Polyester catalytic reaction mechanism

Solution reactions between diacid chlorides and diols or diphenols are carried out in THF or CH2C12 at —10 to 30°C in die presence of tertiary amines such as triethylamine or pyridine, which play a role of both reaction catalyst and HC1 acceptor (Scheme 2.26). This synthetic mediod is also termed acceptor-catalytic polyesterification.295-297 High-temperature solution reactions have also been reported for a number of less soluble, generally semicrystalline, aromatic polyesters.6 They yield high-molar-mass polyesters exhibiting good mechanical properties and thermal stability. 

The production of nylons and polyesters, which were first synthesized in the 1930s, has led to the development of man-made fibers. The complex sequence of catalytic reactions involved in both processes was originally based on 1930s technology but, as the reaction mechanisms came to be understood, catalysts were improved and, in some cases, new petrochemical feeds were introduced. 

Considerable effort has been carried out by different groups in the preparation of amphiphihc block copolymers based on polyfethylene oxide) PEO and an ahphatic polyester. A common approach relies upon the use of preformed co- hydroxy PEO as macroinitiator precursors [51, 70]. Actually, the anionic ROP of ethylene oxide is readily initiated by alcohol molecules activated by potassium hydroxide in catalytic amounts. The equimolar reaction of the PEO hydroxy end group (s) with triethyl aluminum yields a macroinitiator that, according to the coordination-insertion mechanism previously discussed (see Sect. 2.1), is highly active in the eCL and LA polymerization. This strategy allows one to prepare di- or triblock copolymers depending on the functionality of the PEO macroinitiator (Scheme 13a,b). Diblock copolymers have also been successfully prepared by sequential addition of the cyclic ether (EO) and lactone monomers using tetraphenylporphynato aluminum alkoxides or chloride as the initiator [69]. 

Some of the earliest work on the use of imidazolium-derived NHCs as catalysts focused on their ability to serve as initiators for polymerization reaction. Pioneers of this area, Waymouth and Hedrick extensively investigated the synthesis of polyesters under the influence of an NHC catalyst. Their results have been summarized in a number of excellent accounts. In 2002, Hedrick first investigated catalytic living polymerization using NHCs for cyclic esters (Scheme 14.27). Then, Waymouth and Hedrick studied polymerization of lactides and a-caprolactones and explored the chemical and mechanical properties of the resulting polymers. Also, the use of multifunctional alcohol initiators, such as ethylene glycol or pentaerythritol, produced star polymers with good conversion and low PDI (polydispersity index). ... 

The second type of chemically amplified depolymerization resist mechanism depends upon the incorportation of C-O bonds into the polymer backbone which can be cleaved by either hydrolysis or addolysis. This concept was first advanced by Crivello, who proposed that polymers such as polycarbonates and polyesters could undergo photo-induced add catalyzed hydrolysis reaction in polymeric film (9, 76). Although polymers could be designed to undergo catalytic chain cleavage in the presence of add, such an approach depends upon the inclusion of stoichiometic amounts of water in the polymer film. Uttle further work was reported on this concept until recently, when a new system for dissolution inhibition was described based upon the hydrolysis of polysilyl ethers in a novolac resin (24). 

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