Prepolymerization Step Research Articles

Synthesis and Characterization of Poly (Erythritol Sebacate)

AbstractErythritol is a sweetener polyol widely distributed in nature. Its industrial production is based on biotechnological fermentative processes using yeasts. It is used essentially in nutrition and pharmaceutical fields. However, due to its still high price, the use of erythritol is not widespread and is lower than that of other polyols. The use of erythritol for polymer synthesis remains largely unexplored by the scientific community. This work describes the synthesis and characterization of polyester, poly (erythritol sebacate) (PES), obtained by thermal polycondensation of erythritol and sebacic acid in a two steps approach. A prepolymerization step was realized at different temperatures (150 °C, 160 °C and 170 °C, respectively) followed by a cure step at 150 °C. It was found that using a higher temperature allows the same degree of polymerization (50%) to be achieved in a shorter period, but this leads to prepolymers with a more heterogeneous oligomeric composition. This is reflected in the final properties of the polymers after curing. Synthesis at 150 °C produced a polymer with superior mechanical performance (ultimate tensile strength: 0.5 MPa; Young’s modulus: 0.44 MPa: elongation at break: 123%) and higher chemical resistance to solvents than polymers synthesized at 160 °C and 170 °C. The glass transition temperature (Tg) is between − 20 and 0 °C for all polymers and density is 1.08 g/cm3. Based on these results, we believe that PES is a good elastomer with tunable properties and potential for selective absorption of molecules, such as ethanol, that could be useful for beverage industry and biotechnological applications. Graphical Abstract

Novel Thiol‐Ene Photo Resins for Stereolithography with Enhanced Mechanical and Optical Properties

Inside Cover: In article number 2100625 by Andreas Hoffmann and co-workers, a bi- and a trifunctional “ene”-monomer (blue) and a bifunctional thiolmonomer (green) react under UV-light in a thiol-ene click polymerization. Depicted is the influence of a prepolymerization step on the network homogeneity of the polymer network compared to a system synthesized in one step.

An Ionic Cluster Strategy for Performance Improvements and Product Morphology Control in Metal-Catalyzed Olefin-Polar Monomer Copolymerization.

Product morphology control represents a critical challenge for polyolefin production, but it has remained largely unexplored in the field of ethylene-polar monomer copolymerization. Herein, an ionic cluster strategy was designed to control the product morphology during the synthesis of polar-functionalized polyolefins via precipitation polymerization. In addition to product morphology control, simultaneous improvements in the catalytic copolymerization performance (activities, copolymer molecular weights, and comonomer incorporation ratios) were achieved. These results were due to less poisoning of the metal-salt-based comonomers compared with their ester counterparts and the high local concentration of the alkene comonomers induced by ionic cluster formation. Moreover, the ionic cluster strategy is generally applicable to various comonomers and catalytic systems, greatly enhances the catalyst's thermal stability at high temperatures (90-150 °C), and enables the homopolymerization of both terminal and internal polar-functionalized olefins. Finally, polar-functionalized polyolefins and polyolefin composites (generated from a tandem process combining a prepolymerization step and subsequent polymerization) were developed, which showed tunable mechanical properties and great potential as compatibilizing agents for mixtures of polyolefins and other types of polymers.

Lipase-Catalyzed Synthesis and Characterization of Poly(glycerol sebacate).

