Title of Invention: Crosslinking Agent for Polymer Emulsions Technical Field The present invention generally relates to a crosslinking agent for use in aqueous polymer compositions or polymer emulsions, methods for curing or crosslinking these compositions and coatings formed therefrom.

Background Art Polymer emulsions (sometimes called "latexes") are commonly used film formers in the coatings and paints industry. These aqueous-dispersible polymer compositions typically comprise an organic polymer binder phase dispersed in an aqueous solvent phase. These polymer emulsions may be curable / crosslinkable at room temperature conditions (typically around 20 °C - 30 °C). The polymer binder phase of such emulsions is typically comprised of polymers or copolymers having actinic- radiation curable functional groups, such as vinyl groups. A common example of such binders would be polyacrylates or polymethacrylates. A crosslinking agent is usually added to such compositions to increase the hardness of an ultimately formed coating. This is accomplished by increasing the cross-linking density. Apart from enhanced hardness, other benefits of increasing crosslinking density may include, but are not limited to, increased coating resistance to water or chemical solvents (acids, bases).

It is generally preferred that these crosslinking agents be non-volatile or are minimally volatile. This is to reduce out-gassing of volatile organic compounds (VOC) post-curing. At the same time, it is also preferred that these crosslinking agents are non-toxic. Also preferred are crosslinking agents which do not affect the color properties of the coating (e.g., yellowing). At present, the typical crosslinker compound used for ambient curing of polymer emulsions is adipic acid dihydrazide (ADH). ADH has been observed to be particularly effective in crosslinking polyacrylate binders having functionalized monomers such as, acetone monomers, acetoacetoxyalkylethylacrylate (AAEM) monomers, butyl acetoacetate (BAA) monomers or mixtures thereof. ADH is also commonly used as hardeners for epoxy formulations and has been shown to provide excellent water resistance to coatings.

On the other hand, AHD is a toxic chemical which is substantially water-soluble. This poses a significant threat to the environment, in particular, aquatic ecosystems and entails the risk of bioaccumulation and biomagnification in aquatic organisms. ADH is classified as a Chronic Category 2 compound under the Globally Harmonised System of Classification and Labelling of Chemicals (GHS). Furthermore, ADH has also been observed to cause yellowing in coatings. Therefore, there is a need to find a substitute for ADH. However, to date, no viable alternative or replacement crosslinker compound has been identified, which is able to provide comparable crosslinking effectiveness as ADH under ambient conditions. It is therefore an object of the present invention to provide aqueous polymer compositions or polymer emulsions which would overcome or ameliorate the above problems. In particular, it is an object to provide an alternative crosslinker component, which is able to provide comparable if not superior crosslinking properties to ADH, which is able to crosslink polymeric emulsions at ambient conditions, does not result in VOC emissions in a coating, and is non-toxic.

Summary

In one aspect of the present disclosure, there is provided a coating composition comprising: a latex component comprising an acrylic emulsion, said acrylic emulsion having at least one monomer expressing a reactive carbonyl functional group; and a crosslinker component comprising a hyperbranched or dendritic, polymeric or oligomeric crosslinker comprising reactive amine functional groups. Advantageously, the disclosed cross-linker may be non-toxic. The disclosed crosslinker may react with the carbonyl functional group of the monomer unit to thereby crosslink the acrylic emulsion and become integrated into the crosslinked polymerized network. The crosslinker may comprise functional groups that are reactive under ambient temperature and pressure conditions.

In one embodiment, the disclosed crosslinker is a star-shaped or dendritic polymer. The dendritic polymer may have a substantially globular shape and exhibits a substantially monodisperse structure (uniformly or symmetrically branched structure) with a high density of surface (peripheral functional groups).

Dendritic structures are usually formed from a central initiator molecule having two or more reactive sites, wherein further reaction results in the outward growth of the structure with an exponentially increasing number of peripheral functional groups. A dendritic structure may be described by its generation, e.g., a generation 0 dendritic polymer may have 4 functional groups and a generation 1 dendritic polymer may have 8 peripheral functional groups, etc. The disclosed crosslinker may be a generation 0, 1 , 2, 3, or 4 dendritic polymer.

