Silicon‐containing trifunctional and tetrafunctional cyanate esters: Synthesis,cure kinetics,and network properties

The synthesis and physical properties of new silicon‐containing polyfunctional cyanate ester monomers methyl[tris(4‐cyanatophenyl)]silane and tetrakis(4‐cyanatophenyl)silane, as well as polycyanurate networks formed from these monomers are reported. The higher crosslinking functionality compared to di(cyanate ester) monomers enables much higher ultimate glass transition temperatures to be obtained as a result of thermal cyclotrimerization. The ability to reach complete conversion is greatly enhanced by cocure of the new monomers with di(cyanate ester) monomers such as 1,1‐bis(4‐cyanatophenyl)ethane. The presence of silicon in these polycyanurate networks imparts improved resistance to rapid oxidation at elevated temperatures, resulting in char yields as high as 70% under nitrogen and 56% in air in the best‐performing networks. The water uptake in the silicon‐containing networks examined is 4–6 wt % after 96 h of immersion at 85 °C, considerably higher than both carbon‐containing and/or di(cyanate ester) analogs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 767–779     

Differential scanning calorimetric study on the curing behavior of epoxy resin/diethylenetriamine/organic montmorillonite nanocomposite

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A with diethylenetriamine as the curing agent and different amounts of organic montmorillonite were examined with isothermal and dynamic scanning calorimetry. The modified Avrami equation was used to calculate the activation energy and reaction orders in the isothermal experiment. A single peak was observed in each dynamic scan. The curing mechanism and kinetics of the curing reaction were also analyzed by two kinds of methods—Kissinger and Flynn–Wall–Ozawa. The results obtained from those methods under dynamic measurement agreed with those obtained from the modified Avrami equation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 378–386, 2003     

Curing kinetics of epoxy resins with hyperbranched polyesters as toughening agents

The effects of hyperbranched polyesters on the cure kinetics of diglycidyl ether of bisphenol A (DGEBA) in the presence of m‐phenylene diamine were investigated with nonisothermal differential scanning calorimetry. The results showed that the addition of hyperbranched polyesters enhanced the cure reaction of DGEBA with m‐phenylene diamine, and this resulted in a reduction of the peak temperature of the curing curve and the activation energy because of the low viscosity and large number of terminal hydroxyl groups. However, when linear poly(ethylene glycol) was added, the activation energy of the blends also slightly decreased, whereas the peak temperature of the curing curve increased. The curing kinetics of the blends were calculated by the isoconversional method of Málek. The two‐parameter autocatalytic model (i.e., the ?esták–Berggren equation) was found to be the most adequate for describing the cure kinetics of the studied systems. The obtained nonisothermal differential scanning calorimetry curves showed results in agreement with those theoretically calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2649–2656, 2004     

Effect of the initiator content and temperature on the curing of an unsaturated polyester resin

The influence of temperature and the initiator concentration on the curing of an unsaturated polyester resin was studied by means of differential scanning calorimetry (DSC) and Fourier‐transform infrared spectroscopy (FTIR). It was established that there is an isoconversional relationship of the type lnt = a − bln[I]₀ between the curing time, t, and the initial initiator concentration, [I]₀, at a given temperature. This relationship indicates that the degree of conversion curves vs. the logarithm of the curing time at different [I]₀ may be superposed by displacement relative to a reference curve. It was confirmed that the reaction mechanism varies throughout the whole curing process, although it does not vary with the temperature and the [I]₀ at each degree of conversion. It was established that there is a universal isoconversional relationship of the type lnt = d − bln[I]₀ + E/RT that expresses the dependency of the curing time on the temperature, T, and the [I]₀. The parameters a, b, and d depend on the reaction mechanism, and can be calculated on the basis of isothermal experiments at different temperatures and with different [I]₀. The adjustment lnt = d − bln[I]₀ + E/RT shows that there is an equivalence between the effect on the curing kinetics of the temperature and the initiator concentration. The same curing process can be achieved by using different combinations of curing temperatures and the [I]₀. In the two adjustments established, it is not necessary to know the reaction mechanism, and the only assumption made is that for a given conversion the reaction mechanism is invariant with respect to the [I]₀ and the temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 751–768, 1999     