This study demonstrated that immobilized Candida antarctica lipase B (N435) catalysis in bulk leads to higher molecular weight poly(glycerol sebacate), PGS, than self-catalyzed condensation polymerization. Since the glass-transition temperature, fragility, modulus, and strength for rubbery networks are inversely dependent on the concentration of chain ends, higher molecular weight PGS prepolymers will enable the preparation of cross-linked PGS matrices with unique mechanical properties. The evolution of molecular species during the prepolymerization step conducted at 120 °C for 24 h, prior to enzyme addition, revealed regular decreases in sebacic acid and glycerol-sebacate dimer with corresponding increases in oligomers with chain lengths from 3 to 7 units such that a homogeneous liquid substrate has resulted. At 67 h, for N435-catalyzed PGS synthesis, the carboxylic acid conversion reached 82% without formation of a gel fraction, and number-average molecular weight (Mn) and weight-average molecular weight (Mw) values reached 6000 and 59 400 g/mol, respectively. In contrast, self-catalyzed PGS condensation polymerizations required termination at 55 h to avoid gelation, reached 72% conversion, and Mn and Mw values of 2600 and 13 800 g/mol, respectively. We also report the extent that solvent fractionation can enrich PGS in higher molecular weight chains. The use of methanol as a nonsolvent increased Mn and Mw by 131.7 and 18.3%, respectively, and narrower dispersity (Đ) decreased by 47.7% relative to the nonfractionated product.

Elucidating doxycycline loading and release performance of imprinted hydrogels with different cross-linker concentrations: a computational and experimental study

Effective non-covalent molecular imprinting on a polymer depends on the extent of non-bonded interactions between the template and other molecules before polymerization. Here, we first determine functional monomers that can yield a doxycycline-imprinted hydrogel based on the hydrogen bond interactions at the prepolymerization step, revealed by molecular dynamics (MD) simulations, molecular docking, and simulated annealing methods. Then, acrylic acid (AA)-based doxycycline (DOX) imprinted (MIP) and non-imprinted (NIP) hydrogels are synthesized in cross-linker ethylene glycol dimethacrylate (EGDMA) ratios of 1.0, 1.5, 2.0, and 3.0 mol%. Here, molecularly imprinted polymer with 3.0 mol% EGDMA has the highest imprinting factor (1.58) and best controlled drug release performance. At this point, full-atom MD simulations of DOX–AA solutions at different EGDMA concentrations reveal that AA and EGDMA compete to interact with DOX. However, at 3.0 mol% EGDMA, AA attains numerous stable hydrogen bond interactions with the drug. This study demonstrates that the concentration of the cross-linker and functional monomer can be adjusted to increase the success of imprinting, where the interplay between these two parameters can be successfully revealed by MD simulations.Supplementary informationThe online version contains supplementary material available at 10.1007/s10965-021-02740-6.

Enzymatic prepolymerization combined with bulk post-polymerization towards the production of bio-based polyesters: The case of poly(butylene succinate)

An alternative process for the production of poly(butylene succinate) (PBS) was herein applied, divided in two stages, both sustainable and in accordance with the principles of green polymerization. The first stage involved the enzymatic polycondensation of 1,4-butanediol and diethyl succinate, using immobilized Candida antarctica lipase B as a biocatalyst. The suitability of two different solvents (isooctane, toluene), as well as the bulk (solvent-free) system were examined at different reaction temperatures (40 °C, 50 °C, 60 °C), leading to the selection of isooctane as solvent and 50 °C as reaction temperature for the enzymatic prepolymerization step. The formed prepolymers were then submitted to bulk post-polymerization in order to upgrade their quality in terms of molecular weight and thermal properties. The final product was a PBS grade with weight-average molecular weight at ca. 5000 g/mol, melting point at 104 °C and mass fraction crystallinity at 70%, free of thermal degradation and metal catalyst residues.

Micrometric Wrinkled Patterns Spontaneously Formed on Hydrogel Thin Films via Argon Plasma Exposure.

