Broad-polydispersity polymer

The analysis of a broad-polydispersity polymer (PD > 1.2) can be carried out by combining GPC or size-exclusion chromatography (SEC) with MALDI-MS [161-172]. In this approach, a wide-polydispersity polymer is first separated by GPC and fractions at a defined time interval are collected. The time interval is properly chosen so that the individual fraction would contain only a narrow-polydispersity (PD < 1.2) polymer, which can then be analyzed by MALDI-MS for accurate molecular mass determination. The molecular mass information generated from the MALDl analysis of aU individual fractions can be used to convert the time domain in the GPC chromatogram into a mass domain. The polymer distribution can be determined from this chromatogram. 

MALDI mass spectrometry was combined with GPC analysis for broad polydispersity polymers with the use of liquid chromatography interface. Results for PMMA were compared with a blend of five narrow PMMA standards that mimic the broad dispersed material. 24 refs. 

Polydisperse polymers do not yield sharp peaks in the detector output as indicated in Fig. 9.14. Instead, broad bands are produced which reflect the polydispersity of synthetic polymers. Assuming that suitable calibration data are available, we can construct molecular weight distributions from this kind of experimental data. An indication of how this is done is provided in the following example. 

Silicone Resins. Sihcone resins are an unusual class of organosdoxane polymers. Unlike linear poly(siloxanes), the typical siUcone resin has a highly branched molecular stmcture. The most unique, and perhaps most usehil, characteristics of these materials are their solubiUty in organic solvents and apparent miscibility in other polymers, including siUcones. The incongmity between solubiUty and three-dimensional stmcture is caused by low molecular weight < 10, 000 g/mol) and broad polydispersivity of most sihcone resins. 

The formation of relatively ill-defined catalysts for epoxide/C02 copolymerization catalysts, arising from the treatment of ZnO with acid anhydrides or monoesters of dicarboxylic acids, has been described in a patent disclosure.968 Employing the perfluoroalkyl ester acid (342) renders the catalyst soluble in supercritical C02.969 At 110°C and 2,000 psi this catalyst mixture performs similarly to the zinc bisphenolates, producing a 96 4 ratio of polycarbonate polyether linkages, with a turnover of 440 g polymer/g [Zn] and a broad polydispersity (Mw/Mn>4). Related aluminum complexes have also been studied and (343) was found to be particularly active. However, selectivity is poor, with a ratio of 1 3.6 polycarbonate polyether.970... 

The novolac sample, which was provided by Kodak, was synthesized from pure meta-cresol and formaldehyde. It has a weight average molecular weight of 13,000 and a very broad polydispersity of 8.5. The polymer was purified by two precipitations from tetrahydrofuran into hexane. The PAC was a naphthoquinone-1,2-(diazide-2-)-5-sulfonyl ester provided by Fairmount Chemical (Positive Sensitizer 1010). A hydroxyl substituted benzophenone is attached to the sulfonyl ester. The spreading solvent was isopropyl acetate, which was obtained from Aldrich Chemicals and used as received. 

It is important to clarify whether catalyst-transfer condensation polymerization is specific to polythiophene, or whether it is generally applicable to the synthesis of well-defined it-conjugated polymers. We investigated the synthesis of poly(p-phenylene), to see whether a monomer 28 containing no heteroatom in the aromatic ring would undergo catalyst-transfer polymerization. However, all polymers obtained in the polymerization with Ni(dppp)Cl2, Ni(dppe)Cl2, or Ni(dppf)Cl2 possessed low molecular weights and broad polydispersities. Nevertheless, we found that LiCl was necessary for opti-... 

If these specifications are not met, then a living polymerization may produce polymers with very broad polydispersities and degrees of polymerization much higher than the d[M]/[I]0 ratio. Importantly, these prerequisites must be fulfilled in controlled polymerization as well. 

In the case of polydisperse polymers, the limiting compliance increases strongly with the broadness of the distribution of molecular weights. The limiting comphance is not, however, a simple function of the polydispersity index, because its value depends on the shape of the distribution itself. There is indeed no simple correlation with any molectilar weight moments (averages), and moleciilar models will be really helpfid to describe the elasticity of the melt. 

As discussed in this section, the tube-dilation effect, i.e. M J/Me > 1, mainly occurs in the terminal-relaxation region of component two in a binary blend. This effect means that the basic mean-field assumption of the Doi-Edwards theory (Eq. (8.3)) has a dynamic aspect when the molecular-weight distribution of the polymer sample is not narrow. This additional dynamic effect causes the viscoelastic spectrum of a broadly polydisperse sample to be much more complicated to analyze in terms of the tube model, and is the main factor which prevents Eq. (9.19) from being applied... 

Also a number of condensation polymers such as Nylon 6, polycarbonate, and polyesters were studied (see Table 10.2). These polymers usually possess broad MM distributions, the value of the ratio MJM being usually around 2. From the inspection of Table 10.2 it can be seen that MALDl underestimates both and M in the case of condensation polymers and that the ratio M IM derived from MALDl spectra of polydisperse polymers is strongly underestimated, and the MM distribution is much narrower. This evidence indicates that lighter molecules are preferentially detected in MALDI-TOF instruments, causing the underestimation of the presence of larger molecules and limiting the use of MALDl for MM and MMD determinations to "monodisperse" samples. 

The first synthetic route explored to produce cydic polymers made use of ring-chain equilibrium. This approach involves the natural equilibrium that occurs between linear and cydic polymers during condensation polymerizations although, inevitably, this yields linear byproducts and broad polydispersities. As a result, precipitation or preparative gel-permeation chromatography (GPC) was required to obtain cyclic polymers of sufficient purity for further study. This approach is amenable to a broad range of polymerization chemistries, induding the preparation of cyclic polyesters [7,8], polyethers [9], poly(dibutyltin dicarboxylates) [10,11], and poly(siloxanes) [12-15]. 

The main approaches toward hb polymers in one-pot procedures with the potential of branching in each repeating units as outlined in Section 24.2, lead to complex, polymeric structures with multiple structural units within one molecule, a high number of functional end groups, an irregular, highly branched structure, high variations in molar masses, and often with an extremely broad polydispersity. In order to elucidate the success of the synthetic approach, and also to be able to validate and understand the observed materials properties, two major questions must be addressed (i) the verification of the chemical structure in question in as much detail as possible and (ii) the reliable determination of molar mass and polydispersity. 

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