Influence Of Monomer Structure Research Articles

Influence of Monomer Structure, Initiation, and Porosity on Mechanical and Morphological Characteristics of Thiol‐ene PolyHIPEs

AbstractCombining high internal phase emulsion templating with thiol‐ene click chemistry produces porous polymers with high yields and degradable ester linkages. This study compares the influence of the monomer functionalities (tri versus tetra), internal phase volume, and initiation type (photo versus thermal) on the morphological and mechanical properties of poly(high internal phase emulsions) (polyHIPEs). For the synthesis of the polyHIPEs pentaerythritol tetrakis(3‐mercaptopropionate) (PETMP, tetrafunctional), trimethylolpropane tris(3‐mercaptopropionate) (TMPTMP, trifunctional), pentaerythritol tetraacrylate (PETA, tetrafunctional), and trimethylolpropane triacrylate (TMPTA, trifunctional) are used. The main factors influencing the properties of the polyHIPEs are the monomer structures and the internal phase volume, while the initiation type influences the morphology of the trifunctional system (pore size and morphology type) resulting in an interconnected cellular morphology in all cases except in the case of the photopolymerization of the emulsion with 85 vol% of the internal phase. The average pore diameter of the trifunctional system ranges from 8.0 to 27.8 µm, while for the tetrafunctional system it ranges from 8.1 to 12.3 µm. The compression moduli of the trifunctional system range from 0.093 to 0.240 MPa and for the tetrafunctional system they range from 1.906 to 7.670 MPa. The compression moduli decrease with increasing internal phase volume (porosity).

Aromatic tetra-glycidyl ether versus tetra-glycidyl amine epoxy networks: Influence of monomer structure and epoxide conversion

In this work, two epoxy resins, bis(2,7 glycidyl ether naphthalenediol) methane (NNE), tetraglycidyl diaminodiphenylmethane (TGDDM) and a miscible blend of the two are cured with 4,4′-diaminodiphenylsulfone (DDS) to investigate the differences between glycidyl ether and glycidyl amine crosslinked networks. This work explores in depth, and directly compares for the first time, the structure/property relationships of a highly aromatic and thermally stable glycidyl ether epoxy network with a well-known highly aromatic and thermally stable glycidyl amine epoxy network. The highly aromatic naphthalene motif of NNE imparts improved thermal stability and a significantly higher glass transition temperature, above 340 °C depending on the measurement technique. However, it also produces comparatively lower epoxide conversion, higher moisture ingress and lower flexural properties. These properties are attributed to the NNE having higher free volume and glassy state mobility as suggested by the sub-ambient β relaxations. The glycidyl ether groups react primarily via epoxide amino addition displaying only very minor evidence of homopolymerisation or other side reactions even at 240 °C. This contrasts with the glycidyl amine groups of TGDDM which exhibit a much higher degree of non-epoxy amine addition. Increasing cure conversion also increases the glass transition temperature, fracture toughness and reduced coefficient of thermal expansion. Overall, the results show that despite some reduced mechanical and thermal properties the NNE epoxy resin system is a very thermally stable high temperature epoxy resin based upon glycidyl ether functional groups suitable for a wide range of new applications.

The Influence of Monomer Structure on the Properties of Ionogels Obtained by Thiol–Ene Photopolymerization

The influence of ene and thiol monomer structure on the mechanical and electrochemical properties of thiol–ene polymeric ionogels were investigated. Ionogels were obtained in situ by thiol–ene photopolymerization of 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATT), 2,4,6-triallyloxy-1,3,5-triazine (TAT), diallyl phthalate (DAP), and glyoxal bis(diallyl acetal) (GBDA) used as enes and trimethylolpropane tris(3-mercaptopropionate) (TMPTP), pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), and pentaerythritol tetrakis(3-mercaptobutyrate) (PETMB) used as thiols in 70 wt.% of ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImNTf2). The mechanical strength of ionogels was studied by puncture resistance and ionic conductivity by electrochemical impedance spectroscopy. The course of photopolymerization by photo-DSC method (differential scanning calorimetry) as well as characterization of compositions and its components (by IR and UV spectroscopy-Kamlet–Taft parameters) were also studied. The resulting ionogels were opaque, with phase separation, which resulted from the dispersion mechanism of polymerization. The mechanical and conductive properties of the obtained materials were found to be largely dependent on the monomer structure. Ionogels based on triazine monomers TAT and TATT were characterized by higher mechanical strength, while those based on aliphatic GBDA had the highest conductivity. These parameters are strongly related to the structure of the polymer matrix, which is in the form of connected spheres. The conductivity of ionogels was high, in the range of 3.5–5.1 mS∙cm−1.

