Ultimate Molecular Weight Research Articles

Synthesis and Organocatalytic Ring-Opening Polymerization of Cyclic Esters Derived from l-Malic Acid

The synthesis of 3-(S)-[(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (BMD) and 3,6-(S)-[di(benzyloxycarbonyl)methyl]-1,4-dioxane-2,5-dione (malide) from commercially available l-malic acid is reported. Ring-opening polymerization (ROP) studies of BMD are reported showing that the controlled ROP of this monomer is possible in the absence of transesterification side reactions, despite the presence of side-chain esters, using 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea and (-)-sparteine to catalyze the polymerization. The ROP of malide with this system was ineffective. Investigation of the effect of initiating species revealed that the electronic nature of the alcohol had a greater effect on the ultimate molecular weight and hence initiator efficiency than steric considerations. Deprotection of the resultant poly(BMD) using H(2) and Pd/C resulted in hydrophilic poly(glycolic-co-malic acid)s (PGMAs) that were able to undergo autocatalytic degradation in dilute H(2)O solution such that complete degradation was observed within 6 days.

In situ generation of nitroxide from alkoxyamines for controlled acrylate polymerization

AbstractA general strategy for the controlled nitroxide‐mediated polymerization of acrylates from alkoxyamines without addition of excess free nitroxide is outlined. 2,2‐Dimethyl‐3‐(1‐phenylethoxy)‐4‐phenyl‐3‐azapentane (1), prepared in one pot by the addition of 1‐phenylethyl radicals to 2‐methyl‐2‐nitrosopropane, is heated prior to the addition of monomer to afford a mixture of alkoxyamine 1, free nitroxide, and 2,3‐diphenylbutane. With a 30 min preheating period at temperatures up to 125 °C, the kinetics of the subsequent polymerization of n‐butyl acrylate at 125 °C appear largely unaffected, though the ultimate molecular weight of the polymers is dependent upon the preheating temperature. The poly(n‐butyl acrylate) samples, that result from this process, have much narrower molecular weight distributions than those which result in the absence of the preheating process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5128–5136, 2006

Two package waterborne urethane systems

This article is an extensive review of the literature on two component urethane systems that use water as a carrier. It generally covers the period from 1985 through 2000 with special emphasis on patent references since 1993. It includes both ambient temperature cured and baked systems containing unmodified and modified isocyanate building blocks. The main criterion for inclusion into this paper was that the finished urethane group containing polymer reaches its ultimate molecular weight after it is applied to a substrate, so that traditional latex-type materials are not emphasized. The paper describes the raw materials and chemistry used in this field and presents some of the factors that must be considered to make this unique chemistry industrially feasible. The major concern is formulating, mixing, and applying the systems in a manner that limits the water reacting with the highly active isocyanates to avoid defects from generated carbon dioxide. The review also discusses some of the end use areas where two component urethanes have been commercially applied.

The preparation of hyperbranched aromatic and aliphatic polyether epoxies by chloride-catalyzed proton transfer polymerization from ABn and A2 + B3 monomers

Hyperbranched polymers consisting of aromatic or aliphatic polyether cores and epoxide chain-end peripheries were prepared by proton transfer polymerization. AB 2 diepoxyphenol monomer 1 proved to be well suited for the preparation of hyperbranched aromatic polymer 2 by this proton transfer polymerization. The use of chloride-ion catalysis, rather than conventional base catalysis, for the preparation of polymers from diepoxyphenol 1 offered a unique method to control the ultimate molecular weight of the polymer product through variations of the initial concentration of monomer 1 in tetrahydrofuran. An alternative route to hyperbranched polyether epoxies made use of commercially available or easily prepared aliphatic monomers of the types AB 2 , AB 3 , and A 2 + B 3 . Although these aliphatic polymerizations can be initiated with a base, chloride-ion catalysis proved most effective for controlling the polymerization. The hyperbranched epoxies were characterized by NMR spectroscopy, gel permeation chromatography, and multi-angle laser light scattering. Chemical modification of the polymers after polymerization was carried out via nucleophilic addition on the epoxide groups or derivatization of the hydroxy substituents within the hyperbranched polymer structure. Spectroscopic measurements suggested that some such ring-opened materials may adopt reverse unimolecular micellar structures in appropriate solution environments.

