Acrylic polymerization model

Acrylic Polymerization Model. Acrylic polymers are known to have excellent weathering and functional properties as binders for coatings, and they are widely used in the coatings as well as many other industries. To obtain the desirable property/cost balance, random copolymers instead of blends of homopolymers are frequently used. 

Our acrylic polymerization model was developed to meet the need for solving these problems. Kinetics used are based on fairly well accepted and standard free radical polymerization mechanisms. 

Application of the Solvent Formulation System. In contrast to the acrylic polymerization model discussed previously which is extremely complex mathematically and computation wise the solvent formulation system is a growing collection of models which are much less complex mathematically and computation wise. However, the system does allow one to evaluate many properties of solvent blend quickly and with relative ease. The system has been found to be valuable in ... 

The author would like to acknowledge the help provided by Dr. R. G. Lindsey 1n the preparation of this paper by sharing h1s experience 1n the development and application of the acrylic polymerization model. He would also like to thank the E. I. Du Pont De Nemours Co. for permission to publish this paper. 

Acrylic polymerization model capability, 172,173f description, 172... 

Reactivity ratios between acrylated lignin model compound (Fig. 2), defined as Mi, with either MM A or S, defined as M2, were determined experimentally in accordance with standard procedures (15). These involve mixing two different vinyl monomers in various molar ratios with catalyst (i.e., benzoyl peroxide) and solvent, heating the mixture to achieve polymerization, and recovering the polymer by the addition of non-solvent, and centrifugation. The respective molar monomer fractions of the copolymer were determined by UV-spectroscopy in the cases where MMA served as M2, and by methoxyl content analysis in those cases in which S was the M2-species. The results were subjected to numerical treatments according to the established relationships of Kelen-Tiidos (17) and Yezrielev-Brokhina-Roskin (YBR) (18), and this is described elsewhere (15). 

The above example gives us an idea of the difficulties in stating a rigorous kinetic model for the free-radical polymerization of formulations containing polyfunctional monomers. An example of efforts to introduce a mechanistic analysis for this kind of reaction, is the case of (meth)acrylate polymerizations, where Bowman and Peppas (1991) coupled free-volume derived expressions for diffusion-controlled kp and kt values to expressions describing the time-dependent evolution of the free volume. Further work expanded this initial analysis to take into account different possible elemental steps of the kinetic scheme (Anseth and Bowman, 1992/93 Kurdikar and Peppas, 1994 Scott and Peppas, 1999). The analysis of these mechanistic models is beyond our scope. Instead, one example of models that capture the main concepts of a rigorous description, but include phenomenological equations to account for the variation of specific rate constants with conversion, will be discussed. 

Lauryl acrylate polymerizations initiated by a photo-activated mixture of benzoin butyl ethers (Trigonal 14) were performed in Perkln-Elmer model DSC-IB and DSC-2 apparata modified by attachment of a heat-filtered medium pressure mercury lamp. Within specified variable limits, the rate of polymerization may be approximated by the relation Rp = const. 0.55 q0.35 2m]. 6 -316/T I js light intensity C is initiator concentration CM] is monomer concentration T is absolute temperature. 

In total, alkoxyamine systems with large cleavage (activation) rate constants tend to show small coupling (deactivation) rate constants. This provides large equilibrium constants that increase the conversion rates. It must not deteriorate the control since this depends on kd and the product k kc. In comparison, the more recently introduced nitroxides 6, 8, and 9 provide larger equilibrium constants than e.g. 3 (TEMPO). For acrylate-derived radicals, the equilibrium constants are usually smaller than for styryl type radicals, and this may, at least in part, explain the failure of TEMPO-regulated acrylate polymerizations. However, judging from model studies,62-63 this reason does not apply for methacrylates. 

Development of the theoretical basis for the dense-cross-linked systems formation stimulated a new wave of (meth)acrylates polymerization investigations, which were carried out in the 1980s. The results of these studies showed that in all cases experimentally determined regularities are in good agreement with the model prognosis and allow essentially to detail and support this model. 

Fig. 22. Generated monomeric, dimeric, and polymeric model radicals of (meth)acrylates, (From Ref. 50, with permission.)...

PLP-SEC and (iii) single-pulse pulsed-laser polymerization coupled with online time-resolved electron-spin resonance spectroscopy (SP-PLP-EPR). The propagation rate coefficient for MCRs may be obtained via ft-PLP-SEC and SP-PLP-EPR. Termination rate coefficients kt , and kt are only accessible from SP-PLP-EPR," in which different types of radicals can simultaneously be traced as a function of time. Remaining kinetic coefficients can then be obtained via computer modeling. Table 1.5 collates kinetic coefficients for butyl acrylate polymerization as an example. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

Other commercially relevant monomers have also been modeled in this study, including acrylates, styrene, and vinyl chloride.55 Symmetrical a,dienes substituted with the appropriate pendant functional group are polymerized via ADMET and utilized to model ethylene-styrene, ethylene-vinyl chloride, and ethylene-methyl acrylate copolymers. Since these models have perfect microstructure repeat units, they are a useful tool to study the effects of the functionality on the physical properties of these industrially important materials. The polymers produced have molecular weights in the range of 20,000-60,000, well within the range necessary to possess similar properties to commercial high-molecular-weight material. 

The lanthanocene initiators also polymerize EtMA, PrMA and BuMA in a well-controlled manner, although syndiotacticity decreases as the bulk of alkyl substituent increases. Reactivity also decreases in the order MMA EtMA > PrMA > BuMA. Chain transfer to provide shorter polymer chains is accomplished by addition of ketones and thiols.460 The alkyl complexes (190) and (191) also rapidly polymerize acrylate monomers at 0°C.461,462 Both initiators deliver monodisperse poly(acrylic esters) (Mw/Mn 1.07). An enolate is again believed to be the active propagating species since the model complex (195) was also shown to initiate the polymerization of MA. 

Indeed, the above results seem to point toward a free radical mechanism. Sen and coworkers [60] studied a model copper complex (Fig. 13) and concluded that the polymerization proceeds via a free radical mechanism (Scheme 7) and that the copper complex/MAO system is in fact a new example of a redox free radical generator, in which the role of MAO is to reduce copper(II) to copper completing the redox cycle. This rationale also offers a simple explanation for the observation that very high excesses of MAO are required for the ethylene/acrylate copoly -... 

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