Solvent Effect on the Glass Transition Temperature of Syndiotactic Polystyrene Viewed from Time-Resolved Measurements of Infrared Spectra at the Various Temperatures and Its Simulation by Molecular Dynamics Calculation

Investigating microstructure evolution in block copolymer membranes

Block copolymer self-assembly in conjunction with nonsolvent-induced phase separation (SNIPS) has been increasingly leveraged to fabricate integral-asymmetric membranes. The large number of formulation and processing parameters associated with SNIPS, however, has prevented the reliable construction of high performance membranes. In this study, we apply dynamical self-consistent field theory to model the SNIPS process and investigate the effect of various parameters on the membrane morphology: solvent selectivity, nonsolvent selectivity, initial film composition, and glass transition composition. We examine how solvent selectivity and concentration of polymers in the film impact the structure of micelles that connect to form the membrane matrix. In particular, we find that preserving the order in the surface layer and forming a connection between the supporting and surface layer are nontrivial and sensitive to each parameter studied. The effect of each parameter is discussed, and suggestions are made for successfully fabricating viable block copolymer membranes.

Radiolabeling of Micro-/Nanoplastics via In-Diffusion

Micro- and nanoplastics are emerging pollutants with a concerning persistence in the environment. Research into their environmental impact requires addressing challenges related to sensitively and selectively detecting them in complex ecological media. One solution with great potential for alleviating these issues is using radiolabeling strategies. Here, we report the successful introduction of a 64Cu radiotracer into common microplastics, namely polyethylene, polyethylene terephthalate, polystyrene, polyamide, and polyvinylidene dichloride, which allows the sensitive detection of mere nanograms of substance. Utilizing a Hansen Solubility Parameter screening, we developed a swelling and in-diffusion process for tetraphenylporphyrin-complexed 64Cu, which permits one-pot labeling of polymer particles.

Identification of plastic rice in adulterated raw and cooked rice

In the present study, attempts have been made to identify the presence of plastic rice in adulterated raw and cooked rice by comparing the compositional and morphological properties of fake rice and real rice using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) techniques. Various rice samples from the national capital region of India were studied for their compositional and morphological properties. The surface morphology of real rice and plastic rice was analyzed using scanning electron microscopy. Results suggest that plastic rice used as an adulterant in raw or cooked rice is made up of polystyrene, which is a well-known toxic chemical entity. The studies suggest that these techniques can be used as a scientific tool to detect and identify the presence of plastic rice in adulterated raw and cooked rice.

Artificial Neural Network Modeling of Glass Transition Temperatures for Some Homopolymers with Saturated Carbon Chain Backbone

The glass transition temperature (Tg) is an important decision parameter when synthesizing polymeric compounds or when selecting their applicability domain. In this work, the glass transition temperature of more than 100 homopolymers with saturated backbones was predicted using a neuro-evolutive technique combining Artificial Neural Networks with a modified Bacterial Foraging Optimization Algorithm. In most cases, the selected polymers have a vinyl-type backbone substituted with various groups. A few samples with an oxygen atom in a linear non-vinyl hydrocarbon main chain were also considered. Eight structural, thermophysical, and entanglement properties estimated by the quantitative structure-property relationship (QSPR) method, along with other molecular descriptors reflecting polymer composition, were considered as input data for Artificial Neural Networks. The Tg's neural model has a 7.30% average absolute error for the training data and 12.89% for the testing one. From the sensitivity analysis, it was found that cohesive energy, from all independent parameters, has the highest influence on the modeled output.

Mechanical Property of Polypropylene Gels Associated with That of Molten Polypropylenes

This study aims to understand the fundamental mechanical relationship between polypropylene (PP)-gels and solid PPs without solvent through mechanical and thermal analyses, by which the mechanical similarities between molten PPs and PP gels were found, leading to the reliable estimate of the mechanical properties of semi-crystalline gels. The gelation of syndiotactic and isotactic polypropylenes (sPP and iPP) was found when PPs were dissolved in 1,2,3,4-tetrahydronaphthalene (tetralin). Interestingly, it was found that the storage modulus of sPP-gel became higher than that of iPP-gel at low PP concentration (<~40 wt%). The result was distinctly different from the result of neat solid PPs (without solvent), where the modulus of solid sPP is generally significantly lower than that of solid iPP. Such inversion behavior in the mechanical property of semi-crystalline gels had not been reported and discussed before. By further investigation of the storage moduli of neat sPP and iPP, it was found that the storage modulus of sPP became higher than that of iPP above the melting points of PP, which was similar to the behavior of the storage moduli observed in the diluted PP-gels. Such similarity between PP-gels and PP melts was also observed within iPP samples with different molecular weights.

