Star-shaped polymers polystyrene

A method for preparing star-shaped polystyrene by either the incremental or single addition of divinyl benzene to a living polystyryl anion is described. Star-shaped polymers containing up to 34 arms were prepared with polydispersities of less than 1.1. 

On the other hand, as soon as many stars are in the matrix, the entanglement points of the matrix are increased due to additional permanent crosslink points (i.e., centers of star polymers). Thus the average mesh size of the matrix decreases. In consequence, the cooperative diffusion becomes faster. But in the case of 12-arm star polystyrene as the test chain, the effect of star centers was not so obvious. According to the model of star shaped polymers by Daoud and Cotton,there is a region with size around the center of a star, inside which the chains of other polymers do not penetrate. The distance x is a function of the number of arms, i.e., / where f is the arm number of the star. So the unpenetrable distance of 12-arm star is larger than that of a 4-arm star, leading to an effective decrease in the number of entangled points. 

Tetramethylpiperidinyloxy-terminated polystyrene and 4-vinylbenzyl glucoside peracetate and 4-vinylbenzyl maltohexaoside peracetate NMP Core-glycoconjugated star-shaped polymers [66]... 

The correlation between the deviation from bulk behavior and the presence of a layer irreversibly adsorbed onto the host substrate is not limited to star-shaped polymers, but seems to be a universal feature of confined polymers [4]. In particular, in 2011 Napohtano demonstrated that the Tg of thin films of polystyrene (PS) capped in between aluminum layers (no free surface) is affected by prolonged annealing in the liquid state [5]. Surprisingly the timescale required to achieve a steady state in ATg(t) is orders of magnitude larger than the reptation lime, tREP. which in bulk sets the longest relaxation time, corresponding to the time needed to erase memory of previous conformations and thus to reach an equihbrium state. 

Transparent toughened polystyrene polymers are produced by blending polystyrene with SBS block copolymers (see Section 11.8). During the 1970s and 1980s most development was with block copolymers with a radial (or star) shape. Two types were developed block copolymers with a central butadiene block, and block copolymers with a central polystyrene block. 

Platinum-cobalt alloy, enthalpy of formation, 144 Polarizability, of carbon, 75 of hydrogen molecule, 65, 75 and ionization potential data, 70 Polyamide, 181 Poly butadiene, 170, 181 Polydispersed systems, 183 Polyfunctional polymer, 178 Polymerization, of butadiene, 163 of solid acetaldehyde, 163 of vinyl monomers, 154 Polymers, star-shaped, 183 Polymethyl methacrylate, 180 Polystyrene, 172 Polystyril carbanions, 154 Potential barriers of internal rotation, 368, 374... 

The randomly branched polystyrene and two star-shaped polystyrenes were obtained from the Polymer Science Department at the University of Akron, Akron, OH. 

Polymer Separation and Characterization by Thin-Layer Chromatography Table 7. Characteristics of tetrachain-star-shaped and linear polystyrenes... 

When a tetra-chain, star-shaped polystyrene is prepared by a coupling reaction between living polymer and coupler (e.g 1,2,4,5-tetrachloromethyl benzene), the reaction is often carried out with the polystyryl anion in slight excess in order to avoid by-production of types of branched polystyrene other than the tetra-chain. 

The foregoing section dealt with TLC separation of linear and branched polymers, from the standpoint of resolutions with respect to molecular weight. In this section we summarize TLC results of chromatographic distinguishment of linear and star-shaped polystyrenes on the same molecular-weight level. It is now well known that... 

Their findings were that star polymers presented a lower surface tension that linear polystyrene and that this value decreased with increasing number of arms. This behavior was explained by a lattice model considering finite compressibility of the chain and density gradient in the polymer blend. Thus this study implied that when mixed with a linear polymer star-shaped macromolecules would segregate to reduce the surface tension. 

The synthesis and characterization of polystyrene-6-poly(ethylene oxide)-6-poly(e-caprolactone) triblock terpolymers in a linear or star shaped fashion is very interesting because they combine in the same molecule a glassy amorphous block, polystyrene a biocompatible crystalhzable poly(ethylene oxide) block, and a crystalUzable poly(e-caprolactone) block, which is biodegradable and exhibits miscibility with a variety of polymers. 

Interaction chromatography can also be used to fractionate model polymers according to long-chain branching. An application for star-shaped polystyrenes was presented by Chang and co-workers (79). 

---