Side-groups, flexible

Disklike rc-conjugated mesogen Mesogenic side group Flexible spacer Solubilizing side chain... 

Other examples where side group flexibility is important include poly(cyclohexyl thiolmethacrylate) versus poly (cyclohexyl methacrylate) and poly (phenyl thiolmethacrylate) versus poly (phenyl methacrylate). 

Another example of how side group flexibility affects C, is seen on comparing poly(tetrahydropyranylmethyl methacrylate) with poly(cyclohexylmethyl methacrylate) [133]. 

Thus where R and Rjp are hydrogen the molecule is symmetrical, the absence of bulky side groups leads to high intermolecular attraction and the flexibility of... 

Polycarbonates have also been prepared from diphenyl compounds where the benzene rings are separated by more than one carbon atom. In the absence of bulky side groups such polymer molecules are more flexible and crystallise very rapidly. As is to be expected, the more the separating carbon atoms the lower the melting range. This effect is shown in data supplied by Sehnell" Table 20.11). 

The most common backbone structure found in commercial polymers is the saturated carbon-carbon structure. Polymers with saturated carbon-carbon backbones, such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyacrylates, are produced using chain-growth polymerizations. The saturated carbon-carbon backbone of polyethylene with no side groups is a relatively flexible polymer chain. The glass transition temperature is low at -20°C for high-density polyethylene. Side groups on the carbon-carbon backbone influence thermal transitions, solubility, and other polymer properties. 

As was expected, the substitution of PPO with rigid and bulky side groups decreases the flexibility of the polymer chain and the glass transition temperatures of modified polymers increases. This... 

Figure 6. General structure for phosphazenes with mesogenic side groups. Example is a mixed substituent polymer (VII) where R represents the trifluoroethoxy group and the mesogen with flexible spacer is represented by the curlicue and rectangular box.

In recent years, many poly(phosphazenes), [RoPN]n, with a variety of substituents at phosphorus have been prepared and they often exhibit useful properties including low temperature flexibility, resistance to chemical attack, flame retardancy, stability to UV radiation, and reasonably high thermal stability. (1,2) Compounds containing biologically, catalytically, or electrically active side groups are also being investigated. (3,4)... 

The properties of the polycarbonate of bisphenol A are directly related to the structure of the polymer. The molecular stiffness associated with this polycarbonate arises from the presence of the rigid phenyl groups on the molecular chain or backbone of the polymer and the additional presence of two methyl side groups. The transparency of the material arises from the amorphous (noncrystalline) nature of the polymer. A significant crystalline structure is not observed in the polycarbonate of bisphenol A because intermolecular attractions between phenyl groups of neighboring polymer chains in the melt lead to a lack of flexibility of the chains that deters the development of a crystalline structure. 

Below Tg, in the glassy state the main dynamic process is the secondary relaxation or the )0-process, also called Johari-Goldstein relaxation [116]. Again, this process has been well known for many years in polymer physics [111], and its features have been estabhshed from studies using relaxation techniques. This relaxation occurs independently of the existence of side groups in the polymer. It has traditionally been attributed to local relaxation of flexible parts (e.g. side groups) and, in main chain polymers, to twisting or crankshaft motion in the main chain [116]. Two well-estabhshed features characterize the secondary relaxation. 

Flexible segment used to link successive mesogenic units in the molecules of MCPLCs or to attach mesogenic units as side-groups onto the polymer backbone of SGPLCs. 

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