The Effect of Intramolecular Transfer to Polymer on Stationary Free Radical Polymerization of Alkyl Acrylates

Nikitin, A. N.; Hutchinson, Robin A.

doi:10.1021/ma048361c

Cited by 117 publications

(133 citation statements)

References 33 publications

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“…In the meantime it appears The values α s > 1 found in BA and DA polymerization via the RAFT techniques (see Table 1) presumably result from a significant contribution of MCR self-and cross-termination at the higher temperatures of these experiments. The most likely mechanism here is as follows: MCRs are characterized by significantly slower termination than SPRs, [8,13] which means that as MCRs form, the overall termination rate is naturally lowered. This expresses itself as stronger reduction in overall k t with time than that due to increase of SPR chain length alone, meaning that an anomalously high α s is returned -one that reflects both the decrease of k t i,i with SPR chain length and the conversion of some SPRs into more slowly terminating MCRs.…”

Section: Discussionmentioning

confidence: 99%

“…Most studies have concentrated on butyl acrylate (BA), [1][2][3][4][5][6][7][8][9][10][11][12][13] with this monomer being taken as typical of the entire family. Understanding of the polymerization kinetics of acrylate-type monomers is important not just for scientific reasons, but also because the industrial importance of these monomers makes it essential that their kinetic behavior can be well modeled.…”

Section: Introductionmentioning

confidence: 99%

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Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

Buback

Russell

et al. 2011

Macro Chemistry & Physics

147

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SUMMARY:The technique of SP PLP EPR, which is single-pulse pulsed-laser polymerization (SP PLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain-end) radical termination of acrylates. Measurements are performed on methyl acrylate, n-butyl acrylate and dodecyl acrylate in bulk and in toluene solution at -40 °C. The reason for the low temperature is to avoid formation of mid-chain radicals, a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite-model behavior for chain-length-dependent termination rate, is found in this work. However, lower and more reasonable values of α s , the exponent for variation of k t i,i at short chain lengths, are found in the present study.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

Buback

Russell

et al. 2011

Macro Chemistry & Physics

147

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“…A decrease of the effective propagation rate with decreasing monomer content induced by transfer reactions is reflected by a reaction order with respect to monomer concentration that exceeds unity, as was demonstrated by Nikitin and Hutchinson on the example of butyl acrylate polymerization. 34 The formation of MCR and thus the change in effective propagation rate over the course of the reaction may hence be taken into account by utilizing the monomer reaction order x, which approach had been used in the framework of the RAFT-CLD-T (RAFT-Chain Length Dependent-Termination) methodology for the determination of chain-length dependent termination rate coefficients in dodecyl acrylate polymerization. 66 Empirically, the overall polymerization rate may be described by eq.…”

Section: Effective Propagation Rate Coefficientsmentioning

confidence: 99%

The role of mid‐chain radicals in acrylate free radical polymerization: Branching and scission

Junkers

Barner‐Kowollik

2008

J. Polym. Sci. A Polym. Chem.

213

326

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The past 5 years have seen a significant increase in the understanding of the fate of so‐called mid‐chain radicals (MCR), which are formed during the free radical polymerization of monomers that form highly reactive propagating radicals and contain an easily abstractable hydrogen atom. Among these monomers, acrylates are, beside ethylene, among the most prominent. Typically, a secondary propagating acrylate‐type macroradical (SPR) can easily transfer its radical functionality via a six‐membered transition state to a position within the polymer chain (in a so‐called backbiting reaction), creating a tertiary MCR. Alternatively, the radical function can be transferred intramolecularly to any position within the chain (also forming an MCR) or intermolecularly to another polymer strand. This article aims at providing a comprehensive overview of the up‐to‐date knowledge about the rates at which MCRs are formed, their secondary reactions as well as the consequences of their occurrence under variable reaction conditions. We explore the latest aspects of their detection (via electron spin resonance spectroscopy) as well as the characterization of the polymer structures to which they lead (via high resolution mass spectrometry). The presence of MCRs leads to the formation of branched polymers and the partial formation of polymer networks. They also limit the measurement of kinetic parameters (such as the SPR propagation rate coefficient) with conventional methods. However, their occurrence can also be used as a synthetic handle, for example, the high‐temperature preparation of macromonomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7585–7605, 2008

