Polystyrenes branches

Xenidou M. and Hadjichristidis N., Synthesis of model nultigraft copolymers of butadiene with randomly placed single and double polystyrene branches. Macromolecules, 31, 5690, 1998. 

GPC calibration curves are established based on the radius of gyration of known-molecular-weight polymers, such as well characterized, narrow-molecular-weight distribution polystyrene. Branched polymers have a lower radius of gyration for their molar mass than the corresponding linear molecule. Thus, as branching increases the GPC numbers become less and less accurate and so should only be used for trends, and not exact calculations as some authors have done. 

Randomly Branched Polystyrene. Branched molecules in solution are more compact than linear molecules and therefore the overall size of a branched polymer molecule in solution is smaller than the... 

The second system investigated 101) (polystyrene macromonomer and perfluoro-alkyl acrylate) is also of great interest. The polymerization is carried out in trifluoro-benzene with AIBN as the initiator to a conversion of the order of 60 %. The graft copolymer formed is soluble in a number of solvents in which the poly(perfluoro-alkyl acrylate) backbone would be insoluble, e.g. in THF and diethyl ether. The easy formation of foams indicates the low surface energy which is characteristic of fluorinated polymers. Double-detection GPC (UV and refractive index) showed that the distribution of polystyrene branches within the sample was quite uniform. 

Figure 24.10 Several possible polystyrene branch architectures...

This investigation started as a continuation of research into aspects of grafting from1). Our original intention was to prepare thermoplastic elastomers by grafting polystyrene branches from lightly chlorinated polybutadiene backbones in conjunction with alkylaluminum coinitiators ... 

In the presence of appreciable amounts of polystyrene branches, the polybutadiene backbone may be shielded by the branches. Under these conditions preferential ring alkylation, i.e., branchy branch formation may occur. Further data to corroborate this assumption are presented below. 

C. Characterization of Polystyrene Branches in PoIy(butadiene-g-Styrene)... 

An important objective of this research was to determine directly the molecular weights and the molecular weight distribution of polystyrene branches in poly(buta-diene-g-styrene). 

Graft and block copolymers of propylene and styrene have been developed to compatabilize PP/PS blends. Del Giudice et al. (167) and Xu and Lin (168) have synthesized PP-b-PS. Kim et al. (169) and Li et al. (170) first polymerized propylene together with some functional monomers, then polymerized styrene from these monomers units to form polystyrene branches. Diaz et al. (171,172) grafted PP chains onto PS chains based on F-C alkylation reaction when mixing PP/PS blends in the presence of AICI3 catalyst and styrene. All these copolymers help form very... 

If styrene is available, polystyrene branches can be grafted on to the polybutadiene backbone. The grafting efficiency is not high, as separate polystyrene molecules will also be formed. Once the polystyrene concentration reaches 2%, phase separation occurs, with spheres of polystyrene... 

If the suitable functionality (halogen) is not present originally in the polymer molecule, it can be introduced by suitable post-polymerization techniques. For example, polystyrene branches can be grafted onto ethylene-propylene rubber after chlorinating the rubber. Ethylene-propylene copolymer contains tertiary hydrogens which can be readily exchanged for chlorine. Subsequently the tertiary chlorines are easily activated by complexation with A1(C2H5)2C1 and the macro-cation formed is eminently suitable for the polymerization-initiation of, say, styrene. 

The number of monomer units of the trunk polymer per polystyrene branch decreased from 43 to 23 as the reaction proceeded. Namely, one polystyrene branch exists in every 23 monomer units on an average in the most highly branched graft copolymer obtained. The degree of polymerization of the trunk polymer was 970, so the number of polystyrene branches per trunk polymer increased from 22 to 43. 

As the initiator concentration increased in the graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate), the total conversion increased, but the per cent grafting and the graft efficiency decreased (Table 2) (4). The number of monomer units of trunk polymer per polystyrene branch decreased from 104 to 42. Accordingly, the number of branches per trunk polymer increases with increasing initiator cgncentration, even if the graft efficiency becomes lower. 

As seen from Table 7, the graft efficiency was higher than that of about 30% for poly(vinyl p-nitrobenzoate). The number of nitro groups per polystyrene branch was 28 for 24 hr and 20 for 48 hr of the reaction time. These values are smaller than 30 and 23 observed for poly(vinyl p-nitrobenzoate). Therefore, the nitro groups on ethylene-vinyl p-nitrobenzoate copolymer are used more efficiently than those on poly(vinyl p-nitrobenzoate). The values of a were... 

Table 1. Second virial coefficient of polystyrene (branched).

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