Towards predicting the solubility of CO2 and N2 in different polymers using a quasi-SMILES based QSPR approach

The solubility of gases in various polymers plays an important role for the design of new polymeric materials. Quantitative structure–property relationship (QSPR) models were designed to predict the solubility of gases such as CO₂ and N₂ in polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl acetate (PVA) and poly (butylene succinate) (PBS) at different temperatures and pressures by using quasi-SMILES codes. The dataset of 315 systems was split randomly into training, calibration and validation sets; random split 1 led to 214 training (r² = 0.870 and RMSE = 0.019), 51 calibration (r² = 0.858 and RMSE = 0.020) and 50 validation (r² = 0.869 and RMSE = 0.017) sets. The suggested approach based on the quasi-SMILES, which are analogues of the traditional SMILES gives reasonable good predictions for solubility of CO₂ and N₂ in different polymers. The described methodology is universal for situations where the aim is to predict the response of an eclectic system upon a variety of physicochemical and/or biochemical conditions.     

Correlation between glass transition temperature and chain structure for randomly crosslinked high polymers

The empirical form for the dependence, T_g(n) ≅ T_g(∞)·(1 + α/n), of the glass transition temperature T_g on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, T_g(n) ≅ T_g(∞) · [1 + c/(n·N_rot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent N_rot and composition-independent c terms. N_rot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers. © 1996 John Wiley & Sons, Inc.     

In situ measurement of the glass transition temperature of polymers with compressed fluid diluents

In situ measurement of the creep compliance of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA), equilibrated with a pressurized CO₂ phase, is used to determine the glass transition temperature. Corrections due to dilation of the polymer by CO₂ as well as the buoyancy are assessed. Both polymer systems exhibit a recently discovered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental results are predicted semi-quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the polymer. © 1994 John Wiley & Sons, Inc.     

A novel approach toward the prediction of the glass transition temperature: Application of the EVM model,a designer QSPR equation for the prediction of acrylate and methacrylate polymers

We describe an original QSPR model called the EVM model (Energy, Volume, Mass) to calculate the glass transition temperature (T_g) of aliphatic acrylate and methacrylate homopolymers using classical molecular mechanics and dynamics. The latter was used to calculate an energy density function related to the cylindrical volume of a 20 monomer unit polymer segment (TSSV, Total Space around a Standard deviation Volume). We then calculated the T_g as a function of this density function and the repeat unit molecular weight, although no interchain interactions were taken into account. For linear and branched aliphatic acrylate and methacrylate polymers, the standard deviation from linear regression was 12 K, and the r² was 0.96. The model allows calculation of the T_g with an average absolute error of error of 10% for linear and branched derivatives not included in the original linear regression analysis. The results obtained with the EVM model are compared with those obtained with Bicerano's model. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2579–2590, 1997     

Synthesis and structure‐optoelectronic property relationships of a series of PPV and SFTV derived polymers

Engineering of the highest occupied molecular orbital and lowest unoccupied molecular orbitals through synthetic chemical structural modification has been the most widely used method to tuning optoelectronic properties in conjugated polymers. The electronic, thermal, optical, and physical properties can be tuned and exploited for optimization of optoelectronic devices. Through copolymerization of donor and acceptor type conjugated monomers, the frontier orbitals of four polymers were tailored. Through this synthetic engineering, the relationship between structural features, frontier orbital tailoring, and changes in optoelectronic and physical properties are discussed. Spectroscopic, thermal, and electronic analysis of the polymers indicated that polymers containing carbazole monomer moieties gave overall improved optoelectronic properties, but higher band gaps (2.61 and 2.18 eV) in comparison to their phenyl‐ based counterparts. This result is attributed to the higher electron density of the carbazole than the terephthaldicarboxaldehyde, and the possible deviation from planarity in the polymer main chain due to possible steric hindrance of the branched substituents. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2202–2213     

The glass temperature of dendritic polymers

A theoretical treatment of the glass temperature of dendritic polymers is presented. The influences of polymer backbone, end group, initiator core, branching unit, composition and functionality are discussed. In dendritic polymers the glass temperature is dependent only on the generation number of dendritic growth and thus only on the molecular weight of a dendron, but not on the molecular weight of the whole molecule. It is governed primarily by the backbone glass temperature and depends little on branching functionality. Only minor differences between linear polymer and dendrite are obtained, since the influences of end groups and branching compensate each other to a large extent. © 1995 John Wiley & Sons, Inc.     

