Biolignin, a wheat straw lignin produced by acetic acid/formic acid/water hydrolysis, was characterized by 31P and 13C–1H 2D NMR spectroscopy and by size-exclusion chromatography. Biolignin is a ...mixture of low molar mass compounds (M n = 1660 g/mol) made up of S, G, and H units and of coumaric and ferulic acid units. β-5 and β-O-4 interunit linkages are partially acylated in the γ-position by acetate and p-coumarate groups. Deacylated samples with a low content of contaminants were obtained by combining alkaline hydrolysis and solvent extraction. The high phenolic OH content found by 31P NMR reflects the presence of condensed aromatic units, such as 5–5 units. Reaction of purified lignin with ethanol and ethane-1,2-diol yielded esterified lignins much more soluble than Biolignin in common organic solvents. During this reaction, the secondary OH of β-O-4 linkages was simultaneously etherified. Phenol hydroxyethylation by 2-chloroethanol yielded samples containing only aliphatic hydroxyl groups.
Alfa grass lignin obtained by the acetic acid/formic acid/water CIMV pulping process was characterized by FTIR and 1H, 13C–1H 2D HSQC, and 31P NMR spectroscopies. Lignin samples purified by further ...dissolution/precipitation or basic hydrolysis steps were also analyzed. The CIMV alfa lignin is a mixture of low molar mass compounds (M n = 1500 g/mol) of SGH type with β-O-4 ether bonds as the major interunit linkage. The crude lignin contains fatty acids and residual polysaccharides. It also contains large amounts of acetate and hydroxycinnamates, mostly in the γ-position of β-O-4 interunit linkages. Although partial acetylation induced by the process cannot be excluded, the absence of aromatic acetates and acetylated polysaccharides in crude lignin demonstrates the mildness of the process. By combining smooth alkaline hydrolysis and dissolution/precipitation steps to the CIMV pulping, it is possible to produce a purified lignin with a composition and a structure quite analogous to that of the native polymer in the plant.
Hyperbranched polyesters of 2,2-bis(hydroxymethyl)propanoic acid (BMPA) with various molar ratios of tetra(hydroxymethyl)methane (PE) core molecule were characterized by NMR spectroscopy and ...MALDI-TOF mass spectrometry. In all polyesters, the formation of ether groups was observed. The extent of etherification increased with increasing PE content. This was assigned to a higher reactivity of PE towards etherification than BMPA. Intra- and intermolecular etherifications and intramolecular esterifications were detected by MALDI-TOF MS on the core molecule-containing polyesters, resulting in the formation of cycle-containing hyperbranched molecules. The ratio of cycle-containing molecules reached 50% at high reaction time for the polyester without core molecule, but was much lower for the polyesters containing a core molecule. As a consequence of these side reactions, the control of hyperbranched polyester molar mass by varying the core molecule (chain limiter) molar ratio is much more difficult than for linear polyesters.
The existing recommendations for the structure-based nomenclature of regular single-strand organic polymers are extrapolated to complex polymers. The key proposal is that polymeric moieties may be ...named substituents. The types of polymers covered include linear and branched polymers containing more than one block of a single type of constitutional repeating unit (CRU) and branched polymers containing a main chain from which one or more polymeric side chains emanate.
This article extends the “in−out” recursive probability method of Macosko and Miller to the polycondensation of mixtures of polyfunctional monomers bearing A- and/or B-groups. Explicit relationships ...of the theoretical average degrees of polymerization and average molar masses are established in the most general case and can be applied to any linear, hyperbranched, or network polymerizations, leading in the latter case to the value of the conversion at the gel point. These relationships reduce to those of Stockmayer in the case of reactions involving monomers bearing either A- or B-groups. The effect of the elimination of a condensation byproduct is also examined. An approximate explicit expression of the mass-average molar mass is proposed, allowing calculations with an error in the 1−3% range when water is the byproduct. Some examples are treated to illustrate the method, including AA + BB + AB, AB + B g , AB f , A f B g , AB f + B g , and more complex polymerizations. The effect of the functionality of the core molecule on the polydispersity of hyperbranched polymers is examined for various systems.
In order to prepare furanic–aliphatic polyesteramides without the side reactions taking place with furan-2-carboxylic acids or esters, a furan-based diamine, 5,5′-isopropylidenebis(2-furfurylamine), ...was reacted in the bulk, either with (i) ethanediol and dimethyl adipate or (ii) with the corresponding aliphatic polyester (polyethylene adipate). The polycondensation involves both amine–ester and hydroxy–ester interchanges, with elimination of excess ethanediol. High-molar-mass furanic–aliphatic polyesteramides were easily obtained. Method (ii) was more efficient than method (i), but no side reactions were observed with both methods. These polyesteramides behave as amorphous random copolymers.
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•Copolyesteramides were obtained from biobased furanic diester/diamine/diol mixtures.•The initial diester/diamine ratio controls final composition.•Any diol excess is eliminated ...during the reaction.•Minor side reactions leading to furyl endgroups and chain branching were detected.•The copolyesteramides are amorphous, thermally stable polymers.
Polyesteramides based on diethyl 5,5′-(propane-2,2-diyl)-bis(furan-2-carboxylate), a biobased diester, are synthesized by high temperature bulk polycondensation with mixtures of hexane-1,6-diamine and ethane-1,2-diol. The ester/amide ratio in final copolymers is governed by the initial diester/diamine ratio, any diol excess being eliminated during the synthesis via a series of interchange reactions. The copolyesteramides are thermally stable, amorphous compounds. Their structural characterization shows the existence of minor side reactions: diol etherification, and two reactions, specific to furan-2-carboxylate structure, the formation of nonreactive 2-furyl end groups and chain branching resulting from amidine formation by amide–amine condensation.
The kinetic−probability approach taking into account first shell substitution effects (FSSE) is applied to hyperbranched condensation polymerizations. Simple explicit relationships giving the ...mass-average molar mass ( ) and mass-average degree of polymerization ( ) as a function of conversion, of initial monomer mixture composition and of polymer architecture at a given reaction time are derived using the “in−out” recursive probability approach. Three experimentally available parameters, the A-, B-, and AB-branching factors (δA, δB, and δAB) are introduced to describe polymer branching. δB generalizes Frey's degree of branching to polymerizations involving any type of monomer mixture and can directly be used to calculate polymer . δAB characterizes the substitution effects induced on A-group reactivity by the reaction of B-groups (and vice versa). This effect, generally neglected in hyperbranched polymerization studies, may exert a dramatic influence on hyperbranched polymer dispersity ( / ). Two systems, AB f polymerizations and AB f + B g polymerizations, are taken as examples and discussed to illustrate the method. The polymerizations of 2,2-bis(hydroxymethyl)propanoic acid (BMPA) (AB2 polymerization) and of BMPA with Pentaerythritol (AB2 + B4 polymerization) are more specifically studied. The results are compared to experimental data, showing that negative FSSE involving both OH and COOH groups take place, leading to much lower dispersities and branching factors than expected for ideal (random) polymerizations. The method can be extended to any type of condensation polymerizations.
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