Star oligomers for low VOC polyurethane coatings

Conclusion  Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.     

Size exclusion and adsorption column chromatographic studies on functionality distribution of HTPB

Adsorption column chromatography and size exclusion chromatography have been used to determine the functionality distribution of hydroxyl terminated polybutadiene (HTPB), a modern solid propellant binder. The resin after conversion to 3,5-dinitrobenzoyl ester was separated into various fractions on a silica column. The fractions were analysed using a dual detector (UV and differential refractive index) analytical gel permeation chromatograph. The functionality of each fraction calculated from the chromatogram showed a continuous increase with increase in the molecular weight. The adsorption chromatography method is unable to fractionate the polymer into fractions with specific functionality. All the fractions have molecules ranging from monofunctional to multifunctional ones and therefore the apportionment method followed in the conventional adsorption chromatography method yields conflicting results.     

Synthesis and characterisation of telechelic poly(2,6-dimethyl-1,4-phenylene ether) for copolymerisation

Telechelic poly(2,6-dimethyl-1,4-phenylene ether) (PPE) segments are interesting starting materials, for example for copolymerisation. A good method to make partly bifunctional PPE-2OH is by redistribution or depolymerisation of high molecular weight commercial PPE with tetramethyl bisphenol A. The product has a bimodal molecular weight distribution because only ∼70-80% of high molecular weight starting material is depolymerised. The phenolic endgroups can be modified easily by a fast and complete reaction with methyl chlorocarbonyl benzoate. The product after endgroup modification is called PPE-2T and has two terephthalic methyl ester endgroups and a molecular weight of 2000-4000 g/mol. The functionality of these PPE-2T products is around 1.8. The bimodal PPE-2OH and PPE-2T products can be separated in a high and low molecular weight fraction by selective precipitation. The low molecular weight fraction has a narrow molecular weight distribution with a polydispersity between 1.2 and 1.5.     

New analytical methods for epoxy resins, 2. Two-dimensional chromatography

In order to gain information on the functionality type distribution and molar mass of bisphenol A based epoxy resins, on-line coupled two-dimensional chromatography was used. In the first chromatographic dimension, liquid chromatography at the critical point of adsorption separated the samples with respect to functionality. The functionality fractions were automatically transferred into size exclusion chromatography as the second dimension, where the fractions were separated with respect to their molar mass distribution. As a result of the two-dimensional experiment, the samples were mapped in contour plots, providing quantitative information on the interconnected parameters functionality, molar mass, and branching.     

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. II. Measurements for commercial polymers

The functionality averages, functionality distribution, hydroxyl equivalent weight, molecular weight averages, and molecular weight distribution of three commercial hydroxyl terminated polybutadienes have been determined using a dual-detector GPC method used to analyze the polymers before and after derivatization with phenyl isocyanate. The values of these parameters are compared with existing literature data. The determined number-average functionalities were in reasonable agreement with previously published values. However, the distribution of functionality as a function of molecular weight differs from distribution data obtained by column fractionation techniques. Our distribution data appears to be generally consistent with the distribution expected from the polymerization mechanisms. The differences in the variation of hydroxyl content with molecular weight obtained from the dual-detector GPC method and the column fractionation procedures should be resolved since a combination of these procedures could provide additional information regarding the actual amounts of mono-, di-, and polyfunctional polymer and their molecular weight distributions. The dual-detector GPC method should be applicable for the determination of the distribution of a variety of functional groups provided a selective derivatization reaction is available or a second detector which can directly and accurately determine the concentration of the functional group is available.     

Kinetic analysis of AB2 polycondensation in the presence of multifunctional cores with various reactivities

This work is theoretically dealt with the kinetics of polycondensation of AB₂-type monomers in the presence of multifunctional cores (C_f) with various reactivities. The analytical expressions of the molecular size distribution function and the molecular parameters of the resultant hyperbranched polymers were derived. The conversion of A groups (x), feed ratio of the core/monomer (β), functionality of the core (f), and reactivity ratio of C to B (r) significantly effect the molecular weight distribution and the molecular parameters of the products. High feed ratio, functionality and reactivity of the core can improve the molecular weight distribution and decrease the polydispersity for the resultant products. Compared with the polycondensation of equal reactivity, the effect of the core which has enough high reactivity on the polydispersity is equal to doubling the functionality of the core.     