Influence of monomer structure and dose rate on kinetic elements in electron-beam polymerizations

In electron-beam (EB) polymerizations, altering the dose rate can cause property changes in the cured polymer, such as conversion, glass transition temperature (Tg), and physical or mechanical properties. These dose rate effects (DREs) complicate scale-up of EB polymerizations in industrial processes. A predictive relationship between DRE and changes in Tg was used to determine that DREs correlate to the number and lability of available bonds, not monomer size. Furthermore, the relationship between the primary radicals produced during EB irradiation and dose rate was explored via measurement of primary radical radiation chemical yield, G(R•). Namely, G(R•) is independent of dose rate, and instantaneous primary radical concentration is directly proportional to dose rate. Moreover, it was shown that non-reciprocity between dose rate and the rate of polymerization results in DREs. Future developments in radiation chemical yield measurements will aid in determining whether this disproportionality is due to the impact of dose rate on the concentration of propagating radicals or on the kinetic mechanism itself.

Polymer stabilized highly tilted antiferroelectric liquid crystals - the influence of monomer structure and phase sequence of base mixtures

Polymer stabilization offers unique opportunities for improving features of liquid crystals. In particular, it influences the static and dynamic performance of antiferroelectric liquid crystals (AFLCs) due to the stabilization of surface-stabilized geometry of such self-assembling materials forming anticlinic structures. The main advantages of polymer-stabilized AFLCs consist of a significant decrease of the electro-optical switching time, and a lower sensitivity to mechanical shock and temperature changes in working devices. This work experimentally analyzes the effect of functionality of selected mesogenic monomers on the properties of new developed high-tilted AFLC mixtures with different phase sequences, before and after polymer stabilization. It was found that tetrafunctional monomers (especially those with non-chiral terminal chains) reduce the thermal stability of antiferroelectric phase and increase helical pitch at low temperatures before polymerization. However, they reduce values of the tilt angle and spontaneous polarization and simultaneously flatten the temperature dependence after polymerization to a greater extent than bifunctional monomers. Tetrafunctional monomers improve electro-optical characteristics of tested AFLC mixtures after polymer stabilization. On the other hand, polymer-stabilized materials based on bifunctional monomers and LC mixtures with direct SmCA* - Iso phase transition show acceptable electro-optical performance in device cells. Most importantly, the obtained results confirm definite advantages of using mixtures with direct SmCA* - Iso phase transition when designing new polymer-stabilized AFLC materials with appropriate features in effects based on surface-stabilized geometry.

Influence of monomer structure on the properties of blue phase liquid crystal

ABSTRACTIn this paper, four kinds of polymer-stabilized blue phase liquid crystals (PS-BPLCs) with different monomer were designed and prepared. The morphology, temperature ranges and electro-optical properties of the blue phase were studied and discussed. The temperature ranges of four BPLCs are more than 90°C, and all samples can be stabilized well at room temperature. Referring to electro-optical performance, on-state voltage for mono-functional monomers systems is reduced from 75 V to 65 V at 497 nm. On-state voltage for tri-functional monomers systems is reduced from 107 V to 85 V at 497 nm. These results are helpful to the application of display and photonic devices.

Studies on the dispersity of polymethacrylate-grafted carbon black in a non-aqueous medium: the influence of monomer structure

This work aims at studying the structure of monomers on the dispersity of carbon black (CB) in a non-aqueous medium Isopar L. The polymethacrylate-grafted CB nanoparticles were prepared by a redox polymerization method. A series of methacrylate monomers containing alkyl side chain with different length and structure were employed for grafting. The structure and composition of polymethacrylate-grafted CB particles were characterized by a combination of FTIR, TGA and XPS. The particle size distribution, average diameter, contact angle to water and Isopar L and zeta potential of the prepared CB particles were investigated to provide insights into the effects of the monomer structure on the dispersity of modified CB particles in Isopar L. TEM images demonstrated that aggregation of modified CB particles reduced distinctly. The surface of CB particles changed from hydrophilic to hydrophobic after modification. Moreover, it is also found that the more branching or the longer the monomers used in the modification, the narrower the particle size distribution and the higher the zeta potential. The display prototype based on polymethacrylate-grafted carbon black particles showed an improved display performance under the electric field of 0.30 V μm−1. Especially, the EPD based on ethylhexyl methacrylate modified CB particles displayed the highest contrast ratio of 8.36 and minimum response time (527 ms) compared with the ones prepared with other modified particles.

