Poly physical structure

Polypeptides obtained by the anionic polymerization of optically active N-carboxy-a-amino acid anhydrides are apt to have such an ordered structures as a-helices, which is useful for investigation on the relationship between the physical structure and the permeability of the membrane. Takizawa et al.44 46) studied the water permeation and solute separation through poly(n-alkyl L-glutamate) membranes 3. It was concluded that water molecules permeate through relatively large free spaces... 

Morgan RJ, Pruneda CO, Steele WJ (1983) The relationship between the physical structure and the microscopic deftamation and failure process of poly(p-phenylene terephthalamide) fibers. J. Polymer Sci., Polymer Phys. Ed. 21 MSI... 

Bai, Y.X., Qian, J.W., Zhao, Q., Zhu, Z.H. and Zhang, P. 2007. Effect of recovery conditions of poly(ethylene-co-vinyl acetate) membrane on the membrane physical structure and pervaporation properties in the recovery of ethyl acetate from aqueous solution,... 

Some polymers are insoluble in their own monomers and therefore are precipitated during polymerization. Examples are poly(vinyl chloride) and poly(acrylonitrile). Polymerization continues in the precipitated product, but its rate is determined by the diffusion of the monomer to the free radicals and consequently by the physical structure of the coagulate. Factors such as the rate of agitation can thus affect the rate of polymerization quite considerably. The advantage of precipitation polymerization is that the polymers immediately assume solid form. For this reason, polymerizations are often carried out with the addition of substances that precipitate the polymer but that are also solvents for the monomer. 

Fig. 17.5. Physical structure of fibers (a) semicrystalline structure of poly(ethylene terephthalate), PET the broken lines are the borders of a fibril (b) paracrystalline structure of poly(p-phenylene terephthalamide), PPTA.

Categorize the following polymers with regard to their low-temperature physical structure polyethylene isotactic polypropylene poly (ethylene terephthalate) isotactic polystyrene atactic polystyrene atactic poly(vinyl alcohol) atactic poly(vinyl acetate) poly(ethylene-sfflf-propylene) with 50/50 molar composition, and the same polymer but with molar composition 98/2. 

On the other hand, the photodegradation of segmented polyurethanes based on methylene 4,4 -diphenyldiisocyanate (MDI) is dependent on the physical structure of the polymer. Such segmented polyurethanes are formed from poly(ethylene oxide) (PEO) or poly(tetramethylene oxide) (PTMO) with various polyether polyols, which are chain extended with 1,4-butanediol (EDO) [680-682, 1006, 1321]. 

Bonilla J, Fortunati E, Atares L, Chlralt A, Kemy JM (2014). Physical, structural and antimicrobial properties of poly vinyl alcohol-chitosan biodegradable films. Food Hydrocolloid, 35,463-470. 

By the mid-1960s, it became well established that the moduli of the then-available fully drawn semicrystalline fibres were less than about one tenth of the corresponding crystal moduli in the chain direction. This was ascribed to the physical structure, in particular to a low fraction of load-bearing extended tie molecules. The discovery of fibres produced from rigid-chain aromatic polyamides" " gave the most direct proof that this explanation is correct. The modulus of a recently introduced improved type of poly(p-phenyleneterephthalamide) fibre, PRD 149, is 165 GPa, i.e. nearly 70% of the higher estimate of the chain modulus. New processes, developed... 

Heuvel, H. M., and R. Huisman, Effect of Winding Speed on the Physical Structure of As-Spun Poly(ethylene terephthalate) Fibers, Including Orientational-Induced Crystallization, J. Appl. Polym. ScL, 22, 2229-2243, 1978. 

Poly(p-pheny lene)s, PPPs, constitute the prototype of rigid-rod polymers and are currently being intensively investigated [1]. The key role of PPPs follows from their conceptually simple and appealing molecular structure, from their chemical stability, and from their superior physical properties [2], In turn, this is the result of important advances made in aromatic chemistry over the last few years. The following section gives an overview of the most common methods to generate poly(p-phenylene)s via different synthetic approaches. 

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