Concentration Of Reactive Groups Research Articles

Effect of compatibilizers on lignin/bio-polyamide blend carbon precursor filament properties and their potential for thermostabilisation and carbonisation

Biobased blends from hydroxypropyl modified lignin (TcC) and a biobased polyamide (PA1010) were produced by continuous sub-pilot scale melt spinning process. A reactive compatibilization was employed with the help of two different compatibilizers (ethylene-acrylic ester-maleic anhydride (MA) and ethylene-methyl acrylate-glycidyl methacrylate (GMA)) to enhance the compatibility between the TcC and PA1010. The enhanced compatibility between the TcC and PA1010 achieved by reaction between hydroxyl groups with maleic anhydride groups in the MA compatibilizer or epoxy groups in the GMA compatibilizer via nucleophilic substitution, was confirmed by chemical (Fourier infrared measurements), physical (glass transition, melting and crystallization behaviour), rheological, morphological and tensile properties of the filaments from compatibilized blends. MA compatibilizer required a higher concentration (2 phr) than GMA (1 phr) to achieve an optimal performance because of the difference in the reactive group's concentration within the each compatibilizer. The MA compatibilizer though was more effective than GMA. The precursor blended filaments were successfully carbonized in a lab scale experiment to yield coherent carbon fibres with tensile stress values of 192 ± 77 and 159 ± 95 MPa; and moduli of 16.2 and 13.9 GPa respectively for uncompatibilised and 2% MA compatibilized blends. That the compatibilized carbon fibre properties are slightly inferior may be attributed to the need to accurately control and optimise applied stress during the thermostabilisation and carbonization stages. Notwithstanding, these differences, the results indicate the potential benefit of using compatibilized TcC/PA1010 blend filaments as carbon fibre precursors.

Fair Investigation of Cross-Link Density Effects on the Bond-Exchange Properties for Trans-Esterification-Based Vitrimers with Identical Concentrations of Reactive Groups

In this research, we demonstrate effects of cross-link density on the bond-exchange property of trans-esterification-based vitrimers. In most of the past literature, the change of cross-link densit...

Microscopic morphology, rheological behavior, and mechanical properties of polymers: Recycled acrylonitrile‐butadiene‐styrene/polybutylene terephthalate blends

ABSTRACTIn this study, styrene‐acrylonitrile‐glycidyl methacrylate (SAG) series copolymers were specially designed for producing the recycled acrylonitrile‐butadiene‐styrene (rABS)/poly(butylene terephthalate) (PBT)/SAG blends, which were prepared through the process of continuous melt blending and batch feeding. The effects of viscosity composition, SAG chemical composition, and SAG content on the morphology, and rheological and mechanical properties of the blends have been investigated. As demonstrated by morphological observation, the variety of viscosity composition of the blends affects the size of dispersed PBT droplets. Moreover, high viscosity of rABS matrix seems to facilitate the formation of smaller dispersed phase size of blends. Various SAG chemical compositions have different stabilities on the morphology of the blends, which affects the deformation, fragmentation, and coalescence of dispersed phase droplets. In addition, a finer phase morphology can be achieved when the density distribution of epoxy group is optimal in SAG copolymer. Rheological characterization manifested that the rheological properties of the blends depends strongly on its composition and structure, while the crosslinking degree is associated with the concentration of reactive groups and extent of reaction. Thereby, the rheological behavior of the blends during processing can be controlled by changing the reactive sequence and adding the quantity of epoxy group. The test on mechanical properties verified that a recycled product with excellent performance can be obtained by altering processing methods and the blends formula, which may be further applied to the 3D printing materials required by fused deposition modeling technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48310.

Novel Pathway for Efficient Covalent Modification of Polyester Materials of Different Design to Prepare Biomimetic Surfaces.

To form modern materials with biomimic surfaces, the novel pathway for surface functionalization with specific ligands of well-known and widely used polyester-based rigid media was developed and optimized. Two types of material bases, namely, poly(lactic acid) and poly(ε-caprolactone), as well as two types of material design, e.g., supermacroporous matrices and nanoparticles (NPs), were modified via covalent attachment of preliminary oxidized polyvinylsaccharide poly(2-deoxy-N-methacryloylamido-d-glucose) (PMAG). This polymer, being highly biocompatible and bioinspired, was used to enhance hydrophilicity of the polymer surface and to provide the elevated concentration of reactive groups required for covalent binding of bioligands of choice. The specialties of the interaction of PMAG and its preliminary formed bioconjugates with a chemically activated polyester surface were studied and thoroughly discussed. The supermacroporous materials modified with cell adhesion motifs and Arg-Gly-Asp-containing peptide (RGD-peptide) were tested in the experiments on bone tissue engineering. In turn, the NPs were modified with bioligands (“self-peptide” or camel antibodies) to control their phagocytosis that can be important, for example, for the preparation of drug delivery systems.

