WO2018186744A1 - Synthesis and use of carbohydrate-based linear polyesters - Google Patents

Abstract

The invention relates to the field of polymer chemistry, more in particular to the synthesis of novel biobased linear polymers and their applications, among others as rheology modifiers or thickeners in waterborne formulations. Provided is a method for providing a linear carbohydrate-based polyester, comprising (i) reacting a bicyclic acetalized galactaric acid derivative (Galx) with a diol in the presence of a suitable catalyst to obtain a Galx -based polyester; and (ii) subjecting said Galx -based polyester to a hydrolytic deacetalisation reaction to convert at least part of the diacetal moieties to chhydroxide moieties.

Description

Title: Synthesis and use of carbohydrate-based linear polyesters. The invention relates to the field of polymer chemistry, more in particular to the synthesis of novel biobased linear polymers and their applications, among others as rheology modifiers or thickeners in

waterborne (coating) formulations.

Additives have long been used in coating compositions for various purposes. Thus, viscosity control agents, surfactants, sag-control agents, anti-foaming agents and other materials are added to coating compositions in minor amounts for their respective functions. Rheology modifiers are also added to such compositions not only for increasing the viscosity of the coating compositions but to maintain the viscosity at desired levels under varying process conditions and end-use situations. Secondary effects obtained from the rheology modifiers include protective colloidal action, improvement in pigment suspension, leveling and flow. Some of these properties are also desired in similar type compositions, for instance textile treating compositions, cosmetics, paper compositions, well drilling, firefighting foams, detergents, pharmaceuticals, agricultural formulations, and emulsions of all kinds. It can be seen rheology modifiers are used in a variety of compositions.

While the discussion of the reaction products which follows is with reference to them as "rheology modifiers", it should be understood this term is used broadly. That is, "rheology modifiers" as used herein is meant to encompass such terms as thickening agents, thixotropic agents, viscosity modifiers and gelling agents.

The most common used rheology modifiers are bio-based or synthetic polymers. Natural products such as the alginates, casein, and gum tragacanth and modified natural products such as functionalised cellulose, gums (xanthan, guar), proteins (collagen) etc. are useful rheology modifiers. These mostly contribute due to their hydrodynamic volume and

entanglements of the chains. Many well-known rheology modifiers are used with varying degrees of success. Synthetic rheology modifiers have also been used. These materials include the carboxyvinyl ether copolymers, acrylic polymers and maleic anhydride/styrene copolymers. However, the known rheology modifiers have various deficiencies. For example, the natural rheology modifiers are susceptible to biological attack. Synthetic rheology modifiers are not subject to such attack yet most of them do suffer from having less than desirable thickening qualities over a wide range of end uses and/or film forming concentrations.

Generally speaking, there are two main groups of thickeners: -thickeners which rely on (macro)molecular structure factors

(such as high molecular weight and presence of ionic groups), therefore on their chain entanglements and

-thickeners which have as characteristic a dual hydrophilic- hydrophobic type of structure and where the hydrophobic groups tend to cluster both at intra- and inter-molecular level, causing an increase in viscosity of the polymer solution.

To the best of our knowledge, the most investigated classes of the latter group of polymers are hydrophobically modified polyurethanes and polyethers. Despite their relative good performance these modified polyurethane rheology modifiers rely on the use of isocyanates for their synthesis. [1], [2] Thus, even though on one side the possibility of using a waterborne thickener seems already as the better option (as opposed to a mixture based on organic solvent), it still keeps the disadvantage of exposure to relatively toxic and non-environmental friendly components such as isocyanates.[4] This feature is even more relevant when the final application addresses cosmetics or detergents emulsion systems.

It would be desirable to obtain novel bio-based alternative to these, preferably bringing as added value an easy and adjustable synthesis to match the desired application i.e. by varying the feed ratio of one of the monomers in a copolymer structure obtaining a lower or higher thickening effect.

These goals are met by the provision of a two-step synthesis of linear chain novel galactaric acid based (Galx) polyesters by melt

polycondensation, followed by a further hydrolytic (total/ partial)

deprotection of acetal groups. The resulting novel (shear) thickener linear sugar based polyesters have the potential of addressing various water-based applications by way of controlled hydrophilicity of sugar based polyesters by varying the degree of deprotection and/or size/type/ configuration of one of the co-monomers.