The disclosed crosslinker may express reactive peripheral amine groups. These peripheral amine groups may be primary amines capable of reacting with carbonyl compounds to form enamines. In one embodiment, the crosslinker is a dendritic polymer such as polyamidoamine (PAMAM). The crosslinker may be a generation 0, 1 , 2, 3, or 4 PAMAM, having a theoretical number of 4, 8, 16, or 32 peripheral amine functional groups respectively. The amine functional groups may be primary amine, secondary amine or tertiary amine groups. In one embodiment, the crosslinker is PAMAM having from around 4 to around 16 functional groups. In one embodiment, the crosslinker is PAMAM having from around 8 to around 16 functional groups. In one embodiment, the crosslinker is PAMAM having from around 8 to around 32 functional groups. In another embodiment, the crosslinker is PAMAM having from around 16 to around 32 functional groups. In another embodiment, the disclosed crosslinker is a hyperbranched amine functional polymer. The amine functional hyperbranched polymer may be structurally or chemically similar to polyamidoamine, but shows less uniform branching (polydisperse).

In yet another embodiment, the disclosed crosslinker is a mixture of dendritic and hyperbranched polymers according to the present invention.

Advantageously, it has been found that the use of a dendritic or hyperbranched amine functional crosslinker is able to substitute the traditional function of ADH without reducing crosslinking effectiveness. This effect is supported by the comparable coating density and hardness achieved by coatings of the present invention (using the disclosed crosslinkers) when compared to ADH-based coatings. Although dendritic/hyperbranched polymers are known to act as demulsifiers, it was surprisingly found that the introduction of the amine functional dendritic and hyperbranched crosslinkers into the polymer emulsion systems did not result phase separation between the organic binder phase and the aqueous solvent phase. It has been advantageously observed that, apart from coating hardness, the amine functional dendritic and hyperbranched crosslinkers also achieved improved water resistance and abrasion resistance.

Further advantageously, because the amine functional dendritic and hyperbranched crosslinkers are incorporated into the polymerized crosslinked network after curing, coatings according to the present invention also exhibit low or negligible VOC emissions.

Still advantageously, dendritic polymers such as PAMAM are non-toxic, biocompatible and non-immunogenic, which additionally complements their suitability as crosslinking agents.

More advantageously, the amine-carbonyl group reaction is capable of proceeding under ambient conditions, which allows the disclosed crosslinker to cure the polymer emulsion under room temperature conditions. In embodiments, the amine-carbonyl reaction is undertaken or performed under weak acid/neutral conditions, e.g., pH greater than 3 but less than 7. In embodiments, the reaction is undertaken at a pH of between 4 and 7; between 5 and 7; or between 6 and 7, e.g., 4, 4.5, 5, 5.5, 6, 6.5 and 7.

Yet another aspect of the invention relates to a method of forming a coating, said method comprising: providing a latex component comprising an acrylic emulsion, said acrylic emulsion having at least one monomer expressing at least one reactive carbonyl functional group; adding a hyperbranched or dendritic, polymeric or oligomeric crosslinker comprising reactive amine functional groups to said latex component to form a crosslinkable coating composition; applying said coating composition to a surface; and reacting said crosslinker with said latex component under ambient conditions to form said coating.

Definitions

The following words and terms used herein shall have the meaning indicated: The word "substantially" does not exclude "completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1 % of the stated value, and even more typically +/- 0.5% of the stated value. Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. Brief Description of Figures

Fig. 1 is a photograph depicting the effects after applying a wet abrasive scrub test to an in-house paint formulation X prepared with a crosslinker according to the invention (right image) and a paint formulation prepared without a crosslinker according to the invention (left image).

Fig. 2 is a another photograph showing the effects after applying a wet abrasive scrub to an in-house paint formulation Y prepared with a crosslinker according to the invention (right image) and a paint formulation prepared without a crosslinker according to the invention (left image).