Characterization of coal liquids by 13C n.m.r. and FT-i.r. spectroscopy — fractions of oils of SRC-I and asphaltenes and preasphaltenes of SRC-I and SRC-II

Coal-derived products of SRC-I liquefaction of Blacksville coal and vacuum tower bottoms (VTB) of SRC-II liquefaction of Powhatan mine coal (both bituminous and from the Pittsburgh Seam) were separated into fractions by solvent extraction. The SRC-I was first extracted with ethylacetate, and solubles were subsequently separated into oils and a mixture of asphaltenes and preasphaltenes (APA). The VTB was Soxhlet extracted with pentane to remove any residual oils, followed by tetrahydrofuran to recover APA. The APA portions were then separated by sequential elution solvent chromatography (SESC) into fractions differing in chemical functionality, and then examined by ¹³C n.m.r. and FT-i.r. spectroscopic techniques. APA are intermediates and end products of coal liquefaction. SRC-II APA are of higher molecular weight than the APA of SRC-I. The lower numbered fractions of APA of SRC-I in SESC separation have the same functional groups as the corresponding fractions of middle and heavy distillates. However, the higher numbered fractions are rich in oxygen, which is mainly in carbonyl groups. Part of the carbonyl groups are in esters which cross-link aromatic clusters. Therefore, APA and the coal itself are ‘oligomeric’ in structure, with aromatic clusters linked by carbon bridges with different functional groups. The nature of carbonyl groups in APA has been analysed in detail.     

The molecular characteristics of hydroxyl-terminated polybutadiene

Three samples of a commercial hydroxyl-terminated polybutadiene, Arco R45M. were characterised with respect to number-average and weight-average molar mass, intrinsic viscosity, number-average hydroxyl functionality and effective functionality for gelation. Two of the samples were fractionated on the basis of solubility in toluene/methanol mixtures, and the fractions were characterised with respect to number-average molar mass, intrinsic viscosity and number-average hydroxyl functionality. For both sets of fractions, the average functionality was practically independent of average molar mass. It is concluded that the functionality distribution is almost identical at all points in the molar mass range of Arco R45M.     

From coal to single-stage and two-stage products: A reactive model of coal structure

Using detailed chemical analyses of both coal and products from various liquefaction schemes, molecular models have been constructed to show the steps in the conversion process, and the nature of the products. Products from short- and long-contact time dissolution are shown in relation to structures found in the parent coal. Such molecules are highly functional, high molecular weight materials, which are difficult to process by conventional methods and tend to associate causing product stability problems. In contrast, products from two-stage liquefaction have greatly reduced molecular weight and functionality, and are consequently more amenable to downstream processing. The accurate and quantitative presentation of models reflects the analytical data on the coal and liquefaction products in terms of elemental distribution, aromaticity, functional group chemistry, and reactivity.     

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. I. The method and calibration procedure

A method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl-terminated polybutadienes using GPC has been developed. The method is based on the preparation of a UV absorbing derivative of the hydroxyl group and GPC analysis using dual differential refractive index and UV detectors. In order to determine the hydroxyl equivalent weight, quantitative derivatization of the hydroxyl group is required. If the equivalent weight can be determined by an independent method, the derivatization reaction can be less than quantitative if sufficient UV absorptivity can be obtained. The procedure used for calibrating the GPC columns and UV detector are presented. Equations for calculating number- and weight-average functionalities from GPC data were also developed. The number-average functionality is independent of the functionality distribution, but the weight-average functionality is dependent upon the distribution of functionality. The ratio of the weight-average to number-average functionality is indicative of how the functionality is skewed as a function of molecular weight.     

