Monofunctional chain-terminating molecule

Polyester plasticizer n. Any of a broad class of plasticizers characterized by having many ester groups in each molecule. They are synthesized from three components (1) A dibasic acid such as adipic, azelaic, lauric, or sebacic acid. (2) A glycol (dihydric alcohol). (3) A monofunctional chain terminator such as a monobasic acid. Molecular weights are low - from 500 to 5,000. Polyester plasticizers are noted for their permanence and resistance to extraction. 

The Addition of a Monofunctional Compound The monofunctional compound (e.g., —B) acts as a chain terminator since it produces molecules with unreactive ends. Let us consider A-A and B-B with BX. The initial total number of molecules is given by ... 

Hydroxy-terminated PDMS, however, has disadvantages. The monofunctional ends limit the number of connections between the polymer (or oligomer) molecule and the glass network to two. This limitation raises the possibility that some PDMS molecules are not tied at both ends to the glass network if the polycondensation does not go to completion i.e. there may be "dangling" or loose PDMS chains in the final sol-gel material. This occurance of free ends would indeed be anticipated since the extent of reaction most likely is not 100%. Hence, the physical properties, specifically the mechanical behavior of the overall material, would be expected to suffer as a result of loose PDMS chains in the system. Disregarding this potential problem, the mechanical behavior of the sol-gel hybrids are, ultimately, influenced by the mechanical behavior of the modifying elastomer ... 

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