Time-temperature transformation (TTT) cure diagram of an unsaturated polyester resin

The curing of an unsaturated polyester resin was studied by differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), and Fourier-transform infrared spectroscopy (FTIR). The results are presented in the form of a time-temperature-transformation (TTT) diagram. The kinetic analysis was performed by means of the dynamic Ozawa method. This analysis was used to determine the curing times (t) at various conversions (α) and temperatures (T) (isoconversional lines ln t = A + E/RT). The equivalence of the Ozawa method and the isothermal isoconversional adjustment ln t = A + E/RT were demonstrated. The relationship between the glassy transition temperature (T_g) and the conversion α was determined by DSC. It was established that this relationship is one-to-one and independent of mass, initiation system, and curing temperature (T_c). The T_g-α relationship was adjusted using the DiBenedetto equations and heat capacity data. Using the T_g-α relationship and the isoconversional lines, the vitrification curve was determined and it was observed that the vitrification times obtained are consistent with those obtained experimentally when T_c = T_g. Gelation was determined by TMA, the material being considered gelled when it reached sufficient mechanical stability for the TMA measuring probe to become embedded in it. At that moment the conversion reached was determined by DSC. It was seen that the material always gels at constant conversion, regardless of the curing temperature. The gelation line (gel times) were traced from the corresponding isoconversional line. © 1997 John Wiley & Sons, Inc.     

Fundamental studies of grafting reactions in free radical copolymerization. I. A detailed kinetic model for solution polymerization

Graft site initiation occurs by primary radical and/ or polymeric radical attack on the back-bone polymer. The controlling mechanism is determined by the structure of the backbone and the activity of the free radicals. The efficiency of incorporating monomer into the graft chains depends upon the graft site initiation mechanism and the mode of polymer chain termination (recombination or disproportionation). A kinetic analysis results a series of uniquely different expressions describing the graft efficiency, ? corresponding to different combinations of graft site initiation and chain termination mechanisms. The dependency of ? upon monomer, initiator, and backbone concentrations is different from case to case. The complete kinetic model is capable of predicting reaction rate, graft efficiency, graft frequency, graft ratio, and molecular weight averages and distributions. Simulations are provided to compare predicted results with experimental data for two different systems which show contrasting mechanisms of graft site initiation and mode of termination. © 1995 John Wiley & Sons, Inc.     

Curing theory of Af- Ag type free radical polymerization (III)

Evaluation of defects in the polymer network is important to characterize the polymer materials, in which there always exist the defects that affect the physical and chemical properties of polymer network. Taking A_f- A_g type nonlinear free radical polymerization as an example, one type of defects called dangling loops in the gel network is investigated by means of the statistical theory of polymeric reactions. The number of dangling loops and the probability of its formation are obtained by analyzing the polymer network structure in detail.     

Comparative study of kinetics and reactivity indices of free radical polymerization reactions

Density functional theory calculations are used to determine the kinetics and reactivity indices of the first propagation steps of the polyethylene and poly(vinyl chloride) polymerization. Transition state theory is applied to evaluate the rate coefficient from the microscopically determined energies and partition functions. A comparison with the experimental Arrhenius plots validates the level of theory. The ability of reactivity indices to predict certain aspects of the studied propagation reactions is tested. Global softnesses of the reactants give an indication of the relative energy barriers of subsequent monomer additions. The correlation between energy and hardness profiles along the reaction path confirm the principle of maximum hardness. Local indices predict the regioselectivity of the attack of the growing radical to vinyl chloride. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

BMD/UP体系非等温固化动力学研究

不饱和聚酯是最常用的一种热固性材料,其力学性能和耐热性是较受关注的两个方面,利用双马来酰亚胺作为第二组分对不饱和聚酯进行耐热改性的工作取得了较好的效果。研究其动力学过程对于固化反应温度、时间等工艺合理优化控制,制备高性能复合材料具有重要意义。考虑到BMD／UP体系中反应的复杂性,本文采用n级动力学模型,进行了非等温动力学研究。     

Synthesis and kinetic analysis of DPE controlled radical polymerization of MMA

The 1,1‐diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k₂, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10^?5 s^?1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006     

Low viscous unsaturated polyester resin for monomer free UP-resins

It was possible to develop comonomer free unsaturated polyester resins for the application in electrical industry. By testing model compounds and mixtures of model compounds it was possible to find the optimised structure of the resin molecule with respect to the position of the copolymerizable double bonds. By choosing the proper composition of the other components of the resin, e.g. the glycols and modifying dicarboxylic acids, it was also possible to manufacture low viscous resins.     

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     

Modeling the free radical polymerization of acrylates

Acrylates have gained importance because of their ease of conversion to high‐molecular‐weight polymers and their broad industrial use. Methyl methacrylate (MMA) is a well‐known monomer for free radical polymerization, but its α‐methyl substituent restricts the chemical modification of the monomer and therefore the properties of the resulting polymer. The presence of a heteroatom in the methyl group is known to increase the polymerizability of MMA. Methyl α‐hydroxymethylacrylate (MHMA), methyl α‐methoxymethylacrylate (MC₁MA), methyl α‐acetoxymethylacrylate (MAcMA) show even better conversions to high‐molecular‐weight polymers than MMA. In contrast, the polymerization rate is known to decrease as the methyl group is replaced by ethyl in ethyl α‐hydroxymethylacrylate (EHMA) and t‐butyl in t‐butyl α‐hydroxymethylacrylate (TBHMA). In this study, quantum mechanical tools (B3LYP/6‐31G*) have been used in order to understand the mechanistic behavior of the free radical polymerization reactions of acrylates. The polymerization rates of MMA, MHMA, MC₁MA, MAcMA, EHMA, TBHMA, MC₁AN (α‐methoxymethyl acrylonitrile), and MC₁AA (α‐methoxymethyl acrylic acid) have been evaluated and rationalized. Simple monomers such as allyl alcohol (AA) and allyl chloride (AC) have also been modeled for comparative purposes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Kinetics of radical polymerization of dimethylphenyl methacrylates

