Synthesis and Dynamic Rheological Behavior of Polybutadiene Star Polymers

Abstract

Polybutadiene star polymers, of nominal functionality 3, 4, 8 and 12, all with arm lengths of approximately 30 000 g mol -1 , have been synthesized using chlorosilane coupling agents. Dynamic mechanical studies have been carried out using parallel-plate rheometry at various temperatures, and the data frequency-temperature shifted to produce master curves. Fits to the Ball-McLeish constraint release theory indicate an effective entanglement molecular weight somewhat higher than the literature value for a linear polymer. This has been interpreted by considering a dilution of constraints effect caused by the Rouse diffusion of the terminal section of the star arm, leading to a predicted modified entanglement molecular weight similar to that found experimentally. Evidence for the Rouse-like behavior of the terminal section has been obtained from deuterium NMR spectra of a selectively deuterated sample. The presence of small amounts of residual linear chains is shown to be responsible for a further dilution of entanglements. An extension of the theoretical fits to include the high-frequency Rouse mode spectrum shows a divergence between theory and experiment which is indicative of the onset of the glass transition.

HyperMacs – long chain hyperbranched polymers: A dramatically improved synthesis and qualitative rheological analysis

“…Carbon tetrabromide (99%, Aldrich), cesium carbonate (99.995%, Aldrich), triphenylphosphine (99%, Aldrich), dimethylformamide (99.9+%, Aldrich) and 1,1,1-tris(4-hydroxyphenyl)ethane (Aldrich) were all used as received. 2 Polystyrene Macromonomers. The synthesis of polystyrene macromonomers in which the reactive 'A' functionality is an alkyl chloride is described previously [29].…”

“…However, in the overwhelming majority of cases, industrially produced materials have a wide distribution of chain lengths between branch points, making modelling of the material challenging. It is this realisation that has, over a period of decades, resulted in the design and synthesis of well-defined molecular architectures such as star branched polymers [2,3], mikto star polymers [4][5][6] and H-shaped polymers [7,8] with a view to understanding and predicting the relationship between structure and properties. More recently, syntheses of dendrigraft, dendritically branched and arborescent [9][10][11][12][13][14] polymers with a higher degree and complexity of branching have been published, much of this work has recently been reviewed by Gauthier and Teertstra [15].…”

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

“…Yield 94%. 1 PS32-OH 2 was converted to PS32-Alkyne 2 according to the same procedure described above and the product characterized by 1 H-NMR.…”

“…Star polymers with varying numbers of arms have been widely produced and studied [1][2][3][4][5][6][7][8] and branched polymers of increasing complexity and diverse structures have evolved. These include H-shaped polymers [9][10][11][12][13][14][15], comb-shaped polymers [16][17][18][19][20][21][22][23][24][25][26][27][28] and more recently dendritically branched polymers [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”

“…The term "living" was coined to describe a mechanism which proceeds in the absence of inherent termination reactions and, provided initiation is rapid with respect to propagation and the presence of impurities is avoided, anionic polymerisation is capable of producing polymers with predictable molecular weights and very narrow dispersity -molecular weight distributions with a dispersity index of 1.05 or less are easily achievable. Although many strategies have been developed to couple the ends of living polymer chains to produce branched polymers, the combination of living anionic polymerisation and multifunctional chlorosilane coupling agents has proved the most successful in producing star branched polymers with a high degree of structural homogeneity and stars with 3 to 128 arms produced by this method have been reported [1,2,[50][51][52]. The three arm star polymers required for the current study are effectively a series of identical linear polymers with a single branch emanating from the centre of the linear chain.…”