The generation of microstructured patterns on the surface of a specific polymeric material could radically improve their performance in a particular application. Most of the interactions with the environment occur at the material interface; therefore, increasing the exposed active surface considerably improves their range of application. In this article, a simple and reliable protocol to form spontaneous wrinkled patterns using a hydrogel layer is reported. For this purpose, we took advantage of the doctor blade technique in order to generate homogenous films over solid substrates with controlled thickness and large coverage. The hydrogel wrinkle formation involves a prepolymerization step which produces oligomers leading to a solution with increased viscosity, enough for doctor blade deposition. Subsequently, the material was exposed to vacuum and plasma to trigger wrinkled pattern formation. Finally, a UV-polymerization treatment was applied to fix the undulations on top. Interestingly, the experimental parameters allowed us to finely tune the wrinkle characteristics (period, amplitude, and orientation). For this study, two main aspects were explored. The first one is related to the role of the substrate functionalization on the wrinkle formation. The second study correlates the deswelling time and its relationship with the dimensions and distribution of the wrinkle pattern. In the first batch, four different 3-(trimethoxysilyl)propyl methacrylate (TSM) concentrations were used to functionalize the substrate in order to enhance the adhesion between hydrogel film and the substrate. The wrinkles formed were characterized in terms of wrinkle amplitude, wavelength, pattern roughness, and surface Young modulus, by using AFM in imaging and force spectroscopy modes. Moreover, the chemical composition of the hydrogel film cross-section and the effect of the plasma treatment were analyzed with confocal Raman spectroscopy. These results demonstrated that an oxidized layer was formed on top of the hydrogel films due to the exposure to an argon plasma.

A Study of the Strength of a Template Molecule-A Functional Monomer Interaction That Affects the Performance of Molecularly Imprinted Polymers and Its Application to Chiral Amplification.

A novel type of molecularly imprinted polymer (MIP), N-benzoyl-(S)-valine anilide-imprinted polymer (IP-2), was prepared using hydrogen-bonding interactions as a main force in the pre-polymerization step. The performance of the IP-2 was evaluated via batch procedure and compared with a (S)-valine anilide-imprinted polymer (IP-1) that was prepared using an ionic interaction that is stronger than hydrogen bonding. Although both polymers showed a preferential adsorbability for (S)-amino acid derivatives, different performances were observed in terms of adsorbability and enantioselectivity. In addition, the IP-2 was able to recognize the enantiomer of a valine-derived chiral catalyst. This phenomenon was applied to a chiral amplification reaction, and a highly selective asymmetric Mannich-type amination was achieved using the combination of a racemic catalyst and a MIP.

A Study of the Gas Phase Polymerization of Propylene: The Impact of Catalyst Treatment, Injection Conditions and the Presence of Alkanes on Polymerization and Polymer Properties

Propylene is polymerized in the gas phase in a 2.5 L semibatch reactor using a commercially available supported Ziegler–Natta (ZN) catalyst. The mode of injection (wet vs dry), the impact of including a prepolymerization step, and of changing the composition of the gas phase are systematically investigated in terms of their influence on the instantaneous polymerization rate and polymer properties. Prepolymerization is observed to enhance the polymerization activity. This is attributed, at least in part, to the effect of prepolymerization step in decreasing local particle overheating in the initial instants of reaction. Furthermore, a noticeable decrease of the catalyst activity is observed when the catalyst is injected dry as compared to when is first wetted with paraffinic oil before being charged to the reactor. Adding a hydrocarbon to the catalyst can eventually reduce the risk of overheating during the critical initial instants of polymerization since it increases resistance of the diffusion of monomer to the active sites, acting as an “in situ” prepolymerization. Methods that increased the productivity also lead to an improvement of the powder morphology. Finally, it is found that adding vaporized iso‐hexane to the gas phase provokes an increase in the instantaneous polymerization rate, and increases the impact of hydrogen on the rate and molecular weight. image

Modeling prepolymerization step of a serotonin imprinted polymer.

Studies on generating artificial macromolecular receptors by molecular imprinting of synthetic polymers significantly emerged in the literature during last decades. The non-covalent approach, one of the three methods used in MIP synthesis, is more flexible for the choice of functional monomers, possible target molecules, and use of the imprinted materials. This study aims to investigate a serotonin imprinted polymer prepared by non-covalent approach using molecular modeling. The calculations were carried out by using density functional theory at ωB97XD/6-31++G(d,p) level and the polarizable continuum model was used for solvent calculations. Computational results showed that DMSO plays an important role in the MIP formation as it seems to control the size and the shape of the cavity. DMSO performs these tasks through hydrogen bonding and dispersive interactions. Although experimental IR could not verify the specific interaction modes because of broadband structure, computational IR results showed these modes clearly indicating the interactions leading to MIP formation. This model is specific to the studied serotonin-acrylamide-DMSO system but further studies may reveal a general computational protocol for other MIP systems.

