The reactive compatibilization of NBR/EVA blends with oxazoline-modified nitrile rubber

The reactive compatibilization of ethylene-vinyl acetate copolymer (EVA)/nitrile rubber (NBR) blends has been performed using partially hydrolyzed EVA (EVALVA) in combination with oxazoline-functionalized NBR (NBROX). The synthesis of the NBROX has been performed in solution. The presence of 5 wt% of EVALVA in combination with 2.5 wt% of NBROX resulted in a substantial improvement of tensile strength of NBR/EVA (50:50 wt%) vulcanized blends, with a little increase of the elongation at break. The morphologies of these blends were examined by the scanning electron microscopy. A finer morphology has been observed in vulcanized and non-vulcanized blends, compatibilized with the co-reactive EVALVA/NBROX copolymers. Blends of NBROX/EVALVA (50:50 wt%) resulted in insoluble material, constituted by both components, as indicated by Fourier transform infrared analysis. This result indicates the reaction of the co-reactive groups (hydroxyl and oxazoline) during blending.     

Influence of the secondary functionality on the radical‐vinyl chemistry of highly reactive monoacrylates

The impact of secondary functionalities on the radical‐vinyl chemistry of monoacrylates characterized by secondary functionalities that dramatically enhance their polymerization rate was elucidated utilizing experimental and computational techniques. Firstly, bulk interactions affecting the acrylate reactivity towards photopolymerization were removed by polymerizing at 5 wt % monomer in 1,4‐dioxane. Following deconvolution of bulk interactions impacting reactivity towards photopolymerization, a linear correlation between average polymerization rates and Michael addition reaction rate constants was observed on a logarithmic scale. This result indicates that the presence of the secondary functionality intramolecularly alters the monomer chemistry in a manner which impacts both of these distinct reaction types in a similar manner. These monomers exhibited reduced activation energies in both Michael addition and photopolymerization reactions as compared to hexyl acrylate. Reduction up to 20 ± 8 kJ mole^?1was observed for Michael addition reactions and 12 ± 1 kJ mole^?1 for photopolymerization reactions, thereby explaining the higher reactivity of the acrylates characterized by the secondary functionalities. Cyclic voltammetry experiments conducted to investigate the nature of the acrylic double bonds indicated that the rapidly polymerizing acrylates are more readily reduced as compared to traditional acrylates. Further, a distinct monotonic correlation of the irreversible cathodic peak potentials of the (meth)acrylates to photopolymerization and Michael addition reactivity was observed. The computationally estimated acrylic LUMO energies characterized by the secondary functionalities (?2.3 eV to ?2.7 eV) were also found to be lower relative to hexyl acrylate (?2.2 eV). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4859–4870, 2009     

Compatibilized blends of thermoplastic polyurethane (TPU) and polypropylene

Compatibilized blends of thermoplastic polyurethane (TPU) and polypropylene (PP) were developed using amine (primary or secondary) functionalized PP's (PP-g-NH₂ or PP-g-NHR). The strategy of reactive compatibilization is based on fast reactions between amine functional groups and urethane linkages or traces of free isocyanates released by thermal degradation of TPU. Excellent compatibilization between TPU and PP was confirmed by rheological, morphological, and mechanical properties. Much finer domain size, higher interfacial adhesion, and more stable morphologies were clearly observed by scanning electron microscopy. Significant improvements in the overall mechanical properties (tensile, tear, abrasion) imply significantly more reaction between TPU and PP phases in the two TPU/PP blends containing PP-g-NH₂ or PP-g-NHR than a TPU/PP blend using PP-g-MA as a compatibilizing agent.     

Degradation of a poly(ester urethane) elastomer. III. Estane 5703 hydrolysis: Experiments and modeling

Hydrolytic degradation data from a wide variety of experiments on Estane 5703, a commercial poly(ester urethane), are modeled with an A_AC2 mechanism of reversible esterification and hydrolysis together with a cluster model for water concentration. The experimental conditions spanned a range of temperatures from 21 to 95 °C, relative humidities from 0 to 100%, times up to more than 30 years, and different initial molecular weights and acidities. In addition, the experiments were performed in several different laboratories with a number of different instruments and techniques. All the experimental data, both for molecular weight and acidity, are modeled with a single set of concentration‐independent rate coefficients, and the kinetic model fits the data well and constitutes a robust model of the hydrolytic degradation of this polymer. The results also show that ester hydrolysis is the dominant cause of the molecular weight loss of Estane 5703 in indoor storage at ambient temperatures and humidities. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1136–1151, 2003     

Kinetic Investigations of Self-Condensing Group Transfer Polymerization

Hyperbranched methacrylates were synthesized by Self-Condensing Group Transfer Polymerization (SCGTP) of 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) and characterized by multi-detector SEC as well as quantitative ¹³C-NMR. Kinetic measurements revealed that side reactions limit the molecular weights and lower the polydispersity. A maximum degree of branching of DB ≈ 0.4 and a reactivity ratio, r = k _A/k _B = 18 ± 5, was determined.     

