Polymer Structures and Glass Transition: A Molecular Dynamics Simulation Study

Full atomistic molecular dynamics (MD) simulations on five polymers with different chain backbone (C—C, Si—O, and C—O) and different side groups (—H, one —CH₃, and two —CH₃) are performed to study the effects of chain flexibility and side groups on the glass transition of polymers. Molecular dynamics simulations of NPT (constant pressure and constant temperature) dynamics are carried out to obtain specific volume as a function of temperature for polyethylene (PE), poly(propylene) (PP), polyisobutylene (PIB), poly(oxymethylene) (POM), and poly(dimethylsiloxane) (PDMS). The volumetric glass transition temperature has been determined as the temperature marking the discontinuity in slope of the plots of V–T simulation data. Various energy components at different temperatures of the polymers are investigated and their roles played in the glass transition process are analyzed. In order to understand the polymer chain conformations above and below the glass transition temperature, dihedral angle distributions of polymer chains at various temperatures are also studied.     

Transport properties of polyimides containing phenylquinoxaline moieties

The gas permeabilities of a number of new structurally related polyimides containing phenylquinoxaline moieties were studied for the first time. The test polymers had different dianhydride units, whereas their diamine components differed in the presence of flexible ether bonds-O-in the main chain, a structure that is reflected in the effective packing of chains and, as a result, in transport parameters. The permeability, diffusion, and solubility coefficients for the gases H₂, He, O₂, N₂, CO, CO₂, and CH₄, as well as the ideal separation factors for gas pairs, were determined. The transport characteristics of polymers were compared within the given polymer series and with published data for other polymer series.     

RADICAL GRAFTING REACTIONS ONTO STARCH AND OTHER WATER-SOLUBLE COPOLYMERS IN ISOLATED GEL DROPLETS

A novel radical grafting copolymerization process has been designed for water-soluble polymers which avoids the problems of conducting grafting reactions in highly viscous polymerization media. A variety of water-soluble graft copolymers having starch or dextran as the backbone chain with grafted side chains of polyacrylamide (—AM—), poly (acrylic acid ) (—AA—), poly (acrylamide-co-acrylic acid) (—AM—NH_4AA—) or poly ( acrylamide-co-2-acryiamido-2-methyl-l-propanesulphinic acid) (—AM—AMPS—) have been synthesized in gel droplets using aceric sulphate redox initiator, and their properties compared. The reaction conditions were optimized taking into account reaction kinetic data and the observed properties of the products produced under different reaction conditions. The effects of the ratios of [backbone]/[graft monomer], [ AM]/[ AA]/[AMPS] , [Ce~(4+)]/[ S_2O_8=] and pH value on the reaction rate , conversion, grafting degree, grafted chain length and the product molecular weight have been investigated.     

Permeation and sorption in polynorbornenes with organosilicon substituents

Gas sorption properties, permeability coefficients, and diffusion coefficients of a series of norbornene polymers are presented. Introduction of the Si(CH₃)₃ group into the polynorbornene (PNB) backbone chain results in significant increases in glass transition temperature, permeability, and diffusion coefficient for a number of gases (H₂, O₂, N₂, CO₂, CH₄, C₂H₆). The transport properties and sorption isotherms for poly(5-trimethylsilyl norbornene) (PTMSNB) are very similar to those for poly(vinyltrimethyl silane) (PVTMS), which contains the same side-chain group but differs from PTMSNB by the structure of its main chain. For another silicon-containing polymer poly[5-(1,1,3,3-tetramethyl-1,3-disilabutyl) norbornene] (PDSNB) having a bulkier side-chain group, the glass-transition temperature is decreased in comparison with that of PNB, presumably owing to self-plasticization. Both silicon-containing norbornene polymers (PTMSNB and PDSNB) have permeability coefficients for “rapid” gases like H₂ or CO₂ of about 10² Barrer. The high values of the Langmuir sorption capacity C′_H for PTMSNB and PVTMS, as well as the high diffusivity and mobility of spin probes in these polymers, were attributed to a large free volume related to the bulky Si(CH₃)₃ groups attached directly to the main chain. © 1993 John Wiley & Sons, Inc.     

