Aging solid polymers

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Figure 5. Conversion of isoprene to solid polymer as a function of Al/Ti molar ratio and catalyst aging triisohexylaluminum-TiCU catalyst system polymerization time—22 hours.

Environmental aging of cellular polymers is important in most applications. The response of cellular materials to light and oxygen is governed almost entirely by the composition and state of the polymer phase [8]. Expansion into a cellular state increases the surface area reactions of the foam with vapors and liquids are correspondingly faster than those of solid polymer. All cellular polymers deteriorate under the combined effects of light or heat and oxygen this may be alleviated by additives [63],... 

Chemical resistance of foams is generally similar to their solid polymers, but somewhat lower because of the high surface/volume ratio exposed to chemical attack, and also because of orientation strains frozen in during expansion. Aging is similar but somewhat faster, as discussed earlier, for thermal stability. Permeability... 

In this electronic age, it is mandatory to use solid polymer electrolytes for different applications in science and technology. Polymer electrolytes can be shaped in the form of thin film, thereby reducing the internal resistance leading to application as gas sensing material. Few reports appeared on proton-conducting polymer films and their application to gas sensors [65]. 

The factors, which influence the permeability or mass transport, are the following chemical composition of the polymer matrix and its free volume. In fact, crystallinity, molecular orientation, and physical aging in turn influence the free volume of a polymer matrix. In addition, porosity and voids, like free volume, offer sites into which molecules can absorb and are far less of a barrier to transport than solid polymer. Temperature also affects permeability and diffusion properties of small molecules in polymers. With increased temperature, the mobility of molecular chains (in polymer) increases and thermal expansion leads to reduced density therefore, the free volume in the system will increase. External tensile stress applied is expected to increase free volume and open up internal voids or crazes, providing additional sites into which molecules can absorb. Of course, there may be unquantified internal residual stresses, arising from processing, present in the polymers. It is well established that the properties of materials... 

IM Hodge. Physical aging in polymer glasses. Science 267 1945 1947, 1995. BC Hancock, SL Shamblin, G Zografi. Molecular mobility of amorphous pharmaceutical solids below their glass transition temperatures. Pharm Res 12 799-806, 1995. 

Usually, production quantities are made up automatically. The standard automatic make-up plant will consist of a mixing vessel, into which water is admitted at a constant rate. The solid polymer is metered out from a hygroscopically secure hopper, using a screw feeder, into the incoming stream of make-up water. Some automatic systems use an air blower to convey the polymer, entering the air stream via a venturi, to a mixer, where the water enters with a cyclone action to keep the powder away from the mixer walls. From the mixer the product falls into a stirred ageing vessel. 

The physical nature of solid polymer is such that it requires a finite time, at least half an hour, to fully dissolve and for the molecular chain to unwind and become fully functional. Once made up in the mixing vessel, the solution is aged with gentle stirring for the requisite time, usually at least half an hour and up to one hour, before it is transferred to a second tank used for feeding to the decanter. 

The use of chemiluminescence to study the kinetics of the oxidation of solid polymers [721] and polymer ageing [722,1459,1460] has been reviewed elsewhere. 

It is shown from these data that the presence of solvent in the formulated material influences the plasticizer (P2) migration. This study of plasticizer and solvent migration in a solid propellant formulation gave insight into the effects of residual solvents, observed "stabilization periods", and general aging of polymer composites. Similar behavior of plasticizers, stabilizers. 

Al-Malaika, S. and Amir, E.J., Thermoplastic elastomers Part III—Ageing and mechanical properties of natural rubber-reclaimed rubber/polypropylene systems and their role as solid phase dispersants in polypropylene/polyethylene blends, Polym. Degrad. Stab., 26, 31, 1989. 

The unbranched polymer produced by P. polycephalum and related Physarum strains has a weight average molecular weight between 40,000 and 60,000 Daltons and a polydispersity of 1.5-3.0 depending on the culture conditions and the age of the samples [111]. The acid form of poly-/ -malate does not show either a Tg or a Tm in the solid state, by DSC analysis, below its thermal decomposition temperature of 185 °C. 

---