Acceleration of the imine base/isocyanate (IBI)‐mediated polymerization of MMA caused by ionic liquid traces

The brutto rate of the imine base/isocyanate (IBI)‐mediated radical polymerization of methyl methacrylate (MMA) can be significantly increased by use of ionic liquid (IL) traces. At least, catalytic amounts of IL influence both the value of the brutto polymerization rate ν_Br,0 and the necessary reaction temperature of the used IBI mixture. Combinations of 2‐phenyl‐2‐oxazoline (POX) or 1‐methyl pyrazole (1MP) with isocyanates are IBI systems that usually do not initiate MMA at room temperature. By adding traces of 1‐ethyl‐3‐methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([Emim]FAP), polymethyl methacrylate (PMMA) with high average molecular weight can be obtained whereas the initiator mixture (imine base/isocyanate) concentration can be decreased by a factor of 10. The polymerization kinetics of several IBI combinations in the presence of ILs has been determined and a comparison to non‐IL containing initiator mixtures is given. Additionally, the temperature dependence of the IL‐containing polymerizations was measured. The interaction of the IL with MMA and the individual IBI initiator components is studied by means of attenuated total reflection Fourier transformation middle infrared spectroscopy (ATR FT MIR). Furthermore, the IBI brutto polymerization rate constants k_Br,0 were brought into relation to the IL hydrogen bond donating ability α. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Characterization of molecularly imprinted polymers employing crosslinkers with nonsymmetric polymerizable groups

Crosslinking monomers have been developed with a combination of methacrylamide and methacrylate or vinyl ketone polymerizable groups that provide molecularly imprinted polymers (MIPs) with improved binding and selectivity. The differential reactivity rates of the polymerizable groups prompted an investigation into the time‐dependent behavior of the crosslinkers, which suggests a new mechanism for MIP formation. The mechanism involves the formation of long sections of linear poly(vinyl ketone) with pendant methacrylamide groups that form a highly crosslinked network in a subsequent step. This has implications for the sequence morphology of polymers, affecting the structure and improving the binding properties of MIPs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3668–3675, 2004     

Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching

The branching stemming from midchain radical formation in n‐butyl acrylate polymerization is investigated via melt‐state ¹³C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated poly­merizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.

     

Kinetic Modeling of the Suspension Copolymerization of Styrene/Divinylbenzene with Gel Formation

Summary : Experimental and theoretical studies concerning the suspension copolymerization of styrene with divinylbenzene are reported. Experiments were carried out in a batch stirred reactor, at 1.2 dm³ scale, and extended beyond gelation in order to synthesize insoluble material. Looking for real time information concerning the building process of such materials, these polymerizations were In-line monitored using a FTIR-ATR immersion probe. Polymer samples collected before and after gelation were Off-line characterized using a SEC/RI/MALLS system allowing the measurement of monomer conversion, average molecular weights, MWD and also the z-average radius of gyration. The weight fraction of insoluble material (gel) was measured for samples with different reaction times. The experimental program has included the study of the influence of key polymerization parameters on the dynamics of gelation and some properties of the resulting networks, namely the initial mole fraction of crosslinker and the initial proportions between monomers and inert diluent. Variable n-heptane/toluene mixtures were used within this purpose. These experimental observations were complemented with theoretical studies using a general kinetic approach allowing the prediction of MWD and z-average radius of gyration before and also after gelation. Comparison of the experimental measurements with these predictions is being exploited to develop modeling tools useful for the design of operating conditions allowing the improvement of the performance of the final products.     

An Error‐in‐Variables Method for Determining Reactivity Ratios by On‐Line Monitoring of Copolymerization Reactions

Summary: A new error‐in‐variables method was developed to estimate the reactivity ratios in copolymerization systems. It brings the power of automatic, continuous, on‐line monitoring of polymerization (ACOMP) to copolymerization calculations. In ACOMP systems, monomer and polymer concentrations are measured by the monitoring of two independent properties of the system. The reactivity ratios are found by taking into account errors in the monomer concentrations determined from measurements and from calibration of the instruments. All the error sources are taken into account according to the error‐in‐variables method, and their effects are reflected in determining the confidence intervals of the reactivity ratios by the usual error propagation technique.

Distribution of concentrations [a] and [b] for the simulated experiment I. Random errors are 1% of the initial value in both observed variables.     