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“…For acrylates, this reaction occurs at mild conditions, even at 0°C [46,47], and leads to very high SCB levels (8-12 branches per 100 repeat units) under starved-feed conditions at 140°C [48]. Due to the slower addition of monomer to the midchain radicals (Scheme 1b), the observed rates of acrylate polymerization [45,48,49] are significantly lower than would be expected from the chain-end propagation rate coefficient (k p ) measured by pulsed laser polymerization (PLP) [50]. The backbiting rate coefficient (k bb ) and its temperature dependence has been evaluated by various techniques, including analysis of short-chain branching frequency [46,48], and by specialized pulsed-laser techniques which also provide an estimate of the rate at which a monomer adds to midchain radicals [51].…”

Section: Backbiting and Chain B-scissionmentioning

confidence: 99%

“…More recently, the termination kinetics of BA chain-end and midchain radicals has also been investigated using PLP techniques [47]. Thus, the effect of acrylate midchain radical reactions (their formation by backbiting and their subsequent propagation and termination) on the polymerization rate under mild conditions (e.g., <80°C) is now well understood [45,49,52]. At higher temperatures the midchain radicals formed by backbiting not only can propagate and terminate, but can undergo b-scission to produce a terminally-unsaturated polymer chain (a macromonomer), and a chain-end radical [31,53] …”

Section: Backbiting and Chain B-scissionmentioning

confidence: 99%

Free‐Radical Acrylic Polymerization Kinetics at Elevated Temperatures

Wang

Hutchinson

2010

Chem Eng & Technol

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Free-radical acrylic homo-and copolymerization kinetics are reviewed, focusing on secondary reactions that impact the polymerization rate and polymer molecular weight (MW) under industrially-relevant synthesis conditions. Dependent on the monomer type (acrylate, methacrylate, styrene), mechanisms that must be considered include chain-end depropagation, monomer self-initiation, formation and reaction of midchain radicals, and incorporation of macromonomers formed by b-scission of midchain radicals. The relative importance of these reactions varies with temperature and, for copolymerization, monomer composition. A comprehensive treatment of these complexities has been completed for polymerizations conducted up to 180°C, but further work is required to extend the applicability of the model to even higher temperatures. IntroductionThe production of low-density polyethylene and associated copolymers at 200-300°C and high pressure is perhaps the bestknown example of high-temperature free-radical polymerization (FRP). However, an increasing number of acrylic resins, produced from a mixture of monomers selected from the methacrylate, acrylate, and styrene families, are also manufactured under higher temperature conditions (>120°C) in homogeneous solution. Low-molecular-weight acrylic resins are the base polymer components for many automotive coatings due to their excellent resistance to chemicals, solvents, ultraviolet light, and abrasion, as well as their exterior durability after crosslinking on the surface of the vehicle [1]. High-temperature conditions are used to produce a variety of other materials for coatings, adhesives, and paints [2]. These conditions are chosen to increase production rates and to decrease (or eliminate) the solvent employed in the formulation while maintaining reasonable solution viscosity [2][3][4].While commercially advantageous, the high polymerization temperatures greatly promote the occurrence of secondary reactions that have a strong impact on polymerization rate and polymer MW, such as monomer self-initiation, chain depropagation, and the formation and subsequent reaction of midchain radicals and unsaturated polymer chains (macromonomers). These reactions occur in addition to the well-known and well-understood set of basic FRP mechanisms consisting of initiation, propagation, termination, and chain transfer [5,6]. This article provides an overview and summarizes recent experimental and modeling efforts by our group and other researchers to improve the understanding of these mechanisms. As most high-temperature acrylic polymerization processes involve multiple monomers, the complexities of including these reactions in copolymerization will also be addressed. An accurate treatment of high-temperature FRP kinetics is a critical component of larger-scale process models used to predict the influence of the operating conditions on reaction rate and polymer properties, guide the selection and optimization of standard operating conditions for existing and new polymer grades, and guide process ...

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The Effect of Intramolecular Transfer to Polymer on Stationary Free Radical Polymerization of Alkyl Acrylates

Cited by 117 publications

References 33 publications

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

The role of mid‐chain radicals in acrylate free radical polymerization: Branching and scission

Free‐Radical Acrylic Polymerization Kinetics at Elevated Temperatures

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