Polymers molecular flexibility/rigidity

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

Plasticixers arc low-molecular-weight liquids that lower the glass transition temperature of a polymer. A typical example is the use of dioctyl phthalate in poly(vinyl chloride) to convert the polymer from a rigid material to a soft, flexible one. It the glass transition of the two components A and B are known, an estimate can be made of the Tg value of the mixture by one or the other of the equations... 

Among others, chain flexibility/rigidity, crystallinity, hydrophilicity/hydrophobicity, molecular weight, chemical property, biodegradability, thermal property, mechanical property, and electrochemical property of polymers are considered to affect the performance of membranes most strongly. Moreover, these properties are often mutually interrelated. 

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

In this section, we review three representative cases of flow-induced mesophases. PET serves as an example of a semi-rigid polymer with intrinsic rigid building blocks. The shear-induced smectic ordering in the flexible-chain polymer iPP provides a special case of induced rigidity, which is still far from fully understood. PDES has been chosen as an example of a stretch-induced condis crystal. Various experimental techniques have been employed to characterize flow-induced mesophases. While scattering methods probe the ordering, a direct technique to measure the molecular mobility is nuclear... 

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