Abstract 336: Reactive Ion Surface Modification of Vascular Graft Materials Enhances Endothelialization Without Promoting Thrombosis

Previous work demonstrated that poly(vinyl alcohol) (PVA) holds great potential as a cardiovascular biomaterial. PVA prevents thrombosis at least as well as expanded polytetrafluoroethylene (ePTFE) clinical vascular grafts in whole blood studies. However, long term in vivo success of this material will likely depend on its ability to support an endothelial cell (EC) monolayer. To promote EC attachment and growth we are treating the PVA surface with high energy reactive ions. We hypothesize that increasing the concentration of reactive groups on the surface of the PVA will increase endothelial outgrowth cell (EOC, a type of endothelial progenitor cell isolated from whole blood) attachment without increasing thrombosis. To test this hypothesis we exposed PVA films to reactive ion modifications using O 2 , N 2 , and Ar gases at a variety of powers and durations. Treated samples were then characterized with X-ray photoelectron spectroscopy to quantify surface chemistries. Samples were seeded with EOCs to quantify attachment and proliferation using immunohistochemistry. Platelet and fibrin accumulation was measured dynamically in PVA tubes using a baboon arteriovenous shunt with radiolabeled platelets for 1hr. Flow rate was controlled and no anticoagulants were given. O 2 and N 2 treatments encouraged cell adhesion on the PVA films in an energy dependent manner, which correlated to an increase in surface nitrogen. Initial shunt data (n=3) indicate that treated samples did not have increased platelet attachment compared to untreated PVA or ePTFE. In conclusion, reactive ion modified-PVA demonstrates a promising biomaterial by supporting EC growth without increasing thrombosis.

Расчет процесса поликонденсации феноло-формальдегидных смол по критерию активности

Application of the activity criterion for calculating the polycondensation process of phenol-formaldehyde resins is considered in the paper. Reactive groups, their number and structure occupy a very important place in polycondensation oligomers. The obtained formula for calculating the activity criterion is very simple and easy to use. Polycondensation constant - the molar ratio of polycondensation components, is always specified by the synthesis conditions. For determining the criterion of oligomers activity it is necessary to know the concentration of reactive groups in the oligomer. Application of the activity criterion for calculating the polycondensation process greatly facilitates determining the calculation data of polycondensation process. The calculation of activity criterion is given in the paper on the example of two phenol-formaldehyde resins − namely novolac and resole resins. Experimental data allow revealing the dependence of the degree of polycondensation oligomer polymerization on the condensation constant and activity criterion.

The use of anhydride linkages to increase the glass transition temperatures of polymers containing carboxyl end groups: A perspective in powder coatings

A method to increase the glass transition temperature of carboxyl terminated low molecular weight cycloaliphatic polyesters through anhydride linkages is described. Low molecular weight carboxyl terminated cycloaliphatic polyesters, poly(1,4-cyclohexylidenecyclohexane-1,4-dicarboxylate) (PCCD), were synthesized by the polycondensation reaction of cis/trans-1,4-cyclohexane dicarboxylic acid and cis/trans-1,4-cyclohexane dimethanol. The corresponding poly(ester-anhydrides)s were obtained using a mixed anhydride method in melt where the low molecular weight carboxyl terminated cycloaliphatic polyesters were chain extended at the terminal carboxylic acid end groups through reversible anhydride linkages. The poly(ester-anhydrides)s as expected had higher glass transition temperature than the corresponding parent oligomers. PCCD oligomers with no anhydride linkages and PCCD based poly(ester-anhydrides)s with anhydride linkages at comparable molecular weights, had similar glass transition temperatures. However, the latter potentially offer higher reactive group concentration thanks to the reactive anhydride groups. This work was carried out as a proof of concept to show that the glass transition temperature of carboxyl terminated oligomers can be increased by increasing the molecular weight but without sacrificing the reactive group concentration. This approach, the authors suggest, may potentially be used in the design of new carboxyl functional base resins, especially for powder coatings, where both the acid number and glass transition temperature are important.

