Polymer properties, controlling

Polyethylene particle growth, over Ziegler-Natta catalysts, 26 530-531 Polyethylene polymer properties, control of, 17 703... 

Table 4. Polymer Property Control Required for a High Resolution Resist...

Ethylene, hydrogen, co-monomer and a super-high activity catalyst are fed into the reactors (1). Polymerization reaction occurs under a slurry state. The automatic polymer property control system plays a very effective role in product-quality control. Slurry from the reactors is pumped to the separation system (2). The wetcake is dried into powder in the dryer system (3). As much as 90% of the solvent is separated from the slurry and is directly recycled to the reactors without any treatment. The dry powder is pelletized in the pelletizing system (4) along with required stabilizers. 

Circulating bed Better polymer properties control Different reacting zone allows production of product not possible with traditional reactors Complex reactor design, high capital cost Still unproven technology... 

The really interesting issues in control of polymerization are not in the control of the operating conditions (flow, temperature, etc.). These loops are controlled in much the same way as would be done in any other chemical process. The real interest is in the control of polymer properties (monomer conversion, MW, particle size, copolymer composition, etc.). The next sections will review a number of control studies, each using a different approach to deal with the control problems specific to polymer property control (lack of sensors, one-sided control, nonlinearities, etc.). This will be followed by a discussion of an alternative approach to polymerization reactor control, statistical process control, and a discussion of the optimization of operating trajectories. 

The effect of radiation on materials has importance in the areas of wire and cable insulation, heat-shrinkable articles, curing of elastomers, plastics, paints and inks, electron beam lithography, medical sterilization, polymer property control, and outer space applications. 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

Mechanical properties of plastics can be determined by short, single-point quaUty control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests iaclude tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep mpture, and environmental stress-crackiag tests usually result ia multipoint curves or tables for comparison of the original response to post-exposure response. 

Because of the capacity to tailor select polymer properties by varying the ratio of two or more components, copolymers have found significant commercial appHcation in several product areas. In fiber-spinning, ie, with copolymers such as nylon-6 in nylon-6,6 or the reverse, where the second component is present in low (<10%) concentration, as well as in other comonomers with nylon-6,6 or nylon-6, the copolymers are often used to control the effect of sphemUtes by decreasing their number and probably their size and the rate of crystallization (190). At higher ratios, the semicrystalline polyamides become optically clear, amorphous polymers which find appHcations in packaging and barrier resins markets (191). 

Minor (by amount) functionality is introduced into polymers as a consequence of the initiation, termination and chain transfer processes (Chapters 3, 5 and 6 respectively). These groups may either be at the chain ends (as a result of initiation, disproportionation, or chain transfer,) or they may be part of the backbone (as a consequence of termination by combination or the copolymerization of byproducts or impurities). In Section 8.2 wc consider three polymers (PS, PMMA and PVC) and discuss the types of defect structure that may be present, their origin and influence on polymer properties, and the prospects for controlling these properties through appropriate selection of polymerization conditions. 

The functional groups introduced into polymer chains as a consequence of the initiation or termination processes can be of vital importance in determining certain polymer properties. Some such functionality is generally unavoidable. However, the types of functionality can be controlled through selection of initiator, solvent and reaction conditions and should not be ignored. 

Due to the high reaction temperatures required during the last stages of these syntheses, side reactions cannot be avoided. Acetaldehyde, carboxyl endgroups, and vinyl endgroups are formed during PET and PEN synthesis. The formation of 2,2/-oxydiethylene moieties in polymer chains by etherification of hydroxyl endgroups is also a well-known side reaction of EG polyester syntheses.264 These reactions should be carefully controlled since they can exert an important influence on polymer properties such as Ts, mechanical properties, hydrolytic stability, and discoloration. 

Amino acids, the building blocks of giant protein molecules have a carboxyl group and an amino group attached to the same carbon atom. A protein is a linear polymer of amino acids combined by pepfide linkages. Twenfy different amino acids are common in proteins. Their side chains, which have a variety of chemical properties, control the shapes and functions of proteins. Some of these side chains are hydrophobic, others are hydrophilic, and still others occur either on the surface or the interiors of proteins. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

Top A, Kiick KL (2010) Multivalent protein polymers with controlled chemical and physical properties. Adv Drug Deliv Rev 62 1530-1540... 

In the past three decades, industrial polymerization research and development aimed at controlling average polymer properties such as molecular weight averages, melt flow index and copolymer composition. These properties were modeled using either first principle models or empirical models represented by differential equations or statistical model equations. However, recent advances in polymerization chemistry, polymerization catalysis, polymer characterization techniques, and computational tools are making the molecular level design and control of polymer microstructure a reality. 

There is no such thing as a pure polymer. All polymers comprise molecules that exhibit chemical and physical distributions of many variables these include molecular weight, branching, steric defects, molecular configuration, preferential chain orientation, and crystallite size and shape. The properties and characteristics that we exploit in polymers are controlled by the overall balance of these distributions. 

Different lengths of chains play different roles in controlling polymer properties. For instance, shorter chains flow more readily.in the molten state and are more readily incorporated into crystallites because they have fewer entanglements to impede their motion. Conversely, longer chains tend to resist flow and impede crystallization. 

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