Polymer HPLC monomers

High-press (HPLQ is a separation technique employed for the analysis of low- to medium-molecular-weight compounds, typically under 2000 Da. The technique is particularly effective for the separation of multicomponent samples containing nonvolatile, ionic, isomeric, and thermally labile components. Major applications include the determination of residual monomers, additives, and solvents in polymers. HPLCs are normally equipped with UV detectors, diode-array detectors, or other appropriate detectors depending on the nature of the analyte of interest. Options to perform precolumn or postcolumn derivatization for samples that may need introduction of special functionalities for detection are also available. 

Before polyacrylamides are sold, the amount of residual acrylamide is determined. In one method, the monomer is extracted from the polymer and the acrylamide content is determined by hplc (153). A second method is based on analysis by cationic exchange chromatography (154). For dry products the particle si2e distribution can be quickly determined by use of a shaker and a series of test sieves. Batches with small particles can present a dust ha2ard. The percentage of insoluble material is determined in both dry and emulsion products. 

Fig. 3. Graph based on an hplc chromatogram of a commercial PTMEG of molecular weight = 1000. The bars represent the weight percentage of the individual oligomer fractions. The degree of polymerization is the number of repeating monomer units per polymer chain.

An alternative technique to NMR spectroscopy is chromatography. The partially functionalized sample is completely fimctionahzed with a group different from the one present, the product carefully de-polymerized, its structure examined with a chromatographic technique. For example, partially substituted CA was further derivatized with methyl vinyl ether, the product hydrolyzed, the monomers produced examined with gas chromatography [241]. HPLC has been advantageously applied for the determination of substitution pattern for CAs with DS 0.8 to 3.0, by employing the same approach, i.e., further derivatization of the partially derivatized polymer with methyl trifluoroacetate, followed by de-polymerization. The results obtained by this technique compared favorably with those obtained by NMR [242]. 

Use of GPC to separate all polymer from all monomer and subsequent analysis of the monomer using HPLC ... 

Hydrolysis of polyamide-based formulations with 6 N HC1 followed by TLC allows differentiation between a-aminocaproic acid (ACA) and hexamethylenedi-amine (HMD) (hydrolysis products of PA6 and PA6.6, respectively), even at low levels. The monomer composition (PA6/PA6.6 ratio) can be derived after chromatographic determination of the adipic acid (AA) content. Extraction of the hydrolysate with ether and derivatisa-tion allow the quantitative determination of fatty acids (from lubricants) by means of GC (Figure 3.27). Further HC1/HF treatment of the hydrolysis residue, which is composed of mineral fillers, CB and nonhydrolysable polymers (e.g. impact modifiers) permits determination of total IM and CB contents CB is measured quantitatively by means of TGA [157]. Acid hydrolysis of flame retarded polyamides allows to determine the adipic acid content (indicative of PA6.6) by means of HPLC, HCN content (indicative of melamine cyanurate) and fatty acid (indicative of a stearate) by means of GC [640]. Determination of ethylene oxide-based antistatic agents... 

The main limitation of these CSPs is their limited pressure stability, which makes them not very suitable for HPLC application. However, they have proved to be an excellent tool for the preparative separation of drugs by low-pressure HPLC. To make these CSPs accessible to HPLC, silica gel-based phases were developed. " This type of phase is available from Merck (Darmstadt, Germany) under the name Chiraspher. Polymer phases of different types have been developed by Okamoto s group. > They are prepared by the asymmetric polymerization of triphenylmethyl-methacrylate monomers. The original character of these polymers is that they do not possess any chiral centre and therefore their chirality is only due to their helicity. However, clear mechanisms have not been proposed... 

Fig. 3.8 Normal-phase-HPLC chromatograms of PA fractions generated by a combination of solvent extraction and column chromatography on Toyopearl resin (protocol 2). a monomer-rich, b ohgomer-rich, c dimer-rich, and d polymer-rich fractions. Compounds were detected with post-column derivatization using DMACA...

Methacrylate monoliths have been fabricated by free radical polymerization of a number of different methacrylate monomers and cross-linkers [107,141-163], whose combination allowed the creation of monolithic columns with different chemical properties (RP [149-154], HIC [158], and HILIC [163]) and functionalities (lEX [141-153,161,162], IMAC [143], and bioreactors [159,160]). Unlike the fabrication of styrene monoliths, the copolymerization of methacrylate building blocks can be accomplished by thermal [141-148], photochemical [149-151,155,156], as well as chemical [154] initiation. In addition to HPLC, monolithic methacrylate supports have been subjected to numerous CEC applications [146-148,151]. Acrylate monoliths have been prepared by free radical polymerization of various acrylate monomers and cross-linkers [164-172]. Comparable to monolithic methacrylate supports, chemical [170], photochemical [164,169], as well as thermal [165-168,171,172] initiation techniques have been employed for fabrication. The application of acrylate polymer columns, however, is more focused on CEC than HPLC. 

Acrylic Macromers. Thus far we have shown applications of SFC to the characterizations of monomers and crosslinkers. The next couple applications will focus upon the analysis of oligomeric methacrylates, specifically methacrylate macromers. Methacrylate macromers are frequently used as building blocks for larger architecturally designed polymers. Unfortunately, macromers far exceed the capability of GC and do not possess a chromophore for HPLC analysis. Hatada et. al. has used packed column SFC to analyzed the stereoisomers of oligomeric methylmethacrylate (MMA) prepared by anionic polymerization (13). 

The CSPs prepared by the molecular imprint technique have also been used for chiral resolution by CEC [98-100]. Lin et al. [91] synthesized L-aromatic amino acid-imprinted polymers using azobisnitriles with either photoinitiators or thermal initiators at temperatures ranging from 4°C to 60° C. Methacrylic acid (MAA) was used as the functional monomer and ethylene glycol dimethacrylate (EDMA) was used as the cross-linker. The resulting polymers were ground and sieved to a particle size less than 10 pm, filled into the capillary columns, and used for enantiomeric separations of some amino acids at different temperatures. The relationships of separation factor and column temperatures were demonstrated to be linear between the logarithm of the separation factors and the inverse of the absolute temperature (Fig. 24). The authors also compared the obtained chiral resolution with the chiral resolution achieved by HPLC and reported the best resolution on CEC. The chromatograms of the chiral resolution of dl-... 

---