Herewith, the invention also provides a thickener for rheological systems where it is required in order to increase the viscosity and/or stabilise the suspension, emulsion media. This can be used for paints and coatings but also for cosmetic/detergent emulsion systems.

In one embodiment, the invention relates to a method for providing a linear carbohydrate-based polyester, comprising the steps of:

(i) reacting a bicyclic acetalized galactaric acid derivative (Galx) of the general formula I

wherein X is H or a linear aliphatic moiety, preferably a linear C₁-

C₅ alkyl;

R and R' are linear alkyl chains, more preferably C₁-C₃ alkyl; with a diol in the presence of a suitable catalyst to obtain a Galx -based polyester; and (ii) subjecting said Galx-based polyester to a hydrolytic deacetalisation reaction to convert at least part of the diacetal moieties to dihydroxide moieties.

In a preferred bicyclic acetahzed galactaric acid derivative (Galx) of the general formula I, X is a linear C₁-C5 alkyl; and/or R and R' are C₁-C3 alkyl chains.

For example, said bicyclic acetalized galactaric acid derivative is dimethyl- 2,3:4,5-di-0-isopropylidene-galactarate (Galxl)

In a method of the invention, the diol is preferably of the general formula

wherein

is a linear or cyclic ahphatic hydrophobic (e.g. cycloalkyl, aryl) unit. For example, the diol is selected from the group consisting of linear ahphatic α,ω-diols, such as 1,3-propanediol, 1.4- butanediol, 1,5-pentanediol, 1,6-hexanediol. or 2 , 3 : 4.5 - di-O-isopropylidene - galactitol or 2.3 : 4.5 - di-O-methylene-galactitol .

Exemplary homopolyesters that may be provided in step (i) of a method of the invention include the following Galx 1-1, 3 propanediol and Galx1- 2,3:4,5-di-0-isopropylidene-galactitol homopolyesters:

Step (i) of a method according to the invention may comprise reacting the bicyclic acetalized galactaric acid derivative and the alcohol in the presence of one or more further co-monomer(s). In one embodiment, the further monomer comprises a cross-linking moiety, such as an α,β-unsaturated functionality. For example, the further co-monomer is itaconic acid or ester thereof, such as dimethylitaconate or dibutylitaconate. The itaconic acid is preferably obtained from a renewable source. For example, it can be produced on an industrial scale via ferment ation with Aspergillus terreus with a production intensity of 80 g L-l. (T. Willke and K. D. Vorlop, Appl. Microbiol. Biotechnol., 2001, 56, 289-295). Notably, the presence of a cross- linking functionality per se does not result in a cross-linked polyester, but it allows for subsequent cross-linking of the resulting linear co-polyester if so desired e.g. by performing free radical polymerization-crosslinking.

Suitable catalysts for use in a method of the invention include dibutyltin oxide (DBTO) and other organometallic catalyst which act as Lewis acids, such as Ti alkoxides; Sb, Ge, Sn oxides; Zn, Mn, Ca, Co, Cd acetate.

Nevertheless their activity may depend on the reaction conditions, on the solubility in the medium or even on the possibility of catalyzing also secondary reactions.

In step (ii) of a method of the invention, the Galx -based polyester is subjected to a deprotection reaction wherein at least part of the diacetal moieties are hydrolyzed to dihydroxide moieties. Preferably, this is performed by dissolving the Galx-based polyester in an (aqueous) acid solution and incubating at room temperature to obtain the desired degree of deacetalisation. See Scheme 1 below. Suitably, the Galx-based polyester is purified, e.g. to remove catalyst, and dried prior to dissolving it in an acid solution.

Scheme 1: Exemplary polymerisation reaction using a Galx-derivative and an alcohol to form an acetalised poly(galactaric ester), followed by hydrolytic deacetalisation to convert at least part of the diacetal moieties to

dihydroxide moieties. Acn depicts H or

In a preferred embodiment, the solution of acid is a aqueous solution of sulfuric acid, hydrochloric acid, Amberlyst 15, p-toluene sulfonic acid, acetic acid, trifluoroacetic acid, more preferably formic acid. Very good results are obtained with formic acid or trifluoroacetic acid. In a specific aspect, a formic acid solution in chloroform, preferably 88% volumetric, is used. The cleprotection (deacetalisation) reaction can be performed up to the desired degree of hydrolysis is achieved. In one embodiment, it comprises incubating up to 4 hours, preferably up to 3 hours, more preferably up to 2 hours. Good results are obtained wherein step (ii) comprises incubating during a time period of 15 to 180 minutes, preferably 20 to 150 minutes, more preferably 30 to 120 minutes.

