Polymerization reactions monitoring

Since the mid-1990s, there has been plenty of activity regarding the use of spectroscopic techniques for on-line evaluation of polymer properties [143-146]. This has been possible due to the recent development of fiber-optic probes, which allow in-situ measurements in remote and harsh environments (high temperatures, pressures, toxic environments, and so on). An additional advantage is that a fiber-optic probe can be installed in an existing reactor within a short time without expensive modifications. Fluorescent, ultraviolet (UV), infrared (IR), near-infrared (NIR), mid-infrared (MIR) and Raman spectroscopic techniques can be used for polymerization reaction monitoring. These can be divided between absorption- and emission-based techniques. IR, NIR, and MIR are absorption-based. 

Alb AM, Reed WF. Fundamental measurements in online polymerization reaction monitoring and control with a focus on ACOMP. Macromol React Eng 2010 4 470-485. 

In the context of living polymerization reactions monitored by NMR, H NMR spectroscopy was also employed in following reaction kinetics in the case of the (ROP). Thus, a study of Li et al. [160] investigated reaction mechanism for ROP of L-lactide (LLA) in bulk and toluene, respectively, with sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al) as the catalyst. The mechanism of the ROP was postulated to follow the coordination type, based on the analysis of H NMR spectral data of the polymers formed at different reaction times. Quantitative estimations of the... 

In the context of monitoring polymerization reactions, IR spectroscopy has a long history, with early reports of its use related to polymerization reaction monitoring stretching back to at least the 1950s [46,47], with a subsequent report of continuous IR measurements at 805 cm" to monitor ethacrylate polymerization in toluene [48]. IR methods have been extended to offline copolymer sequence length analysis [49, 50], curing reactions [51], picosecond time-resolved studies of initiation events [52], and other aspects of polymer characterization. 

In the past 20 years, IR monitoring has become increasingly common for polymerization reaction monitoring [53,54-57], therefore, a variety of near and mid-IR in situ probes are now commercially available. While IR is well suited to homopolymerization, copolymerization monitoring, while often quite feasible [58-61], can present... 

The HCSTR used in Reference [38] allowed for variation of flow rates, initiator, and other reagent concentrations. The rate constant a could be determined in batch polymerization reactions monitored by ACOMR The system was used to investigate the effects on/, M, and t] of changing the different flow and concentration variables. 

A careful investigation of the reaction kinetics and detailed trapping experiments allow the conclusion that in this case a a-bond metathesis reaction mechanism applies. The polymerization reaction of PhSiH3 by CpCp Hf(SiH2Ph)Cl has been monitored by H-NMR spectroscopy. The data k(75 °C) = 1.1(1) x 10-4 M 1 s AH = 19.5(2) kcal mol" AS = -21(l)euandkH/fcD = 2.9(2) (75 °C) are in good agreement with the proposed mechanism with a metallacycle as transition state [164],... 

In summary, these exploratory data suggest that the chromatographic method used could be a valuable tool for study of this polymerization reaction. Reasonable data were obtained for amount and composition of the copolymer. Formation of graft polymer and/or nitrile rich polymer was detected. More detailed chromatographic study of this batch polymerization could lead to a practical on-line monitoring method... 

To determine the rate behavior of chain growth polymerization reactions, we rely on standard chemical techniques. We can choose to follow the change in concentration of the reactive groups, such as the carboxylic acid or amine groups above, with spectroscopic or wet lab techniques. We may also choose to monitor the average molecular weight of the sample as a function of time. From these data it is possible to calculate the reaction rate, the rate constant, and the order of the reacting species. 

Some TICT-forming fluorescent probes containing the / j - /V. /V - cl i a I k I a m i n o benzylidene malononitrile motif (usually related to 30 in Fig. 11) have been applied to monitor and quantify polymerization reaction, crosslinking, chain relaxation,... 

Bosch P, Peinado C, Martin V, Catalina F, Corrales T (2006) Fluorescence monitoring of photoinitiated polymerization reactions synthesis, photochemical study and behaviour as fluorescent probes of new derivatives of 4-dimethylaminostyryldiazines. J Photochem Photobiol A Chem 180(1-2) 118-129... 

Molecular rotors allow us to study changes in free volume of polymers as a function of polymerization reaction parameters, molecular weight, stereoregularity, crosslinking, polymer chain relaxation and flexibility. Application to monitoring of polymerization reactions is illustrated in Box 8.1. 

Box 8.1 Monitoring of polymerization reactions by means of molecular rotors3 ... 

Two different kinds of cleavage protocols were investigated. The first was a light induced photo-release reaction followed by a chromatographic work-up. Also, reaction monitoring was performed by MALDl/TOF/MS since the LASER cleaves the disaccharide from the support The second is a hydrolytic cleavage reaction under degradation of the polymeric support and subsequent aqueous extraction to yield the pure product The disaccharides (20) were obtained in yields of 27-76%. 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

The first three components were mixed at room temperature and heated at 65°C In a 250 ml round bottom flask equipped with a magnetic stirring bar, reflux condenser and Na blanket. The AIBN was then added to start the reaction. Monitoring of the unreacted free monomers (butyl acrylate and comonomer) was done by GLPC. Additional 10 mg amounts of AIBN were added as needed. The temperature was also Increased to 75 C to finish the polymerization. Host of the reactions took longer than 24 h to reduce the free monomer below 0.7%. A control BA homopolymer and copolymers with butoxymethylacrylamide (BNMA), 2 (R = Et AEP), acrylamidoacetaldehyde dimethyl acetal (AADMA), and N-ethyl-1 (Et-ABDA, 13) were prepared In this way. 

---