Thermal properties of single walled carbon nanotube‐silicone nanocomposites

The effect of single walled carbon nanotube (SWCNT) fillers on the low temperature thermal properties and curing behavior of SWCNT‐silicone nanocomposite are reported for the first time. The SWCNT‐silicone composites were prepared by different mixing procedures and characterized by differential scanning calorimetry (DSC). Solution mix, with the aid of sonication and soaking achieved better dispersion of SWCNTs in the silicone. The adding of SWCNTs in polymer seriously hindered the curing of silicone elastomer. The hindrance increased with increasing concentration of SWCNT and the quality of dispersion. The glass transition temperatures (T_g) of the nanocomposites were found to be independent of the SWCNT addition, although, the steps in the heat capacity (Δc_p) of the glass transition were smaller with increasing SWCNTs concentration. The melt crystallization behavior was strongly dependent on the concentration and dispersion of SWCNT in the polymer. The cooling scan showed that the higher concentration and the better dispersion of SWCNTs in the silicone resulted in higher percentage of melt crystallization of this nanocomposite. The correlation of the change of thermal properties to the dispersion of CNT in polymer may be used to determine the quality of SWCNT dispersion in silicone polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1845–1852, 2008     

Studies on curing kinetics of a novel combined liquid crystalline epoxy containing tetramethylbiphenyl and aromatic ester‐type mesogenic group with diaminodiphenylsulfone

The curing kinetics of a novel liquid crystalline epoxy resin with combining biphenyl and aromatic ester‐type mesogenic unit, diglycidyl ether of 4,4′‐bis(4‐hydroxybenzoyloxy)‐3,3′,5,5′‐tetramethyl biphenyl (DGE‐BHBTMBP), and the curing agent diaminodiphenylsulfone (DDS) was studied using the advanced isoconvensional method (AICM). DGE‐BHBTMBP/DDS curing system was investigated the curing behavior by means of differential scanning calorimetry (DSC) during isothermal and nonisothermal processes. Only one exothermal peak appeared in isothermal DSC curves. A variation of the effective activation energy with the extent of conversion was obtained by AICM. Three different curing stages were confirmed. In the initial curing stage, the value of E_a is dramatically decreased from ～90 to ～20 kJ/mol in the conversion region 0–0.2 for the formation of LC phase. In the middle stage, the value of E_a keeps about ～80 kJ/mol for cooperative effect of reaction mechanism and diffusion control. In the final stage, a significant increase of E_a from 84 to 136 kJ/mol could be caused by the mobility of longer polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3922–3928, 2007     

Carboxylic acid‐containing benzoxazines as efficient catalysts in the thermal polymerization of benzoxazines

The autocatalytic thermal polymerization behavior of three benzoxazine monomers containing carboxylic acid functionalities is reported. Several mixtures of these carboxylic monomers and 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine were prepared and their thermal polymerization behavior was analyzed by differential scanning calorimetry. The acid character of these reactive monomers increases the concentration of oxonium species, thus catalyzing the benzoxazine ring opening reaction. In this way the polymerization temperature decreased by as much as 100 °C in some cases. The existence of decarboxylation processes at high temperatures has been established by FTIR‐ATR and related to the increase in thermal stability observed by TGA in some cases. A relationship between the presence of carboxylic groups in the resulting materials and their flame retardancy behavior has also been established. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6091–6101, 2008     

Novel thermosets obtained by UV‐induced cationic copolymerization of DGEBA with an spirobislactone