In a preferred aspect, the deprotection reaction is not performed to completion such that the resulting polyester still comprises diacetal moieties.

In one embodiment, at least 20%, preferably at least 30%, more preferably at least 50% of the diacetal moieties are converted to dihydroxide moieties. In one embodiment, up to 95%, 90% or 85% of the initial protecting groups is hydrolyzed.

For example, 40-60%>, 50-80%, 60-90% or of the diacetal moieties are hydrolyzed into dihydroxide moieties, thus leaving a significant amount of the Galx-residues in the polymer still in the acetahzed form. In one embodiment, at least 3%, preferably at least 5%, like 7, 8, 9, or 10%) of the Galx-residues in the final linear polymer is still in the acetalized form. See also Example 3 showing that the degree of hydrolytic deacetalisation can be controlled, which is advantageously used to steer the (surface active) properties of the polymer. See Figure 7.

Following the deprotection step (ii), the Galx-based polyester comprising dihydroxide moieties obtained may be precipitated, washed and dried.

The invention also provides a linear Galx-based polyester obtainable by a method according to the invention. The carbohydrate-based polyester can have the numerical average molecular weight between 6000 and 30000 g/mol.

In one embodiment, the invention provides a fully deprotected linear carbohydrate-based polyester of the general formula

In another embodiment, only a part of the acetal moieties is hydrolyzed to provide a partially deprotected linear carbohydrate-based polyester of the general formula

wherein R and R' are C ₁ -C₃ alkyl, and wherein the remaining Acn groups are H.

In one embodiment, 40-60% , 50-80% or 60-90%, of the Acn- groups are H.

In case a further co-monomer comprising an α,β-unsaturated functionality is used in the polymerization reaction of the present invention, the polyester may be of the formula

wherein at least 20%, preferably at least 40%, more preferably at least 60% of the Acn moieties are H.

A linear Galx -based polyester provided in the present invention is not taught or suggested in the prior art. US 3,083,187 describes polyesters with a polymeric backbone constructed by reacting ahphatic or aromatic dibasic acids (A) with aliphatic diols (B). The polymeric backbone is substituted with polyalkyleneglycols, i.e. the polyalkyleneglycols are not part of the polymeric backbone. The polymeric backbone is substituted with monoalkylethers of polyalkyleneglycols using two methods. In the first method, the substitution is established by reacting such polyalkylene glycols with reactive centers in the polymeric backbone: the hydroxyl groups of dibasic acids of e.g. mucic acid. In the second method, reactive hydroxyl groups in e.g. mucic acid are used as a starting point for ethylene oxide polymerization. In both methods of US 3,083, 187, the resulting products are substituted with polyalkyleneglycols. In contrast, according to the present invention, acetalized galactaric acid is reacted with hnear or cychc aliphatic diols to yield an acetalized polyester which is further de-acetalized. Hence, the products of US 3,083, 187 are structurally distinct.

Lavilla et al. (Biomacromolecules, Vol. 12, no. 7, 2011, pp. 2642-2652; ref.

[9]) discloses carbohydrate-based polyesters made from bicyclic acetalized galactaric acid. Unlike the present invention, the polyesters are fully protected by acetal groups. Lavilla et al. is completely silent about converting at least part of the acetal groups to hydroxides.

It was surprisingly found that a hnear (partially) deacetalised Galx -based polyester as provided herein has unique properties, and is advantageously used as rheology modifier or thickener.