Rubber Nanodomains Reinforced Epoxy Resin

ABSTRACTIt has been reported that the addition of liquid rubbers, like poly(dimethylsiloxane) (PDMS), to epoxy resins alter the final morphology, increase the toughness and influence the curing kinetics. Due to immiscibility, there is phase separation of the elastomeric phase during curing giving rise to microdomains embedded in the epoxic matrix. The resultant heterogeneous morphology obtained after the reaction controls to an important extent the properties of the epoxy composite. Here we report a method to obtain well-dispersed rubber nanodomains of silyl-diglycidyl ether terminated polydimethyl siloxane (PDMS-DGE) in diglycidyl ether of bisphenol-A (DGEBA) epoxy by using a prepolymerization step. Light scattering and optical microscopy showed that initial mixing of pre-polymerized rubber produced phase separation with micron-scale droplet formation. However, as the curing reaction proceeded, the rubber domains decreased below optical resolution, light scattering intensity reached a maximum and then decreased. Finally, rubber nanodomains of about 100 nm size were formed at the end of curing reaction, as revealed by transmission electron microscopy (TEM). The pre-polymerization step induced a two-fold increase in gel time, tgel, due to lesser active groups available for reaction. Strikingly, tensile modulus and toughness increased, suggesting rubber-epoxy interaction. The final nanocomposite also exhibited higher thermal stability and char formation.

Synthesis of nano-sized stereoselective imprinted polymer by copolymerization of (S)-2-(acrylamido) propanoic acid and ethylene glycol dimethacrylate in the presence of racemic propranolol and copper ion

A new chiral functional monomer of (S)-2-(acrylamido) propanoic acid was obtained by reaction of (l)-alanine with acryloyl chloride. The resulting monomer was characterized by FT-IR and HNMR and then utilized for the preparation of chiral imprinted polymer (CIP). This was carried out by copolymerization of (l)-alanine-derived chiral monomer and ethylene glycol dimethacrylate, in the presence of racemic propranolol and copper nitrate, via precipitation polymerization technique, resulting in nano-sized networked polymer particles. The polymer obtained was characterized by scanning electron microscopy and FT-IR. The non-imprinted polymer was also synthesized and used as blank polymer. Density functional theory (DFT) was also employed to optimize the structures of two diasterometric ternary complexes, suspected to be created in the pre-polymerization step, by reaction of optically active isomers of propranolol, copper ion and (S)-2-(acrylamido) propanoic acid. Relative energies and other characteristics of the described complexes, calculated by the DFT, predicted the higher stability of (S)-propranolol involved complex, compared to (R)-propranolol participated complex. Practical batch extraction test which employed CIP as solid phase adsorbent, indicated that the CIP recognized selectively (S)-propranolol in the racemic mixture of propranolol; whereas, the non-imprinted polymer (NIP) showed no differentiation capability between two optically active isomers of propranolol.

Millimeter‐size polyethylene hollow spheres synthesized with MgCl2‐supportedZiegler‐Natta catalyst

