Thermal polymerization kinetics

Figure 22 includes the temperature dependent polymerization rates (1), (2) and (3). The thermal polymerization kinetics (1), they — (2), and the UV photopolymerization kinetics (3) have been investigated by the method of diffuse reflection spectroscopy and other methods The activation energy of the thermal reactions (2) and (3) following the photoinduced dimerization processes, (150 + 30) meV, is appreciable lower than those of the dimer DR intermediates. However, the processes which dominate the polymerization reaction are determined not by the short diradicals with n 6 but by the long chains with n 7, which all have a carbenoid DC or AC structure. The discrepancy of the activation energies therefore may be due to the different reactivities of the diradical and carbenoid chain ends. The activation energies of the thermal addition reactions of the AC and DC intermediates at low temperatures have not been determined and therefore a direct comparison with those of the diradicals is not possible. 

E. Botines, L. Franco, X. Ramis, J. Puiggali, Synthesis of poly(glycolic acid-alt-12-aminododecanoic acid) the thermal polymerization kinetics of sodium V-chloroacetyl-12-aminododecanoate, J. Polym. Sci.A Poly. Chem. 44 (2006) 1199-1213. 

Thermal polymerization kinetics that obey the Diels-Alder mechanism were studied. Expressions for rate of propagation and molecular weight were derived. The rate of propagation varies as the cube of monomer concentration. Subcritical damped oscillations can be expected under certain conditions. Reaction in a circle representation of free radical reactions was used to analyze the stability of reactions. Oscillations in concentration were discussed for systems of three and four reactions in a circle and the results generalized to n reactions in a circle. 

Most published studies relate only to isothermal experiments. Hence, in order to make such comparisons we modified our computations to assume isothermal conditions. Figure 11 compares our kinetic model with data by Hui and Hamielec for styrene thermal polymerization at 1A0°C. Figure 12 compares out kinetic model with data by Balke and Hamielec (7) for MMA at 90 C using 0.3 AIBN. Figure 13 compares our kinetic model with data by Lee and Turner ( ) for MMA at 70°C using 2% BPO. Our model compares quite favorably with these published experiments. The percent error was less than S% in most of the ranges of conversions. 

Nair et al. studied the kinetics of the polymerization of MMA at 60-95 °C using N,1SP-diethyl-NjW-di(hydroxyethyl)thiuram disulfide (30a) as the thermal in-iferter [142]. The dependence of the iniferter concentration on the polymerization rate was examined. The chain transfer constant of the propagating radical of MMA to 30a was determined to be 0.23-0.46 at 60-95 °C, resulting in the activation energy of 37.6 kj/mol for the chain transfer. Other derivatives 30b-30d were also prepared and used to derive telechelic polymers with the terminal phosphorus, amino, and other functional aromatic groups [143-145]. Thermal polymerization was also investigated with the end-functional poly(St) and poly(MMA) which were prepared using the iniferter 13 [146]. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

The effect of the nitrone stmcture on the kinetics of the styrene polymerization has been reported. Of all the nitrones tested, those of the C-PBN type (Fig. 2.29, family 4) are the most efficient regarding polymerization rate, control of molecular weight, and polydispersity. Electrophilic substitution of the phenyl group of PBN by either an electrodonor or an electroacceptor group has only a minor effect on the polymerization kinetics. The polymerization rate is not governed by the thermal polymerization of styrene but by the alkoxyamine formed in situ during the pre-reaction step. The initiation efficiency is, however, very low, consistent with a limited conversion of the nitrone into nitroxide or alkoxyamine. 

In Vienna, Mark published a number of fundamental papers. Their topics include polymerization mechanism (46, 47, 48), thermal polymerization (49, 50), polymerization kinetics (51), the effect of oxygen on polymerization (52), and measurement of molecular weight distribution (53). Guth and Mark expanded their modeling of extended and balled thread molecules to include rubber. The result of their studies was a series of very important papers in which the thermal effect on expansion and relaxation of rubber is explained (54, 55, 56). 

In order to tailor the physical properties of the polyaromatic networks obtained by thermal curing, it is important to ascertain the relationship between structure and physical properties for both the starting oligomer and its resultant network. We therefore sought a reactive group whose mechanism of thermal initiation, kinetics, and thermodynamics of polymerization are known. 

Any study of the polymerization kinetics of a bisbenzocyclobutene monomer is complicated by the lack of understanding of the resulting polymer s structure and the fact that as the polymerization proceeds, the reaction mixture crosslinks and vitrifies. This vitrification limits somewhat the number of quantitative methods which can be used to study the bisbenzocyclobutene polymerization kinetics. Some techniques are however useful under these constraints and good kinetic results have been obtained by both infrared and thermal analysis methods. 

