Polysilane block copolymers

The Synthesis, Self-Assembly and Self-Organisation of Polysilane Block Copolymers... 

Fig. 4 Approaches to the synthesis of polysilane block copolymers by living polymerization techniques (a) via anionic polymerization of masked disilenes (b) via anionic ring-opening polymerization of cyclotetrasilanes...

Self-Assembly of Polysilane Block Copolymers in Solution... 

The first self-assembling block copolymers were PS-fe-PMPS- -PS synthesised by Matyjaszewski and Moller. They observed micellar aggregates by ATM after casting dilute dioxane solutions (a solvent selective for the PS block) of the copolymer. The observed micelles were taken to have internal PMPS cores and were measured at 25-30nm in diameter [73], The hrst self-assembling amphiphilic polysilane block copolymers to be investigated was the PMPS-PEO multi-block copolymer with normal distribution PMPS blocks and uniform low polydispersity PEO blocks. After dialysis aqueous dispersions of this copolymer formed micellar as well as vesicular structures [78, 79] as shown in Eig. 19. 

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

Dendrimers, or arborols, or cascade, or cauliflower, or starburst polymers, were first synthesized in the early 1980s [3,4]. In 1985 Tomalia et al. [5] and Newkome et al. [6] presented the first papers dealing with dendrimers. A multitude of dendrimers have been presented in the literature ranging from polyami-doamine [7,8],poly(propylene imine) [9,10], aromatic polyethers [11-13] and polyesters [14, 15], aUphatic polyethers [16] and polyesters [17], polyalkane [18-19], polyphenylene [20], polysilane [21] to phosphorus [22] dendrimers. Combinations of different monomers as well as architectural modifications have also been presented. For example, chirality has been incorporated in dendrimers [23,24]. Copolymers of linear blocks with dendrimer segments (dendrons) [25-27] and block-copolymers of different dendrons have been described [28]. 

Photopolymerization using polysilanes can also be carried out to yield block copolymers containing runs of silicon atoms, for instance polysilane-methyl methacrylate. The resulting copolymer can then be used as a macro-photoinitiator for further free-radical polymerizations.144145... 

The use of polysilanes as photoinitiators of radical polymerization was one of the hrst means whereby they were incorporated within block copolymer structures [38 0], albeit in an uncontrolled fashion. However the resulting block copolymer structures were poorly defined and interest in them principally lay in their application as compatibilisers for polystyrene (PS) and polymethylphenylsilane blends PMPS. The earliest synthetic strategies for relatively well-defined copolymers based on polysilanes exploited the condensation of the chain ends of polysilanes prepared by Wurtz-type syntheses with those of a second prepolymer that was to constitute the other component block. Typically, a mixture of AB and ABA block copolymers in which the A block was polystyrene (PS) and the B block was polymethylphenylsilane (PMPS) was prepared by reaction of anionically active chains ends of polystyrene (e.g. polystyryl lithium) with Si-X (X=Br, Cl) chain ends of a,co-dihalo-polymethylphenylsilane an example of which is shown in Fig. 2 [43,44,45]. Similar strategies were subsequently used to prepare an AB/ABA copolymer mixture in which the A block was poly(methyl methacrylate) (PMMA) [46] and also a multi- block copolymer of PMPS and polyisoprene (PI) [47]. 

The PHEMA-fe-PMPS-fc-PHEMA amphiphilic ABA block copolymers were used to generate patterned calcium carbonate hlms with dimensions of several hundreds of microns using the photolithographic properties of the polysilane component [77]. PHEMA-fe-PMPS-fc-PHEMA was spin cast from THF solution onto glass substrates. On this polymer layer continuous hhns of calcium carbonate,... 

There are several reports in recent literature on the application of silicon-containing compounds as the initiators of cationic ring-opening polymerization. This apparently is related to the attempts to prepare block copolymers containing polysiloxane or polysilane segments. (CfL SiCFAgClCL system was used to initiate cationic polymerization of tetrahydrofuran... 

The anionic polymerization of masked disilenes proceeds via living anions, and therefore block copolymerization with a conventional vinyl monomer is possible. Recently, interesting hydrophobic block copolymer of PMHS with poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(methacrylic acid) (PMMA) have been prepared (Scheme 11). These polymers can be self-assembled and are transformed into polysilane micelles, shell cross-linked micelles (SCM), and nanometer-sized hollow particles. ... 

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