Amorphous polymer definition

The free volume is considered to represent the difference between the actual volume of the liquid (or the amorphous polymer) and the minimum volume which it would occupy if its molecules were packed firmly in contact with each other. Incompressible molecules with rigid dimensions are implied in this definition of a free volume. The unrealistic nature of this implication undermines precise determination, or even an exact definition, of the free volume. The concept has proved useful nevertheless. 

From these definitions one may corroborate the intention of HTS in chemistry and materials science. The total speed-up factor of this part of the R D (Research and Development) process, as stated earlier, is between 5 and 50, but contrary to most of the pharma applications true (semi-) quantitative answers will result. As a result, this approach is essentially applicable in any segment of R D. On the other hand, this approach requires methods of experimentation that have almost the same if not the same accuracy as in the traditional one-experiment-at-the time approach. This is key as (i) in process optimisation accuracy is key and (ii) in research, also in academic research, accuracy is important as some polymer properties do not span a wide range of values (e.g., the elastic modulus of amorphous polymers) or may depend critically on molecular weight distribution or molecular order. 

By definition, thermoplastics have limitations at elevated temperatures. It is in this particular property that fibrous glass can lead to remarkable improvements. However, a sharp division exists for reinforced thermoplastics. The various reinforced thermoplastics can be put in two groups relative to DTUL. These consist of amorphous and crystalline or semicrystalline polymers. The amorphous polymers such as styrene-acrylonitrile, polystyrene, polycarbonate, poly (vinyl chloride), and acrylo-nitrile-butadiene-styrene are generally limited to modest DTUL improvements, usually on the order of 20°F with 20% glass. However, crystalline polymers such as the nylons, linear polyethylene, polypropyl-... 

The character of the polymethyl methacrylate data is essentially similar to that found for systems atactic polystyrene-benzene at 25°, 35°, and 50° C. [Kishimoto, Fujita, Odani, Kurata and Tamura (1960) Odani, Kida, Kurata and Tamura (1961)] and also atactic polystyrene-methyl ethyl ketone at 25° C. [Odani, Hayashi and Tamura (1961)], and appears to be fairly general for amorphous polymer-solvent systems in the glassy state. On the other hand, the cellulose nitrate data shown in Fig. 8 appear to manifest features characteristic of crystalline polymer-solvent systems. For example, the earlier data of Newns (1956) on the system regenerated cellulose-water (in this case, water is not the solvent but merely a swelling-agent) and recent studies for several crystalline polymers all show essentially similar characters [see Kishimoto, Fujita, Odani, Kurata and Tamura (I960)]. To arrive at a more definite conclusion, however, more extensive experimental data are needed. 

Thermo-reversible has the following meaning if an amorphous polymer is heated to above Tg, it readily reaches thermodynamic equilibrium by definition the sample has then "forgotten" its history, any previous ageing it may have undergone below Tg having been erased. In other words it is completely rejuvenated. Ageing therefore is a thermo-reversible process to which one and the same sample can be subjected an arbitrary number of times. It has just to be retreated each time to the same temperature above Tg. 

The addition of glass fibers increases the number of nucleation sites in semicrystalline jxrlymers. This produces an increase in the degree of crystallinity and, consequently, an enhanced heat distortion temperature. By definition, amorphous polymers are noncrystalline and, as such, this mechanism is inoperable. 

The precise definition of the average amount of free volume present in a totally amorphous polymer remains unclear, but it must also depend to some extent on the thermal history of the sample. A number of suggestions have been made. 

Classification Thermoplastic polymer Definition Polymer of methyl methacrylate hard transparent amorphous material Empirical (CsH802)x Formula [CH2CCH3COOCH3]n Properties Powd., gran., cast sheet and block sol. in ethyl acetate, chlorinated soivs. m.w. 60,000 (molding grades), 1,000,000 (cast sheet) dens. 1.188 ref. index 1.4100 tens. str. 72 MPa tens, mod. 2400 MPa... 

Synonyms Atactic polypropylene Isotactic polypropylene Polypropene PP Propathene 1-Propene, homopolymer Propene polymer Propene polymers Propylene polymer Syndiotactic polypropylene Classification Thermoplastic polymer Definition Polymer of propylene monomers three forms isotactic (fiber-forming), syndiotactic, atactic (amorphous)... 

A whole series of indications suggest that X-ray amorphous polymers possess a certain order. However, a definite number of vacant sites must... 

A noncrystalline polymeric material that has no definite order or crystallinity. A polymer in which the macromo-lecular chain has a random conformation in solid (glassy or rubbery) state. On the one hand, an amorphous polymer may show a short range order, while on the other, a crystalline polymer may be quenched to the amorphous state (viz., polyethylene terephthalate (PET)). The maximum value of a periodically varying function, e.g., used to describe the energy transmitted from the ultrasonic welding horn to the weld joint. 

In Chapter 9 the techniques which can be used for the study of molecular interfaces were considered and provide us with the tools to ask the question What are the factors that make definition of the surface difficult In order to help our consideration of the answer it is appropriate to divide the diseussion into three types of system crystalline polymers, amorphous polymers and polymer blends. 

The random coil model has remained essentially the same until today (17), although many mathematical treatments have refined its exact definition. Its main values are two-fold By all experiments, it appears to be the best model for amorphous polymers, and it is the only model that has been extensively treated mathematically. It is interesting to note that by its very randomness, the random coil model is easier to understand quantitatively and analytically than models introducing modest amounts of order (19). 

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