Fig. 3 is an IR spectra of a latex formulation comprising an AAEM monomer and a polyamine crosslinker CYD-100A according to the invention. Fig. 4 is a comparative IR spectra of a latex formulation comprising an AAEM monomer and an ADH crosslinker. Detailed Disclosure of Embodiments

Non-limiting embodiments of the disclosed coating composition and the relevant crosslinker are further discussed hereafter. In embodiments, the disclosed dendritic/hyperbranched cross-linker may be used in combination with a melamine-based crosslinker and/or a dihydrazide crosslinker (e.g., ADH). In other embodiments, the coating composition may be substantially absent of a melamine-based crosslinker and/or ADH. The latex or the polymer emulsion used in the disclosed coating composition is not particularly limited. It is preferable that the polymer emulsion is prepared from monomer units comprising at least one a ketone functional group. In one embodiment, the monomer of the emulsion comprises at least one reactive carbonyl group of a ketone moiety capable of undergoing enamine formation with a di-amine functional group.

The monomer units may comprise acrylate monomers having at least one vinyl group and a carboxylic acid group. The acrylate monomers may additionally comprise at least one or more of a ketone functional group, an ester functional group or an amide functional group.

In one embodiment, the monomer unit may comprise the following structure: H ₂ C=C(CH3)-(CO)0-(CH2)n-0(CO)-CH2-(CO)-CH ₃

, wherein n can be an integer selected from 1 , 2, 3, 4, 5, or 6. In one embodiment, n is 2 to 6, 2 to 5, 2 to 4, 2 to 3 or 2. In another embodiment, the monomer unit may comprise the following structure R-CH ₂ -C(0)-CH ₃ , wherein R is alkylacrylate, wherein the alkyl group may comprise 1 to 6 carbon atoms. In other embodiments, the polymer emulsion comprises a mixture of one or more different acrylate monomers disclosed herein.

In another embodiment, the monomer units are acrylate-based monomers (or acrylic monomers) expressing one or more of the following functional groups:

0 0 o

In another embodiment, the monomer unit may be an alkylacetoacetate having the following structure: R ¹ -0-C(0)-CH ₂ -C(0)-CH ₃ , wherein R ¹ is C1 -6 alkyl selected from methyl, ethyl, propyl, butyl, pentyl and hexyl.

In embodiments, the disclosed latex or polymer emulsion may comprise acetoacetoxyethyl methacrylate monomer units, tert-butyl acetoacetate monomer units, diacetone acrylamide and mixtures and blends thereof. Without being bound by theory, it is postulated that the crosslinking between the dendritic / hyperbranched crosslinker and the acrylate monomers may be due to enamine formation between the reactive carbonyl functionality of the ketone group or ester group and the peripheral amine functional groups of the crosslinker. Due to the high density of surface amine groups expressed by the crosslinker, greater crosslinking density can be achieved as opposed to the use of crosslinkers which do not exhibit the globular dendritic/hyperbranched structures.

The hyperbranched or dendritic, polymeric or oligomeric crosslinker may have a molecular weight of greater than 250, or greater than 500. The average molecular weight of the cross-linker may be selected from: 250 - 500, 500 - 20,000, 500 - 10,000, 500-7500, 500 - 5,000, 500 - 2500, 500-2000, 500 - 1500, 500 - 1000, 500-900, 500-800, 500-700, or 500-600. The crosslinker may be selected to have a molecular weight that allows it to retain dispersibility or solubility in the emulsion, while exhibiting little or no volatility.

In embodiments, the crosslinker according to the invention may experience a weight loss of less than 10 wt. % post-curing, preferably less than 5 wt. %, more preferably less than 2 wt. % and less than 0.5 wt. %. In embodiments, the crosslinker may exhibit a weight loss of less than 0.1 wt. % after curing.

When a dendritic crosslinker is used, the theoretical number of surface amine functional groups may be selected from 4, 8, 16, 32 or 64. Due to imperfect branching, these are theoretical numbers based on the dendritic polymer generation. Actual number of functional groups per dendritic molecule may be from about 1 to 80. In embodiments, the number of functional groups per dendritic molecule may be around 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80 or a range thereof. In one embodiment, a generation 0 polyamine having around 4 amine functional groups per molecule is provided as crosslinker. In another embodiment, a generation 1 polyamine having around 8 amine functional groups per molecule is provided as crosslinker. In yet another embodiment, the crosslinker may comprise mixtures of dendritic polyamine having different generations.

When a hyperbranched crosslinker is used, the number of functional groups per dendritic molecule may be from about 10 to 80, 10 to 70, 10 to 60, 10 to 50, 10 to 40, 10 to 30, 20 to 80, 20 to 70, 20 to 60, 20 to 50, 20 to 40, 30 to 80, 30 to 70, 30 to 60, 30 to 50, 40 to 80, 40 to 70, 40 to 60 or 40 to 50. In one embodiment, a hyperbranched polyamine having around 20 to 50 amine functional groups per molecule is provided as crosslinker.

