Styrene/CO copolymerisation

Unlike ethene, the largely predominant path to chain termination in styrene/CO copolymerisation consists of a fast p-hydrogen elimination from the last inserted... 

A more recent in situ P H HP NMR study of styrene/CO copolymerisation by the same [(R,S)-BINAPHOS]Pd-acyl complex applying both diffusion-controlled (non-spinning sapphire NMR tube) and reaction-controlled (flow NMR cell) conditions has provided evidence for other intermediate species as well as information on the relative rates of CO insertion into isomeric Pd-acyls [6b, 7gj. Figure 7.15... 

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has contributed remarkably to unravelling the termination and initiation steps of the styrene/CO copolymerisation catalysed by the highly active bis-chelated complex [Pd(bipy)2](Pp5)2 in TFE [40]. Chain-end group analysis of the material produced in the absence of BQ showed that the termination by P-H elimination is accompanied by three different initiators two palladium alkyls from Pd-H formed by reaction of the precursor with CO and water (a and b) and a palladium carboalkoxy species formed by reaction of the precursor with the fluorinated alcohol and CO (c) (Chart 7.4). The suppression of the chain-transfer by alcoholysis was proposed to be responsible for the enhanced stability of the palladium acyl intermediates and hence for the high molecular weight of the copolymers produced. 

The most common alkenes employed in the Pd-catalysed synthesis of alternating polyketones are ethene, styrene, propene and cyclic alkenes such as norbomene and norbornadiene. Even though the mechanism does not vary substantially with the alkene, the reactions of the various co-monomers are here reported and commented on separately, starting with the ethene/CO copolymerisation, which is still the most studied process. As a general scheme, the proposed catalytic cycles are presented first, then the spectroscopic experiments that have allowed one to elucidate each single mechanistic step. 

The general mechanistic features of the ethene/CO copolymerisation cycle (Scheme 7.2) are substantially valid also for styrene. In particular, the propagation steps are similar for both alkenes and consist of subsequent alternated migratory insertions of alkyl to CO and of acyl to olefin, with P-chelate and y-chelate resting states. The structures of the first intermediates in the syndiotactic copolymerisation of styrene derivatives with CO have been determined by an in situ NMR study using [(Pr DAB)Pd(Me)(NCMe)]BAr4 as precursor (Scheme 7.21) [38]. 

The mechanism of propene/CO copolymerisation by palladium catalysis is essentially analogous to those of ethene and styrene (i. e., chain propagation proceeds via alternating insertions of CO into Pd-alkyl and alkene into Pd-acyl controlled by p-chelates) [1]. 

Several types of bidentate ligands, different from diphosphines, for example bipyridines and phenantrolines, have been proven to give active catalysts, particularly in the CO-styrene copolymerisation [25], but, particularly with ethene, diphosphines give higher performances. 

Iggo and coworkers have studied the asymmetric copolymerisation of styrene with CO catalyzed by Pd-(R,S)-BINAPHOS complexes under both diffusion- and... 

Coordination polymerisation via re complexes comprises polymerisation and copolymerisation processes with transition metal-based catalysts of unsaturated hydrocarbon monomers such as olefins [11-19], vinylaromatic monomers such as styrene [13, 20, 21], conjugated dienes [22-29], cycloolefins [30-39] and alkynes [39-45]. The coordination polymerisation of olefins concerns mostly ethylene, propylene and higher a-olefins [46], although polymerisation of cumulated diolefins (allenes) [47, 48], isomerisation 2, co-polymerisation of a-olefins [49], isomerisation 1,2-polymerisation of /i-olcfins [50, 51] and cyclopolymerisation of non-conjugated a, eo-diolefins [52, 53] are also included among coordination polymerisations involving re complex formation. 

Similarly, the same catalysts that promote the syndiospecific polymerisation of styrene also polymerise ethylene and a-olefins [106,107], ring-substituted styrenes [6] and conjugated dienes [44,74,108-110], These monomers can also be copolymerised with each other [111-114], Substituted styrenes, which yield syndiotactic polymers by polymerisation run with syndiospecific catalysts, form copolymers with styrene the polymerisation rate increases with increasing nucleophilicity of the comonomer. The random copolymers formed are co-syndiotactic [6,111,112]. 

The copolymerisation of (J5), (36) and (38) was carried out with styrene (also terpoly-merisation with 1-vinylimidazole) and n-lauryl-methacrylate (Table Mixing of CO- copofymeiisation... 

A versatile, simple and inexpensive method has been recently proposed for the synthesis of sequence-controlled multiblock copolymers by one-pot polymerisation at ambient temperature. Aciylic block copolymerisation under UV irradiation 360 nm) was obtained in the absence of conventional photoredox catalysts and dye-sensitizers, by means of low concentrations of CuBra in synergy with MCe-Tren [MCe-Tren Tren = tris(2-aminoethyl)amine]. The potential of the method was demonstrated by alternating four different aciylate monomers in various combinations within the polymer composition. Quantitative conversion and narrow dispersity were achieved. " The procedure is versatile, as demonstrated by polymerisation of a number of (meth)aciylate monomers, including poly(ethylene glycol) methyl ether aciylate (PEGA480), te/t-butyl aciylate, methyl methaciylate, and styrene. Moreover, hydrojyl- and vic-diol-functional initiators are tolerated, forming a,co-heterofunctional poly(aciylates). Notably, temporal control is... 

There are several cases where NMR spectroscopy has been used to investigate copolymers which deviate from the terminal model for copolymerisation (see also chapter 3). For example, Hill and co-workers [23, 24] have examined sequence distributions in a number of low conversion styrene/acrylonitrile (S/A) copolymers using carbon-13 NMR spectroscopy. Previous studies on this copolymer system, based on examination of the variation of copolymer composition with monomer feed ratio, indicated significant deviation from the terminal model. In order to explain this deviation, propagation conforming to the penultimate (second-order Markov) and antepenultimate (third-order Markov) models had been proposed [25-27]. Others had invoked the complex participation model as the cause of deviation [28]. From their own copolymer/comonomer composition data. Hill et al [23] obtained best-fit reactivity ratios for the terminal, penultimate, and the complex participation models using non-linear methods. After application of the statistical F-test, they rejected the terminal model as an inadequate description of the data in comparison to the other two models. However, they were unable to discriminate between the penultimate and complex participation models. Attention was therefore turned to the sequence distribution of the polymer. 

FUNCTIONAL POLYMERS. I.xni. EMULSION COPOLYMERISATION OF MALEIMIDE TYPE MONOMERS WITH ACRYLONITRILE AND STYRENE IN ABS LATEXES Bartus J Simonsick W J Vogl O Brooklyn,Polytechnic University DuPont de Nemours E.I., Co.Inc. 

Kharas and co-workers [35] and Washall and Wampler [33] applied this technique to a study of the thermal degradation of trisnbstitnted ethylenes and halogen ring substitnted ethyl-2-cyano-l-oxo-3-phenyl-2-propenylcarbamates, copolymerised with styrene. These materials were also examined by DSC. 

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