They also find their use as surfactant. Hence, also provided is an emvdsion composition comprising a linear (partially) deacetahsed Galx-based polyester according to the invention. For example, said composition is a cosmetic or detergent composition, an adhesive, coating or paint composition

A still further embodiment relates to a hydrogel comprising a linear

(partially) deacetalised Galx-based polyester according to the invention. LEGEND TO THE FIGURES

Figure 1. FTIR analysis comparison before and after deacetalisation of A- GlG2-ol-62 polyester showing the formation of a broad peak in the 3500- 3300 cm- 1 area corresponding to the O-H stretch in alcohol groups as the acetal groups are being removed

Figure 2. Overlay 1H NMR spectra of A-GlG2ol-62 polyester sample before deacetalisation and after 0.5 hours, 1 hour, 2 hours, 4 hours respectively 5 hours of incubation at room temperature Figure 3. (A) Conversion deacetalisation A-GlG2ol-62 polyester in HCOOH 88% as function of the reaction time. (B) the degree of acetal removal can be controlled by adjusting the concentration of the used aqueous acid, hydrolytic removal of the acetal group by using a solution of trifluoro acetic acid (TFA). Two samples of 200 mg of dry and catalyst -free A-GlGlol-64 polyester were dissolved in a volume of 1ml TFA 65% solution in water, respectively in 1ml TFA 90% solution in water.

Figure 4. Viscosity as a function of temperature measured for G1PD-58 10wt% in water measured at fixed shear rate= 9.6 s^-1

Figure 5. Viscosity as function of shear rate measured for G1PD-58 in water at 2.5wt%, 5wt.%. and 10wt.%

Figure 6. Viscosity as function of shear rate measured for: G1PD-58, GlG2ol-62 at a concentration of 2wt.% in water a) and for G1PD-58 and GlGlol-64 4wt.%. in water b)

Figure 7. Viscosity as a function of shear rate measured for GlGlol-64 samples partially and fully acetal deprotected at 4wt% concentration in water. Figure 8. Viscosity as function of shear rate measured for GlG2ol-62 2wt.% in water at pH=4, or at pH=7, respectively.

Figure 9. Overview surface tension as function of concentration of fully and partially deprotected G1PD-58 and GlGlol-64 samples in water.

EXPERIMENTAL SECTION

Methods and equipment

Characterisation of the solid-state thermoplastics

For confirming the structure of the obtained polyesters, NMR (Nuclear Magnetic Resonance) and FTIR (Fourier Transform Infrared Spectroscopy) analysis methods were used.

The NMR spectra were recorded using a Varian Mercury Plus equipment operating at 400MHz. Approximately 10 respectively, 50mg of sample were dissolved in 1 niL of deuterated solvent for 1H NMR and 13C NMR. A total of 64 scans were acquired for the 1H and 5000 for the 13C spectra, with a relaxation delay of Is.

The FTIR spectra were recorded with a Shimaclzu IR Tracer 100 equipped with an ATR accessory (diamond crystal, Graseby Specac), using a Happ- Genzel apodisation. For an absorbance spectrum, 64 scans were recorded with a 4cm ¹ resolution in the range 4000-600 cm ^-1.

The average molecular weight and polydispersity of the polymer samples prior to the deprotection reaction were determined using a Viscotek Gel Permeation Chromatography system. Chloroform was used as mobile phase and the molecular weight values of the samples were determined based on a universal calibration method. For calibration, polystyrene standards were used. Rheological characterization of the poly(galactaric ester) samples in water

Dry and catalyst free poly(galactaric esters) powder samples were

suspended in water at different concentrations starting from 0.2% up to 4%. The polymer powder was swelled in water at room temperature for several hours until complete dissolution by visual inspection. Samples which did not dissolve completely were kept in the ultrasonic bath for few minutes until a stable dispersion was formed.

For the samples prepared in basic environment the same procedure as described above was first applied and subsequently 20-40 μΐ NaOH 0.1M were added to the volume of 2 ml polymer-water dispersion.

The rheological measurements were performed with a Thermo Fisher Scientific Haake Mars III rheometer. A volume of 2 ml of poly(galactaric esters) in water was placed in the cone-plate unit and the viscosity response was measured as function of a shear rate increasing from 0.1 to 1750 s ^-1. The surface tension of the polymer solutions was determined with a

DataPhysics OCA equipment at room temperature with the pendant drop method. The values were calculated as average of 7 recorded measurements.

EXAMPLE 1 : Polymerisation in melt of linear poly(galactaric esters)

This example describes an exemplary general protocol for synthesising the acetalized poly(galactaric esters).