Kinetics of Controlled ‘Living’ Free Radical Polymerization: I. Ideal Case

ABSTRACTThe kinetics of an ideal controlled ‘living’ free radical polymerization (LFRP) are studied using a combination of analytic and numeric methods. It is shown that the ideal LFRP kinetics are characterized by the fast capping/uncapping reactions and the slow propagation of polymer radicals. The polymerization rate is determined by the rate of initiation, monomer and free capping agent concentrations, as well as, the rate of capping/uncapping. The molecular weight is shown to be a linear function of conversion, and the ultimate molecular weight is determined by the initial monomer to initiator concentration ratio. The polydispersity is determined by the ultimate molecular weight and polymerization rate.

Palladium-Catalyzed Formation of Poly(imide-amides). 2. Reactions with Chloroiodophthalimides and Diamines

High molecular weight poly(imide-amides) can be readily formed by the palladium-mediated carbonylation and condensation reactions of activated chlorophthalimide monomers and aromatic diamines. The presence of iodide ion greatly accelerates the rate of reaction and increases the ultimate molecular weight of the polymer. Polymerizations proceed best using a protocol of high CO pressure (90 psig) for 2-4 h, followed by lower CO pressure (20 psig) in DMAc or NMPfor 24-48 h at 100°C using 0.3-3.0% PdCl 2 L 2 (L=PPh 3 ) as the catalyst with 2-6 equiv of PPh 3 /Pd and 0.3-1.0 equiv of an iodide/ chloro group

Characterization of a thermally imidized soluble polyimide film

AbstractA soluble aromatic poly (amic acid) film was converted to a soluble polyimide by staging at 25°C intervals to 325°C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly (amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry, and infrared spectroscopy analyses. The results of this study serve to increase our fundamental understanding of how polyimides are thermally formed from poly (amic acid)s.

Photochemical Crosslinking and Isolation of Block Copolymers in Selective Solvent

Three block copolymer, poly (styrene/butadiene/styrene) micellized in selective solvents is photochemically crosslinked, using benzoyl peroxide as a photochemical initiator. It is found that the ultimate molecular weight of crosslinked micelles increases with the increase in concentration of copolymer and volume percent of precipitant, whereas it decreases with temperature. For isolation purposes of these crosslinked micelles, the nitrobenzene was mixed to the reaction mixture and nitrogen gas was bubbled through the system during precipitation. The micelles were precipitated by dropwise addition of methanol alongwith rigorous stirring. These precipitated micelles were dried at lower than 15°C under vacuum and the molecular weight of so precipitated micelles was found to be the same as before precipitation.

Studies on the synthesis of poly(1,4-butyleneterephthalate) by the direct polycon densation and its properties. (Part 3) Polycondensation of poly(1,4-butyleneterephthalate) prepolymer.

Polycondensation reaction conditions of poly (1, 4-butyleneterephthalate) (PBT) prepolymer obtained by direct esterification of terephthalic acid (TA) with butanediol-1, 4 were investigated. It was found that1) the amount of tetrahydrofurane formed as a by-product decreases with lowering the conversion of TA at the esterification stage, while the ultimate molecular weight of PBT obtained decreases with lowering the conversion.2) the optimum reaction temperature is lower than that in the synthesis of other poly (alkylene terephthalates).3) the catalyst is favorably added at stages of both initial esterification and subsequent polycondensation, although its total concentration does not affect an ultimate molecular weight of the resulting PBT.To obtain the Mark-Houwink-Sakurada viscosity equation of PBT in o-chlorophenol at 25°C, the samples having the molecular weight in the range from 8, 400 to 67, 000 were prepared and the following viscosity equation was obtained:

Physical properties of some ribosomal proteins in solution and evidence for molecular interactions between isolated ribosomal proteins.

Many previous studies have been directed toward obtaining a physical visualization of the relationship between the protein and RNA in the ribosomal subunits isolated from Escherichia coli. The current study is the first report where an attempt has been made to directly assess interactions between a pair of isolated ribosomal proteins separate from the intact system by means of sedimentation equilibrium analysis. The molecular weights of the proteins S3, S4, S5, S6, S7, S8, and S20 from the 30S subunit of the E. coli ribosome were determined under conditions of assembly of the subunit by sedimentation equilibrium. All of the proteins exhibited molecular weights consistent with monomeric behavior (i.e., in agreement with the measurement of the ultimate molecular weight in denaturing solvents as reported in other studies as well as in the current study) except S8 which indicates a tendency to self-associate. Hydrodynamic measurements on the proteins indicate that these proteins are not completely disorganized in solution such as a random coil, although not as compact as globular proteins. The frictional coefficient ratios found for these ribosomal proteins range from 1.4 to 1.9. The hydrodynamic data are discussed as containing some evidence that stable interaction sites could exist in the proteins. The molecular weight data are considered pertinent to a sedimentation equilibrium study of protein-protein interactions that may be occurring in the ribosomal subunits. Two proteins, S3 and S5, considered in this investigation were found to exhibit no tendency to self-associate under conditions of reassembly. When the two proteins are mixed under those same conditions, however, a species with a molecular weight greater than that of either S3 or S5 is observed to be formed. The interpretation is presented that a molecular interaction between S3 and S5 is the cause. The system is described as containing S3, S5, and a complex between S3 and S5 with a stoichiometry of 1:1 and an association equilibrium constant of 5.7 times 10-5 l./mol (delta G-o equals minus 7.25 kcal/mol). Since the association appears to be specific and of moderate strength, it is concluded that the interaction could have some pertinence with respect to conferring a structural arrangement in the ribosomal subunit. Moreover, it is concluded that protein-protein interactions, in general, must be considered in addition to the well documented significant RNA-protein relationships when models for ribosome structure and assembly are formulated.