Telechelic siloxanes with hydrogen‐bonded polymerizable end groups. I. Liquid rubbers and elastomers

AbstractFunctional siloxanes are widely used in the synthesis of model networks used in rubber elasticity studies, and various functional siloxanes are also used in the synthesis of silicone rubbers. We present here the results of studies of two classes of telechelic, free‐radically polymerizable siloxanes carrying either amide or urea groups attached at both ends of siloxane chain. The presence of polar, hydrogen‐bonding end‐groups favors the formation of aggregates which is reflected in the drastically increased viscosity of the resulting “liquid rubbers.” In addition, such aggregation accounts for high local concentrations of reactive groups thus making it possible to have high molecular weight precursors undergo facile room temperature polymerization. In this article, we study the effect of the nature of these functional groups on the viscosity of polymerizable “liquid rubbers,” finding that the different endgroups lead to dramatically different viscosities. We also study the silicone rubber films obtained by a UV‐initiated free‐radical polymerization of the liquid rubbers, using dynamic mechanical analysis and large‐strain uniaxial deformation. We find here that important properties such as plateau modulus and Young's modulus are highly dependent on both endgroup type and precursor molecular weight. The crosslinking of telechelic siloxanes in dilution was also studied to further explore the effect of crosslink density of the mechanical properties of the model networks. Finally, we evaluated the role of dangling ends within the networks through the incorporation of monofunctional macromers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Multifunctional Stretchable Plasma Polymer Modified PDMS Interface for Mechanically Responsive Materials

Multifunctional Stretchable Plasma Polymer Modified PDMS Interface for Mechanically Responsive Materials

STUDIES ON APPARENT KINETICS AND RHEOLOGICAL BEHAVIOR OF EPOXY/ACRYLATE IPNS AS VACUUM PRESSURE IMPREGNATION RESINS

The apparent kinetics and cure behavior of novel interpenetrating polymer networks (IPNs) based on cycloaliphatic epoxy resin (CER) and tri-functional acrylate have been investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The results of DSC measurements show that the curing reaction of the TMPTMA component is much earlier than that of the CER component, which can lead to the formation of the IPNs. In contrast to neat anhydride-CER system, the anhydride-CER/TMPTMA systems exhibit relatively lower curing temperatures. The activation energy for initiating the reaction of the anhydride-CER system slightly increases, whereas the activation energy for propagating the reaction markedly reduces during the full IPNs formation. The FT-IR spectroscopic changes are interpreted in terms of curing mechanism of CER and TMPTMA components. The extent of reaction is calculated from FT-IR absorption bands, which depends on the reactive group concentration. The experimental results of FT-IR measurements are in good agreements with those of DSC measurements. The rheological behavior of anhydride-CER/TMPTMA systems during IPNs formation is studied in this paper. It is confirmed that the introduction of TMPTMA monomer into anhydride-epoxy resin has significant effects on the rheological behavior of the system.

Synthesis and Rheological Properties of Responsive Thickeners Based on Polysaccharide Architectures

New thermothickening copolymers were synthesized by grafting responsive poly(ethylene oxide-co-propylene oxide) [PEPO] onto three different polysaccharide backbones: carboxymethylcellulose [CMC], alginate [ALG], and carboxylated dextran [DEX]. The coupling reaction between carboxylic groups of biopolymers and the terminal amine of PEPO was activated at low temperature ( T < 10 degrees C) in water by using carbodiimide and N-hydroxysuccinimide. In these conditions it was shown that the formation of amide bonds strongly depends on the concentration of reactive groups, which is limited by the viscosity of the polymer sample. While a full conversion was obtained for the low molecular weight dextran, the efficiency of grafting remains low (between 30 to 40%) for CMC and alginate, which give a solution of high viscosity even at low concentration. When studied in the semidilute regime, all the copolymer solutions clearly exhibit thermothickening behavior with a large and reversible increase of viscosity upon heating. The association temperature and the gelation threshold were shown to depend on polymer concentration as it is expected from the phase diagram of PEPO precursor. Similarly, the influence of added salt on PEPO solubility in water has been used to control the self-assembling behavior of copolymer formulations. The relative comparison between the three copolymers reveals that the amplitude of the viscosity jump induced by heating mainly depends on the proportion of responsive material inside the macromolecular architecture rather than the dimensions of the main chain. The high increase of viscosity, which can reach several orders of magnitude between 20 degrees C and body temperature, clearly demonstrates the potentiality of these copolymers in biomedical applications like injectable gels for tissue engineering.