The photocuring process of the diglycidyl ether of bisphenol A (DGEBA) with the bislactone 1,6‐dioxaspiro[4,4]nonane‐2,7‐dione (s(γ‐BL)) was studied. Triarylsulfonium hexafluoroantimonate was employed as photoinitiator. FTIR/ATR was used to study the evolution of epoxy, lactone, and intermediate spiroorthoester groups to identify the different reactions that take place during the photocuring process. Photo‐DSC and DSC were used to study the thermal evolution of the photocuring process and to assess the T_g of the fully cured material. Thermogravimetric analysis (TGA) was used to determine the thermal stability of the fully cured material. The thermomechanical properties of the materials were investigated using dynamic mechanical‐thermal analysis. Shrinkage undergone during photocuring and gelation was studied with TMA. A strong influence of the photocuring temperature on the photocuring process of the DGEBA‐ s(γ‐BL) system was observed. Differences in the reactivity of the different species were observed with respect to the thermally cured system using ytterbium triflate as cationic thermal initiator. As a consequence, photocured materials exhibited a superior thermal stability and lower flexibility. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5446–5458, 2007     

Fluoropolyether coatings: Relationships of electrochemical impedance spectroscopy measurements,barrier properties,and polymer structure

Ten model coatings, selected and obtained from a family of fluorinated resins synthesized by the reaction of perfluoroether oligomeric diols of different molecular weights with polyisocyanurates of hexamethylenediisocyanate (HDI) and isophoronediisocyanate (IPDI), were characterized with differential scanning calorimetry, mechanical testing, and electrochemical impedance spectroscopy measurements. The electrochemical and chemico‐physical measurements show that the glass‐transition temperature of the starting isocyanate trimers greatly influences the properties of the final urethane coatings; the IPDI trimer gives harder coatings with lower water permeabilities than the corresponding HDI‐based materials. Moreover, for each class of materials (from IPDI or HDI), the fluorine content plays a relevant role: the higher the fluorine percentage, the lower the water absorption into the coatings. Furthermore, the chain length of the polyols used for the synthesis of the prepolymers is a variable that exhibits great influence on the coating properties: coatings containing shorter perfluoropolyether segments show better barrier properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 52–64, 2002     

Kinetics studies on the accelerated curing of liquid crystalline epoxy resin/multiwalled carbon nanotube nanocomposites

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′‐bis(2,3‐epoxypropoxy) biphenyl (BP), 4,4′‐diamino‐diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef‐CNT). The ef‐CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef‐CNT. At 10 wt % of ef‐CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef‐CNT was replaced by thermal‐insulating TiO₂ nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high‐thermal conductivity of CNT and aligned LC epoxy resin. However, at ef‐CNT concentration higher than 2 wt %, the accelerating effect of ef‐CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effect of organoclay on the curing reactions in bismaleimide/diallyl bisphenol a resin

4,4′‐Bismaleimidodiphenyl methane (BMPM)/2,2′‐diallyl bisphenol A (DBA)/organoclay nanocomposites were synthesized. The effects of organoclays on the curing reactions in the BMPM/DBA system at low temperatures (ene reaction) and high temperatures (Diels–Alder reaction, homopolymerization of BMPM, and alternative copolymerization) were investigated with differential scanning calorimetry and Fourier transform infrared techniques. The results showed that these reactions were affected to different extents in the presence of organoclays. The ene reaction was accelerated to different degrees depending on the acidity of the modifier and the accessibility of the organoclays used. The exfoliation degree of organoclays in the prepolymers showed great effects on the curing behavior of BMPM/DBA. When an organoclay was less intercalated, the curing behavior of the system was different from that of neat BMPM/DBA. On the other hand, when the organoclay was better exfoliated in prepolymers, the curing behavior of the system was similar to that of the neat BMPM/DBA system. However, even in this case, the reactions at high temperatures occurred in different ways in the presence of an organoclay. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 994–1006, 2005     

Noncovalent functionalization of multiwalled and double‐walled carbon nanotubes: Positive effect of the filler functionalization on high glass transition temperature epoxy resins