Novel elastomeric polyurethanes with pendant epoxy groups as highly reactive auxiliary groups for further derivatizations

The introduction of pendant, reactive groups into polyurethane macromolecules is a challenging problem. A variant of the nondegradative modification of polyurethanes with epoxy groups attached to the urethane sites is proposed. Two types of commercial elastomeric segmented polyurethanes, represented by a poly(ether urethane) and a poly(urethane urea), were functionalized by base‐induced N‐glycidylation of the urethane hard segments with an excess of epibromohydrin in dimethylacetamide solutions at low temperatures. This resulted in the modification of polymers with 0.30–0.44 mmol/g of pendant epoxy groups. Lithium or potassium tert‐butoxides were used as bases to initiate the reaction. A nonpolymeric urethane model (ethyl N‐p‐tolylcarbamoate) was used to verify the course of glycidylation. One of the polymers was subjected to epoxy ring opening with 1‐propanethiol, demonstrating the versatility of pendant glycidyl groups as auxiliary groups for further bulk modifications of polyurethanes. These functionalized polyurethanes are useful for the further covalent attachment of suitable moieties (stabilizing or biocompatibility‐enhancing agents). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4378–4385, 2002     

Surface‐dependent effect of functional silica fillers on photocuring kinetics of hydrogel materials

Two types of silica: precipitated (P, prepared in non‐polar media, a new type, submicrometer sized) and fumed (F, nanosized), both unmodified and surface modified are investigated as functional fillers for potential applications in nanocomposites with poly(2‐hydroxyethyl methacrylate) matrix. Special attention is paid to the kinetics of composite formation in an in situ photopolymerization process. Silica‐containing formulations polymerize faster; this effect is much stronger for silica P having much larger particle size than silica F. Surface treatment leads to further acceleration of the polymerization in case of silica P but to retardation in case of silica F; the effect of modification of the filler surface on properties of composites is different for each of the silicas. The obtained results are discussed in terms of effects of curvature of silica particles, surface properties, solvation cell, interphase region, viscosity changes, and morphology of the resulting composites. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3472–3487     

Analysis of association constant for ground‐state dye‐electron acceptor complex of photoinitiator systems and the association constant effect on the kinetics of visible‐light‐induced polymerizations

We investigated the formation of ground‐state donor/acceptor complexes between xanthene dyes [rose bengal (RB) and fluorescein (FL)] and a diphenyliodonium (DPI) salt, which is dissolved in 2‐hydroxyethyl methacrylate (HEMA) monomer. To characterize the association constant of the complex, we have suggested a new analysis model based upon the Benesi–Hildebrand model. Because the assumption of the original Benesi–Hildebrand model is that the absorption bands are only due to the presence of the complex and that the absorption by the free component is negligible, the model cannot be applied to our systems, which is a dye‐based initiator system. For each dye, the molar absorptivity of the ground‐state complex was evaluated as a function of wavelength, and this analysis confirmed the validity of the modified Benesi–Hildebrand model. In addition, we observed that the RB/DPI photoinitiator system failed to produce a perceptible polymerization rate but the FL/DPI photoinitiator system provided high rates of polymerization. On the basis of the association constant for these complexes, we concluded that the observed kinetic differences arise from the different association constant values of the ground‐state dye‐acceptor complex, resulting in back‐electron transfer reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1429–1439, 2009     

Morphology of PC/SAN blends: effect of reactive compatibilization,SAN concentration,processing, and viscosity ratio

This article examines the effects of dispersed phase concentration, processing apparatus, viscosity ratio, and interfacial compatibilization using an SAN–amine compatibilizer on the morphology of blends of bisphenol A–polycarbonate (PC) with styrene–acrylonitrile (SAN) copolymers. For uncompatibilized blends, the dispersed phase particle size increased significantly with SAN concentration, and was found to exhibit a minimum at a viscosity ratio of approximately 0.35 for a fixed concentration of 30% SAN in the blend. Although the morphology of uncompatibilized PC/SAN blends mixed in a Brabender mixer, single‐ and twin‐screw extruders were quite similar, the twin‐screw extruder produced significantly finer morphologies in blends containing SAN–amine. The average particle size for blends compatibilized with the SAN–amine polymer was approximately half that of uncompatibilized blends and was relatively independent of viscosity ratio and dispersed phase composition. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 71–82, 1999     

Dark‐cure studies of cationic photopolymerizations of epoxides: Characterization of the active center lifetime and kinetic rate constants