Influence de la structure sur les proprietes mesomorphes des polyesters—I

A new series of thermotropic liquid crystalline polymers has been synthesized. Mesogenic elements are separated by flexible spacers —(CH₂)_n— in the backbone. The thermal properties of these polymers are analogous to liquid crystals.     

On the structure and the chain conformation of side-chain liquid crystal polymers

Abstract

Backbone anisotropy and the structure of the mesophases of a series of side-chain liquid crystal polymers have been studied in the bulk by neutron scattering. The backbone conformation is obtained by small-angle neutron scattering on mixtures of hydrogenous polymers with deuteriated backbones. The components of the radius of gyration parallel, R _⊥ and perpendicular, R ∥ to the magnetic field are determined as a function of temperature for both the nematic phase and the smectic phase. It is shown that the polymer backbone is deformed in both phases. When the polymer exhibits only a nematic phase, it adopts a prolate conformation, where the average backbone direction is more or less parallel to the aligned mesogenic groups. Upon transition from the smectic phase to a nematic phase, the backbone in the nematic phase assumes a slightly oblate shape. This tendency towards oblate shape is due to the smectic fluctuations which are always present in such nematic phases. The exentricity of the oblate backbone conformation in the smectic phase is always larger than in the nematic phase. This is attributed to a periodic distribution of the backbone between the mesophase layers. Then, the backbone anisotropy depends not only on the smectic structure (S_A1, S_Ad), but also on the temperature dependence of the density of aligned mesogenic groups in the layers. On the other hand, it is shown that the isotopic mixtures are no longer ideal when polymers deuteriated in the mesogenic moieties are mixed with the corresponding hydrogenous polymers.     

Gas sorption and transport in substituted polystyrenes

The effects of pendant groups on gas transport were investigated using a series of substituted polystyrenes. Permeability coefficients were measured at 35°C and 1 atm for He, N₂, O₂, CH₄, and CO₂, and diffusion coefficients were calculated from time lag data. The absolute permeabilities for the polystyrenes are correlated reasonably well using a free volume model. All pendant group substitutions resulted in a reduction of the mobility selectivity for CO₂/CH₄ separation relative to polystyrene, although there was very little effect on the O₂/N₂ selectivity. The effects of the various substituents were individually analyzed in terms of their size, rigidity, and polarity. The addition of a methyl group to the backbone significantly decreases transport, while attachment to the para ring position increases permeation. Bulky rigid groups, such as t-butyl, enhance permeation even more. Methoxy and acetoxy substitutions provided an excellent means of examining plasticization of polymers by CO₂, such as cellulose acetate, which contain these same moieties. The response of these polymers indicates that the degree of plasticization is related to the polarity and flexibility of the pendant group.     

Charge carrier mobilities in liquid crystalline mesomorphic poly(DI-n-Alkylsilylene)s; influence of backbone conformation

The charge transport properties of a series of symmetrically substituted mesomorphic poly(di-n-alkylsilylene)s are studied using the pulse-radiolysis time resolved microwave conductivity (PR-TRMC) technique. The observed conductivities for these polymers could be correlated with different backbone conformations present both in the crystalline solid phase and in the liquid crystalline mesophase. The transition from the solid phase to the mesophase is accompanied by a disordering of the silicon backbone that results in a decrease of the conductivity of up to two orders of magnitude. The charge carrier mobilities found varied from 5×10⁻⁵ m² /Vs for the all-trans conformation in the solid phase to 6×10⁻⁷ m² /Vs for the disordered backbone conformation in the mesophase. The anisotropic radiation-induced conductivity observed for aligned poly(di-n-hexylsilylene) samples demonstrate that charge carrier migration takes place preferentially in the direction of the polymer backbone.     