An equimolar mixture of dimethyl-2,3:4,5-di-O-isopropylidene-galactarate (Galxl) with a linear aliphatic or cyclic diol are brought into a 3-neck cylindrical flask equipped with a magnetic coupling stirrer. A Lewis acid catalyst, i.e. dibutyltin oxide (DBTO), is added to the mixture and the flask is connected to a distillation setup. Prior to the reaction, nitrogen is flushed through the reaction setup and subsequently a constant flow is maintained during the first stage of the reaction in order to remove the formed byproduct. During the second stage, the distillation setup is replaced with a vacuum adapter and high vacuum is applied until the end of the reaction.

The average molecular weight of the obtained polyesters can be adjusted by increasing the reaction time. Since no solvent is used during the

polymerisation, there are some practical limitations related to the higher viscosity of the melt with longer reaction times (i.e. difficulty in the removal of the formed by-product). Even so, in most cases, the numerical average molecular weight varies between 6000 and 30000g/mol.

Besides DBTO [9], [10], other organometallic catalysts which act as Lewis acids have been reported for similar reaction systems. Notable examples are Ti alkoxides; Sb, Ge, Sn oxides; Zn, Mn, Ca, Co, Cd acetate [3], [5], [6].

Nevertheless, their activity may depend on the reaction conditions, on the solubility in the medium or even on the possibility of catalysing also secondary reactions.

Example 1A An equimolar mixture of dimethyl-2,3:4,5-di-0-isopropylidene-galactarate (Galxl) and 2,3: 4,5-di-O-isopropylidene-galactitol (Galxlol) together with an amount corresponding to 0.4%mol (to the monomers) of DBTO, were brought into a 3-neck cylindrical flask equipped with a magnetic coupling stirrer, a nitrogen gas inlet and a temperature controlled distillation setup. The temperature of the reaction was set to 142°C (temperature of the oil bath) and a 250 ml/min nitrogen flow was set during the first stage of the reaction (3.5 hours). During the second stage, high vacuum was applied (0.01 mbar) for 5 hours. The resulting product is dissolved in chloroform and precipitated in diethyl ether. The polymer powder is recovered by vacuum filtration and it is dried of solvent until constant weight in the vacuum oven.

Scheme 2. Chemical structure of an A-GlGlol homopolyester

Table 1.1 herein below provides an overview of exemplary acetahzed poly(galactaric esters).

Example IB This example describes a method wherein a bicychc acetalized galactaric acid derivative and alcohol are reacted in the presence of a co-monomer comprising a cross-linking moiety.

A mixture of 3 mmol Galxl , 3.7 mmol Galx lol and 0.5 mmol dimethyl itaconate (DMI) together with an amount corresponding to 0.4%mol (to the monomers) of DBTO, were brought into a 3-neck cylindrical flask equipped with a magnetic coupling stirrer, a nitrogen gas inlet and a temperature controlled distillation setup. Before the start of the reaction 0.5wt.% radical inhibitor. 4-methoxy-phenol, was added and the reaction was started under a 100 ml/min nitrogen flow at 142°C (temperature of the oil bath). After 4 hours, high vacuum was applied (0.01 mbar) for 2 more hours.

The resulting acetalized co-poly(galactaric ester) product is dissolved in chloroform and precipitated in diethyl ether. The polymer powder is recovered by vacuum filtration and it is dried of solvent until constant weight in the vacuum oven.

Scheme 3. Chemical structure of an A-IGlGlol random co-polyester

Table 1.2 Overview exemplary acetalized co-poly (galactaric esters).

EXAMPLE 2: Deprotection of the acetal group

This example describes the general deacetalisation procedure of a method according to the invention. The hydrolytic deprotection of the acetal group can be performed b using an aqueous acid solution.

Scheme 4. Hydrolytic deacetalisation reaction of Galxl derived groups under acidic conditions

A sample of purified and vacuum dried acetalised poly(galactaric ester) is dissolved in the aqueous acid solution and kept at room temperature. The concentration and the reaction time are chosen depending on the desired degree of deacetalisation (see examples below). Subsequently, the polymer solution is precipitated and washed several times with a cold non-solvent, mostly diethyl ether. The recovered product is dried in the vacuum oven until constant weight.