Advantageously, the disclosed crosslinkers were found to provide effective crosslinking, even when provided in a latex:crosslinker weight ratio of 1000:1 . The latex:crosslinker weight ratio may be from 1000: 1 to about 5:1 , e.g., 1000/1 , 900/1 , 800/1 , 700/1 , 600/1 , 500/1 , 400/1 , 300/1 , 200/1 , 100/1 , 90/1 , 80/1 , 70/1 , 60/1 , 50/1 , 40/1 , 30/1 , 20/1 , 10/1 , 9/1 , 8/1 , 7/1 , 6/1 , or 5/1 . The latex may form around 5 to 95 wt. % based on the weight of the coating composition. In embodiments, the latex is provided in an amount of around 5 - 50 wt. %, 10 to 50 wt. %, 20 to 50 wt, %, 30 to 50 wt. %, 5 to 60 wt.%, 10 to 60 wt. %, 20 to 60 wt. %, 30 to 60 wt. %, 40 to 60 wt. %, 50 to 60 wt. %, 5 to 70 wt. %, 10 to 70 wt. %, 20 to 70 wt. %, 30 to 70 wt. %, 40 to 70 wt. %, 50 to 70 wt. %, or 60 to 70 wt. %.

The hyperbranched or dendritic polyamine crosslinker may be provided in an amount of from 1 wt.% to 25 wt.% based on the weight of the coating composition. The polyamine may be provided in an amount from of at least 4 wt. % to 20 wt.% based on the weight of the latex composition. It has been observed that providing the crosslinker in an amount lower than 4 wt,% or exceeding 20 wt.% may lead to reduced resistance against water damage.

The latex composition may comprise acrylic monomers comprising at least one or more of a ketone functional group, an ester functional group, or an amide functional group, wherein these acrylic monomers are present in amounts of from about 0.1 to about 20 weight percent based on the total weight of the latex composition. In embodiments, the disclosed functionalized acrylic monomers may be present in an amount of about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 .0, 1 .2, 1 .4, 1 .6, 1 .8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, or 20 wt. %, or in a range having an upper and lower limited selected therefrom. In one embodiment, the latex composition comprises the functionalized acrylic monomers in an amount of from 0.1 to 10 weight percent. The functionalized acrylic monomers may be AAEM monomers as disclosed herein, the acetoacetate monomers as disclosed herein or a blend thereof.

The disclosed coating composition may be formulated in such a way so that the molar ratios between the crosslinkable functional groups of the dendritic crosslinker (e.g., NH ₂ ) and the reactive functional groups of the acrylic monomers are between 1 :4 to 4:1 , e.g., 1 :4, 1 :3.5, 1 :3, 1 :2.5, 1 :2, 1 :1 .5, 1 :1 . 1 .5:1 , 2:1 , 2.5:1 , 3:1 , 3.5:1 or 4:1 .

In one embodiment, the molar ratio of the groups to the crosslinkable functional group (e.g., NH ₂ ) is around 1 :4 to 4:1 . In one o

embodiment, the molar ratio of the ~CH ₃ ~C~CH ₃ g _r0U p _S to the crosslinkable functional group is around 1 :4 to 4:1 . In another embodiment, the molar ratio if O O o

the total amount of ~°~ ~ ^CH¾ ~ ^c ~ ^{C i} and ~ ½~&

crosslinkable functional group is around 1 :4 to 4:1 .

In embodiments, the coating composition may be a clear coat, which comprises around 77 to 98% by weight of the latex component, and about 0.1 to about 25 wt. % crosslinker, preferably from 4 wt.% to 20 wt.%, 0 to 30 wt. % one or more additives, wherein the total weight percentage does not exceed 100% or is 100%. In embodiments, the coating composition may be a pigmented coat, which comprises around 15 to 50% by weight of the latex component, and about 0.01 to about 25 wt. % crosslinker preferably from 4 wt.% to 20 wt.%, 10-30% pigment or organic filler, 0 to 30 wt. % one or more additives, wherein the total weight percentage does not exceed 100% or is 100%.

