Styrene hving polymerization

Anionic polymerization, if carried out properly, can be truly a Hving polymerization (160). Addition of a second monomer to polystyryl anion results in the formation of a block polymer with no detectable free PS. This technique is of considerable importance in the commercial preparation of styrene—butadiene block copolymers, which are used either alone or blended with PS as thermoplastics. 

Zhao and Brittain [280-282] reported the LCSIP of styrene on planar silicon wafers using surface modifications of 2-(4-(ll-triethoxysilylundecyl)phenyl-2-methoxy-propane or 2-(4-trichlorosilylphenyl)-2-methoxy-d3-propane respectively. Growth of PS brushes from these SAMs has been successfully achieved factors that influence PS thickness included solvent polarity, additives and TiC concentration. Sequential polymerization by monomer addition to the same silicate substrate bearing the Hving polymer chains resulted in thicker PS films. FTIR-ATR studies using a deuterated initiator indicated that the initiator efficiency is low, and the... 

The addition reaction of the functional DPE derivative to a Hving anionic polymer is not, in itself, a termination reaction. After the reaction, the chain-end anion is changed to a DPE-derived anion, which can initiate an anionic polymerization of additional monomers, such as styrene, 2-vinylpyridine, or methyl methacrylate, to extend the chain or to form a new block (Scheme 5.17). Thus, this reaction offers the potential of providing a quite novel chain-functionalization procedure, with which the functional groups can be introduced at essentially any position in a polymer chain [174]. Accordingly, functionalization using functional DPE derivatives is a versatile procedure, not only for the preparation of chain-end-functionaUzed polymers but also for in-chain-functionalized polymers that are difficult to synthesize by any other method [172-174]. 

PCL with the TEMPO 2,2,6,6-tetrameihYlpiperidinoxyl) moiety behaved as a polymeric counter-radical for the polymerization of styrene, resulting in the quantitative formation of PCL-fo-PSt. The radical polymerization was found to proceed in accordance with a living mechanism, without undesirable side reactions. The thermal analysis of the block copolymer indicated that the components of PCL and PSt were completely immiscible and microphase-separated. Incorporation of the TEMPO moiety into PEO chain-ends in the radical form was also achieved [53]. In this case, TEMPO-Na was used as an initiator in a hving anionic polymerization of ethylene oxide (Scheme 11.10), under conditions such that the stable nitroxyl radical at the end of the PEO chain could not be destroyed. 

Yoshida and Sugita [72, 73] have described the synthesis of polytetrahydrofuran (PTH F) possessing a nitroxy radical by terminating the Hving cationic ring-opening polymerization (CROP) of THF with sodium 4-oxy TEMPO. The polymer obtained in this way acted as a counter-radical in the polymerization of styrene, in the presence of a free radical initiator, to yield PSt-f)-PTHF (Scheme 11.16). 

In the subsequent step, a radical polymerization of styrene was carried out with an alkoxyamine-terminated PTHF. Although an increase in conversion with polymerization time was observed, and block copolymers with polydispersities dose to those of the prepolymers were readily formed, the initiation effidency of )-aIkoxyamine PTHF was rather poor. This was attributed to the relativdy slow decomposition and initiation of alkoxyamine attached to unsubstituted methylene groups. Recently, it was reprorted that aUroxyamines containing an unsubstituted carbon atom are very slow to decompose, and that the o -methyl group is essential for the conventional radical polymerization to proceed with a truly Hving character [76]. 

Bromo-functionalized PTHFs obtained this way were used as initiators in the ATRP of styrene, MMA, and MA to yield AB- and ABA-type block copolymers. Notably, in the case of styrene and MA, the formation of triblock copolymers was significantly slower. It was also reported [79] that PSt with chlorine termini, synthesized by hving cationic polymerization without any additional reaction, was an efficient macroinitiator for living ATRP of styrene, MMA, and MA (Scheme 11.20). With some variations in the initiator design, more complex structures such as block, graft, and miktoarm-starblock copolymers having PTH F [80-85] chains as the cationic segment were synthesized. 

Polypropylene-g-PS copolymers were synthesized by combination of metallocene and TEMPO living free-radical polymerization techniques (41). The backbone was synthesized by copolymerization of propylene and a TEMPO-fimctionalized derivative containing a a-double bond. The TEMPO groups were then used for the pol5mierization of styrene by hving free-radical pol5onerization (Fig. 7). 

Parcel, C., Charleux, B. and Pirri, R. (2001) Poly( -butyl acrylate) homopolymer and poly[n-butyl acrylate-b-(n-butyl acrylate-co-styrene)] block copolymer prepared via nitroxide-mediated hving/controUed radical polymerization in miniemulsion. Macromolecules, 34, 3823-3826. 

Matyjaszewski K, Patten TE, Xia IH (1997) Controlled/hving radical polymerization. Kinetics of the homogeneous atom transfer radical polymerization of styrene. 1 Am Chem Soc 119 674-680... 

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