Compositional heterogeneity of copolymers

Dawkins JV (1995) Compositional heterogeneity of copolymers by coupled techniques with chromatographic columns and multidetectors. In Provder T, Barth HG, Urban MW (eds) Chromatographic characterization of polymers. Hyphenated and multidimensional techniques, chap 15. Adv Chem Ser 247, American Chemical Society, Washington, DC... 

The first volume concentrates on separation techniques. H. Pasch summarizes the recent successes of multi-dimensional chromatography in the characterization of copolymers. Both, chain length distribution and the compositional heterogeneity of copolymers are accessible. Capillary electrophoresis is widely and successfully utilized for the characterization of biopolymers, particular of DNA. It is only recently that the technique has been applied to the characterization of water soluble synthetic macromolecules. This contribution of Grosche and Engelhardt focuses on the analysis of polyelectrolytes by capillary electophore-sis. The last contribution of the first volume by Coelfen and Antonietti summarizes the achievements and pitfalls of field flow fractionation techniques. The major drawbacks in the instrumentation have been overcome in recentyears and the triple F techniques are currently advancing to a powerful competitor to size exclusion chromatography. 

During recent years an increasing evidence has accumulated that discernible types of centers exist in Z—N catalysts, particularly in their heterogeneous versions. The centers may differ in their kp values, monomer coordination abilities, stereospecificities and reactivities in copolymerization. This concept can explain — at least qualitatively — wide MWD of polyolefins, composition heterogeneity of copolymers and specific responses of the catalyst performance to electron-donor additives. The origin of the differently behaving centers should be seen in a diversity of chemical processes... 

Compositional Heterogeneity of Copolymers by Coupled Techniques with Chromatographic Columns and Multidetectors... 

The use of multiple detectors has also introduced the possibility of determining the compositional heterogeneity of copolymers, in those cases where the average chain composition varies with chain length [35] (see Section 11.2.3). For this purpose ultraviolet diode array spectroscopy, IR spectroscc y, NMR or mass spectrometry [35] detectors can be utilized. 

V. A. Myagchenkov, S. Ya. Frenkel Compositional Heterogeneity of Copolymers, Khimiya, Leningrad (1988) (in Russian). 

Compositional heterogeneity of the substituted PMMA For all systems investigated (36), the substituted PMMA are characterized by a fairly high chemical homogeneity over the whole range of DSm(DSm<0.76), quite comparable to that of a radical azeotropic S-MMA copolymer (40) (a = 1.6x10 ). The mean square standard deviation o related to two copolymers of DPn =... 

This section is devoted to presenting a variety of TLC results on the compositional heterogeneity of polar copolymers which have been reported to date. For the sake of simplicity, sample copolymers to be discussed were classified into two categories, which are designated polar and nonpolar copolymers. The former refers to copolymers for which the polarities of comonomers are either relatively high or appreciably different from one another, while the latter means those composed of comonomers with lower polarities. 

When one wants to determine the compositional heterogeneity of a given binary copolymer, a series of reference samples with different composition are required to... 

Zhou, Z. and B. Chu. 1988. Anomalous micellization behavior and composition heterogeneity of a triblock ABA copolymer of (a) ethylene oxide and (b) propylene oxide in aqueous solUM laaromolecules 21 2548-2554. 

However, no indications are given of the molecular weights nor of the compositional heterogeneity of the graft copolymers, their properties or potential applications. The existence of a microphase separation was evidenced however on methyl metha-crylate/polyisobutene graft copolymers by means of DSC measurements. Two glass transitions were observed at —68 °C (polyisobutene) and at 102 °C (PMMA), i.e. at the same temperatures at which they occur in the corresponding hono-polymers. 

Size exclusion chromatography is the premier polymer characterization method for determining molar mass distributions. In SEC, the separation mechanism is based on molecular hydrodynamic volume. For homopolymers, condensation polymers and strictly alternating copolymers, there is a correspondence between elution volume and molar mass. Thus, chemically similar polymer standards of known molar mass can be used for calibration. However, for SEC of random and block copolymers and branched polymers, no simple correspondence exists between elution volume and molar mass because of the possible compositional heterogeneity of these materials. As a result, molar mass calibration with polymer standards can introduce a considerable amount of error. To address this problem, selective detection techniques have to be combined with SEC separation. 

Techniques such as SEC-LC (liquid chromatography other than the size exclusion separation mode) are required to characterize copolymers in accurate detail. Several techniques for nonexclusion liquid chromatography (NELC) to separate copolymers according to composition have been developed and reported within the past several years. These techniques can give the information on chemical heterogeneity of copolymers thus, SEC-NELC is required to determine both distributions. 

The molecular weight and compositional heterogeneity of 2M5 VP-AA copolymers having various molecular weights and composition have been studied by spectroturbidimetric titration [66]. The fractionation of copolymers in a mixture of methanol/toluene and methanol/diethyl ether leads to the precipitation... 

Using RI and UV detectors, Ogawa and Sakai (20) were able to determine the compositional heterogeneity of certain copolymers (1) nylon 12 and polytetramethylene ether glycol and (2) nylon 6 and natural rubber. Dichloromethane was employed as the eluant for copolymer 1, with a UV detector set at 230 nm, and 1,1,2,2-tetrachloroethane was used for copolymer 2 at 260 nm. 

---