Polystyrene branched polymeric

A procedure used in the self-branching polymerization reaction for the preparation of dendritic polystyrenes is outlined in Scheme 7. Oligomeric polystyryl-lithium chains are reacted with a coupling agent such as 4-(chlorodimethyl-silyl)styrene (CDMSS), which contains both a polymerizable double bond as well... 

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. 

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 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. 

Polymers are produced by one of two processes, addition or condensation polymerization. Addition polymerization occurs by one of three mechanisms, radical (e.g., low density branched polyethylene), cationic (e.g., butyl rubbers), or anionic (e.g., polystyrene). Condensation polymerization is used to produce Nylon 6,6 from adipic acid and hexamethylenediamine with the elimination of water. Industrially,... 

The properties of a polymer depend not only on its gross chemical composition but also on its molecular weight distribution, copolymer composition distribution, branch length distribution, and so on. The same monomer(s) can be converted to widely differing polymers depending on the polymerization mechanism and reactor type. This is an example of product by process, and no single product is best for all applications. Thus, there are several commercial varieties each of polyethylene, polystyrene, and polyvinyl chloride that are made by distinctly different processes. 

In the early days of polymer science, when polystyrene became a commercial product, insolubility was sometimes observed which was not expected from the functionality of this monomer. Staudinger and Heuer [2] could show that this insolubility was due to small amounts of tetrafunctional divinylbenzene present in styrene as an impurity from its synthesis. As little as 0.02 mass % is sufficient to make polystyrene of a molecular mass of 2001000 insoluble [3]. This knowledge and the limitations of the technical processing of insoluble and non-fusible polymers as compared with linear or branched polymers explains why, over many years, research on the polymerization of crosslinking monomers alone or the copolymerization of bifunctional monomers with large fractions of crosslinking monomers was scarcely studied. 

Fig.46. Dependence of [r ] on theMn of polymers prepared by anionic polymerization of 1,4-DVB in THF. The symbols represent linear ( ) branched (V) and microgel ( ) structures. The dashed line represents the [iq]/Mn relationship of anionically prepared polystyrene. [Reproduced from Ref. 231 with permission, Hiithig Wepf Publ., Zug, Switzerland].

In his famous work of 1920 Hermann Staudinger first described the correct structure of polystyrene (10). It was Staudinger, too, who gave polystyrene its name and elucidated the mechanism of its formation (11). The polymerization of styrene provided access to a big class of substances and made a significant contribution to the understanding of natural polymers and to the synthesis of industrial plastics. A whole new branch of the chemical industry is based on the key substance polystyrene. 

Wooley and Bolton recently published a paper concerning hyperbranched polycarbonates obtained by polymerization of a monomer derived from 1,1,1-tris(4 -hydroxyphenyl)ethane [99]. A degradative technique was used to determine the degree of branching, which was found to be close to 0.53. Apparent molecular weights were in the range 16-82 kDa as determined by GPC relative to linear polystyrene standards. 

Copolymers. Mixtures of two or more different bifunctional monomers can undergo additional polymerization to form copolymers. Why copolymerize Well, polymers have different properties that depend on their composition, molecular weight, branching, crystallinity, etc. Many copolymers have been developed to combine the best features of each monomer. For example, polystyrene is low cost and clear, but it is also brittle with no toughness. It needs internal plasticization. By copolymerizing styrene with a small amount of acrylonitrile or butadiene, the impact and toughness properties are dramatically improved. 

It was known that polystyrene and poly- >-methoxystyrene initiated by tin tetrachloride have a branched structure, due to aromatic substitution in the course of the polymerization (186). Haas, Kamath and Schuler (93, 124) studied the ionic chain transfer reaction between a polystyrene carbonium chain and poly-/>-methoxystyrene. They were able to separate the homopolymers from the graft copolymers by extraction with methylcyclohexane. 

---