkyl based ones. The ionic conductivity of alkyl ether based-PILs in the best case increases up to 4.0 × 10⁻⁶ S cm⁻¹ at 30 °C, and reaches 7.6 × 10⁻⁵ S cm⁻¹ at 60 °C, and outperform their ammonium counterparts with alkyl side chain that were synthesized as references.     

Solid-state F MAS and H→F CP/MAS NMR study of the phase transition behavior of vinylidene fluoride-trifluoroethylene copolymers: 1. Uniaxially drawn films of VDF 75% copolymer

The changes in the phase structures and molecular mobility caused by the ferroelectric-paraelectric phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer, P(VDF₇₅/TrFE₂₅), were analyzed using variable temperature (VT) solid-state ¹⁹F MAS and ¹H→¹⁹F CP/MAS NMR spectroscopy. The CF₂ signal of the VDF chain sequence and the CHF signal at the head-to-head linkage of VDF-TrFE sequence showed higher frequency shift in the temperature range 43-92 °C, whereas no change was found for the CHF signal at the head-to-tail linkage of VDF-TrFE up to 92 °C. Hence, VT ¹⁹F MAS spectra revealed that the VDF-TrFE head-to-tail sequence is the most stable part in polymer chains against trans-gauche conformational exchange motions below the phase transition temperature (Curie temperature, T_c) on heating. However, all chain sequences including TrFE units undergo conformational exchange at around T_c. The phase transition behavior is clearly recognized in the ¹⁹F spectral shapes, in which the broad signals of the ferroelectric immobile phase disappeared between 115 and 119 °C. In addition, T_1ρ^F for all peaks decreased to a unique value (ca. 20 ms) at 119 °C, indicating that uniform molecular motion accompanied by a full chain rotation occurred at the temperature. The significantly longer T_1ρ^F for all peaks (ca. 20 ms) in the paraelectric phase (119 °C) than that in the amorphous domain (<4 ms) at ambient temperature supports the conclusion that there is restricted rotational motion of polymer chains around the chain axis in the paraelectric phase. On cooling from 119 to 85 °C, a gradual decrease in gauche conformers in the paraelectric phase was confirmed by the low-frequency displacement of CF₂ signals in VDF sequences accompanied by slight decreases in T₁^F and T_1ρ^F. The phase transition was observed between 85 and 77 °C on cooling, in which the characteristic signals of the paraelectric phase disappeared, the T_1ρ^F values of all peaks quickly increased, and the broad crystalline signals abruptly appeared at 77 °C.     

Correlations between alkyl side chain length and dynamic mechanical properties of poly(n-alkyl acrylates) and poly(n-alkyl methacrylates)

In the present paper, dynamic mechanical properties of poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) with different alkyl side chain length were studied. The results show that with the increase of alkyl side chain length, the storage modulus changes more steadily, and the loss modulus peak and the tanδ peak become broader for PnAA and PnAMA. At the same time, the tanδ peak is more and more apart from the loss modulus peak and the point where the storage modulus begins to drop. For quantitative discussion, three variables, the steepness index (S), the transition wideness (W) of storage modulus and the integration area (A) of tanδ were defined to investigate the potential correlation between the dynamic mechanical properties and alkyl side chain length. It can be observed that S decreases while W and A increase with increasing alkyl side chain length. Moreover, the relaxation spectra of the two series of polymers are calculated from the corresponding mechanical spectra. The shapes of the relaxation spectra are broader and broader with the increase of the alkyl side chain length. These phenomena are interpreted by the perspective of fragility, molecular packing efficiency and intermolecular coupling.     

Dispersion polymerization in supercritical carbon dioxide using comb-like fluorinated polymer surfactants having different backbone structures

Comb-like fluorinated polymers with different backbone structures, poly(heptadecafluorodecyl acrylate) (PA-R_f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R_f), and poly[p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R_f), were used as surfactants in dispersion polymerization to examine the effect of backbone structure on the formation of polymer particles. Dispersion polymerization of monomers with different polarities using these comb-like fluorinated polymer surfactants in CO₂ showed that PEO-R_f containing a polar oxyethylene backbone was an effective surfactant for the dispersion polymerization of a polar monomer, such as N-vinyl-2-pyrrolidone, whereas PA-R_f was effective for less polar monomers, such as methyl methacrylate and N-vinyl caprolactam.     

脂肪族含氧有机物沸点的定量构效关系

引言沸点是化合物最基本的物理性质之一,也可以用来预测和估算化合物的其他物理化学性质,如临界性质、闪点等。沸点与分子结构和分子间作用力密切相关,实验测定是获得沸点最直接的方法,但     

Shape memory behavior of poly(methyl methacrylate)-graft-poly(ethylene glycol) copolymers

This paper describes a shape memory behavior of graft copolymers poly(methyl methacrylate)-graft-poly(ethylene glycol) (PMMA-g-PEG). In shape memory test, the sample was deformed from its original shape to a temporary shape above glass transition temperature (T_g), cooled below T_g to fix the temporary shape, and subsequently heated above T_g for spontaneous recovery to the original shape. By grafting PEG onto PMMA backbone, shape memory ability was drastically enhanced than PMMA homopolymer. The shape recovery ratio was decreased with the increase in the shape deformation temperature. With considering a good miscibility of backbone and side chain in PMMA-g-PEG, this shape memory ability may be related to a physically cross-linked network structure by chain entanglement of the comb-like graft copolymer. Stress relaxation measurements were investigated in order to confirm the effect of the graft chains on the shape memory behavior.     

