Monomers branched

Figures 2 and 5 show the increase of the mass average molar mass, R i, with conversion for the systems with branched and linear prepolymers, respectively. These results indicate that addition of the branching monomer in the first stage yields much higher values of R, and the gel point is reached at lower conversion than addition in the third stage. Translated into practical properties this means that the processing and application qualities (e.g. flow) of a paint based on formulation F40 will be inferior to those of one on the basis of for-...

On the other hand, branched building blocks [30] possess inherent branching points remote from the site of connection. These monomers can be simple or complex in design and have been used in both divergent and convergent synthetic strategies. In addition, branched monomers can also be used to install utilitarian functionality within cascade molecules. 

As will be demonstrated, surface branching has afforded a series of dendri-mers lacking site-specific [31-33] characteristics whereas, the use of branched monomers has the unique ability to instill tailored loci capable of site-specific molecular recognition and encapsulation. 

Alternatively, the one-step polymerization of branched monomers results in what is called a hyperbranched polymer [53] possessing a higher degree of polydispersity and lower degree of branching compared to the analogous dendrimer. 

Frdchet et al. reported the synthesis of a unimolecular micelle (Fig. 6) generated by a convergent approach starting with 3,5-dihydroxybenzyl alcohol, as the key branched monomer unit [65]. Fourth generation dendrimer 15 with 32 carboxylic acid moieties on the periphery was synthesized and its correspond-... 

Fatty acids have also been converted to difunctional monomers for polyanhydride synthesis by dimerizing the unsaturated erucic or oleic acid to form branched monomers. These monomers are collectively referred to as fatty acid dimers and the polymers are referred to as poly(fatty acid dimer) (PFAD). PFAD (erucic acid dimer) was synthesized by Domb and Maniar (1993) via melt polycondensation and was a liquid at room temperature. Desiring to increase the hydrophobicity of aliphatic polyanhydrides such as PSA without adding aromaticity to the monomers (and thereby increasing the melting point), Teomim and Domb (1999) and Krasko et al. (2002) have synthesized fatty acid terminated PSA. Octanoic, lauric, myristic, stearic, ricinoleic, oleic, linoleic, and lithocholic acid acetate anhydrides were added to the melt polycondensation reactions to obtain the desired terminations. As desired, a dramatic reduction in the erosion rate was obtained (Krasko et al., 2002 Teomim and Domb, 1999). 

R+, may rearrange to a secondary or tertiary ion during the cracking of the activated complex. In reverse, these same rules successfully predict that branched-chain olefin polymers will be obtained from either straight-chain or branched monomers. With little modification, the structures of paraffin-olefin alkylates from acid catalysts may be predicted in the majority of cases. 

Thus, the use of alkyllithium initiation offers the synthetic chemist a tool of enormous flexibility for "tailor-making" polymers of precise structure. Control of molecular weight, molecular-weight distribution, diene structure, branching, monomer-sequence distribution, and functionality can conveniently be achieved by such techniques as incremental or sequential addition of monomer, initiators, or modifier, programming of temperature, continuous polymerization, or the use of multifunctional reagents. 

Frechet et al. 8fi reported a branched-monomer approach to the convergent synthesis of dendritic macromolecules this approach permits an accelerated growth by the replacement of the simplest repeat unit with a larger repeat unit of the next generation. In essence, the traditional AB2 monomer is replaced with an AB4 unit. Scheme 5.28 depicts the transformation of the AB4 unit (115) to the trimethylsilyl protected tetraester 116... 

Scheme 5.28. The branched-monomer approach leads to dendrimers possessing differentiated generation connectivity.

When we do not care much about obtaining a product with precise size and structure, branched monomers can be condensed randomly. The polymeric materials obtained in this way are called hyperbranched polymers (Fig. 3.10). 

Hgure 2.11 (a) Linear and ethyl-branched monomers that, when copolymerized together at various ratios, give polymers with a wide range of different ethyl branch con-... 

Three l-(2-nitrophenyl)ethyl phosphoroamino acid building blocks (68), (69) and (70) for solid-phase peptide synthesis have been described (Figure 17). A new straightforward method of synthesis of dendrimers, using two branched monomers (CA2 and DB2) has been desribed (Figure 18). ... 

With the system TiCl3/AlEt3, the rate of isomerization of cA-2-butene to 1-butene can be increased by the incorporation of a late transition metal component such as NiC. 435 Isomerization polymerization using 2-butene has also been shown to be useful for the synthesis of co-polymers of 1-butene with ct-carbon-branched 1-alkenes having low polymerization activity.436 The difference in reactivity between the branched monomer and 1-butene is compensated for by the low concentration of 1-butene formed by isomerization from 2-butene. 

Other branched monomers that have been homopolymerized with metallocenes include 3-methyl-1-butene,943,944 3-methyl-1-pentene,943,945,946 4-methyl-1-hexene,947 allylbenzene,948,949 vinylcyclohexane,929 and 1-vinylcyclohexene.950... 

To expedite the synthesis of densely packed dendrons, Percec and co-workers110 have utilized the triply branched monomer 37, methyl 3,4,5-trihydroxy-benzoate.84-85 111-113 The materials were synthesized by coupling the phenolic groups of the monomer to 3 equiv of a benzylic chloride, followed by transformation of the focal ester functionality to a chloromethyl group, via LiAlFF reduction and SOCT chlorination. This procedure could be repeated up to the fourth generation. 

Thermally stable copolymers of 3-(trimethylsiloxyl)- and 3,5-bis(trimethylsiloxyl)benzoyl chloride (4A) or 3-acetoxy- and 3,5-diace-toxy-benzoic acid (4B) were prepared with mole ratios of AB AB2 monomer ranging from 160-5.32 Polymers containing 10-20 mole % of branching monomers were insoluble in CHC13 but soluble in polar solvents, such as A,A-dimethylformamide (DMF) or a mixture of pyridine and benzene. Compared to the linear homopolymer of 3-hydroxy-benzoic acid, the branched polymer showed lower crystallinity and slower crystallization. There was an inverse linear relationship between percent crystallinity and the number of branches in the chain. Similarly, in an attempt to improve moldability and decrease anisotropy of rigid aromatic polyesters, 0.3-10 mole % of 1,3,5-trihydroxybenzene, 3,5-di-hydroxybenzoic acid, and 5-hydroxyisophthalic acid were copolymerized with p-hydroxybenzoic acid/terephthalic acid/4,4 -dihydroxy-diphenyl.33 The branched polymer showed a lower orientation and possessed improved flex properties. 

Photopolymerizable compositions have found their use in the production of thick (5-100 pm) relief images, especially in the field of printed plates and micromachinery. The compositions contain a monomer, matrix polymer (binder), and photoinitiator. The branched monomers are used most frequently. Many photosensitive compounds generating radical and ion centers upon UV irradiation are used as a part of the compositions. Polymethylmethacrylate and its derivatives are very often used as polymer binders. 

Frdchet proposed to use the ratio of the number of fully branched monomer units to the total number of monomer units contained within the polymer N ) to describe the degree of structural perfection of hyperbranched polymers... 

In a branched polymer, some monomers become part of side chains, branching off the main chain or off other branches. Monomers with a functionality of three or greater may form branched polymers, since three parts of the polymer molecule can extend from a single monomer wherever a trifunctional monomer is located. The degree of branching of the polymer will depend on the number of multifunctional monomers present during the reaction. 

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