Pyrolysis studies of organic oxygenates: 3. High temperature rearrangement of aryl alkyl ethers

Thermal chemistry pathways of aryl alkyl ethers have been investigated under coal conversion-like conditions. Anisole is a thermally reactive compound having an oxygen functionality found in such coal precursors as lignins. Pyrolysis of anisoles was carried out using small batch autoclaves. Under thermolysis conditions anisole yielded a product distribution strongly dependent upon experimental parameters. Phenol, methane, CO and benzaldehyde are the low molecular weight products and polyphenyls and polyethers are the predominant high molecular weight products. The generation of CO is explained by a high temperature rearrangement of the phenyl group from O- to C- followed by rapid thermal decarbonylation of the benzaldehyde. Carbon monoxide formation from aryl alkyl ethers can thus be an important mechanistic pathway in coal conversion processes. By investigating the rearrangement using para-fluoroanisole it was shown that this rearrangement proceeds via a three-centered intermediate to para-fluorobenzaldehyde. No meta isomer was observed.     

Study of the condensation products of abietic acid with formaldehyde

Abietic acid and paraformaldehyde, taken in various molar ratios, were condensed in acid catalysis (p-toluenesulfonic acid). Toluene was used both as reaction medium and carrier for aqueous condensate. The obtained polymeric products (resins) were characterized by determination of acid number, melting point, molecular weight and viscosity. Spectral methods, e.g. I. R. and ¹H-NMR, were also used in the same scope. The experimental data evidence the fact that abietic acid is a substance with a functionality of minimum 3 as against formaldehyde. There have been obtained some condensation products with three-dimensional structure and low molecular weight. The polymerization average degree of the resins was found to be 3, although some fractions with polymerization average degree of 6 have been observed. The chemical bonds established between the structural units can be of both methylenic and dimethylene ether type, depending on the molar ratio of reacting substances.     

H.p.l.c. separation and g.c. characterization of polynuclear aromatic fractions of bitumen,heavy oils and their synthetic crude products

Characterization of bitumen, heavy oils, crude oil distillation residues and their processed products involves separation of the mixtures into several compound classes according to their molecular structure. However, these fractions are still very complex and often need further separation in order to get a better insight into their composition as well as the processing reactions involved in their upgrading. In this paper, the polynuclear aromatic fraction is divided into three subfractions by high performance liquid chromatography. Gas chromatography is then used to quantify these fractions and to determine their average molecular weight by a new method derived from simulated distillation. Crude oil distillation residues and their hydrocracked products are used to demonstrate this method.     

Effect of heat on triglycerides of corn oil

Results of a study on the effect of heating corn oil in air to a 200C temp are reported. Heated oil was separated on a silicic acid column into 8 fractions. The first four fractions, constituting about 62% original oil, were found to be unchanged triglycerides. The remaining 4 fractions constituted polymeric and degraded products of high molecular wt. Percentage losses from the respective positions in the oleo- and linoleoglyceride fractions suggest that fatty acids in primary positions are slightly more susceptible to heat than those in the 2-position. Assuming a 1,3-random 2-random distribution, triglyceride fraction in the heated oil contained 6.7% trilinolein as compared to 17.7% in fresh oil. Evidence is presented which shows presence of branching in short chain unsaturated acids and of hydroxy acids in the saponified polymeric fractions. Presented in part at the AOCS Meeting, New Orleans, 1962     

Synthesis of carboxy‐terminated telechelic oligostyrenes by Dead End Polymerization

Styrene was polymerized with 4,4′‐azobiscyanovaleric acid (ACVA) in order to obtain carboxy‐telechelic polystyrene (CTPS) using the Dead‐End Polymerization (DEP) conditions. First, we focused on experimental conditions leading to oligomers with molecular weights about 2000 g mol^?1. Second, we demonstrated by‐products of ACVA radicals are also synthesized in the DEP conditions by combination or by disproportionation. The purification of CTPS was investigated in order to extract the by‐products of ACVA. An extraction of these by‐products in H₂O pH 7 is suggested. Finally, the acid functionality of oligostyrene is evaluated by ¹H NMR and conductimetric titrations. A functionality about 2 is obtained that confirmed the synthesis of CTPS. Copyright © 2002 Society of Chemical Industry     