Examples of suitable acids for the acetal removal reaction are: sulfuric acid, hydrochloric acid, para-toluene sulfonic acid, acetic acid, formic acid, trifluoracetic acid etc. Examples include strongly acidic resins of the styrene-divinylbenzene type, e.g. sold, inter alia, under the trade name Amberlyst 15. Formic acid and trifluoracetic acid are preferred.

Scheme 5. General chemical structures of p oly (gal ac t aric esters), a) and b), respectively of random galactaric co-polyester, c) (upon deacetalisation)

Example 2A

The hydrolytic removal of the acetal group was performed using a solution of formic acid (HCOOH). 20 mg of dry and catalyst-free A-GlG2ol-62 polyester sample was dissolved in a volume of 1 ml HCOOH 88% solution in chloroform and with 2% water. The resulted polymer solution was kept at room temperature and samples were taken after 0.5, 1, 2, 4 respectively 5 hours. The sampled polymer was precipit ated and washed several times with cold diethyl ether. The recovered products were dried in the vacuum oven until constant weight.

Scheme 6. Complete hydrolytic deacetalisation reaction of A-GlG2ol-62 polyester using HCOOH 88% solution

Figure 1 shows the FTIR analysis comparison before and after

deacetalisation of A-GlG2-ol-62 polyester. The formation of a broad peak in the 3500-3300 cm ¹ area is observed, which corresponds to the O-H stretch in alcohol groups resulting from the acetal groups are being removed

Example 2B A sample of 200 mg dry and catalyst free A-IGlGlol-MP3 polyester was dissolved in 1 ml TFA solution 90% vol. and kept at room temperature reacting for 30 minutes. Subsequently, the polymer solution was

precipitated and washed several times with ice cold diethyl ether. The recovered product was dried in the vacuum oven until constant weight. Table 2. Overview examples poly(galactaric esters) respectively co- poly (galactaric esters).

*Μn and D as determined from GPC (universal calibration, PS standards) of the acetahzed starting polymer;

** composition of the itaconate unit in the random co-polyesters, as determined from the 1H NMR spectra

EXAMPLE 3: Controlling the degree of hydrolytic deacetalisation.

This example demonstrates that the degree of deprotection in step (ii) of a method of the invention can be controlled in order to accommodate for specific properties of the resulting polymer. i) By adjusting the deacetalisation reaction time

Figure 2 shows an overlay 1H NMR spectra of A-GlG2ol-62 polyester sample before deacetalisation and after 0.5 hours, 1 hour, 2 hours, 4 hours and 5 hours of incubation at room temperature, respectively.

The gradual hydrolytic deacetalisation reaction was confirmed by the decrease in intensity until complete disappearance of the chemical shift corresponding to the protons from the acetalic methyl groups in the 1.3-1.4 ppm region. As another example, conversion from the fully isopropylidene protected GlG2ol-62 polymer to about 50% acetalisation is achieved in less than one hour in an aqueous HCOOH (88%) solution with a complete removal of all acetal groups within 5 hours (see figure 3A). ii) By adjusting the concentration of the aqueous acid solution

The hydrolytic removal of the acetal group is suitably performed by using a solution of trifluoroacetic acid (TFA). Two samples of 200 mg of dry and catalyst-free A-GlGlol-64 polyester were dissolved in a volume of 1ml TFA 65% solution in water, respectively in 1ml TFA 90% solution in water. The resulted polymer solutions were kept at room temperature for 0.5 hours. Subsequently the polymer was precipitated and washed several times with cold diethyl ether. The recovered products were dried in the vacuum oven until constant weight. Similarly to varying the deacetalisation time, the degree of acetal removal can also be controlled by adjusting the concentration of the used aqueous acid. By treating the A-GlGlol-64 sample with a TFA solution 65vol%, the conversion of the acetal groups to free OH groups is less than 40%, reaching almost complete conversion when increasing the concentration to 90vol. % (see Fig. 3B).

EXAMPLE 4: Application of poly(galactaric esters) as rheology modifiers

This example demonstrates the added value of these novel poly(galactaric esters) by showing their rheological and surface tension in water as response to the change of different parameters. Depending on the concentration and/or pH, the poly(galactaric esters) can be dissolved or suspended in water. Since the molecular weight of the polymers is in the 10³- 10⁴ g/mol region, no (or up to a low extent) associative behaviour due to chain entanglements is expected to happen. More likely, strong intermolecular interactions such as hydrogen bonding between the free OH groups and the water molecules along with hydrophobic strong associations between the internal non-polar units are the ones assumed to give the thickener response of the polyester samples in an aqueous system.

