Processing, polymer history

There are many sources of information about polymer history [Martuscelli et al., 1987 Seymour and Cheng, 1987 Vogl and Immergut, 1987 Alper and Nelson, 1989 Morris, 1989 Seymour, 1989 Sperling, 1992 Mark, 1993 Sparke, 1993 Utracki, 1994, 1998a]. The abbreviations used in this text are listed in Appendix 1. International Abbreviations for polymers and polymer processing. 

During processing, polymers evolve primarily from molten state into final products. Molten state evolves as an intermediate stage of processing. The effect of order that exists upon subsequent chain arrangement becomes important. Many polymer properties are affected in the melt, which includes crystalline properties snch as melt history effect, rate of crystallization, and nucleation intensity. Other properties such as electrical conductivity, solubility, and rheology are not restricted to crystalline polymer. 

B1A Bianchi, U., Cuniberti, C., Pedemonte, E., and Rossi, C., Energy contents of amorphous polystyrene with different thermal histories, J. Polym. Sci. PartA-2, 5, 743, 1967. 1967SCH Schreiber, H.P. and Waldman, M.H., Isothermal calorimeter for studies of polymer solution processes,/. Polym. Sci. PartA-2, 5, 555, 1967. 

With the plethora of competing events, process engineers often find it difficult to operate the polymerization reactor in a way that maintains the production of a polymer with specified PSD characteristics. This is due, in some cases, to the fact that the control of the PSD is practiced by controlling its characteristic variables (e.g., the mean and variance) or olha- easily measured process variables (e.g., temperature, convasion and concentrations). These formulations are not enough for fine PSD control and thus fail in most circumstances when iQiplied to the real process. Moreover, the properties of the polymer formed are influenced by the process/kinetic history. Any unprecedented disturbances in the operating conditions (e.g., tanperature, pressure, flow rates, etc.) may cause drastic irreversible changes in product quality. One should add to this the fact that any reactants (e.g., monomer, initiator, and surfactant) introduced to the process cannot be removed. 

The polymer is exposed to an extensive heat history in this process. Early work on transesterification technology was troubled by thermal—oxidative limitations of the polymer, especially in the presence of the catalyst. More recent work on catalyst systems, more reactive carbonates, and modified processes have improved the process to the point where color and decomposition can be suppressed. One of the key requirements for the transesterification process is the use of clean starting materials. Methods for purification of both BPA and diphenyl carbonate have been developed. 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

It is not feasible here to go in any detail into the history of processing methods let it suffice to point out that that history goes back to the Victorian beginnings of polymer technology. Thus, as Mossman and Morris (1993) report, the introduction of camphor into the manufacture of parkesine in 1865 was asserted to make it possible to manufacture more uniform sheets than before. Processing has always been an intimate part of the gradual development of modern polymers. 

The thermal polymerization of S has a long history.310 The process was first reported in 1839, though the involvement of radicals was only proved in the 1930s. Carefully purified S undergoes spontaneous polymerization at a rate of ca 0.1% per hour at 60 C and 2% per hour at 100 °C. At 180 aC, 80% conversion of monomer to polymer occurs in approximately 40 minutes. Polymer production is accompanied by the formation of S dimers and trimers which comprise ca 2% by weight of total products. The dimer fraction consists largely of cis- and trans-1,2-diphenylcyclobutanes (90 and 91) while the stereoisomeric tetrahydronaphthalenes (92 a nd 93) are the main constituents of the trinier fraction.313... 

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... 

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