Siloxane-containing block copolymers preparation

The properties of siloxane-containing block copolymers prepared from the functionally terminated siloxanes are influenced by the molecular weight distribution of the material which is typically Gaussian. The range of potential applications of the block copolymers can be extended if the molecular weight distributions of the siloxane blocks can be minimized. Thus, the impetus for evaluating supercritical fluid fractionation, aside from its utility as a characterization tool, as a means of improving end product performance is established. 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

Siloxane-containing block copolymers are often prepared by step-growth or condensation polymerization of preformed diftmctionalized siloxane oligomers with other diftmctionalized monomers or oligomers. Our current work (3, 4, 6-8) on siloxane chemistry includes the preparation of a number of functionalized oligomers, with emphasis on equilibration processes with the commonly available cyclic tetramer, octamethylcyclotetrasiloxane (D4), in the presence of a functionalized disiloxane or end blocker. 

The synthesis and characterization of poly(hexamethylene sebacate-tiimethyl-siloxane) block copolymers, prepared by coupling Cl- or McjNH-terminated dimethylsiloxanes with OH-terminated poly(hexamethylene sebacate), have been studied. The copolymers containing 19—90% siloxane were characterized by n.m.r., viscosity, DSC and CPC. All the polymers were found to be crystalline. The copolymers containing <69% siloxane, when cast from solution or melts, indicated a reduction in spherulite size as the siloxane concentration increased, although only a small m.pt. depression was observed. All the copolymers have critical surface tensions similar to dimethylsiloxane homopolymers. Polycarbonate-Siloxane Copolymers.—A model has been proposed to predict the micromorphology and mechanical properties of block copolymers of bisphenol-A polycarbonate and poly(dimethylsiloxane). N.m.r. data upon 65 35 (wt%) copolymer of poly(dimethylsiloxane) and bisphenol-A polycarbonate, with block lengths of 20—100 monomer units, were found to be in agreement with the predictions of a spin-diffusion model. ... 

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

One of the most important uses of end-functionalized polymers is the preparation of block copolymers.73,74 The reactions are identical to the chain extensions already mentioned, except that the sequences being joined are chemically different. In the case of the -OSilCR Y chain ends mentioned above, R is typically (CH2)3 5 and Y can be NH2, OH, COOH, CH=CH2, and so on The siloxane sequences containing these ends have been joined to other polymeric sequences such as carbonates, ureas, urethanes, amides, and imides. 

Mixed urea block copolymers consisting of amine-terminated polydimethyl-siloxane were prepared by Sherman [3] and used as pressure sensitive adhesives. Other urea-based pressure sensitive adhesives containing polydimethyl-siloxanes are described by Zhou [4]. 

At present we are engaged in the preparation of siloxane polymers and block copolymers with a larger number of ftinctional groups attached to the chain. In the following we report on siloxanes containing vinyl groups. 

For the controlled polymerisation of siloxanes only a few publications have appeared but these constitute a couple of steps forward in the elucidation of methods to find conditions where controlled polymerisation can be performed. Block copolymers of S and D3 were obtained with close to 100% conversion of D3 under /Bz,THF/sBuLi/-20 °C//TMCS/ conditions (M = 49 kg/mol Mw/Mn = 1.03 with 68% S in the PS-PDMS) [73]. Block copolymers of D3 and diene monomers were obtained with close to 100% conversion under /CHX/sBuLi/0°C/HMPA/TMCS/ conditions (6 < M /(kg/mol) < 17 1.07 < mjm < 1.14) [74]. In the preparation of block copolymers containing siloxanes it is a known problem that the crossover from the very reactive carbanion species to siloxane monomers is actually quite slow under apolar conditions. A possible solution to this problem has been found. Di- and triblock copolymers of PDMS and PS or PaMS were obtained by low-temperature polar polymerisation of S or aMS followed by reaction with EDS. The resulting Li silanolate polymerised D3 in THF at 25 °C. Termination with TMCS or DMDCS yields diblock or triblock copolymers, respectively. The use of EDS alfords a much faster crossover reaction than is normally obtained between S or aMS and D3(27 < A/ /(kg/mol) < 190 1.07 < Mw/M < 1.28) [75]. 

The morphology of ferrocene-containing polymers has been examined in some detail. In the block copolymer of poly(ferrocenyldimethylsilane-b-dimethyl-siloxane) (PFDMS-b-PDMS) with a 1 6 block ratio long rodlike micelles are observed rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The reasons for these observations are subsequently discussed in detail. A further series of mixed ferrocene cobaltocenium dendrimers have been obtained these have been prepared in the reaction of the acyl chlorides of ferrocene and the cobaltocenium PF " with polypropylene dendrimers. ... 

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