Double‐walled carbon nanotubes (DWCNTs) and multiwalled carbon nanotubes (MWCNTs) were modified using melamine to attach ? NH₂ to the surface of these fillers, without previous oxidation of their graphene layers. FT‐Raman, elemental (chemical) and thermogravimetric analysis, confirmed the modification, which was more extensive for DWCNTs. The potential of this modification was evaluated by adding the melamin‐modified nanotubes to thermosets based on diglycidyl ether of bisphenol A (resin) and polycyclic amine (hardener). Broadening of the glass transition interval and an increase between 7 and 8 °C of the glass transition temperatures show better filler/matrix interaction for the nanocomposites based on melamine‐modified nanotubes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1860–1868, 2009     

ROMP of Functionalized Cyclooctene and Norbornene Derivatives and their Copolymerization with Cyclooctene

In this work, two novel monomers, a cyclooctene and a norbornene derivative, including the trifluoromethylphenyl ester group, are prepared by chemical modification of 1,5-cyclooctadiene and 5-norbornene-2-carboxylic acid, respectively. The ring-opening metathesis polymerization of each one of these monomers, as well as the commercial carboxylic acid, is confirmed in the presence of Grubbs’ second generation catalyst in CH₂Cl₂. The three functionalized monomers are subsequently copolymerized with cis-cyclooctene in order to obtain modified polycyclooctenes. Solubility is enhanced by the incorporation of the functional group. The thermal properties of the obtained homopolymers and copolymers are studied by DSC and TGA, showing that crystalline behavior strongly depends on the cyclooctene content.     

Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were isothermally crystallized at various crystallization temperatures (T_c) ranging from 70 to 97.5 °C. The T_c dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min⁻¹. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing T_c, whereas peak H decreased. The T_c dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of T_c. T_m(L), T_re, and ΔH increased almost linearly with T_c, whereas T_m(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar T_c dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, T_m(L), T_m(H), and T_re almost coincided with each other at the same T_c. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same T_c. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005     

Determination of the crystallinity of polyethylene/α‐olefin copolymers by thermal analysis: Relationship of the heat of fusion of 100% polyethylene crystal and the density

The heat of fusion measured with differential scanning calorimetry (DSC) is typically divided by a constant value of the heat of fusion of 100% polyethylene (PE) crystal (ΔH) for the estimation of the fraction crystallinity of PE copolymers, regardless of the density [i.e., the short‐chain branching (SCB) concentration]. In this work, values of ΔH of about 288 J/g were determined with a combined DSC and X‐ray diffraction (XRD) method for a series of PE copolymers containing SCB from 0 to 50 Br/1000 C (density = 0.965–0.865 g/cc). There was no systematic change in ΔH observed across this density range. This result supports the suitability of determining the fraction crystallinity of PE of any density by the simple division of the observed heat of fusion determined by DSC by a constant value of ΔH. This DSC method yielded values of PE crystallinity in good agreement with corresponding values determined by XRD for a series of PE copolymers. The determination of ΔH involved a small precision error for higher density (lower SCB) PEs, but the precision error increased for lower density (i.e., higher SCB) PEs. This was due to the difficulty in measuring the heat of fusion for lower density PEs, which exhibited low values of the heat of fusion and melted only slightly above room temperature, and due to the difficulty of measuring lower values of crystallinity by XRD. The crystal thickness measured by small‐angle X‐ray scattering for this series of PE copolymers decreased exponentially from about 280 to 6 Å. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1637–1643, 2002     

Thiol‐functionalized 1,3‐benzoxazine: Preparation and its use as a precursor for highly polymerizable benzoxazine monomers bearing sulfide moiety