Aluminium Disoaps as Drag Reducing Agents

Recent articles1–3 dealing with the drag reduction of aluminium disoaps in non-aqueous solvents suggest that some disoaps may be more effective than others in reducing turbulent friction in pipe flows or the like and further that critical concentrations of some disoaps must be exceeded before drag reduction is actually observed. According to the available literature data4 aluminium disoaps may be prepared in a variety of molecular weights, the ultimate molecular weight depending upon the extent of polar impurities, the conditions of preparation for both soap and soap dispersions and ageing effects. So subtle is the influence of soap preparation on the final product, however, that soap batches prepared in nominally the same fashion yielding the same elemental analyses result in colloids of quite different maximum molecular weights4. None the less, when plots of intrinsic viscosity against number-average molecular weight were made, most of the disoap data seem to lie on a common curve irrespective of fatty acid residue4. The available data suggest, for example, that it would be difficult to say that aluminium dilaurate always forms higher molecular weight colloids (or “polymers” of greater length) than does aluminium distearate, or the converse. In order to test for the presence of soap critical drag reducing concentrations and to determine whether or not drag reduction effects increased as disoap monomer weight decreased, I decided to prepare carefully two aluminium disoaps.

Synthesis and characterization of poly(p‐phenylene pyromellitamic acid)

AbstractPoly(p‐phenylene pyromellitamic acid)s were synthesized over the weight‐average molecular weight range 8,000 to 22,000. The polymers were recovered as amorphous powders composed of 3–4 × 1–2 μ platelets 0.1–0.2 μ thick containing 20–30% associated solvent. Consumption of reactants and attainment of the ultimate molecular weight of the polymer were found to occur within the first few minutes of reaction. The polymers were characterized by scanning electron microscopy; ultraviolet, visible, near‐infrared, and infrared spectroscopy; x‐ray analysis; viscometry; and light‐scattering photometry. The intrinsic viscosity–molecular weight relation for the polymer in DMF was \documentclass{article}\pagestyle{empty}\begin{document}$ [\eta ] = 25.2 \times 10^{ - 4} \bar M_w^{0.56} $\end{document}.

The Effect of Impurities on the Molecular Weight Distributions of Anionic Polymers

The deactivating influence of impurities in anionic polymerizations is considered from the point of view of the ultimate molecular weight distributions obtained with various systems. With the assumption that initiation is much faster than propagation, theoretical expressions for the weight distribution functions and the weight-to-number average chain length ratios are derived for the cases in which mono- and bifunctional growing chains are subjected throughout the course of polymerization to given, fixed ratios of monomer to impurity concentrations. The relationships obtained are shown to be applicable to systems of practical interest. The molecular weight distributions of both mono- and bifunctional anionic polymers derived from the foregoing model are found to broaden with increasing impurity content in the monomer supply. The molecular weight distributions for the latter are narrower than those for the former at corresponding levels of impurity content. For moderate degrees of deactivation, the weight distribution function for bifunctional polymers exhibits the characteristic maximum as well as the rudiments of a second relative maximum at lower molecular weight.

Native tobacco mosaic virus protein of molecular weight 18,000.

X-RAY diffraction data on tobacco mosaic virus have been interpreted in terms of protein repeat units with a molecular weight of about 18,000 arranged in a helix1. Amino-acid analyses and end-group titrations2 yield a similar minimal value but do not answer the question whether the ultimate molecular weight is 18,000 or some integral multiple of it. Thus far, the smallest native protein particles obtained by degradation of tobacco mosaic virus3–5 have shown molecular weights of about 100,000. We have now been able to dissociate tobacco mosaic virus protein into undenatured particles with a sedimentation coefficient consistent with a molecular weight of 18,000.