Synthesis and photophysical properties of poly(aryleneethynylene)s bearing dialkylsilyl side substituents

A series of poly(aryleneethynylene)s bearing dialkylsilyl (-SiR₂H) side substituents has been synthesized by Sonogashira cross-coupling reactions of 1,4-diethynyl-2,5-bis(dialkylsilyl)benzene and diiodoarylene compounds. Their photophysical properties in solution have been studied. All of the polymers showed intense fluorescence with high quantum yield. Compared with their analogues containing para-phenylene units, the polymers with meta-phenylene units in the main chain showed absorption and emission maxima at shorter wavelengths, whereas the polymers having thiophenylene units in their backbones showed bathochromically shifted spectra. For polymers having the same conjugated parent backbone, silyl substituents have been found to exert negligible effect on their photophysical properties.     

Semicrystalline poly(vinyl ether)s with high and phototunable glass transition temperature: application for thermally stable and reworkable adhesives

The photoinduced solid–liquid phase transition of azobenzene-based polymers is an attractive method to synthesize stimuli-responsive functional materials. As the structure–property relationships of such materials are not fully understood, a new class of polymer backbone, that is, poly(vinyl ether) (PVE), was studied for the development of azobenzene-based polymers with high thermal stability. For this purpose, a series of azobenzene-based PVEs with different monomer structures were synthesized using a Lewis acid catalyst-based cationic polymerization method. Typical PVEs are viscous polymers with low glass-transition temperatures (T_g's). The flexibility of the polymer backbone improves with the use of alkylene spacers, changing the order of alignment of the mesogenic azobenzene moieties attached to the backbone, leading to high T_g's of the azobenzene-based PVEs. One of the synthesized PVEs shows a high glass-transition temperature of 94 °C, which is 14 °C higher compared to that of the corresponding polymethacrylate. Furthermore, the PVE exhibits photoinduced solid–liquid phase transition from the semicrystalline state. This phase transition material, with its high thermal stability, has the potential for broader applications, such as for the phototuning of adhesion. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 568–577     

Self-organizing cyclolinear methylcyclohexasiloxane polymers carrying reactive vinyl groups

Atactic cyclolinear organosilicon polymers containing vinyl substituents in RSiO_1.5, R₂SiO or both moieties have been synthesized through the heterofunctional polycondensation of trans,cis-2,8-dihydroxymethyl(vinyl)cyclohexasiloxanes with 2,8-dichloromethyl(vinyl)cyclohexasiloxanes. The structure of the polymers has been studied by ¹H and ²⁹Si NMR and IR spectroscopy, molecular mass measurements, and elemental analysis. The phase behavior of these copolymers in the bulk has been examined by DSC, X-ray diffraction, and polarization optical microscopy. It has been shown that the copolymer can exist in the mesomorphic state in the temperature range from ?100 to +200°C. The X-ray data indicate changes in the interlayer spacing and the type of packing of cyclolinear poly(methylvinylsiloxanes) with an increase in the content of vinyl substituents in the repeating units of the polymer. The ability of cyclolinear poly(methylvinylsiloxanes) to spread over the water/air interface and to form mono-and multilayers has been investigated. As the content of vinyl substituents in the polymer unit is increased to two or four, the ability of polymers to form multilayers is preserved. The incorporation of vinyl substituents into RSiO_1.5 or R₂SiO moieties of polymer units is accompanied by the formation of monolayers.     

Highly phenylated poly(aryl ether phthalazine)s

Two series of novel amorphous poly(aryl ether phthalazine)s have been prepared via an intramolecular ring closure reaction of poly(aryl ether ketone)s (PAEKs) with hydrazine monohydrate. Fluorinated PAEKs, which display solubility in solvents incorporating a ketone functionality such as acetone or ethyl acetate, were converted to poly(aryl ether phthalazine)s to observe if these polymers would display similar solubility characteristics. The poly(aryl ether phthalazine)s have glass transition temperatures in the range of 278–320°C and show 5% weight loss points greater than 500°C in air and nitrogen atmospheres. The fluorinated poly(aryl ether phthalazine)s were not soluble in ketonic solvents. A series of poly(aryl ether phthalazine)s incorporating pendant 2-naphthalenyl moieties has been prepared in an attempt to produce amorphous, thermally stable polymers with high glass transition temperatures. The polymers have glass transition temperatures in the range of 287–334°C and show 5% weight loss points greater than 500°C in air and nitrogen atmospheres. Poly(aryl ether phthalazine)s undergo an exothermic reaction above the glass transition temperature. The major product of this reaction is a rearrangement of the phthalazine moieties to quiazoline moieties, however some crosslinking of the polymers occurs. Cured samples of the poly(aryl ether phthalazine)s show a small increase in the polymer T_g and are insoluble in all solvents tested. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1897–1905, 1996     