The one or more additives may be selected from the group consisting of: a pigment, a photoinitiator, a surfactant, a biocide, a coalescent, a defoamer and an anti-freeze agent. Advantageously, because the polyamine crosslinker may also function as a pH buffering agent or an anti-freeze agent, the coating compositions of the invention may optionally omit these additives.

The coating composition may be formulated as a one-pack coating composition or a two-pack coating composition. When formulated as a one-pack composition, the ketone/carbonyl groups of the monomer units may be coupled to a protecting group to avoid premature crosslinking. For example, the diketone groups or the carbonyl groups of the acetoacetoxyethyl methacrylates may be reacted with an amine protecting group, which may be capable of decoupling from these functional groups during the curing process and thereby free up the carbonyl groups for reaction with the polyamine crosslinkers.

Accordingly, another embodiment of the invention relates to a two-pack coating composition comprising: in a first pack, a latex component as defined herein; and in a second pack, a polyamine crosslinker as described hereinabove. The present disclosure further relates to a method of forming a coating on a surface, said method comprising: providing a latex component comprising an acrylic emulsion, said acrylic emulsion having at least one monomer expressing at least one reactive carbonyl functional group; adding a hyperbranched or dendritic, polymeric or oligomeric crosslinker comprising reactive amine functional groups to said latex component to form a crosslinkable coating composition; applying said coating composition to the surface; and reacting said crosslinker with said latex component under ambient conditions to form said coating.

The hyperbranched or dendritic, polymeric or oligomeric crosslinker may be a dendritic or hyperbranched polyamine as disclosed herein. The latex component and its associated acrylate monomers may be as disclosed hereinabove.

The disclosed method may expressly exclude a step of adding a melamine based crosslinker or a dihydrazide crosslinker (e.g. ADH) to the latex component. In other embodiments, melamine crosslinkers or ADH may be added in combination with the dendritic or hyperbranched polyamine.

There is also provided a method for crosslinking a polymer emulsion having the acrylate monomers as defined herein, wherein the method comprises the step of reacting said polymer emulsion with a dendritic or hyperbranched polyamine as disclosed herewith under ambient condition to cause said crosslinking. The present invention further provides the use of a dendritic polyamine as a crosslinker for crosslinking an aqueous polymer composition, wherein the aqueous polymer composition may be an acrylic emulsion as disclosed herein.

In one embodiment, the reacting step takes place under mildly acid conditions. Advantageously, this allows the latex composition containing the acrylate monomers and the polyamine crosslinkers to be stored in a single pack system under stable conditions, i.e., no premature reaction. For instance, the latex composition may be stored under alkaline conditions, wherein the alkali component is selected to be one that is volatile under room temperature conditions. Upon mixing and application, the alkali may evaporate from the applied latex composition, resulting in the formation of a mildly acidic system. The acidic condition then facilitates the enamine formation reaction between the polyamine crosslinkers and the acetoacetate group of the monomers (specifically the ketone group).

An exemplary crosslinking reaction between the carbonyl group of the latex monomer and the reactive amine group of the hyperbranched/dendritic crosslinker may be generically illustrated by the reaction shown in scheme 1 .

Scheme 1 a i !s» — — c— ^■ ¾» ^■ ½— «;— * — »—

CS* _A OH,.

. , — ** * ^» *S J** ¾j ^ jp< J

In this scheme, P represents a part of the latex monomer unit that is coupled to an acetoacetate functional group; and R represents the crosslinker structure. The reaction illustrated in scheme 1 is an equilibrium reaction. RT refers to residence time.

As illustrated herein, the reactive carbonyl group is of the ketone group. Amine functional groups (including primary amines and second amines with at least one active hydrogen) can react with ketones to form enamines with H ₂ 0 as a side product. Under alkali conditions, e.g. at pH of 8- 10, the reaction may be suppressed. Conversely, mildly acidic conditions, e.g., pH is≥5 or <7 may result in the dehydration of the water and shift the reaction equilibrium to the product side.

For the application of the coating composition, it is usually cast as a film over a substrate intended for coating. During this process, water may evaporate from the film, forcing the polyamine (crosslinker) to come into contact with the acetoacetyl groups.