煤液化油馏分热力学性质的研究进展

为便于了解煤液化油品的性质,介绍了煤液化油组成的分析方法,详细介绍了煤液化油馏分的密度、分子量、黏度、临界性质、表面张力、蒸气压、蒸发焓和比热等热力学性质测量与估算的方法以及研究进展,可为煤液化工程设计提供参考。     

Dynamic rheological properties of bromine-terminated polybutadiene melts

The viscous and elastic properties of bromine-terminated polybutadiene were investigated as functions of temperature, molecular weight, and molecular weight distribution. They were found to depend on these variables in a manner similar to other polybutadienes. It was shown that the effect on the viscous properties due to bromine terminal functionality is not as great as for carboxyl and/or hydroxyl terminal functionality. In this study it was shown that the viscosity resultant from the blending of two samples of the same polymer differing in molecular weight is dependent on the polydispersity of the polymers from which the blend is prepared. A form of the Ninomiya and Ferry theory was modified and compared with experiment. As a result of the experiments involving blending, it was shown that the temperature dependency of elasticity is less for polymers exhibiting greater polydispersity.     

Liquid Chromatographic fractionation of oil-sand and crude oil asphaltenes

Asphaltenes extracted from Alberta oil sands (Athabasca, Cold Lake, and Peace River) and crude oils (Taber South and Fenn-Big Valley) were fractionated by sequential elution solvent chromatography (SESC) involving 10 organic solvents on a silica column. Athabasca asphaltenes and SESC fractions were further studied by elemental analysis, i.r., u.v., and n.m.r. spectroscopy. Incomplete extraction of maltenes from the oil-sand bitumens increased the yields of the first two SESC fractions, the saturates and aromatics, of oil-sand asphaltenes relative to the crude oil asphaltenes. About 55 wt% of the asphaltenes elute in fractions 3–5. Two distinct molecular types are present in the asphaltenes; namely, lower functionality species with lower heteroatom content and the higher functionality species with higher heteroatom content. Compounds eluting in fractions 3–10 are predominantly polynuclear aromatics with alkyl substituants and probably bridged by cycloalkanes. The extent of bridging as well as the location, number and type of heteroatoms determines the fraction in which each compound appears. Complexity of compounds eluting increases with time: earlier fractions are composed of smaller-size polynuclear aromatic centers and contain heteroatoms in predominantly ring locations, whereas later fractions contain a larger proportion of complex species and more functional heteroatom groups.     

Contribution to the ultrasonic degradation of polystyrene solutions

Narrow fractions of polystyrene and more heterogeneous samples were subjected to ultrasonic irradiation in tetrahydrofuran and toluene. Degraded products were investigated by gel permeation chromatography. Compared with Ovenall's results, the kinetic analysis of the degradation process shows an additional effect of molecular weight on rate. Experimental chromatograms obtained with classical styragel columns do not reveal clearly the non-random character of the degradation. However, bimodal distribution curves characteristic of a chain scission near the centre of the molecule are observed for degraded products of very narrow fractions analysed by high resolution microstyragel packings. It appears that the breakage does not occur exclusively near the centre but the probability of chain rupture decreases very rapidly out of the central part of the chain.     

Branching and molecular weight distribution of polyethylene SRM 1476

A method of determining the distribution of branching in a polymer is developed employing limiting viscosity numbers (intrinsic viscosity), gel permeation chromatography (GPC), and absolute molecular weight determinations of fractions of the whole polymer. A molecular weight calibration of the GPC column set is first determined empolying these fractions. From the limiting viscosity number measurements of these fractions and their molecular weight distribution determined from the GPC chromatogram, the viscosity–molecular weight relationship is determined by a nonlinear least-squares fitting procedure. For the same molecular weight, the limiting viscosity number of the branched polymer is less than the limiting viscosity number of the linear polymer. From the ratio of the two, the number of branches per unit molecular weight of the branched polymer is calculated. The method was applied to SRM 1476, the standard reference branched polyethylene issued by the National Bureau of Standards. The branching density for the constituents of SRM 1476 rise from zero at molecular weights less than 10,000 to about 6 to 8×10^?5 at molecular weights of 50,000 and above. The branching of SRM 1476 was also determined by the method of Drott and Mendelson, giving a result in fair agreement with the above method.