The kinetics of free radical polymerization of all six existing isomeric dimethylphenyl methacrylates were studied in bulk at 60°C, initiated by dilauroyl peroxide, using dilatometry. The different polymerization rates observed, resulting from the different monomer structures, are discussed in terms of steric and other effects, considering also the previous results for tolyl methacrylates. © 1993 John Wiley & Sons, Inc.     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.     

Sequential photodecomposition of bisacylgermane type photoinitiator: Synthesis of block copolymers by combination of free radical promoted cationic and free radical polymerization mechanisms

A block copolymer of cyclohexene oxide (CHO) and styrene (St) was prepared by using bifunctional visible light photoinitiator dibenzoyldiethylgermane (DBDEG) via a two‐step procedure. The bifunctionality of the photoinitiator pertains to the sequential photodecomposition of DBDEG through acyl germane bonds. In the first step, photoinitiated free radical promoted cationic polymerization of CHO using DBDEG in the presence of diphenyliodonium hexafluorophosphate (Ph₂I⁺PF) was carried out to yield polymers with photoactive monobenzoyl germane end groups. These poly(cyclohexene oxide) (PCHO) prepolymers were used to induce photoinitiated free radical polymerization of styrene (St) resulting in the formation of poly(cyclohexene oxide‐block‐styrene) (P(CHO‐b‐St)). Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as NMR, IR, and DSC spectral measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4793–4799, 2009     

Kinetic analysis of styrene atom transfer radical polymerization: Extraction of radical‐radical termination rate coefficients

Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical‐radical termination rate coefficients (<k_t>). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical‐radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, <k_t> values of approximately 2 × 10⁸ L mol^?1 s^?1 at 110 °C in 50 vol % anisole were determined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5548–5558, 2004     

Simulation and analysis of free radical branching copolymerization kinetics

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Macrothiuram disulfide for the free radical synthesis of PDMS-vinyl triblock copolymers. I. Syntheses and polymerization kinetics

PDMS-based macrothiuram disulfides of different molecular weights capable of being used as macro-thermal iniferters towards deriving PDMS-containing triblock copolymers were synthesized and characterized. The synthesis of ω-(secondary amine)-terminated PDMS were accomplished by the hydrosilylation reaction of silyl hydride terminated PDMS with allyl-N-methylamine. Macroamines were eventually transformed to macroiniferters by the thiocarbamylation reaction and oxidative coupling. Kinetics of polymerization studied in the case of MMA and styrene in bulk, and as in toluene solution in case of MMA, revealed that the macroiniferters are as efficient as their microanalogues from the point of view of their initiating and chain-terminating properties. The different kinetic parameters were determined and discussed. © 1993 John Wiley & Sons, Inc.     

Activity of the furfuryl ring in the free radical polymerization of acrylic monomers

The effect and the participation of the furfuryl ring, in particular the hydrogen at position C-5 in the free radical polymerization are analyzed following the polymerization of furfuryl acrylate (FA) and furfuryl methacrylate (FM) initiated by AIBN under photochemical activation. The results obtained indicate that the polymerization of FA deviates from the classical free radical kinetic scheme, giving rise to crosslinked polymers even at a degree of conversion lower than 7%. This behavior is well explained taking into consideration the participation of the furfuryl ring which acts as a degradative transfer agent. This was demonstrated by the kinetic analysis of the free radical polymerization of MMA initiated by the thermal decomposition of AIBN in the presence of different concentrations of furfuryl acetate. © 1996 John Wiley & Sons, Inc.     

Kinetics of thermoset cure and polymerization in the glass transition region

A theoretical approach to thermoset cure kinetics based on Arrhenius kinetics and mobility was developed by considering the activation of the reacting group and chain mobility as elementary steps for reaction. This extended kinetic equation was successfully applied to the curing of an epoxy by an amine, the trimerization of a cyanate, and to the polymerization of methyl methacrylate. Full agreement between theory and experimental data was obtained in all cases. The activation energies for chain mobility were exceptionally low (0.3–1 kJ/mol for bisphenol-A-based epoxy and cyanate) which indicates that the structural units must undergo only small-angle rotational oscillations to allow a reaction. A theoretical time–temperature–transformation (TTT) diagram is also presented. © 1993 John Wiley & Sons, Inc.     

Curing theory of A f -A g type free radical polymerization (I)

By means of polymer statistical theory, the sol fraction and the gelation condition of A _f -A _g type nonlinear free radical polymerization are obtained by introducing the probabilities with respect to initiation and chain addition. With Lagrange expansion theorem, the equilibrium number fraction distribution of A _f -A_g type is obtained, and its invariant property is proved. Moreover, the evaluation of average polymer quantities for post-gel regime is simplified by this invariant property. Project supported by the National Natural Science Foundation of China (Grant No. 29673018), and the Ph.D.-funds of the State Education Commission of China.