Effect of residual solvent on performance of acrylamide-containing dental materials

OBJECTIVE

Methacrylamide-based monomers are being pursued as novel, hydrolytically stable materials for use in dental adhesives. The impact of residual solvents, due to the chemical synthesis procedures or the need for solvated adhesives systems, on the kinetics of polymerization and mechanical properties was the aim of the present investigation.

METHODS

Two base monomers (70wt% BisGMA or HEMAM-BDI - newly synthesized secondary methacrylamide) were combined with 30wt% N,N-dimethylacrylamide. Eethyl acetate (EtOAc), or 75vol% ethanol/25vol% water (EtOH/H2O) were added as solvents in concentrations of 2, 5, 15 and 20wt%. The resins were made polymerizable by the addition of 0.2wt% 2,2-dimethoxy-2-phenyl acetophenone (DMPA) and 0.4wt% diphenyliodonium hexafluorophosphate (DPI-PF6). Specimens (n=3) were photoactivated with a mercury arc lamp (Acticure 4000, 320-500nm, 250mW/cm2) for 5min. Degree of conversion (DC, %) was tracked in near-IR spectroscopy in real time and yield strength and modulus of elasticity were measured in three-point bending after dry and wet storage (n=6). The data was subject to one-way ANOVA/Tukey's Test (p≤0.05), or Student's t-test (p≤0.001).

RESULTS

In all groups for both BisGMA and HEMAM-BDI-based materials, DC and DC at Rpmax increased and maximum rate of polymerization decreased as solvent concentration increased. Despite the increased DC, BisGMA mixtures showed a decrease in FS starting at 5wt% EtOAc or 15wt% EtOH/H2O. Yield strength for the HEMAM-BDI groups was overall lower than that of the BisGMA groups, but the modulus of elasticity was significantly higher.

SIGNIFICANCE

The presence of residual solvent, from manufacturing or from practitioner's handling, affects polymerization kinetics and mechanical properties of resins. Methacrylates appear to be more strongly influenced than methacrylamides.

Increased Production and Molecular Weight of Artificial Polyhydroxyalkanoate Poly(2-hydroxybutyrate) Above the Glass Transition Temperature Threshold

Poly(2-hydroxybutyrate) [P(2HB)] is an artificial polyhydroxyalkanoate (PHA) synthesized using engineered 2-hydroxyalkanoate-polymerizing PHA synthase. In the present study, the effect of temperature on P(2HB) synthesis was investigated. Recombinant Escherichia coli harboring PHA synthetic genes were cultivated with 2HB and 3-hydroxybutyrate (3HB) supplementation at varied temperatures ranging from 24 to 36°C for the synthesis of P(2HB) and natural PHA P(3HB), respectively. P(2HB) production and its molecular weight increased considerably at a threshold temperature of 32-34°C. The trend was not observed during the synthesis of P(3HB). Notably, the threshold temperature was close to the glass transition temperature (T _g) of P(2HB) (30°C), while the T _g of P(3HB) (4°C) was much lower than the cultivation temperature. The results suggest that thermal motion of the polymer chains influenced the production and molecular weight of the obtained polymer. According to the results, the production and molecular weight of PHA drastically changes at the threshold temperature, which is linked to the T _g of the polymer. The hypothesis should be applicable to PHAs in general, and potentially explains the inability to biosynthesize high-molecular-weight polylactate homopolymer with a T _g of 60°C.

Nonsolvent-induced morphological changes and nanoporosity in poly(l-lactide) films

The role of a nonsolvent in controlling the crystallization and morphology of solvent-crystallized poly(l-lactide) (PLLA) films was investigated using various microscopy techniques and small- and wide-angle X-ray scattering (SAXS/WAXS). PLLA films crystallized in THF and acetone had 40-80 μm spherulites. When water was present in the solvent, a completely different morphology was observed with nanosized voids and the surfaces of the films were smooth. In contrast, SEM studies revealed that the films crystallized in acetone and THF which had macroporous structures, had larger voids and film surfaces were rough because of the presence of globular structures. Voids appeared within the spherulites in the THF/water treated film, whereas crystals nucleated at the surface of the nanosized voids in acetone/water treated PLLA films. The formation of such voids is attributed to the interface-enhanced crystal nucleation in a solvent/nonsolvent system where the nonsolvent increases the polymer crystal nucleation and the subsequent evaporation of the nonsolvent. The method described in this work can be extended to other polymers to control the morphologies of polymer films during solvent-induced crystallization.

Functional polymer particles via thiol–ene and thiol–yne suspension “click” polymerization

Highly functionalized, water-borne, micron-sized polymer particles were synthesized using thermally or photochemically initiated thiol–ene and thiol–yne “click” suspension polymerizations.