The water-polyester system shows relatively good stabihty in the room temperature domain with a gradual decrease in viscosity when increasing the temperature. Figure 4 shows the thickening effect of the exemplary poly(galactaric ester) G1PD-58 (10 wt% in water) as a function of

temperature.

As expected in this case, the response to the steadily increasing shear rate is a high viscosity in the low shear rate range (0.01-1 s ^-1) with a lower viscosity in the intermediate and high shear rate region (1-1000 s ^-1). This type of behaviour is characteristic to a pseudoplastic or shear-thinning fluid.

Different shear thinning response can be observed when modulating different parameters of the water-polyester thickener system. Concrete examples are depicted in Figures 5 and 6. Figure 5 illustrates the dependence on the concentration of polymer in the water solution/ dispersion. Shown is the viscosity as function of shear rate measured for GlPD-58 in water at 2.5wt%, 5wt.% and 10wt.%. Surprisingly, by increasing the concentration of the polymer, a higher viscosity response is obtained while maintaining the shear thinning behaviour.

Figure 6 illustrates the dependence on the type of co-monomer (type of hydrophobic unit). Shown is the viscosity as function of shear rate measured for (panel A) GlPD-58, GlG2ol-62 at a concentration of 2wt.% in water; and (panel B) for GlPD-58 and GlGlol-64 4wt.% in water. The strength of the formed hydrophobic clusters and therefore the

thickening effect is dependent on parameters such as distance or size of the hydrophilic spacer but also on the molar volume of the associative

hydrophobic units. Therefore, due to its flexibility an alkyl unit can contribute to stronger associative interactions than a cyclic structure.

(figure 6A). Furthermore, the number of hydrophobic groups along with their internal distribution inside the chain will influence the rheological behaviour. As depicted in figure 6B, a hydrophobic unit of 3 carbon atoms contributes to stronger interactions than a -CH2- group.

Figure 7 illustrates the dependence of the shear thinning behaviour on the degree of deacetalisation. Shown is the viscosity as a function of shear rate measured for GlGlol-64 samples partially (30%) and fully acetal

deprotected at 4wt% concentration in water.

This demonstrates that, related to the type of monomer influence on the rheological properties, a partial removal of the acetal groups (therefore influencing the hydrophilicity- hydrophobicity ratio but also the chain conformation possibilities) has an effect on the overall shear thinning response. On one side the initial viscosity at very low shear rates will be comparable. However, the sample which still contains some residual bulky acetal groups favours fewer inter-molecular and more intra-molecular associations and thus a lower viscosity value at high sheer rates.

Figure 8 demonstrates the dependence on the change in pH. Shown is the viscosity as function of shear rate measured for GlG2ol-62 2wt.% in water at pH=4, or at pH=7, respectively.

The poly(galactaric esters) show a better solubility in water at pH > 7 (concentration dependent). There is little influence on the rheological profile of the solution as shown in figure 8. However, with respect to practical applications of the polymer and from the compounding point of view, an increased solubihty will also reduce the possibility of the polymer

precipitating from the water phase.

EXAMPLE 5: Surfactant activity Figure 9 shows the surface tension as a function of the concentration of exemplary polyesters GlPD-58 and GlGlol-64 samples in water. Even in the dilute concentration region (up to 4wt.%) the surface tension of the water can be decreased by adding the hydrophilic poly(galactaric esters). The figure also shows the surface tension of partly deprotected Galx polyesters. Dispersions of 4wt.% GlPD-58 and GlGlol-64 (30% deprotected) in demineralised water were prepared. The determined surface tension values are comparable with the ones obtained for the fully deacetalised homologues polyesters at 1.5wt% concentration in water. REFERENCES

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doi: 10.1016/j.cocis.2010.07.007. [9] Lavilla, C, Alia, a, de Ilarduya, a M., Benito, E., Garcia-Martin, M. G., Galbis, J. a, & Mmioz-Guerra, S. (2011). Carbohydrate-based polyesters made from bicyclic acetalized galactaric acid. Biomacromolecules, 12(7), 2642-52. http://doi.org/10.102 l/bm200445w [10] Mmioz Guerra, S., & Lavilla Aguilar, C. (2013). Sintesis de

homopoliesteres y copoliesteres aroniaticos y alifaticos a partir de derivados de alditoles y acidos aldaricos diacetalizados, asi como homopoliesteres y copoliesteres aroniaticos y alifaticos obtenidos de dicho procedimiento. Spain: Universitat Politecnica de Catalunya.