Synthesis, photophysical and photochemical studies of benzophenone based novel monomeric and polymeric photoinitiators

Abstract Four novel benzophenone-containing photoinitiators (monomers PI-1 and PI-2 and their polymers PPI-1 and PPI-2) were prepared from alkyl α-hydroxymethacrylates. PI-1 was synthesized from reaction of tert-butyl α-bromomethacrylate and 4-hydroxybenzophenone followed by cleavage of tert-butyl groups using trifluoroacetic acid. PI-2 was synthesized from reaction of ethyl α-bromomethacrylate and 3-benzoylbenzoic acid. Thermal polymerization of PI-1 and PI-2 was performed using 2,2′-azobis(isobutyronitrile). PI-1 and PPI-1 show UV absorption (289 and 294 nm) which are red-shifted compared to benzophenone (252 nm), PI-2 (255 nm) and PPI-2 (252 nm). All of the photoinitiators give phosphorescence emissions from their n–π* states. The photopolymerizations of triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and hexanediol diacrylate initiated by PI-1, PI-2, PPI-1, PPI-2 and benzophenone were studied by photo-differential scanning calorimeter using N,N-dimethyl-p-toluidine as coinitiator. Polymeric photoinitiators were found to have higher efficiencies than benzophenone and monomeric ones. Photopolymerization results are also compared to that of an alkyl α-hydroxymethacrylate-based photoinitiator previously reported by us; and the influence of monomer structure on polymerization efficiency is discussed.

Synthesis, photopolymerization, and adhesive properties of hydrolytically stable phosphonic acid-containing (meth)acrylamides

Three novel dental monomers containing phosphonic acid groups (1a and 2a, based on diethyl amino(phenyl)methylphosphonate and 3a based on diethyl 1-aminoheptylphosphonate) were synthesized in two steps: the reaction of α-aminophosphonates with acryloyl chloride (for monomers 1a and 3a) or methacryloyl chloride (for 2a) to give monomers with phosphonate groups, and the hydrolysis of phosphonate groups by using trimethyl silylbromide. Their (and the intermediates') structures were confirmed by FTIR, 1H, 13C, and 31P NMR spectroscopy. All the monomers dissolve well in water (1<pH<2) and are hydrolytically stable. Their homo- and copolymerizations with 2-hydroxyethyl methacrylate (HEMA) and HEMA/glycerol dimethacrylate were investigated with photo-DSC. Thermal polymerization of the new monomers in water or in ethanol/water solution was investigated, giving polymers in good yields. X-ray diffraction results showed only dicalcium phosphate dehydrate formation upon interaction of 1a-3a with hydroxyapatite indicating its strong decalcification and that monomer-Ca salts are highly soluble. Some results were also compared to those with a bisphosphonic acid-containing methacrylamide (4a) previously reported; and the influence of monomer structure on polymerization/adhesive properties is discussed. These properties, especially hydrolytic stability and good rates of polymerization, make these new monomers suitable candidates as components of dental adhesive mixtures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 511–522

Influence of Monomer Structures on the High Temperature Properties of Poly[(Alkylamino)Borazine)]s Derived BN

Preceramic polymers to boron nitride (BN) have been synthesized by thermal condensation of different (alkylamino)borazine monomers. Crystalline BN was obtained by pyrolysis of those polymeric precursors in NH3 and then in Ar. The influence of monomer structure on the chemical composition, microstructure, oxidation resistance and high temperature stability of BN was investigated by a combination of elemental analysis (EA), density measurement, FTIR, XPS, XRD, HRTEM and TGA. With similar chemical composition, BN derived from symmetric monomer exhibited a higher crystallinity, better oxidation resistance and higher temperature stability. This was because that the structure of the precursor polymerized from symmetric molecular was close to that of hexagonal BN (h-BN).