ABSTRACTPolyethylene hollow spheres with diameters of 0.4–2 mm were synthesized by a two‐step slurry polymerization in a single reactor with a spherical MgCl2‐supported Ziegler‐Natta catalyst activated by triethylaluminum, in which the first step was prepolymerization with 0.1 MPa propylene and the second step was ethylene polymerization under 0.6 MPa. The prepolymerization step was found necessary for the formation of hollow spherical particles with regular shape (perfectly spherical shape). The effects of adding small amount of propylene (propylene/ethylene < 0.1 mol/mol) in the reactor after the prepolymerization step were investigated. Average size of the polymer particles was increased, and the polymerization rate was markedly enhanced by the added propylene. Development of the particle morphology with polymerization time was also studied. The polymer particles formed by less than 20 min of ethylene polymerization showed hollow spherical morphology with thin shell layer. Most of the particles had ratio of shell thickness/particle radius smaller than 0.5. By prolonging the ethylene polymerization, the shell thickness/particle radius ratio gradually approached 1, and the central void tended to disappear. Central void in polymer particles formed from smaller catalyst particles disappeared after shorter time of polymerization than those formed from bigger catalyst particles. The shell layer of the hollow particles contained large number of macro‐, meso‐ and micro‐pores. The mesopore size distributions of four typical samples were analyzed by nitrogen adsorption–desorption experiments. A simplified multigrain model was proposed to explain the morphogenesis of the hollow spherical particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2016,133, 43207.

Synthesis of aqueous and hydroxy-terminated polyurethanes: Impacts of formulation parameters by orthogonal matrix design

Abstract Aqueous and hydroxy-terminated polyurethanes (AHPUs) were synthesized using poly(caprolactone) glycol, isophorone diisocyanate, dimethylolpropionic acid (DMPA) as main raw materials, trimethylolpropane (TMP) as crosslinking agent, ethylenediamine (EDA) as chain extender, and tris(hydroxylmethyl) aminomethane as chain terminator. The optimum synthesis condition of AHPUs was elected by L 16 (4 5 ) orthogonal experiments with the content of DMPA ( A ) and TMP ( B ), molar ratio of isocyanate to hydroxyl in the prepolymerization step ( C ) and the molar ratio of amino groups in EDA to residual isocyanate groups of prepolymerization ( D ) as factors and the transmittance, relative viscosity and particle size of dispersions as evaluation index, and the tack-free drying time, gloss, hardness, adhesion and water resistance of coatings were discussed, too. The results demonstrate that the synthetic AHPUs have good physical properties, such as relative viscosity, transmittance and particle size, what's more, the two-component films have good air-drying ability, gloss, hardness, adhesion and water resistance when synthesis parameters are A = 7.0 wt%, B = 5.0 wt%, C = 1.6 and D = 0.2.

Nitrogen‐Doped Inverse Opal Carbons Derived from an Ionic Liquid Precursor for the Oxygen Reduction Reaction

AbstractThree‐dimensionally macroporous nitrogen‐doped carbon materials are fabricated via carbonization of an ionic‐liquid‐based small molecule precursor, 1‐ethyl‐3‐methylimidazolium dicyanamide, using opal silica colloidal crystals as a hard template. As compared to traditional polymerizable monomer‐based precursors such as furfuryl alcohol, the entire process involving ionic liquid does not require any acid catalyst and prepolymerization step. More importantly, nitrogen heteroatoms can be incorporated into the carbon skeleton in situ. The obtained inverse opal carbons possess large surface areas and pore volumes, and high nitrogen content. When acting as metal‐free electrocatalysts, the inverse opal carbons exhibit high catalytic activity and selectivity towards the oxygen reduction reaction in alkaline electrolyte, much better than that of the furfuryl‐alcohol‐derived inverse opal carbon and close to that of commercial Pt/C catalysts.

Inkjet printed nanohydrogel coated carbon nanotubes electrodes for matrix independent sensing.

Polyacrylamide (PA) based hydrogels are used in several applications including polyacrylamide gel electrophoresis and sensing devices. Homogeneous and compact PA films can be prepared based on chemical or photopolymerization processes. However, the accurate and reproducible coating of substrates with nanohydrogel patterns is challenging due to the in situ polymerization and deposition requirements. Herein, we report an inkjet printing (IJP) concept with simultaneously performed UV photopolymerization of a specifically prepared acrylamide/N,N'-methylenebis(acrylamide) containing ink. A prepolymerization step of the hydrogel precursor molecules was implemented in the ink formulation protocol to adjust the viscosity of the ink and to enhance the rate of polymerization during printing. After the optimization of the printing parameters, a nanometer thin PA hydrogel coating with well distributed nanopores was achieved on top of a stand-alone carbon nanotubes (CNTs) pattern. Batches of fully inkjet printed PA/CNT modified electrodes were prepared that showed outstanding improvements for the electrochemical detection of antioxidants in complex matrices such as untreated orange juice and red wine samples thanks to the properties of the PA coating.