Where the acetoacetyl groups were initially protected by a volatile amine group, the protecting group may also decouple from the monomer unit and leave the film (as evaporated ammonia). This lowers the pH to about 6.5 and advantageously accelerates the cross-linking reaction. This is illustrated by scheme 2. Scheme 2

Step 1 :

Ste 2:

As the curing process progresses and more ammonia (protecting group) leaves and evaporates, the ketone group is freed up for reaction with the polyamine crosslinker. Within 20-26 hours, the ratio of diamine enamine groups to ammonia enamine groups may be around 2:1 . This ratio increases with curing time. Within 24-48 hours, the ratio may be around 3:1 . When subjected to curing / drying temperatures of around 60°C the ratio may be 5:1 to 6:1 (e.g., 5.5:1 ) within 72-96 hours. Examples

Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Raw materials:

Unsubstituted poly(amido)amine (PAMAM) hyperbranched polymer and dendritic polymers, specified in Table 1 below, obtained from Weihai CY Dendrimer Technology Co., Ltd., China.

[Table 1]

2. PRIMAL SF240 and AVANSE MV100, bought from Dow Chemical

3. Texanol: Coalescing agent (Ci ₂ H ₂₄ 0 ₃ Propanoic acid, 2-methyl-, monoester with 2,2,4-trimethyl-1 ,3- pentanediol)

4. Ethylene glycol (Antifreeze agent) 5 Evonik Tego 815: defoamer that is an emulsion of a polyether siloxane copolymer and contains fumed silica

All other raw materials are commercially available and described by their trade names in the examples provided herewith.

General Analysis Procedure

1. Gel content analysis

Gel content is analyzed using an in-house method relying on acetone solvent as dissolving medium for the analysis.

A latex film was prepared on a glass panel using an initial weight of the coating composition (0.5 grams to 1 gram). The film is cured for more than 7 days at room temperature and removed from the glass panel by peeling off.

The removed film is then folded neatly and placed into the middle of a Whatman filter paper #54. The filter paper is secured by stapler. The film and filter paper are suspended from a copper wire and lowered into a glass bottle.

200 ml of acetone solvent is added into the bottle and filter paper containing the latex film is then fully or partially immersed into acetone while continuing to be suspended and supported by the copper wire. This is to prevent the filter paper from coming into contact with a magnetic stirrer placed at the bottom of the glass bottom for physical agitation. The bottle's contents are stirred using the magnetic stirrer at 500 rpm for 24 hours at room temperature.

The filter paper and its contents are removed from the solvent after 24 hours. The film and the filter paper are then air dried. The film is then dried again in oven at 1 10 °C for 30 minutes. Thereafter, the film is cooled to room temperature before its final weight measurement is taken.

The calculation of the gel content is based on following equation: % gel content = (Weight of latex film after solvent, 24 hours) X100

Weight of latex film before solvent

2. Water resistance test

Latex film was casted on glass panel and cured at room temperature for more than 7 days. A glass tube (diameter measuring 2cm and 4cm in height) was used to contain the latex film surface. Cotton wool with equal weight was placed into the glass tube to cover the film surface. 2 ml of de-ionized water is dropped into the glass tube to wet the cotton wool. The cotton wool is then pressed down to ensure fully contact with the film surface. Water contact for 30 minutes is allowed before removing the glass tube and cotton wool to observe latex film appearance for severity of whiteness or formation of spots.

3. Wet abrasion scrub test

A latex film was casted on a BYK byko-charts black scrub panel (#PB-5015). The filme is cured at room temperature for more than 7 days before proceeding with the test.

A sheen instrument wet abrasion scrub tester was used for the experiment. A 3M scouring pad is used instead of using the standard brush. This is to accelerate the abrasion effect. One thousand scrub cycles is chosen for the benchmarking comparison. After the scrub cycles, the abrasive wear on the film is physically inspected and a grading is given.

4. FTIR-ATR analysis A mixture comprising a predetermined weight ratio of AAEM with PAMAM material (or the comparative ADH crosslinker) is prepared under methanol medium and allowed to react. The ambient crosslinking reaction is then monitored using Fourier Transform Infrared spectroscopy - Attenuated Total Reflection (FTIR-ATR). The mixture liquid was spotted on a sample compartment and blown dry using hair drier before the IR spectrum is collected.