We describe a new strategy for preparation of benzoxazine monomers based on in situ preparation of a thiol‐functionalized benzoxazine and successive chemical modification of the thiol moiety. The thiol‐functionalized benzoxazine can be prepared from its precursor bearing two benzoxazine moieties linked by disulfide bond. Reductive cleavage of the disulfide bond of the precursor with using triphenylphosphine as a reducing agent allows successful preparation of the thiol‐functionalized benzoxazine. By performing this reduction process in the presence of epoxides and acrylates, the formation of the thiol moiety and its successive reaction with those electrophiles proceed efficiently to give the corresponding benzoxazines with sulfide moieties. The benzoxazine monomers thus prepared exhibit much higher polymerization ability than those without sulfide moiety. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1448–1457     

Effect of new nonionic curing agent on curing kinetics and mechanical properties of epoxy resin

The current research work presents a novel nonionic curing agent (AEDA) synthesized by utilizing ethylene glycol diglycidyl ether (EGDE), 3,4-dimethoxyaniline (DI), and triethylenetetramine (TETA). Infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structure of AEDA curing agent. Non-isothermal scanning calorimetry was used to determine the activation energy and curing conditions of epoxy resin in the curing process. An impact testing machine, a tensile testing machine and a scanning electron microscope (SEM) were used to analyze the impact strength, tensile strength, bending strength, and micromorphology of the AEDA/E-51 system with different mass ratios. The results show that AEDA is an effective high-temperature curing agent. For the AEDA/E-51 system with the optimal mass ratio of 10:100, the best curing temperature is 92.15°C, and the post-curing temperature is 135.65°C. Furthermore, the apparent activation energy (E_a) of 1670 J/mol, the pre-exponential factor (A) of 3.7 × 10^?4, and the reaction series (n) value of 0.76 are obtained for the AEDA/E-51 system. The impact strength of AEDA/E-51 epoxy resin polymer is 7.82 kJ/m², tensile strength is 14.2 MPa, and bending strength is 18.92 MPa. The micromorphological results of the AEDA/E-51 system are consistent with the results of DSC test and mechanical properties test. Hence, this study provides theoretical support for the practical applications of AEDA as curing agent.     

Investigation of Water-Based Emulsions: Surface and Film-Forming Properties

Summary: In the present study, reaction components such as emulsifiers, emulsifier combinations, and initiators were used for the particle stabilization of water-borne vinyl acetate - butyl acrylate copolymer latexes. The effects of these parameters on the colloidal film-forming properties of the vinyl acetate-co-butyl acrylate latex colloidal, physicochemical, surface, and film forming properties were investigated, in particular the aspect of their surface coating applications.     

含羧基硅氧烷的制备及其固化动力学研究

通过氯丙基甲基硅氧烷与过量的对苯二甲酸的缩合反应制备了一种新型的含羧基硅氧烷(CCS),CCS可以同双酚A型环氧树脂固化,根据Kissinger和Crane方程,用差热分析(DSC)对CCS和环氧树脂组合物的固化性能进行了分析。分析结果表明组合物固化反应的表观活化能为71.41 kJ.mol-1,反应级数为0.911;还给出了加热速度为10℃.min-1时的固化反应方程。     

Dielectric Analysis of Short-Term and Long-Term Curing of Novel Photo-Curing Dental Filling Materials

Highly glass powder filled photo-curing dental filling materials based on acrylic resins are used as an alternative for classical amalgam fillings for almost two decades. To improve the performance of the fillings nowadays nano-particles are introduced in these resins. However, surprisingly less is known about their curing kinetics and how it is affected by the composition of the resin and the kind of the filler. It is shown how the dielectric analysis (DEA) can be used to trace both the short-term photo-curing (Figure 1) as well as the long-term post-curing of such resins when measuring its ion viscosity. Especially if assisted by other thermo-analytical methods the DEA allows for a deeper insight in the processes occurring in the dental filling materials. Long-term measurements over several days using DEA and DMA (dynamic mechanical analysis) exhibit that there are going on significant changes of the properties of the dental material which are relevant for the long-term performance (Figure 2). The DEA is an easy to handle and cost efficient method to investigate the curing kinetic either for dental composite material engineering as well as for quality insurance purposes.