Polystyrene controlled radical polymerization

KINETIC MODELING OF POLYSTYRENE CONTROLLED RADICAL POLYMERIZATION... 

Kinetic Modeling of Polystyrene Controlled Radical Polymerization... 

In this context numerous changes were made. The chapter Properties of Polymers was revised and a new section Correlations of Structure and Morphology with the Properties of Polymers was added. The chapter Characterization of Macromolecules was revised and enlarged. 15 examples have been deleted as they did no longer represent the state of the art and/or were of minor educational value. Several new experiments (plus background text) were added, as, for example controlled radical polymerization - enzymatic polymerization - microemulsions - polyelectrolytes as superabsorbants - hyperbranched polymers - new blockcopolymers - high impact polystyrene - electrical conducting polymers. 

Fig. 4 Reaction scheme for synthesizing cyclic polystyrene using controlled radical polymerization...

Recent investigations in our laboratory involve the controlled radical polymerization of styrene, initiated by dicumyl peroxide 8 in the presence of Tempo [71,72]. Molecular weights are obtained in the range 2500-300000 with narrow polydispersity (Mw/Mn = 1.5). From such capped Tempo polystyrene 9, polysty-rene-6-chloromethylstyrene (PS-6-PCMSty) [171], PS-h-PBd and PS-h-PBd- -PS block copolymers are prepared with Mw = 50000 and Mw/Mn = 1.5 [72] ... 

A considerable number of papers describe the resulting molecules from the pyrolysis of polystyrene [2-26], etc. These studies include pyrolysis in inert conditions, in the presence of various catalysts [4], in the presence of carbon black [27], pyrolysis of H-T and H-H polymers, pyrolysis of polymers with different average molecular weights, pyrolysis of stereoregular polystyrene [28], pyrolysis of polystyrene obtained by controlled radical polymerization in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (stable nitroxide) [29], pyrolysis in the presence of water in subcritical conditions [30], pyrolytic studies for the understanding of large scale processes [31-36], etc. 

Metal-catalyzed living radical polymerizations of vinylpyridines were investigated with the copper-based systems. One of the difficulties in the polymerization is a decrease of catalytic activity imposed by the coordination of the monomers by the metal complex. Controlled radical polymerization of 4-vi-nylpyridine (M-33) was achieved by an initiating system consisting of a strong binding ligand such as L-32 and a chloride-based system [1-13 (X = Cl)/ CuCl] in 2-propanol at 40 °C.214 The Mn increased in direct proportion to monomer conversion, and the MWDs were narrow (MJMn = 1.1 —1.2). In contrast, 2-vinylpyridine (M-34) can be polymerized in a controlled way with chlorine-capped polystyrene as an initiator and the CuCl/L-1 pair in / -xylene at 140 °C.215 Block copolymers with narrow MWDs (Mw/Mn = 1.1 —1.2) were obtained therein. 

Such a controlled radical polymerization can be performed even in the absence of free initiators, where larger amounts of Cu(II) species are added in the system.369 The polystyrene layer obtained from S-3 in the presence of 5 mol % Cu(II) relative to Cu-(I) increased up to 20 nm in thickness, in direct proportion to the Mn of the polymers prepared in the other experiments with ethyl 2-bromopropionate but without surface-confined initiator under similar conditions. For MA, the layer thickness increases up to 60 nm. Block copolymer layers were also prepared by block copolymerization of MA or tBA from the polystyrene. Modification of the hydrophilicity of a surface layer was achieved by the hydrolysis of the poly (styrene-A/oc7c-tB A) to poly (styrene- block-acry lie acid) and confirmed by a decrease in water contact angle from 86° to 18°. 

An azo-type initiator (S-5) can also be attached to the silicon wafer and induces the controlled radical polymerization of styrene in the presence of CuBr2.365 The block copolymerization of MMA from the surface-confined polystyrene macroinitiator was also conducted. 

In 1993, Georges et al. reported on the controlled radical polymerization of St initiated by benzoyl peroxide and mediated by 2,2,6,6-tetramethyl-l-piperidinyl-oxyl (TEMPO), a stable nitroxide radical [38]. TEMPO was able to bond reversibly to the polystyryl chain end and provide polystyrenes with predetermined molecular weights and low polydispersities. Nitroxides used earlier to control radical polymerizations were less successful [37, 57]. Scheme 3 illustrates the mechanism of the St polymerization, using a generalized structure of radical initiator I-I, and details the structure of TEMPO. Although several types of nitrox-... 

Mather, B. D., Lizotte, J. R., and Long, T. E. 2004. Synthesis of chain end functionalized multiple hydrogen bonded polystyrenes and poly(alkyl acrylates) using controlled radical polymerization. Macromolecules 37 9331-9337. 

Currently, ATRP is the most widely used controlled radical polymerization in anion-to-radical transformation methodology. The first such example was reported by Acar and Matyjaszewski [61], and utilized for the preparation of AB- and ABA-type block copolymers. The macroinitiators, PSt and polyisoprene-b-polystyrene (PIP-fc-PSt) containing 2-bromoisobutyryl end groups were prepared by living anionic polymerization and a suitable termination agent. These polymers were then used as macroinitiators for ATRP to prepare block copolymers with methyl acrylate (PSt-b-PMA), butyl acrylate (PSt-b-PBA), methyl... 

The kinetic modeling of styrene controlled radical polymerization, initiated by 2,2 -asobis(isobutimitrile) and proceeding by a reversible ehain transfer meeha-nism was carried out and accompanied by addition-fragmentation in the presenee dibenzyltiitiocarbonate. An inverse problem of determination of the unknown temperature dependences of single elementary reaction rate eonstants of kinetic scheme was solved. The adequacy of the model was revealed by comparison of theoretical and experimental values of polystyrene molecular-mass properties. The influence of process controlling factors on polystyrene molecular-mass properties was studied using the model. 

The kinetic model developed in this research allows an adequate description of molecular-mass properties of polystyrene, obtained by controlled radical polymerization, which proceeds by reversible chain transfer mechanism and accompanied by addition-fragmentation. This means, that the model can be used for development of technological applications of styrene RAFT-polymerization in the presence of trithiocarbonates. 

Controlled radical polymerization Dibenzyltritiocarbonate Mathematical modeling Polystyrene... 

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