Analysis of Homopolymers

Infrared (IR) spectra of thin films of a polymer in the region up to 2.5 lm are characteristic of the polymer. Computerised retrieval from data in a library of standard polymers has been used in the IR fingerprinting technique to facilitate polymer identification [1]. 

Alexander [2] has described a method for obtaining spectra of thin films of polymer that are free of interference fringes. 

Various methods have been used to prepare polymers for IR spectroscopy  

Alternatively, the sample material can be dissolved in a suitable organic solvent and a film cast onto glass or a cell window. 

A new sample handling accessory with which films of constant thicknesses can be prepared has been introduced by Phillips Analytical. The plastic film press contains a thermostatically controlled oven unit that is calibrated up to 300 °C. It also contains a cooling facility which may be connected to a low-pressure compressed air supply to cool the prepared films rapidly. Reproducible thickness is ensured by using a set of brass dies that can be heated and cooled quickly. The dies can produce films of 20, 50, 100, 200, and 500 pm thickness. 

---

It was found that acid enhances grafting and homopolymer formation. Analysis of homopolymers shows that acid reduces the chain length but increases the number of grafted chains. 

Thermal analysis of homopolymer samples are simpler than those of blends. Separate thermal analysis of individual polymer components are made before doing the same for a blend in order to get more accurate and proper information on thermal characteristics. 

In analysis of homopolymers the critical interpretation problems are calibration of retention time for molecular weight and allowance for the imperfect re >lution of the GPC. In copolymer analysis these interpretation problems remain but are ven added dimensions by the simultaneous presence of molecular weight distribution, copolymer composition distribution and monomer sequence length distribution. Since, the GPC usu y separates on the basis of "molecular size" in solution and not on the basB of any one of these particular properties, this means that at any retention time there can be distributions of all three. The usual GPC chromatogram then represents a r onse to the concentration of some avera of e h of these properties at each retention time. 

The aim of qualitative analysis of homopolymers by infrared spectroscopy is the elucidation of polymer structure and compound identification. This often entails the identification of the functional groups and the modes of attachment to the polymer backbone [2,4,25,26], In the case of mixtures, the aim of qualitative... 

Infrared or NMR analysis of homopolymers nearly always indicates one terminal vinyl and one methyl group per chain. Other structures with branching or internal unsaturation occur very infrequently. One can imagine schemes in which the vinyl group forms first (65), but termination by / -hydride elimination seems more likely, at least until evidence to the contrary... 

In the case of copolymers, any single detection method will have variable sensitivity for each type of mer. If the copolymer composition is itself a variable, then the use of dual or even multiple detectors will be required for accurate results. Calibrations for both homopolymers should be followed, if possible, by an analysis of homopolymers of similar molecular weights, before attempting an analysis of the copolymers themselves. 

The study of the macromolecular microstructure gives information on the stereochemical mechanism of polymerization. The NMR analysis of homopolymers and copolymers of selectively deuterated propylenes allowed the determination of the mechanism of addition to the double bond in the stereospecific polymerizations. The causes of the steric control may be also evidenced by micro-structural analysis on suitable macromolecules. 

Other applications of FTIR in microstructural analysis of homopolymers include 1,4-diazophenylene - bridged Cu-phthalocyanine [63], isobornyl methacrylate [64], polypropylene [65, 66], polyaniline [67, 68], polycaprolactone [69], viscose fibres [70], Kevlar [71], polystyrene sulfonic acid [66, 72], syndiotactic polystyrene [73], isotactic polypropylene [66,74,75], polyurethane [76], PMMA [75, 77], poljmrethane ether [78], PE [79-80], fluorinated acrylates [81], rigid PU [82], N-(2-biphenyl)4-(2 phenylethynyljphthalamide [83], polyacrylic acid [84], polysodium styrene sulfonate [84], and polyacrylic acid [85]. 

---