Attempts to elucidate the polymerization or copolymerization kinetics of ethynyl and maleimide-functionalized monomers have been undertaken via vibrational spectroscopy (137). The thermal polymerization of A-(3-ethynyl-phenyl) maleimide (the structure is given in Fig. 48) was studied via IR and Raman spectroscopy. This model compound is interesting because it carries maleimide and ethynyl groups attached to the same aromatic ring. Kinetic studies indicate that both the acetylene and maleimide group react at the same rate, which strongly suggests the formation of a copolymer rather than a mixture of homopolymers. 

The thermal and kinetic models discussed above are the basis for determining the processing conditions for reactive processing by ionic polymerization,29 addition polymerization, vulcanization of rubbers and radical polymerization, although in the latter case additional assumptions of a constant initiation rate and a quasi-stationary concentration of radicals are made.89 These models can also be used to solve optimization problems to improve the performance and properties of end-products. 

The mechanism by which emulsifiers could influence the rate of the thermal initiation reaction is obscure. Most probably the emulsifiers increase the efficiency with which one of the radicals produced in the thermal initiation process escapes into the aqueous phase so that emulsion polymerization may begin. If so those emulsifiers for which exchange between the micelle or the adsorbed layer on a latex particle and true solution in the aqueous phase is most rapid should be most effective in promoting the thermal polymerization. Recently the kinetics of micellization has attracted much attention (29) but the data which is available is inadequate to show whether such a trend exists. 

The thermal polymerization of /3-carboxymethyl caprolactam results in a novel polyimide which has been identified as a poly(2,6-dioxo-l, 4-piperidinediyl)trimethylene. The formation of this structure is explained by a mechanism that consists in an initial isomerization of the caprolactam derivative to 3-(3-aminopropyl)glutaranhydride or its linear dimer and subsequent polymerization by condensation involving the terminal amino group and the anhydride moiety. Suggested reaction schemes and corresponding kinetic equations are based upon the premise that the extent of polymerization is represented by the concentration of imide linkages. Results of rate studies carried out at 210°-290°C. support the proposed mechanism. 

In conclusion, the results of our study indicate that the principal features of the formation of poly (2,6-dioxo-l,4-piperidinediyl) trimethylene by thermal polymerization of / -carboxymethyl caprolactam consists in an initial isomerization of the caprolactam derivative to a reactive species and subsequent polymerization of the latter by condensation. The reactive intermediate is in all probability either or both the 3-(3-aminopropyl)-glutaranhydride or its linear dimer. Both the conversion of the lactam by isomerization and the polycondensation follow second-order kinetics. 

Ballard and Van Lienden 16) showed that irradiation of Zr(CH2Ph)4 solutions in the presence of vinyl monomer increased the rate of thermal polymerization by a factor of four. Kinetic rate data suggested that the mechanism of styrene polymerization was wavelength dependent. For... 

Eqs. (1) to (3) indicate that conversion studies under conditions where thermal polymerization prevails can only yield e and the product nyo, whereas the photon-induced reaction provides information on the product nq. To disentangle chain initiation and chain propagation effects an independent determination of the kinetic chain length is required. 

Representative for systems exhibiting sigmoidal conversion curves Fig. 1 shows experimental results for the rate constant of the reaction of TS, evaluated from thermal and y-polymerization data according to K = (1 — X) dX(t)/dt, and normalized to the rate constant in the low conversion limit. It is obvious, that at low conversion K depends on X, contrary to what is to be expected for a simple first order reaction. The functional form of KPC) is different for the two modes of polymerization. The overall increase of K with increasing X reveals an autocatalytic reaction enhancement. A measure for its efficiency is the ratio K(X = 0.5)/K(X = 0) which tirnis out to be about 200 for TS under thermal polymerization conditions. This effect is often observed with disubstituted diacetylenes albeit with different kinetic... 

ESR (electron spin resonance) and optical absorption spectroscopy at low temperatures were used to analyse the individual reaction steps of the optical and thermal polymerization reactions and their kinetics. The reaction steps are the photoinitiation, the chain propagation and chain termination reactions. 

It appears that the reaction mechanism and the intermediates involved in the solid-state polymerization of diacetylenes are reasonably well understood. However, experimental results obtained with special monomers should not be generalized. It is not possible to design a monomer with desired properties. Inspection of Table 1 shows that on the basis of the crystallographic data and the monomer packing the absolute reactivity and the polymerization kinetics caimot be quantitatively predicted, e.g. it is not possible, to date, to explain why certain diacetylenes can be polymerized thermally whereas others with equal packing are thermally inactive. A more realistic kinetic model should include the various energy transport processes and the complex side group motions which are connected to the reaction. 

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