Influence of Monomer Structure on the Propagation Kinetics of Acrylate and Methacrylate Homopolymerizations Studied via PLP‐SEC in Fluid CO2

AbstractSummary: Propagation kinetics of free‐radical homopolymerizations of methyl acrylate, dodecyl acrylate, butyl methacrylate, dodecyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate in solutions containing 40 wt.‐% CO2 were studied applying the PLP‐SEC technique. The obtained apparent propagation rate coefficients, kp,app, are by up to 40% below the associated bulk kp values. This reduction is assigned to a lowering of local monomer concentration, cM,loc, at the site of the free‐radical chain end rather than to a decrease of the actual propagation rate coefficient. With the alkyl (meth)acrylates, intersegmental interactions between polar groups of the same polymer molecule are responsible for deviations of cM,loc from the analytical overall monomer concentration, cM,a. Increasing size of the flexible alkyl ester group reduces the differences between cM,loc and cM,a due to shielding effects. Methacrylates with cyclic ester groups do not follow this trend. In case of isobornyl methacrylate, which polymerizes to a rigid material with large side groups, relative size of monomer and CO2 matters and reduces cM,loc significantly below cM,a.image

Mixtures of lattice polymers with structured monomers.

The influence of monomer structure on the thermodynamic properties of lattice model polymer blends is investigated through Monte Carlo computations. The model of lattice polymers with monomer structure has been used extensively in the context of the lattice cluster theory (LCT), a thermodynamic theory for polymer mixtures in the liquid state. The Monte Carlo computations provide the first unequivocal test of the accuracy of the LCT predictions for binary mixtures of polymers with structured monomers. Four types of monomer structures are analyzed, corresponding to to the monomers of polyethylene, polypropylene, polyethylethylene, and polyisobutylene (PIB). Most computations use chains with M=12 and 24 beads and the total volume fraction of the beads is phi=0.6. Both structurally symmetric and asymmetric blends are investigated. For the symmetric case, the predictions of the LCT for the energies of mixing and the liquid-liquid coexistence curves are in qualitative agreement with the Monte Carlo computations, except for the PIB/PIB symmetric blend. For structurally asymmetric blends, the LCT does not capture contributions to the energy of mixing arising solely from structural differences between the components. Computational estimates of the nonideal entropy of mixing indicate that the LCT also underestimates the entropic cost of mixing chains with different structures, thus explaining some discrepancies between the theoretical and the Monte Carlo liquid--liquid coexistence curves.

Coexistence curves for melts of lattice polymers with structured monomers: Monte Carlo computations and the lattice cluster theory

The influence of monomer structure on the vapor–liquid coexistence curves of lattice polymer melts is investigated through Monte Carlo calculations. The extended lattice model used in the computations has been introduced as the underlying model for the lattice cluster theory (LCT), a thermodynamic theory for polymer mixtures in the liquid state. The LCT model is essentially a bare-bones united atom model defined on a cubic lattice. The computational method employed is a variant of the density of states Monte Carlo algorithm. Chain architectures analogous to those of polyethylene, polypropylene, polyethylethylene, and polyisobutylene are considered. The computational results are compared with the coexistence curves predicted by the LCT. Qualitative and quantitative disagreements between the theoretical and the computed values are observed, casting doubts on the reliability of the LCT in the study of the phase behavior of melts and solutions of polymers with structured monomers.

Molecular Influences on Miscibility Patterns in Random Copolymer/Homopolymer Binary Blends.

The lattice cluster theory (LCT) is used to study the microscopic molecular factors affecting the miscibilities of AxB1-x/C binary mixtures (where the homopolymer C is either different or identical to the AxB1-x random copolymer species). A prime goal of this study lies in describing gross departures of LCT predictions from the prevailing random copolymer Flory-Huggins (FH) theory. These departures are illustrated by analyzing computed constant pressure spinodal (and binodal) curves, and some computations are compared with experimental data. Different miscibilities are predicted for several AxB1-x/A and AxB1-x/B systems with x = 1/2, departing considerably from predictions of FH random copolymer theory. These differences are partially explained in terms of the entropic structural parameter that provides one measure of blend structural asymmetry. The computed phase diagrams of AxB1-x/C not equal A,B blends exhibit richer miscibility patterns than those derived from FH random copolymer theory. The illustrations focus on the influence of monomer structure, interaction energies, and pressure on the phase behavior of random copolymer/homopolymer systems. Applications to polyolefins employ a model for interaction energies based on Lennard-Jones parameters for these olefins.

Radical concentrations, environments, and reactivities during crosslinking polymerizations

AbstractRadical environments and concentrations during the crosslinking polymerizations of multiethylene glycol dimethacrylates were characterized with electron spin resonance spectroscopy. The relative concentrations of free and trapped radicals were used as a measure of certain structural features in the evolving polymer, especially with respect to microgel formation. The influence of monomer structure and crosslinking density on the polymer structure was studied by examining the radical behavior during the polymerization of diethylene glycol dimethacrylate, poly(ethylene glycol 200) dimethacrylate, and poly(ethylene glycol 600) dimethacrylate. The extent of radical trapping and microgel formation was found to increase with increasing crosslinking density. The influence of the rate of initiation on radical trapping was also investigated, and slower rates of polymerization led to a higher fraction of trapped radicals with respect to the total radical population. Finally, the termination mechanism of radicals was characterized (long‐term and short‐term) and the corresponding kinetic constants quantified.