EXAMPLES 1 to 29 (Latex Film Samples) 29 latex film samples are prepared in accordance with the compositions provided in Tables 2-5 as follows: The latex composition is gradually dosed with the crosslinker component under constant stirring to achieve homogeneity. A latex film of 100 microns in thickness is then casted on a glass panel and left to cure under ambient conditions for more than 7 days to ensure complete curing. The latex film is peeled and collected for analysis under General Analysis procedures 1 and 2 (Gel Content and water resistance)

[TABLE 2]

Weight percentages of components in Examples (wt. %)

1 2 3 4 5 6 7 8 9

Latex SF 240 96.95 95.95 94.95 92.95 88.95 96.95 95.65 94.45 91 .95

MV100

Polyamine CYD-100A 1 2 4 8

Crosslinkers CYD1 10A 1 .3 2.5 5.0

CYD120A

CY WU438

Conventional ADH

crossl inker

Coalescing Texanol 2 2 2 2 2 2 2 2 2 agent

Antifreeze EG 1 1 1 1 1 1 1 1 1

(antifreeze)

Defomaer Evonik 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

Tego 815

(defoamer)

Total 100 100 100 100 100 100 100 100 100

[TABLE 3]

Weight percentages of components in Examples (wt. %)

10 11 12 13 14 15 16 17 18

Latex SF 240 86.95 95.55 94.15 91 .35 85.75 95.35 93.85 90.65 84.35

MV100

Polyamine CYD-100A

Crosslinkers CYD1 10A 10.0

CYD120A 1 .4 2.8 5.6 1 1 .2

CY WU438 1 .6 3.1 6.3 12.6

Conventional ADH

crossl inker

Coalescing Texanol 2 2 2 2 2 2 2 2 2 agent

Antifreeze EG 1 1 1 1 1 1 1 1 1

(antifreeze)

Defomaer Evonik 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

Tego 815

(defoamer)

Total 100 100 100 100 100 100 100 100 100 [TABLE 4]

[TABLE 5]

Weight percentages of components in Examp es (wt. %)

28 29

Latex SF 240

MV100 73.7 71 .6

Polyamine CYD-100A

Crosslinkers CYD1 10A

CYD120A

CY WU438 21 .3

Conventional ADH 23.4

crossl inker

Coalescing Texanol

agent

Antifreeze EG 5 5

(antifreeze)

Defomaer Evonik

Tego 815

(defoamer)

Total 100 100 Results and Discussion

The gel analysis and water resistance test results are tabulated in Table 6. The performance of the various films are graded according to the following scale:

5 - Best (no observable blistering and/or color changes)

4- Superior (low degree of blistering and/or color changes)

3 - Moderate (Some blistering and/or color changes)

2 - Inferior (high degree of blistering and/or color changes)

1 - Bad (Significant blistering and color changes)

[Table 6]

[Table 6 continued]

Table 6 continued]

These experiments show that addition of different type of polyamine crosslinkers (e.g. PAMAM) in the coating compositions significantly increased the amount of gel content most possibly as a result of increased crosslinking density.

As the crosslinking density increased, the water resistant property is improved correspondingly. The results obtained are comparable (if not superior) to the crosslinking effect of ADH addition which is shown in Examples 19 and 29. It is further noted that the effect of adding PAMAM or varying its concentration could not be readily predicted. For instance, increasing the amount of PAMAM did not lead to enhancement of all the desired coating properties. For instance, in Examples 1 to 5 (which uses the same latex SF240 and same type of PAMAM (CYD-100A)), only Example 4 demonstrated good water resistance. Without being bound by theory, it is postulated that when the addition of PAMAM is in excess, the crosslinking reaction does not complete optimally and the excess of hydrophilic components induces water absorption, which may lead to the softening of the latex film. Examples 23, 24, 27 and 28 appear to support the effects of adding excess crosslinkers.