Modeling the Chemical Conversion of Organic Compounds in Sodium Borohydride Reduction Reactions

In this paper we propose a new modeling concept for the prediction of the chemical conversion of reducible species as a function of reductant concentration in sodium borohydride reduction reactions. This concept is applicable to organic compounds of unknown reactive group concentrations, such as mixtures of organic or colloidal materials. In addition to the prediction of chemical conversion, the calculation of model fitting parameters also provides values for an “apparent, conditional equilibrium constant” and an effective reactive group concentration. These models are derived on the basis of simple chemical principles and a chemical equilibrium assumption. The model-fitting parameters can be easily determined with standard mathematical software. Nevertheless, these models capture the overall behavior of the chemical reduction reaction sufficiently well for accurate predictive needs. This modeling concept can be applied in two possible ways. First, model predictions allow the transfer of experimental chemical conversion data to new, similar target compounds, assuming that the necessary requirements are fulfilled. This leads to shorter time-frames required for process development. Second, these models can be applied as heuristic tools in order to test the feasibility of a proposed overall reaction mechanism and/or effective reactive group concentration.

Influence of macromer molecular weight and chemistry on poly(β‐amino ester) network properties and initial cell interactions

A library of photocrosslinkable poly(beta-amino ester)s (PBAEs) was recently synthesized to expand the number of degradable polymers that can be screened and developed for a variety of biological applications. In this work, the influence of variations in macromer chemistry and macromer molecular weight (MMW) on network reaction behavior, overall bulk properties, and cell interactions were investigated. The MMW was controlled through alterations in the initial diacrylate to amine ratio (> or =1) during synthesis and decreased with an increase in this ratio. Lower MMWs reacted more quickly and to higher double bond conversions than higher MMWs, potentially due to the higher concentration of reactive groups. Additionally, the lower MMWs led to networks with higher compressive and tensile moduli that degraded slower than networks formed from higher MMWs because of an increase in the crosslinking density and decrease in the number of degradable units per crosslink. The adhesion and spreading of osteoblast-like cells on polymer films was found to be dependent on both the macromer chemistry and the MMW. In general, the number of cells was similar on networks formed from a range of MMWs, but the spreading was dramatically influenced by MMW (higher spreading with lower MMWs). These results illustrate further diversity in photocrosslinkable PBAE properties and that the chemistry and macromer structure must be carefully selected for the desired application.

Shrinkage and Springback Behavior of Methylsilsesquioxanes Prepared by an Acid/Base Two-Step Processing Procedure

We report on the effect of water concentration on the shrinkage and springback behavior of methylsilsesquioxane (MSQ) materials prepared by an acid/base two-step procedure in ethanolic solutions. The morphologies of the MSQ gels were characterized by SEM, nitrogen sorption, and mercury porosimetry. The chemical structures of these gels were also determined by solid-state 1 3 C and 2 9 Si NMR. As expected, shrinkage decreases as the volume of macropores in the material increases. Some samples, however, display shrinkage followed by expansion (springback phenomenon) even in the absence of surface modification or solvent exchange. The springback effect is attributed to the intrinsic properties of MSQ monoliths, namely, hydrophobicity and a low concentration of reactive groups on the surface. The implications of these findings for the development of low-shrinkage materials are discussed.

Rheological characterization of interfacial reaction in reactive polymer blends

An original method has been developped which allows to study the influence of chain diffusion on the reaction kinetics in reactive polymer blends. Blends with controlled multilayer morphologies were directly prepared in a rotational rheometer and time-dependent dynamic mechanical measurements allowed to follow the progress of the reaction. Model miscible copolymers with different acrylic monomers were prepared for this study by controlling the composition, molecular weight and average number of reactive groups per chain. Reduced variables for the modulus and the reaction time were introduced to compare the results obtained for different concentrations of reactive groups. In comparison to homogeneous blends, the normalized results for the multilayered structures show that the extent of the reaction depends directly on the chain length and is thus controlled by chain diffusion.

Intramolecular Reactions in Randomly End-Linked Polymer Networks and Linear (Co)polymerizations

This work studies intramolecular reactions in irreversible linear and nonlinear random (co)polymerizations with computer simulations. We find a relative rate for the formation of rings of i chains proportional to i-3/2 in agreement with predictions of rate theory based on Gaussian chain statistics. This result is used to develop a general ansatz for ring formation in irreversible random polymerizations or in cyclization equilibria. Using the approximation cext ≫ cint for the concentrations of reactive groups on the external molecules cext and on the selected molecule cint, this ansatz reduces to a result previously found by Suematsu. In this special case we find that the ring size distribution Ri is proportional i-5/2[(f − 1)(g − 1)pApB]i-1, where f and g denote the functionality of two different types of molecules A and B, and pA and pB are the conversions of the reactive groups on the molecules, respectively. Our findings explain preceding experiments, simulations, and all results within this work as we...