Influence of monomer structure on chemo‐ and stereoselectivity of 1,3‐diene polymerization

AbstractMAO/CpTiCl3 is an active catalyst for the polymerization of various types of 1,3‐dienes. Butadiene, (E) ‐ and (Z) −1,3‐pentadiene, (E) −2‐methyl‐1,3‐pentadiene and 2,3‐dimethylbutadiene yield, at room temperature, polymers with a cis‐1,4 or a mixed cis/1,2 structure. 4‐Methyl‐1,3‐pentadiene and (E,E) −2,4‐hexadiene give, respectively, a 1,2 syndiotactic and a trans‐1,4/1,2 polymer. MAO/CpTiCl2·2THF and MAO/(CpTiCl2)n are less active than the CpTiCl3 catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)‐1,3‐pentadiene: a cis‐1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis‐η4 at +20°C and may be trans‐η2 at −20°C. Results obtained with catalysts from CpTi(OBu)3 and Ti(OBu)4 are reported for comparison. An interpretation is given of the formation of cis‐1,4 isotactic poly(2‐methylpentadiene) and of 1,2 syndiotactic poly(4‐methylpentadiene), as well as of syndiotactic polystyrene.

Lattice cluster theory of compressible diblock copolymer melts

We generalized to diblock copolymer systems the lattice cluster theory, which includes the influence on thermodynamic properties of monomer structure, local correlations, and compressibility (often called ‘‘equation of state effects’’). The thermodynamic properties are expanded in powers of the inverse lattice coordination number and the van der Waals interaction energies. This cluster expansion for the Helmholtz free energy is represented diagrammatically similar to the case of blends, but diblock copolymers introduce new features into the theory due to the presence of correlations in the region of the junction between two blocks. The theory predicts the composition and molecular weight dependence for both the entropic and enthalpic portions of the effective interaction parameter. The influence of monomer structure on thermodynamic properties is illustrated using model calculations for the order–disorder transition temperature as a function of composition and pressure.

Investigation of polyimides containing naphthalene units: 1. Monomer structure and reaction conditions

A series of novel polyimides with naphthalene units in the chain has been synthesized. The polyimides were prepared from 1,3- and 1,4-bis(1,8-dicarboyxlic anhydride-4-naphthaloyl)benzene (III) and six diamines in m-cresol in the presence of various catalysts. The influence of monomer structure and the reaction conditions on polymer properties were investigated.

Side-Chain Crystallization of Comb-Like Copolymers Obtained from Isopropenyltriazines with Comonomers Having Octadecyl Group

Copolymerizations of 2-amino-4-anilino-6-isopropenyl-1,3,5-triazine and 2-amino-4-(N-octadecylanilino)-6-isopropenyl-1,3,5-triazine with octadecyl acrylate, octadecyl methacrylate, N-octadecylacrylamide, and N-octadecylmethacrylamide were carried out in order to investigate the side-chain crystallization of the resulting comb-like copolymers. Crystallization exothermic and melting endothermic peaks due to the side-chains of the comb-like copolymers were observed in differential scanning calorimetry (DSC) thermograms. When the content of isopropenyltriazine unit in the copolymer was high, glass transition temperature was observed above the melting point of the side-chain crystallites. The influence of monomer structure and copolymer composition on the crystallinity of the side-chains and glass transition temperature are discussed.

Light induced polymer and polymerization reactions, 35. Influence of monomer structure and binder composition on the photoinduced polymerization of multifunctional acrylic esters

AbstractPhotocalorimetry, differential scanning calorimetry and ESR‐spectroscopy were used to analyse the photoinduced polymerization of multifunctional acrylic esters in various polymeric binders. Limiting conversion, maximal polymerization rate, inhibition time, and the time necessary to reach the maximum of the polymerization reaction rate were used to compare the reactivity of the photopolymer systems investigated in this work. Significant correlations exist between the limiting conversion and chemical structure of the acrylic esters used. A relation was also found between the glass transition temperature and oxygen permeability of the binder and the limiting conversion measured calorimetrically. A good correlation does not exist for the other reactivity parameters, because other factors such as phase change and changing diffusion conditions can have a complex influence on those values.