Example 30

Emulsion paint (named as Paint-X) containing latex SF240

Paint-X was produced in-house according to the formulation in Table 7. Firstly deionized water was added to the dispersion tank, controlling speed at 800-1000 rev / min, and then adding (sequentially) raw materials 2-8, i.e., HEC thickeners, AMP- 95, sodium polycarboxylate-based dispersants, silicone defoamers, titanium dioxide, talcum, kaolin were added to the dispersion tank. An interval of 2 to 3 minutes was provided in between the addition of each raw material component to ensure adequate mixing; then the speed was raised to 1500-1800 rev/min and maintained for 15 to 20 minutes, then reduced to 500-800 rev/min, followed by adding raw materials 9-14, i.e., acrylic emulsion, coalescent, in-can preservative, biocide, polyurethane (PU) thickener and deionized water. Likewise, an interval of 2 to 3 minutes was provided in between adding components to ensure the adequate mixing. Finally a suitable amount of water was added, if necessary, to achieve a desired viscosity.

[Table 7].

Example 31

Emulsion paint (named as Paint-Y) containing latex MV100

Paint-Y was produced in-house according to the formulation in Table 8. Firstly deionized water was added to the dispersion tank, controlling speed at 800-1000 rev/min, and then adding (sequentially) raw materials 2-7, i.e., HEC thickeners, AMP-95, sodium polycarboxylate-based dispersants, silicone defoamers, titanium dioxide, kaolin were added to the dispersion tank. During addition, an interval of 2 to 3 minutes was provided in between was adding each component to ensure adequate mixing; The rev speed was raised to 1500-1800 rev/min and maintained for 15 to 20 minutes, then reduced to 500-800 rev/min, followed by adding raw materials 8-12, i.e., acrylic emulsion, coalescent, in-can preservative, biocide and deionized water. Again, an interval of 2 to 3 minutes was provided in between adding each component to ensure adequate mixing. Finally a suitable amount of water was added, if necessary, to achieve a suitable viscosity. [Table 8].

Example 32

Wet abrasion scrub test for emulsion paint containing latex SF240

Emulsion paint prepared according to Example 31 is used. CYD-120A (polyamidoamine crosslinker) is post added into the paint formulation and the preparation of the paint film is according to General Analysis Procedure #3. Applying the wet abrasion scrub test demonstrated improvement in the paint comprising a crosslinker according to the presentinvention as seen in Figure 1 . The incorporation of CYD-120A appears to have significantly increased the crosslinking density of the paint film resulting in the mechanical wear improvement.

Example 33

Wet abrasion scrub test for emulsion paint containing latex MV100

An emulsion paint is prepared according to Example 31 . CYD-120A is post added into the paint formulation and the preparation of the paint film is according to General Analysis Procedure #3. Applying the wet abrasion scrub test showed improvement as can be observed by comparing Figures 2. The incorporation of CYD-120A appears to have increased the crosslinking density of the paint film resulting in the mechanical wear improvement. Example 34

FTIR- ATR monitoring for AAEM- PAMAM crosslinking reaction

A mixture of 1 gram of AAEM monomer with 0.2 gram CYD-100A was prepared according to General Analysis Procedure # 4. The simulation crosslinking reaction is monitored under Fourier transform infrared spectroscopy - Attenuated total reflection (FTIR-ATR). The result is shown in Fig 3.

As can be noticed, there are two emerging new bands at 1600-1700cm ^"1 range. These bands intensity keep increasing while the reaction duration prolonged. At the same time, the keto group of AAEM at 1716cm ^"1 keeps diminishing over time. Both the new bands are correspond to the (C-C=N) stretching vibration around 1640cm ^"1 and (C=C-N) bending vibration at around 1600cm ^"1 for imine and enamine group respectively. The formation of these new bands was the reaction result of keto group on AAEM with amino group of PAMAM. The IR spectra clearly articulate the basic chemical principles of the present invention.

Example 35

FTIR- ATR monitoring for AAEM- ADH crosslinking reaction

A mixture of 1 gram of AAEM monomer with 0.2 gram ADH was prepared according to General Analysis Procedure # 4. The simulation crosslinking reaction was monitored under Fourier transform infrared spectroscopy - Attenuated total reflection (FTIR-ATR). The result is shown in Fig 4. As seen, a new band appeared at 1 136cm ^{" 1} in the initial mixture corresponded to the (C-C=N) stretching vibration. When the mixture is aged, another new band at 1612cm ^"1 is found appeared which was the (C=C-N) bending vibration. This proved that the ambient crosslinking is taking place to form imine first and later converted to a more stable form of enamine. This served as a reference similar reaction to what demonstrated in the present invention.