Polymer spacer concept

Fig. 9.18 The polymer spacer concept for the construction of a biomimetic cell membrane on solids. Mesogenic units, coupling groups and the flexible polymer can be combined either in form of a statistical terpolymer (above). Variation of the ratio of the three monomers allows an easy tuning of the system. In an alternative system, an end-functio-nalized linear hydrophilic polymer chain bearing a coupling group at the proximal and the mesogen at the distal end was employed.

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

The first studies of the orientational distribution function in liquid crystalline side chain polymers have employed NMR on selectively labeled polymers [31]. By revealing a gradient of decreasing order from mesogen via spacer to main chain, these studies have shown the basic validity of the spacer concept [98,99], namely, the decou-... 

Structure of linear LC polymers. The concepts of the structure of LC polymers is based on data obtained by different methods. The most systematic study of polymers of related structure (Table 5.1) was conducted in [62,63] with the same mesogenic fragment and different types of spacer groups ... 

There are different polymer structures that exhibit LC phases. The extension of the mesogen s rigid aromatic core leads to main chain polper systems. Other approaches are based on the spacer concept. Here rigid cores that are common in LMWLCs are decoupled by flexible alkyl chains. The mesogenic units can be placed either in the main or in the side chain. Also combined MCLCP/SCLCPs have been prepared (figure 3). 

Investigations in the past years have proved that applying the concept of flexible spacer, polymers can be synthesized systematically, which exhibit the l.c. state. Owing to the flexible linkage of the mesogenic molecules to the polymer main chain, very similar relations can be expected with respect to 1-l.c., like chemical constitution and phase behavior, or dielectric properties and field effects for the l.c. side chain polymers. This will be in contrast to main chain polymers, where the entire macromolecule, or in case of semiflexible polymers parts of the macromolecules, form the l.c. structure. The introduction of a flexible spacer between backbone and mesogenic group can be performed in a broad variety of chemical reactions. Some arbitrarily... 

The final class of important synthetic lipids are those with a polymerizable substituent. A significant concept present is the introduction of a hydrophilic spacer group between the hydrophobic core and the polymerizable group. Only in polymers made of spacer lipids does the polymer chain remain flexible enough to decouple its movements from those of the membrane in order to... 

In the case of conventionally produced polymers, the positioning of functional groups at the end of a spacer arm involves a multi-step synthesis, in addition to those needed for the introduction of the functional groups themselves. For the copolymer resins produced by the active ester method, the concept of spacer arm is an integral element of the polymer design. Thus, the desired functionality, already positioned at the end of a 1- to 9-bond spacer... 

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