We have characterized the effective rate constants for termination/trapping (k_t/t) and propagation (k_p) for solvent‐free cationic photopolymerizations of phenyl glycidyl ether for conversions up to 50%. We have performed dark‐cure experiments in which active centers are produced photochemically for a specified period of time until the initiating light is shuttered off, and then the polymerization rate is monitored in the dark. This method is especially well suited for characterizing cationic polymerizations because of the long active center lifetimes. Our analysis provides profiles of the instantaneous kinetic rate constants as functions of conversion (or time). For photopolymerizations of phenyl glycidyl ether initiated with iodonium photoinitiators, k_t/t and k_p remain essentially invariant for conversions up to 50%. For the photoinitiator (tolycumyl) iodonium tetrakis (pentafluorophenyl) borate (IPB), the values of k_t/t at 50 and 60 °C are 0.027 and 0.033 min^?1, respectively. The corresponding values of k_t/t for diaryliodonium hexafluoroantimonate (IHA) are 0.041 and 0.068 min^?1. The values of k_p at 50 °C for IPB and IHA are 0.6 and 0.4 L mol^?1 s^?1, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2064–2072, 2003     

Reactive compatibilization of nylon copolymer/EPDM blends: experimental aspects and their comparison with theory

In situ reactive compatibilization was first time applied to a low melting nylon (nylon 6 and 66 copolymer) and EPDM blend system. The effects of in situ compatibilization and concentration of compatibilizer on the morphology and mechanical properties of nylon/EPDM blends have been investigated. The influence of EPM‐g‐MA on the phase morphology was examined by the scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The compatibilizer concentrations used were 0, 1, 2.5, 5, and 10 wt%. The graft copolymer (nylon‐g‐EPM) formed at the interface showed relatively high emulsifying activity. A maximum phase size reduction was observed when 2.5 wt% of compatibilizer was added to the blend system. This was followed by a leveling‐off at higher loadings indicating interfacial saturation. The conformation of the compatibilizer at the interface was deduced based on the area occupied by the compatibilizer at the blend interface. The experimental compatibilization results were compared with theoretical predictions of Noolandi and Hong. It was concluded that the molecular state of compatibilizer at interface changes with concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties. Measurement of tensile properties shows increased elongation as well as enhanced modulus and strength up on compatibilization. At higher concentrations of compatibilizer, a leveling‐off of the tensile properties was observed. A good correlation has been observed between the mechanical properties and morphological parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Substituent effects of N‐alkyl groups on thermally induced polymerization behavior of 1,3‐benzoxazines

Thermally induced polymerizations of a series of 1,3‐benzoxazines with a variety of substituents on the nitrogen atom were investigated in detail, particularly in the following three aspects of the polymerization: (1) N‐alkyl‐1,3‐benzoxazines are much more reactive than N‐phenyl‐1,3‐benzoxazine. (2) The polymerization rate depended on the bulkiness of the N‐substituent. The bulkier the substituent was, the slower the polymerization was. (3) The polymerizations accompanied weight loss due to the elimination of the corresponding imine (R‐N = CH₂), and its extent became larger when R was more bulky. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2777–2782, 2010     

Synthesis and characterization of original functional polymers of tetrafluoroethylene and 4,5,5‐trifluoro‐4‐ene pentyl acetate

The bulk radical copolymerization of tetrafluoroethylene (TFE) with 4,5,5‐trifluoro‐4‐ene pentyl acetate (FAc), initiated by tert‐butyl peroxypivalate to synthesize original, functionalized fluorinated poly(TFE‐co‐FAc), was investigated. FAc monomer was prepared from a five‐step process. The copolymerization was carried out in batch at different initial monomer molar ratios ([TFE]_o/[FAc]_o ranging from 95/5 to 10/90 mol %) and at different initiator concentrations (ranging between 0.075 and 1.100 mol % about the monomers) at 70 °C. All the experiments revealed the production of fluorooligomers as evidenced by an allylic‐transfer reaction from FAc. The microstructure of these copolymers (i.e., the molar percentage of both monomers in the copolymers) was assessed by ¹⁹F NMR spectroscopy. From the kinetics of copolymerization, two key characteristics were determined. First, the reaction order to the initiator (being 1.07) and that of FAc monomer (0.85) showed a heterogeneous character of the copolymerization and monomolecular chain‐transfer reaction to FAc. Second, from the Tidwell and Mortimer method, the reactivity ratios of both comonomers were determined, showing a tendency to alternance in a wide range of initial monomeric ratios (30/70–70/30): r_FAc = 0.20 ± 0.26 and r_TFE = 0.18 ± 0.15. Alfrey and Price's Q and e values of FAc were calculated by Greenley's technique [Q_FAc = 0.098 (from Q_TFE = 0.032) and e_FAc = 1.23 (vs e_TFE = 1.63)], indicating that FAc is a strong electron‐withdrawing monomer as TFE. The normalized monomer‐diad and triad fractions as a function of the polymer composition were obtained from the comonomer sequence‐distribution procedure. The average molecular weights and molecular weight distributions as well as the thermal properties (glass‐transition temperature and decomposition temperature) of the fluorocopolymers were assessed and are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1693–1706, 2004