Gas permeability of cardo-poly(ether-ether-ketone) and poly(phenylene sulfide)

The gas permeability and sorption of CO₂ and N₂O was measured on cardo-poly(ether-ether-ketone) (C-PEEK) and poly(phenylene sulfide) (PPS) at 298 K. The results are discussed on the basis of the dual-mode model. Results obtained from measurements at 308 K are compared with literature data of poly(phenylene oxide) (PPO), poly(sulfone) (PSU) and poly(carbonate) (PC). While C-PEEK shows similar transport properties as PC and PSU, the values of PPS are distinctly lower. The solubility of CO₂ in the various polymers as well as the correlation of the permeability coefficients of the same polymers for He, Ar, CO₂, N₂, and CH₄ with the kinetic molecular diameter of the gases indicate a simple relation of the transport properties with the polymer density.     

Poly[bis(phosphinatoalanyl)phosphonates]

A series of coordination polymers, poly[bis(phosphinatoalanyl)phosphonates], [X(Y)AlOP(R)(O)OAl(Y′)(X′)]_n, were synthesized in which the terminal alanyl substituents (X,Y,X,′Y′) consisted of phosphinato (OPRR′O) or fluoro (F) moieties. The properties of the polymers were primarily dependent upon the type of terminal substituent and the hydrocarbon moieties (R,R′) on phosphorus. Polymers with four phosphinato moieties gave molecular weights M?_n to 120000 with intrinsic viscosities [η] from 1.5 to 18; the corresponding solids were partially crystalline, melted before decomposition, and were film-forming when larger phosphorus substituents were incorporated. Sequential replacement of the phosphinato moieties with fluorine resulted in molecular weights below 10000 and low viscosities. The properties of the polymers are examined, and the roles of substituents on probable structures are discussed.     

Thermally reversible covalently bonded linear polymers prepared from a dihalide monomer and a salt of dicyclopentadiene dicarboxylic acid

Alkali and earth‐alkali salts of dicyclopentadiene dicarboxylic acid (DCPDCA) were prepared and employed as monomers in the polyesterification with an α,ω‐dihalide monomer, such as 1,4‐dichlorobutane (DCB), 1,4‐dibromobutane (DBB), α,α′‐dichloro‐p‐xylene (DCX), and α,α′‐dibromo‐p‐xylene (DBX). Novel linear polymers that possessed repeating moieties of dicyclopentadiene ( DCPD ) in the backbone were thus prepared. The IR and NMR spectra indicated that poly(tetramethylene dicyclopentadiene dicarboxylate) (PTMDD) with a number‐average molecular weight (M_n ) of about 1× 10⁴ and poly(p‐xylene dicyclopentadiene dicarboxylate) (PXDD) with a M_n of 4–6 × 10³ were obtained with an yield of about 80% via the polyesterification of the alkali salts with DBB and DCX, respectively. The reaction was carried out in the presence of a phase transfer catalyst, such as BzMe₃NBr or poly(ethylene glycol), in DMF at 100 °C for 4 h. Oligomers with a lower M_n (1–2 × 10³) were obtained when the earth‐alkali salts were employed as salt monomers. Compared to the irreversible linear polymers, poly(p‐xylene terephthalate) (PXTP) and poly(p‐xylene maleate) (PXM), prepared through the reaction between DCX and the potassium salts of terephthalic and maleic acid, respectively, the specific viscosities (η_sp) of the new linear polymers increased abnormally with the decrease of the temperature from 200 °C to 100 °C. This occurred due to the thermally reversible dedimerization/redimerization of  DCPD moieties of the backbone of the polymers via the catalyst‐free Diels–Alder/retro Diels–Alder cycloadditive reactions. The ratio of the η_sp at 100 °C and 200 °C of the reversible polymers was found to be much higher than that of PXTP and PXM, even when the heating/cooling cycle was carried out several times under a N₂ atmosphere. The obtained results indicated that thermally reversible covalently bonded linear polymer can be obtained by introducing the  DCPD structure into the backbone of the polymer through the polymerization of a monomer containing the  DCPD moiety. The reversible natures of the polymers and oligomers might be useful in preparing easily processable and recyclable polymers and thermosensor materials. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1662–1672, 2000     

