Vinylaromatic monomers

Anionic polymerizations initiated with alkyllithium compounds enable us to prepare homopolymers as well as copolymers from diene and vinylaromatic monomers. These polymerization systems are unique in that they have precise control over such polymer properties as composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even copolymer monomer sequence distribution. Attempts have been made in this paper to survey these salient features with respect to their chemistry and commercial applications. 

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. 

Ever since their original discoveries, Ziegler Natta catalysts and Phillips catalysts have been used for both the homopolymerisation and the copolymerisation of olefins. Moreover, Ziegler-Natta catalysts also allowed the copolymerisation of olefins with vinylaromatic monomers, conjugated dienes and cycloolefins. Other coordination catalysts such as group 8 metal compounds, especially cationic Pd(II) complexes, enabled the alternating copolymerisation of olefins and carbon monoxide [2,29,30,37,43,46,241,448 450],... 

Isospecific Polymerisation of Vinylaromatic Monomers with Coordination Catalysts... 

Although the isospecific polymerisation of styrene monomers has much less steric demands for the Ziegler-Natta catalysts than that of x-oldins, it proceeds with much lower propagation rate constants by comparison with the polymerisation of x-olefins for example, on a molar basis, styrene is ca 100 times less reactive than propylene in the polymerisation [30,33], Also, compare the relatively slow polymerisation of styrene and other vinylaromatic monomers with the relatively fast polymerisation of vinylcyclohexane [20,31,34-36]. 

Reactivities of ring-substituted styrenes depend on the type and position of the substituents [18,19,27,40], Table 4.1 lists the relative reactivities of different vinylaromatic monomers in polymerisation with the heterogeneous TiCU AlEt3 catalyst [41],... 

Table 4.1 Relative reactivity of vinylaromatic monomers in coordination polymerisation with heterogeneous Ziegler-Natta catalyst ...

Prior to the development of the universal nitroxide IV, the SAM technique was mainly limited to the preparation of block copolymers containing only vinylaromatic monomers. This is because TEMPO-based NMRP does not work well for other monomers. Although several papers appeared claiming to have successfully prepared block copolymers with acrylates using TEMPO chemistry, it is doubtful that they were very pure. 

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of s-PEEK) supplied by Victrex, which may be better suited to PEM fuel cell fabrication applications. In March 2002, U.S. Patent 6359019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluoro-vinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The structures of BAM membranes have been studied by way of small-angle neutron scattering or SANS. ° The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nafion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the manbrane s mechanical and transport properties. 

Currently, most of the LFRP research is focused on the use of nitroxides as the stable freeradical. The main problems associated with nitroxide mediated radical polymerizations (NMRP) are slow polymerization rate and the inabihty to make high molecular weight narrow polydispersity PS. This inabihty is hkely due to side reactions of the living end leading to termination rather than propagation (243). The polymerization rate can be accelerated by the addition of acids or anhydrides to the process (244). The mechanism of the accelerative effect of the acid is not certain. Another problem with nitroxides is that they work well for vinylaromatic monomers, but not for acrylate and diene monomers. This has... 

Very interesting results have been obtained in the case of coisotactic copolymers between chiral a-olefms and achiral vinylaromatic monomers [87]. Copolymers of — -methylstyrene or 1-vinylnaphthalene with (7 )-3,7-dimethyl-l-octene show optical rotation at the sodium [D] -line higher, in absolute value, than the corresponding homopolymeric mixture, indicating that the aromatic unit assumes a preferential conformation of a single chirality (Table XX) [88]. This is not evident in the analogous copolymers of styrene... 

Chiroptical properties of polymers from vinylaromatic monomers... 

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