Synthesis, Characterization, and Properties of Stars Consisting of Many Polyisobutylene Arms Radiating from a Core of Condensed Cyclosiloxanes

Abstract

Novel stars of many polyisobutylene(PIB) arms radiating from a core of condensed methylcyclosiloxanes are described. The synthesis involves hydrosilation of allyl-terminated PIB prearms by small methylcyclosiloxanes (e.g., D4 H , D6 H ) and competitive moisture-mediated core-core coupling. The effect of conditions (e.g., time, temperature, stoichiometry, nature and molecular weight of prearms, and size of methylcyclosiloxane) on synthesis was investigated. The processes can be controlled and well-defined 21-28 arm stars have been perpared. Microstructures were characterized by various techniques. The intrinsic viscosities of stars are much lower than those of linear PIBs of the same molecular weight over the 30-100 °C range. Branching coefficients depend on the number of arms. Hydrodynamic volumes of stars and combs (polysiloxane backbone carrying PIB branches) are similar, indicating that both assume radial conformations. The stars are resistant to strong acids and bases indicating that resistant PIB coronas protect acid-and base-vulnerable cores. The temperature resistance of stars is similar to that of PIB.

Novel thermoplastic elastomers. II. Properties of star-block copolymers of PSt-b-PIB arms emanating from cyclosiloxane cores

“…3 PSt/PIB block compositions of triblocks and starblocks were characterized by 1 H-NMR (Varian Gemini Spectrometer, 200 and 600 MHz) spectroscopy. 3,6 Glass transition temperatures were determined by differential scanning calorimetry (Perkin-Elmer, DSC7). The samples were heated to 200°C at 20°C/min to remove thermal history effects and then cooled to Ϫ110°C.…”

“…Figure 8 shows a representative DSC thermogram of a primary star-block, D 6 [PIB(30)-PSt (9)] 5 . The DSC trace clearly indicates two distinct T g s (PIB at ϳ Ϫ61°C and PSt at ϳ 99°C) and suggests microphase separation between the PSt and PIB domains.…”

“…The thermal stability of star-blocks has been studied by TGA. As shown by the thermogram in Figure 9, the thermal stability of a star-block is high (e.g., 5% weight loss at ϳ 375°C in N 2 for D 6 [PIB(30)-PSt(9)] 5 ). …”

Novel thermoplastic elastomers. I. Synthesis and characterization of star-block copolymers of PSt-b-PIB arms emanating from cyclosiloxane cores

“…The preparations of various types of cyclosiloxane cores have been described. 12 The cyclosiloxane-linking agents used were 2,4,6,8,10,12-hexamethylcyclohexasiloxane (D 6 H ) and 2,4,6,8,10,-12,14,16,18,20,22,24-dodecamethylcyclododecasiloxane (D 12 H ). They were fractionally distilled, and their purity was checked by gas chromatography (GC).…”

“…The higher-order star-blocks were prepared by corecore coupling of primary stars by the use of an extension of our strategy developed for the synthesis of higher-order stars with only PIB arms radiating from cyclosiloxane cores. 12 The critical parameters that control the formation of primary and higher-order star-blocks are the [ 12 Structural information in regard to both primary and higher-order star-blocks was obtained by the use of triple-detector (RI, UV, and LLS) GPC and 1 H-NMR spectroscopy.…”