Synthesis and characterisation of polymethacrylates containing para-, meta- and ortho-monosubstituted azobenzene moieties in the side chain

Three sets of novel side-chain liquid crystalline polymers with monosubstituted azobenzene moieties in the side-chain have been studied. These are poly(p-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PPHABM), poly(m-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PMHABM) and poly(o-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (POHABM). The chemical structure of the monomers was confirmed by ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The structural characterisation of the polymers was performed by ¹H NMR spectroscopy and gel permeation chromatography, and their phase behaviour and liquid crystalline properties were studied using differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. The results show that the transitional behaviour of side-chain liquid crystalline polymers containing monosubstituted azobenzene moieties depends strongly on the position of the substituent on the azobenzene moiety; for example, the ortho-monosubstituted polymers do not form liquid crystalline phases, but all the para- and meta-monosubstituted polymers exhibit a smectic A phase. Furthermore, the glass transition temperature (T_g ) of the polymers decreases in the order, para > meta > ortho. For the PPHABM and PMHABM polymers the isotropic temperature (T_i ) and liquid crystalline range (ΔT, from T_g to T_i ) are found to be in the order, para > meta, although it is surprising that the associated enthalpy changes in these polymers is the opposite order, meta > para.     

Preparation and Curing of Poly (Perfluoroalkylene Oxides)†

Abstract

A series of functionally terminated poly(perfluoroalkylene oxides), a new class of curable, liquid, fluorinated polymers, has been prepared by the photopolymerization of perfluorooxydipropionyl fluoride, O(CF₂CF₂COF)₂, and related perfluoroacyl fluoride monomers. Polymerization proceeds by ultraviolet-induced scission of CF₂COF groups and coupling of the CF₂—radicals thus formed. Polymer molecular weight and functionality increase with photolysis time. The acid fluoride-terminated polymers (Mn 1000–5000, functionality 2–5) are liquids possessing low T_g (about ?60°C) and excellent, thermal stability. Other functional end groups (e.g., COOH, COOR, CH₂OH, etc.) have been prepared using standard reactions.     

Bandgap Engineering through Controlled Oxidation of Polythiophenes

The use of Rozen’s reagent (HOF?CH₃CN) to convert polythiophenes to polymers containing thiophene‐1,1‐dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3‐alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60 % TDO moieties in the polymer backbone. The resulting polymers have a markedly low‐lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well‐defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.     

Properties of a nanocomposite polymer electrolyte from an amorphous comb-branch polymer and nanoparticles

Three fully amorphous comb-branch polymers based on poly(styrene-co-maleic anhydride) as a backbone and poly(ethylene glycol) methyl ether of different molecular weights as side chains were synthesized. SiO₂ nanoparticles of various contents and the salt LiCF₃SO₃ were added to these comb-branch polymers to obtain nanocomposite polymer electrolytes. The thermal and transport properties of the samples have been characterized. The maximum conductivity of 2.8×10^–4 S cm^–1 is obtained at 28 °C. In the system the longer side chain of the comb-branch polymer electrolyte increases in ionic conductivity after the addition of nanoparticles. To account for the role of the ceramic fillers in the nanocomposite polymer electrolyte, a model based on a fully amorphous comb-branch polymer matrix in enhancing transport properties of Li⁺ ions is proposed.     

The stable inner salt 2,2‐dimorpholino‐2‐ethyl­ium‐1‐di­thio­ate

The title compound, C₁₀H₁₆N₂O₂S₂, is considered to maintain an inner‐salt structure in the crystal, where the planes of the carbenium and the thio­carboxyl­ate moieties are nearly perpendicular to each other [77 (2)°], and the backbone C—C bond length [N₂C—CS₂ 1.510 (2) Å] is significantly shorter than a normal C—C single‐bond length.