In situ monitoring of reaction‐induced phase separation with modulated temperature DSC

AbstractA linearly polymerizing and network forming epoxy‐amine system, DGEBA‐aniline and DGEBA‐MDA, respectively, will be modified with 20 wt% and 50 wt% of a high‐Tg thermoplastic poly(ether sulphone) (Tg=223°C), respectively, both showing LCST‐type demixing behavior. Reaction‐induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES‐rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature‐conversion‐transformation diagram unambiguously shows the LCST‐type demixing behavior of this system, while the relation between the composition/glass transition of the PES‐rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non‐isothermal post‐cures.

Functionalization of LDPE by Melt Grafting with Glycidyl Methacrylate and Reactive Blending with Polyamide‐6

AbstractLow‐density polyethylene (LDPE) was functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed for reactive blending with polyamide‐6 (PA6). The effect of the reaction procedure on the grafting degree of LDPE‐g‐GMA samples (0.5–12.5 wt.‐% GMA) was analyzed as a function of the concentration of GMA monomer, radical initiator (BTP), and addition of styrene as co‐monomer. Optimized grafting conditions were obtained when the amount of the monomer is below 10 wt.‐% and that of peroxide in the range 0.2–0.4 wt.‐%. Binary blends of PA6 with LDPE‐g‐GMA (3.5 wt.‐% GMA) and with LDPE at various compositions (80/20, 67/33, 50/50 wt.‐%) were prepared in an internal mixer and their properties were evaluated by torque, SEM and DSC analyses. Morphological examination by SEM showed a large improvement of phase dispersion and interfacial adhesion in PA6/LDPE‐g‐GMA blends as compared with PA6/LDPE blends. The average diameter of dispersed polyolefin particles was about 0.4 μm for LDPE‐g‐GMA contents &lt; 50 wt.‐%. A marked increase of melt viscosity was observed for the compatibilized blends depending on the concentration of grafted polyolefin, and it was accounted for by the reaction between the epoxy groups of GMA and the carboxyl/amine end‐groups of PA6. The variation of torque was thus related to the molar ratio of reactive group concentration. The analysis of crystallization and melting behavior pointed out marked differences in the phase structure of the blends due to the presence of the functionalized polyolefin. Finally, the in situ formation of a graft copolymer between LDPE‐g‐GMA and PA6 was investigated by means of a selective dissolution method (Molau test) and by FT‐IR and DSC analyses.SEM micrograph of fracture surface of PA6/LDPE‐g‐GMA 50/50 blend.magnified imageSEM micrograph of fracture surface of PA6/LDPE‐g‐GMA 50/50 blend.

Bulk hydrosilylation reaction of poly(dimethylsiloxane) chains catalyzed by a platinum salt: Effect of the initial concentration of reactive groups on the final extent of reaction

AbstractModel silicone networks obtained by curing linear poly(dimethylsiloxane) (PDMS) chains with end‐vinyl groups, (B2), with a polyfunctional silane‐terminated crosslinker of functionality f, (Af), through a hydrosilylation reaction have been widely used. In these networks, the principal characteristics of their ultimate molecular structure are strongly affected by the final extent of reaction reached during the crosslinking reaction. This work analyzes the effect of the initial concentration of the reactive end groups on the maximum attainable extent of reaction under normal bulk crosslinking conditions. This was accomplished by examining the reaction between linear B2 PDMS chains with difunctional and trifunctional silanes. The experimental results were fitted by an exponential equation to have an empirical equation able to predict the maximum extent of reaction to be obtained as a function of the initial concentration of reactive groups. Molecular parameters relevant to this study, such as the degree of polymerization, the weight‐average molecular weight for the A2 + B2 system, or the weight fraction of solubles for the A3 + B2 system, were calculated with a mean field theory (recursive approach). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1099–1106, 2003

Dynamics of rough interfaces in chemical vapor deposition: experiments and a model for silica films

We study the surface dynamics of silica films grown by low pressure chemical vapor deposition. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state compatible with the Kardar-Parisi-Zhang (KPZ) equation in three dimensions. At intermediate times the surface undergoes an unstable transient due to shadowing effects. By varying growth conditions and using spectroscopic techniques, we determine the physical origin of KPZ scaling to be a low value of the surface sticking probability, related to the surface concentration of reactive groups. We propose a stochastic equation that describes the qualitative behavior of our experimental system.