Polymeric microstructures, molding

In thermally initiated reaction injection molding the relative slow polymerization starts at elevated temperatures (up to 150 °C) after filling of the microstructured mold inserts with the low viscosity resin. Typical polymerization times necessary for a... 

Shah, J., Y.-C. Su, and L. Lin, Implementation and Analysis of Polymeric Microstructure Replication by Micro Injection Molding, Proceedings of ASME Micro-Electro-Mechanical Systems, Nashville, TN, 295-302,1999. 

The facts that the LCST of PNIPAAm is only 32 °C and the polymerization reaction is highly exothermic can also lead to problems with reproducibility of the gel synthesis. If the solution is deliberately warmed above the LCST during polymerization, an opaque gel with a permanently phase separated microstructure is formed [65]. Depending upon the initial solution temperature, initiator concentration and type, and heat transfer characteristics of the gel mold, the solution temperature can rise substantially during polymerization and alter the gel s properties. 

The procedure for micromolding in capillaries (MIMIC) for fabricating the microstructure of polymeric materials has been reported [155-157], Vacuum-assisted MIMIC was later reported. These methods are essentially casting a soft curable polymer against a mold [158],... 

As the number of technological applications of MIPs continues to increase, there is a growing demand for MIPs tailored to specific physical forms. Polymerization methods to yield the MIPs in the form of size-defined spherical particles at the micro- or nanoscale, monoliths, thick and thin films and molded microstructures have all been published in the last few years [Biffis et al., 2012]. 

The polymer can be made by suspension, emulsion, solution, or bulk polymerization methods. Most of the PVC used in calendering, extrusion, and molding is prepared by suspension polymerization. Emulsion polymerized vinyl resins are used in plastisols and organisols. ° Only a small amount of commercial PVC is prepared by solution polymerization. The microstructure of PVC is mostly atactic, but a sufficient quantity of syndio-tactic portions of the chain allow for a low fraction of crystallinity (about 5 percent). The polymers are essentially linear, but a low number of short-chain branches may exist. The monomers are predominantly arranged head to tail along the backbone of the chain. Due to the presence of the chlorine group, PVC polymers are more polar than polyethylene. The molecular weights of commercial polymers are M = 100,000 to 200,000 ... 

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