Ring-opening polymerization monitoring

However, the danger of this approach is that the traps themselves may cause /3-proton elimination which lead to undetectably low concentration of active (or temporarily deactivated) chain ends. Malonate traps and H NMR analysis of the resulting terminal ester groups have been used successfully to monitor the growing chains in vinyl ether polymerizations [209], This technique measures the sum of dormant species and growing carbenium ions. Another method first used to monitor the active species in ring-opening polymerizations traps the active and dormant chain ends with phosphines [Eq. (135)]. 

The consumption of cyclosiloxane during polymerization and copolymerization was monitored by GC. The conversion of D3 was nearly 100 % (Fig. 1). In contrast, the ring-opening polymerization of d/ yielded a conversion of about 60 % only (Fig. 2). During the copolymerization with D3 the cyclic vinylsiloxanes showed a similar behavior as observed during homopolymerization. 

Kinetics and Mechanism. Since the ring-opening polymerizations of by MeOTf and Mel are clean reactions, they are amenable to a kinetic study. The kinetic analysis was carried out by monitoring the polymerization reaction using NMR spectroscopy. 

The activity of CALB immobilized on resins 1 to 4 (see Table 1) was assessed by s-CL ring-opening polymerizations. All immobilized resins have similar CALB loading (5.1 to 5.7 %-by-wt) and water content (1.4 to 1.9%). As shown previously , different chemical shifts are observed for methylene protons (-OC//2-) of e-CL monomer, PCL internal repeat units and chain terminal -012-OH moities. Hence, by in situ NMR monitoring, monomer conversion and polymer number average molecular weight (A/ ) were determined. 

Other compounds present in the polymer are trace amounts of initiators, coinitiators, and catalysts. Most effective and commonly used initiators for ring-opening polymerization of lactide are based on tin, and include tin(II) 2-ethylhexanoate. Due to its low toxicity, tin(II) 2-ethylhexanoate has been approved by the FDA. The residual concentration of tin(II) 2-ethylhexanoate in the polymer is strictly controlled to a safe level and is monitored. In addition, many studies have been conducted on development of a new range of initiators and catalysts based on metals that are more biocompatible, including magnesium and calcium. 

Confirmation that the polymerizations proceed via metallacyclic intermediates was obtained by studying the ROMP of functionalized 7-oxanorbornadienes. These polymerize slower than their norbornene analogs, allowing NMR identification of the metallacyclobutane resonances and subsequent monitoring of ring opening to the first insertion product. In addition, the X-ray crystallographic structure of complex (212) has been reported.533... 

The ring-opening metathesis polymerization of dicyclopentadiene was monitored by ultrasonic spectroscopy.16 The thermoset poly(dicyclopentadiene) is formed by ringopening and cross-linking in a reaction injection molding system. A reaction cell with a plastic window was constructed for use with pulse echo ultrasonic spectroscopy. Realtime measurements of density, longitudinal velocity, acoustic modulus and attenuation were monitored. Reaction kinetics were successfully determined and monitored using this technique. 

Monitoring and evaluation of the crossover reaction in ring-opening metathesis polymerization (ROMP) via MALDI methods were reported recently by Binder et al. [97]. The crossover reactions as well as the polymerization kinetics of the various monomers were studied in the presence of different catalysts by kinetic analysis and MALDI MS. Whereas the classical kinetic analysis enabled the qualitative monitoring of the chain-growth reaction, MALDI method allowed the monitoring of the reaction directly at the point of the crossover reaction, thns enabling a better evalnation of the different monomers and catalysts employed in the polymerization reactions. 

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