Surfactant chain length effect on the hexagonal-to-cubic phase transition in mesoporous silica synthesis

In this study, silica-based mesoporous materials (the M41S family mesoporous molecular sieves) are synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n+1N(CH₃)₃Br, n = 10, 12, 14, 16) as templates. The resulting silica structures are characterized by X-ray diffraction and are found to exhibit the phase transformation from the hexagonal mesophase MCM-41 to the cubic mesophase MCM-48 (with the space group of Ia3d). The structural phase transition in our study is controlled by the alkyl chain length of the surfactant: with an increase in the surfactant chain length (from C10 to C16), the structure goes from MCM-41 (synthesized by C10), through an intermediate structure (synthesized by C12), to MCM-48 (synthesized by C14 and C16). The amount of ethanol, which is used as a cosolvent, affects the pore size of the structured mesoporous silica, but only to a small extent. In the mean time, the autoclaving time has some effect, though not distinctively, on the structure integrity as well. With increased surfactant to silica ratio, the phase transformation can be shifted to longer chain template.     

Localization of spherical nanoparticles within lamellar AB diblock copolymer melts through self-consistent field theory

Here we report the results of a three dimensional hybrid self-consistent field theoretic (HSCFT) model describing the equilibrium particle distribution of spherical nanoparticles within symmetric AB diblock copolymer melts. Holding the polymer composition and morphology fixed, we consider a comprehensive parameter space comprised of the Flory interaction parameter describing interactions between B segments and the particle surface compared to the segment-segment interaction parameter (χBP/χAB), the particle volume fraction (?_P), and the ratio of the particle diameter to block copolymer domain spacing (dP/dAB). Analysis of the free energy over this parameter space yields phase diagrams showing the conditions under which particles segregate to the intermaterial diving surface (IMDS) or the center of the domain. Interestingly, w e predict a particle concentration-dependent “reentrant” phase transition in which particles move from the domain interior, to the IMDS, and back as ?_P increases. These results are interpreted as a subtle consequence of the competition between enthalpic polymer-particle interactions and the chain packing frustration imposed by the particulate inclusion. These results are consistent with recent experiments on block copolymer nanocomposites.     

Sulfonated poly(ether imide) and poly(ether sulfone) blends for direct methanol fuel cells. I. Sulfonation of PEI and characterization of the products

This investigation examines characteristics of sulfonated polyether imides (SPEI) with various ion exchange capacity values (IEC) and completes previous work to enable its blends to be adopted as polyelectrolyte in direct methanol fuel cells (DMFC). Polyether imides (PEI) were sulfonated by using chlorosulfonic acid as the sulfonating agent and chloroform as the solvent. The structure of SPEI was observed by FTIR and ¹H NMR. The sulfonate or sulfonic acid content of the polymers, expressed as a number per repeat unit of the polymer, was accurately determined by elemental analysis and conductometric titration. Physical properties such as solubility, intrinsic viscosities, thermal stability, and glass transition temperature (T_g) were studied for both PEI and SPEI. TGA‐FTIR verified that sulfonic groups, attached to the aromatic ring in the PEI backbone, are split at 230–350°C, but the main‐chain splitting temperature of SPEI is similar to that of pure polymer. The sulfonated samples exhibited good solubilities and increased glass transition temperatures (T_g values) as degree of sulfonation (DS) increased; two T_g values were detected when IEC was sufficiently high. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effect of different lithium salts on conductivity of comb-like polymer electrolyte with chelating functional group

The behaviors of lithium ions in a comb-like polymer electrolyte with chelating functional group complexed with LiCF₃SO₃, LiBr and LiClO₄ were characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, AC impedance, and ¹³C solid-state NMR measurement. The comb-like copolymer was synthesized from poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). FT-IR spectra reveal the interactions of Li⁺ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. FT-IR spectra also indicate an increasing anion-cation association consistent with increasing LiCF₃SO₃ concentrations. Moreover, the ¹³C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. T_g and T_d of copolymers doped with salts clearly increase, as shown by DSC and TGA measurements. These results indicate the interactions of Li⁺ with both PEGMEM and GMA-IDA segments form transient cross-links inside the copolymers. The Vogel-Tamman-Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chain in this study. The maximum conductivity of copolymers relates to the composition of the copolymers and the concentration of doping lithium ions. In summary, the GMA-IDA unit in the copolymer promotes the dissociation of the lithium salt, the mechanical strength and the conductivity of the polyelectrolyte.     

Grafting PEG and alkyl comb polymers onto bleached wood pulp fibres

Comb polymers were prepared by reacting a poly(ethylene-alt-maleic anhydride) with alkyl amines or poly(ethylene glycol) (PEG) amines. The resulting polymers were used to modify bleached softwood kraft pulp fibre surfaces by catalyst-free grafting in a process suitable for pulp mill implementation. Pulp fibres were impregnated with a polymer solution and cured above 100°C. High grafting yields were obtained despite having up to 88% of the anhydride groups consumed by amine derivatization. Grafting yields were more than 90% when the polymer dosage was <13 g/kg (dry polymer/dry fibre) for alkyl derivatives and < 38 g/kg for PEG derivatives. We propose that the upper dosage limit for efficient grafting reflects the need for direct contact between cellulose and every polymer chain for ester linkage formation. For a given polymer dosage, the cured pulp sheets had a maximum wet tensile index, TI_max, when either curing time or temperature was increased. Both the alkyl and PEG derivatives fit the power law for the wet TI_max~βΓ_ru^0.54–0.62 where β values were the estimated conversion of succinic acid moieties to anhydrides when the pulp sheets were cured, and Γ_ru is the dimensionless polymer content that is numerically equal to the amount of applied polymer in mmol repeat units/g dry fibre. However, high polymer dosages give experimental TI_max values that fall below the power law, irrespective of curing intensity, because the pulp sheets contain unfixed polymer chains that lubricate fibre/fibre joints, lowering wet strength.