Claims

Claims

1. A method for providing a linear carbohydrate-based polyester, comprising the steps of:

(i) reacting a bicyclic acetalized galactaric acid derivative (Galx) of the general formula I

wherein X is H or a linear aliphatic moiety, preferably a linear C₁- CV, alkyl;

R and R' are linear alkyl chains, more preferably C₁-C₃ alkyl; with a diol in the presence of a suitable catalyst to obtain a Galx-based polyester; and

(ii) svibjecting said Galx-based polyester to a hydrolytic deacetalisation reaction to convert at least part of the diacetal moieties to dihydroxide moieties.

2. Method according to claim 1, wherein X is a linear C₁ -C₅ alkyl. 3. Method according to any one of the preceding claims, wherein said bicyclic acetahzed derivative is selected from the group consisting of dimethyl-2,3:4,5-di-0-isopropylidene-galactarate and dimethy1-2,

3:4,5-di-O- methylene-galactitol.

4. Method according to any one of the preceding claims, wherein said diol is of the general formula

wherein

is a linear or cyclic aliphatic hydrophobic unit.

5. Method according to claim 4. wherein said diol is selected from the group consisting of linear aliphatic α,ω-diols. such as 1,3-propanediol, 1,4- butanediol, 1,5-pentanediol, 1,6-hexanediol, or 2.3 : 4 , 5 - di - O -isopropylidene - galactitol or dimethyl-2,3:4,5-di-0-methylene-galactitol.

6. Method according to any one of the preceding claims, wherein step

(i) comprises reacting said bicyclic acetalized galactaric acid derivative and said alcohol in the presence of a further co-monomer comprising a cross- linking moiety.

7. Method according to claim 6, wherein said further co-monomer comprises an α,β-unsaturated functionality, preferably wherein the co- monomer is itaconic acid or ester thereof, such as dimethylitaconate or dibu tyli tacon a te .

8. Method according to any one of the preceding claims, wherein the catalyst used in step (i) is selected from the group consisting of DBTO and other organometallic catalyst which act as Lewis acids, such as Ti alkoxides; Sb. Ge, Sn oxides; Zn, Mn, Ca, Co, Cd acetate.

9. Method according to any one of the preceding claims, wherein step

(ii) comprises dissolving the Galx-based polyester in an acid solution and incubating at room temperature to obtain the desired degree of

deacetalisation, preferably wherein said solution of acid is an aqueous solution of sulfuric acid, hydrochloric acid, -toluene sulfonic acid, acetic acid, trifluoroacetic acid, more preferably formic acid.

10. Method according to any one of the preceding claims, wherein at least 20%, preferably at least 40%, more preferably at least 60% of the diacetal moieties are converted to dihydroxide moieties.

11. Method according to any one of the preceding claims, further comprising step (iii) wherein the Galx-based polyester comprising dihydroxide moieties obtained in step (ii) is precipitated, washed and dried.

12. A linear carbohydrate-based polyester obtainable by a method according to any one of claims 1-11.

13. Linear carbohydrate-based polyester of the general formula

or

wherein is a linear or cyclic aliphatic hydrophobic unit and

wherein at least two but not all of the Acn groups together form

wherein R and R' are C₁-C₃ alkyl, and wherein the remaining Acn groups are H, for a partially deacetalised structure

14. Use of a hnear carbohydrate-based polyester according to claim 12 or 13 as rheology modifier.

15. Use of a hnear carbohydrate-based polyester according to claim 12 or 13 as surfactant.

16. A water-borne emulsion comprising a linear carbohydrate-based polyester according to claim 12 or 13, preferably wherein said composition is a cosmetic or detergent composition, an adhesive, coating or paint

composition.