Structure of side groups

In this section, poly(HAMCL)s are largely subdivided into two types based on the structures of side groups these are PHAs containing only 3-hydroxy-n-alkanoates and PHAs containing substituted 3-hydroxy-n-alkanoates. 

The effect of the length and structure of side groups on the conformation of polymer molecules and the equilibrium rigidity of the main chain has been studied systematically for homologous series of poly(alkyl acrylate)s... 

In addition to backbone bonds, the chemical structure of side groups and irregularities in the molecular structure play a role. Side group cleavage can take place... 

Rgur 37 Structures of side-group precursor 39, diluted potymer 40, end phase transitiow of 39, the bonopolyner 18, and copolytaer 40 (in Q. (Fhim Rel 37.)... 

Branching can to some extent reduce the ability to crystallise. The frequent, but irregular, presence of side groups will interfere with the ability to pack. Branched polyethylenes, such as are made by high-pressure processes, are less crystalline and of lower density than less branched structures prepared using metal oxide catalysts. In extreme cases crystallisation could be almost completely inhibited. (Crystallisation in high-pressure polyethylenes is restricted more by the frequent short branches rather than by the occasional long branch.)... 

TABLE 1 Summary of Side Group Structure-Property Relationships in Polyphosphazenes... 

The approximately random placement of side groups in atactic polymers prevents them from developing regular structures. For this reason, atactic polymers are non-crystalline and behave as rubbers or glasses, depending on whether they are above or below their glass transition temperature. 

The substituents on the phenyl group can also sterically influence the chiral recognition ability. The main-chain structures of 23a and 23x look similar, but the conformations of side groups are not the same. Three aromatic groups of... 

Although the main-chain conformations of polysilanes have been described as random coil, 73- (deviant helical), 157 (transoid helical), and 2i (all anti, planar) structures, it is now generally accepted that most polysilanes tend to adopt helical main-chain structures, regardless of side groups and temperature.39 It... 

In practice it is most common and convenient to side-step one of the problems associated with strong orthogonality. We can work with an orbital basis which satisfies (11) independently of the choice of the physical structure of the groups of electrons a basis for which (11) is guaranteed for all R, S. Any orbital basis which forms an orthogonal set will fulfill this condition all overlap integrals are then zero.6)... 

Figure 8.1 Structure of side-chain groups (R) of amino acids except for proline, for which the entire structure is presented.

Free Volume Versus Configurational Entropy Descriptions of Glass Formation Isothermal Compressibility, Specific Volume, Shear Modulus, and Jamming Influence of Side Group Size on Glass Formation Temperature Dependence of Structural Relaxation Times Influence of Pressure on Glass Formation... 

The polymer seems to change from a stiff rod to a more flexible worm-like molecule with an increase in its length. The proposed structure consists of a helical conformation, involving four monomer units per turn. This structure requires side groups at 90° along the chain and predicts a distance of 4.3 A between adjacent side groups. 

The first polyphosphazenes to be developed commercially were polymers with two different types of fluoroalkoxy side groups attached to the same chain.142 145a A typical example is shown in 3.73. Polymer 3.73 has a more complicated structure than is implied by the illustration. The polymer is synthesized by the reaction of a mixture of CF3CH2ONa and CFB CFj CHjONa with poly(dichlorophosphazene). This means that the two nucleophiles compete for replacement of the available chlorine atoms, a process that could lead to a random distribution of side groups, but could also generate repeating units in which the phosphorus atoms bear two of the same side groups. 

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