Effect of methylcellulose on the formation and drug release behavior of silk fibroin hydrogel

In this study, methylcellulose (MC) was used to control the gelation time of silk fibroin (SF) aqueous solution. The gelation time was measured using a Vibro Viscometer at 50 °C. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and a texture meter were used to investigate the effect of MC on the hydrogelation of SF solution. SF/MC hydrogels could be formed by the addition of MC, although their gelation time was increased with MC content. To examine the conformational change of SF/MC hydrogels, time-resolved FT-IR spectra were obtained at constant temperature using a custom-made IR chamber. From FT-IR spectra focused on the amide I peak position, the transition of SF molecules in SF/MC solution from a random coil to a β-sheet structure was inhibited in the presence of MC molecules. In addition, the drug release of SF/MC hydrogels loaded with 5-aminosalicylic acid was studied in 2-dimensional (2-D) and 3-dimensional (3-D) conditions in vitro. The drug release behavior of SF or SF/MC hydrogels was measured using UV-Vis spectroscopy. The release rate of 5-aminosalicylic acid in SF/MC hydrogel was lower than that of SF hydrogel, which may be closely associated with the hydrophilic interaction between MC and 5-aminosalicylic acid. This approach to controlling the sol-gel transition and the drug release of SF hydrogels by the addition of MC will be useful in the design and tailoring of novel materials for biomedical applications.

Modification of the solid-state nature of sulfathiazole and sulfathiazole sodium by spray drying

Solid-state characterisation of a drug following pharmaceutical processing and upon storage is fundamental to successful dosage form development. The aim of the study was to investigate the effects of using different solvents, feed concentrations and spray drier configuration on the solid-state nature of the highly polymorphic model drug, sulfathiazole (ST) and its sodium salt (STNa). The drugs were spray-dried from ethanol, acetone and mixtures of these organic solvents with water. Additionally, STNa was spray-dried from pure water. The physicochemical properties including the physical stability of the spray-dried powders were compared to the unprocessed materials. Spray drying of ST from either acetonic or ethanolic solutions with the spray drier operating in a closed cycle mode yielded crystalline powders. In contrast, the powders obtained from ethanolic solutions with the spray drier operating in an open cycle mode were amorphous. Amorphous ST crystallised to pure form I at ≤35 % relative humidity (RH) or to polymorphic mixtures at higher RH values. The usual crystal habit of form I is needle-like, but spherical particles of this polymorph were generated by spray drying. STNa solutions resulted in an amorphous material upon processing, regardless of the solvent and the spray drier configuration employed. Moisture induced crystallisation of amorphous STNa to a sesquihydrate, whilst crystallisation upon heating gave rise to a new anhydrous polymorph. This study indicated that control of processing and storage parameters can be exploited to produce drugs with a specific/desired solid-state nature.

Study on the crystalline structure transition of syndiotactic polystyrene film during heat treatment by two-dimensional infrared correlation spectroscopy

The crystal structure transition of syndiotactic polystyrene film from the helical conformation to the more stable planar zigzag conformation during a heating process was studied using Fourier transform infrared (FT-IR) spectroscopy in combination with two-dimensional (2D) correlation analysis and perturbation-correlation moving-window 2D analysis. The sequence of different conformations during the transition was investigated by analyzing two-dimensional FT-IR correlation spectra in the spectral ranges of 800-700 cm(-1) and 600-500 cm(-1). It was observed that the conformation of delta helical changes prior to gamma helical, and the gamma helical phase is faster than the alpha' planar zigzag phase. By utilizing the 2D asynchronous correlation spectra, the 744 cm(-1) band, which is usually incorporated in the broad 750 cm(-1) band, can now be uniquely attributed as the alpha' zigzag configuration for the first time. Furthermore, by employing thermal perturbation, the shorter helical segments consisting of m = 7-12 and m = 12-20 monomeric units were disturbed in a shorter time than the longer helical segments m = 20-30 during the heating process.

A fundamental approach for the estimation of the mechanical glass transition temperature in gelatin

The paper constitutes an attempt to overcome the empiricism prevalent in the estimation of the glass transition temperature (Tg) of gelatin networks using rheological techniques. In doing so, it presents a study of the viscoelastic properties of a well-characterised gelatin sample covering the structural properties from the rubbery region to the glassy state. The pattern of oscillatory behaviour on shear is given by a master curve produced by shifting data obtained at different temperatures along the logarithmic time scale. Data reduction does not hold for all temperatures thus giving rise to thermorheological complexity. Within the temperature range at which molecular processes are represented by a simple distribution of relaxation times, a fundamental argument is developed to pinpoint the mechanical Tg. This should improve confidence in measured glassy properties over the empirical indicators found in the literature. As a demonstration, the glass transition temperature of gelatin at "zero moisture" obtained using the proposed framework of analysis is contrasted with earlier attempts to identify the mechanical Tg of gelatin solids.