Interactions in a blend of two polymers greatly differing in glass transition temperature

Blends of poly(N‐methyldodecano‐12‐lactam) PMDL with poly(4‐vinyphenol) PVPh have been studied by the DSC and ATR FTIR methods. The difference in glass transition temperature T_g between the components is 206 °C. A single composition‐dependent T_g suggests miscibility of the system, that is, homogeneity on the scale of about 10 nm. Fitting of the equation of Brostow et al. to the T_g data indicates relatively strong specific interactions and high complexity of the system. The Schneider's equation applied separately to low‐ and high‐PVPh regions provides good agreement with experiment; the calculated curves cross at the point of PVPh weight fraction 0.27. In the low‐PVPh region, the analysis indicates weak interactions with predominance of segment homocontacts and strong involvement of conformational entropy. In the high‐PVPh region, strong specific interactions predominate and entropic effects are suppressed. Composition dependences of the heat capacity difference at T_g and the width of glass transition indicate strong interactions in the system and existence of certain heterogeneities on segmental level, respectively. According to ATR FTIR, hydrogen bonds between PVPh as proton donor and PMDL as proton acceptor induce miscibility in blends of higher PVPh content (above about 0.28 weight fraction). In low‐PVPh blends, it is conformational entropy that enables intimate intermolecular mixing. Hydrogen bonds adopt several (distorted) geometries and are on average stronger than average hydrogen bonds formed in self‐associating PVPh. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis of cyclic olefin polymers with high glass transition temperature by ring‐opening metathesis copolymerization and subsequent hydrogenation

Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefin, exo‐1,4,4a,9,9a,10‐hexahydro‐9,10(1′,2′)‐benzeno‐l,4‐methanoanthracene (HBMN), with high glass transition temperature (T_g), excellent thermal stability, high transparency, and improved mechanical performance, have been achieved by ring‐opening metathesis polymerization and subsequent hydrogenation. The “first‐generation Grubbs” catalyst, RuCl₂(PCy₃)₂(CHPh) (Cy = cyclohexyl) ( G1 ), displays very high activity for homo/copolymerization with complete conversion. Homopolymer of the HBMN after complete hydrogenation showed a highest T_g of 223.6 °C. Copolymerization of HBMN with tricyclo[4.3.0.12,5]deca‐3‐ene or 5‐n‐hexylnorbornene was also carried out. These two series of COPs were characterized by gel permeation chromatography, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The T_g of the resulted COPs linearly increased with HBMN content, which is easily controlled by changing feed ratios. The tensile test indicates that these copolymers have good mechanical performance as all these copolymers show a higher strain at break compared with commercial products (TOPAS^®). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2654‐2661     

Combined QSAR/QSPR and molecular docking study on fluoroquinolones to reduce biological enrichment

With the aim of reducing the adverse effects of fluoroquinolones in the environment, a complete design and screening system for the low biological enrichment and high photodegradabilities of 29 fluoroquinolones was established through a three-dimensional quantitative structure–activity relationship (3D-QSAR) model and molecular docking. The interaction mechanisms of the fluoroquinolones with Gram-negative bacteria (DNA gyrase in Escherichia coli) and Gram-positive bacteria (Topoisomerase IV in Staphylococcus aureus) were also evaluated. Consequently, the 3D-QSAR model showed that the 3- and 18-positions of the fluoroquinolones strongly affected their biological enrichment, and that the introduction of electropositive or hydrophobic groups at these positions reduced the logarithm of the octanol-water partition coefficient. Using nadifloxacin as a template, 23 derivatives with lower biological enrichment than nadifloxacin (decreased by 30.12%–94.18%) were designed. Meanwhile, the photodegradabilities of 15 derivatives were increased compared with nadifloxacin. Finally, the further screening by molecular docking of nadifloxacin and the above 15 derivatives with DNA gyrase and Topoisomerase IV showed that 13 of the derivatives had lower biological enrichment (decreased by 0.30%–16.76%) than nadifloxacin in the bacteria.     

Modified calculation scheme for evaluation and prediction of glass transition temperatures of polymers

A modified calculation scheme was developed for evaluating and predicting the glass transition temperatures of linear and cross-linked polymers. It was proposed to separate the contributions of weak (dispersion) and strong (dipole–dipole and hydrogen bonding) interactions between the same atoms and polar groups in the backbone and side chains of a polymer. The considered model is based on analyzing the system of anharmonic oscillators formed by pairs of atoms entering the intermolecular interaction. The critical temperature of destabilization of this system of oscillators on heating is the glass transition temperature T_g. As a result, without resorting to correction factors of various kinds, one can calculate the T_g of a large number of linear and cross-linked polymers of different classes and various structures with good accuracy.     

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers has been developed, which takes into account the influences of end groups, branching, and crosslinking, and their functionality distribution. DiBenedetto's theory was found to correctly characterize the influence of crosslinks on the glass temperature. Normalized to constant crosslink functionality, the crosslink constant is a universal parameter suggesting that the entropic theory of glasses is applicable to crosslinked systems. Data on linear polymers and networks from the crosslinking of polymer chains, vinyl/divinyl-copolymers and step-growth polymers, such as polyurethanes, amine-cured epoxies, or inorganic glasses, are presented.