Polyamides rigid-flexible

M. Aharoni, Rigid Backbone Polymers.XVIII. Strictly Alternating Rigid-Flexible Polyamides, J.Polym. Sci.Polym. Phys.Ed., i9 28l (1981). 

Aharoni S M (1981) Rigid-backbone polymers. 18. Strictly alternating rigid-flexible polyamides, J Polym Sci Part B Polym Phys 19 281-292. 

Chuah H H, Kyu T and Helminiak T E (1989) Scaling analysis in the phase separation of poly(j> phenylene benzobisthiazole)/Nylon-66 rigid-rod molecular composites, Polymer 30 1591-1595. Chang K Y, Chang H M and Lee Y D (1994) Molecular composites. 2. Novel block copolymer and semi-interpenetrating polymer network of rigid polyamide and flexible polyamide polyimide, J Polym Sci Part A Polym Chem 32 2629-2639. 

Polymeric hindered amine light stabilizer is excellent for protection against ultraviolet degradation. Applications include polyolefins (polypropylene, polyethylene), olefin copolymers such as EVA as well as blends of polypropylene with elastomers. Also effective in polyacetals, polyamides, polyurethanes, flexible and rigid PVC, and PVC blends. 

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). 

Polymers Unsaturated fatty-acid chains offer opportunities for polymerisation that can be exploited to develop uses in surface coatings and plastics manufacturing. Polyunsaturated fatty acids can be dimerised to produce feedstocks for polyamide resin (nylon) production. Work is also ongoing to develop polyurethanes from vegetable oils through manipulation of functionality in the fatty-acid chains, to produce both rigid foams and elastomers with applications in seals, adhesives and moulded flexible parts (see Chapter 5 for more information). 

Note-. 2 - sufficient thermal stability and limited reactivity with polymer allows broad use, 1 = marginal thermal stability or potential reactivity with polymer restricts use, 0 = generally unsuitable for use. FPVC, Flexible Polyvinyl Chloride RPVC, Rigid Polyvinyl Chloride PS, Polystyrene LDPE, Low Density Polyethylene HDPE, High Density Polyethylene PP, Polypropylene ABS, Acrylonitrile-butadiene-styrene copolymer PET, Polyethylene terephthalate PA, Polyamide PC, Polycarbonate... 

Polyester fibers, similar to polyamide fibers, represent another important family of fiber. Polyester fiber was discovered in England in 1941 and commercialized in 1950. Two common trade names of polyester are Dacron in the US and Terylene in the UK. The term polyester fiber represents a family of fibers made of polyethylene terephthalate. Dimethyl terephthalate is reacted with ethylene glycol in the presence of a catalyst, antimony oxide, to produce polyethylene terephthalate or polyester. The chain repeat structure of PET is given in Fig. 4.6. Although polyesters can be both thermosetting and thermoplastic, the term polyester has become synonymous with PET. Note that the PET chain structure is different from the simpler structure of nylon or polyethylene. In PET, the aromatic ring and its associated C-C bonds provide a rigidity to the structure. The polyester structure is also bulkier than that of nylon or polyethylene. These factors make polyester less flexible than nylon and polyethylene, and the crystallization rate of PET slower than that of nylon or polyethylene. Thus, when polyester is cooled from the melt, an appreciable amount of crystallization does not result. 

It should be taken into account that in very rigid chains, such as those of poly-(alkyl isocyanate)s and para-aromatic polyamides, apart from rotation about valence bonds another mechanism can contribute to flexibility the deformation of valence angles and bonds during thermal chain motion just as it should occur in ladder structures (p. 100). When several flexibility mechanisms exist, the resulting rigidity of the homopolymer chain can be evaluated if the flexibilities, resulting from different mechanisms, are considered to be additive and the following equations are used ... 

The copolymerization of PCHA and caprolactam can yield copolymers with a flexibility intermediate between those of the two components. In this case, just as for aromatic polyamides (Fig. 44), the rigidity (number of monomer units S per segment) of the copolymer can be evaluated a priori from the relative composition Z and rigidities Sj and 2 of the components by using the rule of the additivity of flexibilities (Eqs. (74) and (75)). This is demonstrated in Fig. 50 which shows that minute amounts of a more flexible component can greatly reduce chain rigidity. 

Recent developments in the substitution of completely aromatic LC polyesters have produced polymers which show improved solubilities and reduced transition temperatures (29). The presence of these side groups provides a method for producing polymers that are compatible with other similarly modified polymers. In this way, blends of rigid and flexible polymers can be prepared. Substituents have included alkyl, alkoxy (30) and phenyl alkyl groups (21), some of which lead to mesophases that have been reported as being "sanidic" or board-like. This approach has been used with both polyesters and polyamides and has lead to lyotropic and thermotropic polymers depending on the particular composition used. Some compositions even show die ability to form both lyotropic and thermotropic mesophases (22). 

Note A = acrylic CA = cellulose acetate CAB = cellulose acetate butyrate CN = cellulose nitrate E = epoxy EC = ethyl cellulose N = nitrile P = phenolic PC = polycarbonate PA = polyamide PE = polyethylene PET = polyester, thermoset PP = polypropylene PS = polystyrene PVA = polyvinyl acetate PVC = polyvinyl chloride UFF = urethane flexible foam UFR = urethane rigid foam. 

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