Microwave-assisted rapid synthesis of poly(glycerol-sebacate) elastomers.

Poly(glycerol-sebacate) (PGS) was introduced a decade ago as a potential material for soft tissue repair. All of the proposed copolymerization reactions in the literature include a two-stage (prepolymerization and curing) synthesis where the reaction times can take as long as several days. This study, on the other hand, proposes a new route that eliminates these disadvantages and enables a rapid synthesis of PGS elastomers via microwave-assisted prepolymerization in minutes instead of days. No purge gas, catalyst or vacuum is needed in the first prepolymerization step. The curing stage was carried out at 150 °C for 4, 8, 16, and 24 hours. The glass transition temperature (Tg) and melting temperatures for the glycerol and sebacic acid fragments (Tm1 and Tm2 ) of these PGS elastomers were found as -35.61 °C, -15.82 °C, and 61.70 °C, respectively. The Young's modulus and tensile strength values were found as 0.50 ± 0.02 MPa and 0.27 ± 0.06 MPa, respectively.

Synthesis and characterization of high‐impact polystyrene using a multifunctional cyclic peroxide as the initiator

AbstractThis work deals with the synthesis of high‐impact polystyrene (HIPS) using a novel cyclic multifunctional initiator, the diethyl ketone triperoxide (DEKTP), analyzing its effect on the prepolymerization step and its influence over the HIPS final properties. DEKTP showed a low selectivity toward grafting reactions at any of the concentrations of initiator and temperatures evaluated, and when it was used under a temperature ramp (120–130°C, heating rate = 2°C/min), the synthesis of HIPS was possible with an adequate development of morphology and impact strength (i.e., 67 J/m) depending on DEKTP concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation of Aqueous Polyurethane Dispersions Using Aromatic Diisocyanate

AbstractAqueous polyurethane dispersions were prepared by the reaction of hydroxyl‐terminated poly(ethylene adipate), ethylene glycol, dimethylol propionic acid and aromaic diisocyante, 4,4′‐diphenylmethane diisocyanate. The influence of molecular weight of oligoester and molar ratio between isocyanate and hydroxyl groups (NCO/OH) in the prepolymerization step were investigated. Molecular weight, particle size and particle size distribution were measured and compared. It was verified that the molecular weight increases with increasing in NCO/OH molar ratio. The results suggest that the hard segment content plays an important role in particle size and particle size distribution of the dispersions.

Emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate and methyl methacrylate

AbstractThe emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate (EHMA) and methyl methacrylate (MMA) was carried out with the bifunctional initiator 1,4‐butylene glycol di(2‐bromoisobutyrate). The system was mediated by copper bromide/4,4′‐dinonyl‐2,2′‐bipyridyl and stabilized by polyoxyethylene sorbitan monooleate. The effects of the initiator concentration and temperature profile on the polymerization kinetics and latex stability were systematically examined. Both EHMA homopolymerization and successive copolymerization with MMA proceeded in a living manner and gave good control over the polymer molecular weights. The polymer molecular weights increased linearly with the monomer conversion with polydispersities lower than 1.2. A low‐temperature prepolymerization step was found to be helpful in stabilizing the latex systems, whereas further polymerization at an elevated temperature ensured high conversion rates. The EHMA polymers were effective as macroinitiators for initiating the block polymerization of MMA. Triblock poly(methyl methacrylate–2‐ethylhexyl methacrylate–methyl methacrylate) samples with various block lengths were synthesized. The MMA and EHMA reactivity ratios determined by a nonlinear least‐square method were ∼0.903 and ∼0.930, respectively, at 70 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1914–1925, 2006