THIIRANE-TERMINATED POLYSULFIDE POLYMERS

The present invention relates to a novel group of functional group-terminated polysulfide polymers in which the terminating group is a thiirane (episulfide) group, to compositions comprising such thiirane-functional polysulfide polymers and epoxidized polysulfide polymers, to a process to prepare these novel compounds and compositions, and the use thereof.

Epoxy-functional polysulfide polymers are known from the July 2003 Thioplast™ EPS brochure of Thioplast Chemicals GmbH&Co KG (which can be found on www.thioplast.com), WO 03/076487, and WO 2004/099283, which disclose epoxy-terminated polysulfide polymers of the formula

o p _v

H ₂ C / \ CH — R' S R S R C /H —\ CH ₂

wherein R = the polysulfide polymer structure -(CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ -SS) _n - CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ - n = 8-20, and R' = CH ₂ or DGEB A/F (diglycidyl ether of bisphenol A or F). They also disclose the uses of such epoxy-terminated polysulfide polymers in a coating, sealant, adhesive and/or paint composition.

JP 0797556A discloses an adhesive composition containing a polysulfide- modified epoxy resin of the formula

wherein R' is an organic group containing a bisphenol backbone and R is a polysulfide backbone of the formula -(CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ -Sm) _n -, wherein m is 1 -3 and n is 1 -50. The other component of the adhesive is a triazine amine.

Epoxidized polysulfide polymers are polymers that can be suitably used as a binder in coatings, sealants, and adhesives. They are characterized by such properties as the ability to cure at ambient temperature, good adhesion to different substrates, an adjustable flexibility, a high impact resistance, high corrosion stability, a good chemical resistance to a number of diluted acids, alkalis, and organic solvents, and efficient repair. They can be combined with a wide range of curing agents such as aliphatic and aromatic (poly)amines, (poly)amides, (poly)thiols, and hydroxyl-containing resins such as phenolic resins, polycarboxylic acids and anhydrides, optionally in the presence of a catalyst. Until now, different epoxidized polysulfide polymers with a different viscosity have been prepared, i.e. to a certain extent they can be tailor-made for different applications.

However, epoxy-functional polysulfide polymers (EPS) suffer from a number of drawbacks. Their reactivity to amine curing compounds and their thermal stability are both subject to improvement. Some of the epoxy-functional polysulfide polymers characterized by an aliphatic polymer backbone in particular have a relatively low reactivity to a number of curing agents.

Accordingly, there is a need in the art for epoxidized polysulfides that do not suffer from the above-indicated drawbacks. More specifically, there is a desire for polysulfide polymers with a good balance between a sufficiently low viscosity and a sufficiently high reactivity towards curing agents. Also, there is a desire for polysulfide polymers with improved thermal stability.

The present invention now provides thiirane-functional polysulfide polymers of the formula

x X / \ / \

H ₂ C- -CH — R S R S- -R- -CH — CH ₂ (I)

wherein R = the polysulfide polymer structure -(CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ -SS) _n - CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ - n = 8-20, R' = CH ₂ or DGEB A/F (diglycidyl ether of bisphenol A or F), X is O or S, with the proviso that at least one X is S.

Further, the present invention provides compositions comprising the above thiirane-functional polysulfide polymer and the corresponding epoxy-functional polysulfide polymer of formula (I), wherein X = O.

As demonstrated by the examples, the thiirane-terminated polysulfide polymers of the present invention have an improved reactivity to curing agents and a better thermal stability compared to the epoxidized polysulfide polymers of the state of the art, while they do not show any deterioration of the other desired properties, such as the mechanical properties, manifested by the state of the art epoxidized polysulfide polymers.

Chino et al., "Novel Rapid-Cure Adhesives for Low-Temperature Using Thiirane Compound" (Journal of Applied Polymer Chemistry, Vol. 81 , pp. 2953-2957, 2001 ) disclose the synthesis of bisphenol F thiirane and bisphenol A thiirane and the use of these compounds in an adhesive. Neither thiirane compound contains a polysulfide polymer backbone. They can be prepared by reacting the corresponding epoxy resin with potassium thiocyanate or thiourea in a polar solvent. The resulting compound, bisphenol F thiirane, is said to be partly thiirane- and partly epoxide-terminated. When used in a curable (adhesive) composition with an amine hardener, their curing is said to be faster than that of the corresponding epoxides and their storage stability is said to improve. However, Chino et al. neither suggest the improved thermal stability of the thiirane compounds compared to the epoxy-functional compounds, nor do they offer any disclosure of a good balance between viscosity and curing agent reactivity.

The thiirane-functional polysulfide polymer (TPS) of the invention can be prepared by a process wherein the corresponding epoxy-functional compound

is reacted with thiourea or a thiocyanate ion-providing compound in the presence of a catalyst and a solvent for 2 to 15 hours at an elevated temperature.

The thiocyanate ion-providing compound can be an inorganic thiocyanate, for instance a thiocyanate salt (e.g. ammonium thiocyanate, potassium thiocyanate or sodium thiocyanate), or an ion exchange resin or silica gel containing thiocyanate ions. These last two have the benefit of the reaction mixture being easier to purify, as they can be separated off by a simple filtration. However, the best yields are found using thiocyanate salts. Preferably, ammonium thiocyanate is used.

The catalyst can be selected from the group of organic acids such as oxalic acid or acetic acid, and derivatives thereof such as their hydrated salts or anhydrides. Preferably, the catalyst is oxalic acid.

The solvent can be an organic solvent selected from the group of CrC ₄ alkanols, CrC ₄ dialkyl ketones, halogenated CrC ₄ alkanes, and CrC ₄ nitriles. Preferably, the solvent is selected from the group of acetonitrile, methanol, ethanol, dichloromethane, acetone, methylethyl ketone, methylbutyl ketone. Most preferred is acetonitrile.

By elevated temperature is meant a temperature between room temperature and the boiling point of the used organic solvent. Preferably, the reaction is performed under reflux conditions.

As demonstrated by elemental, NMR, and GPC analysis, actually a mixture of both the epoxy-functional and the thiirane-functional polysulfide compound results (hereinafter also referred to as TPS mixture), which compounds can be separated by separation methods known to the skilled person, for example by HPLC.

Adhesion tests performed with mixtures of TPS and epoxidized polymers, such as bisphenol A and EPS, prove the improved adhesive properties of the TPS polymer.

The TPS polymer or TPS mixture may be used as a binder in a coating, sealant or adhesive composition.

Accordingly, the present invention also provides a coating, adhesive or sealant composition comprising the above thiirane-functional polysulfide polymer, optionally an epoxy-functional polysulfide polymer, and a curing agent selected from the group of (poly)amines, (poly)amides, (poly)thiols, (poly)alcohols, and mixtures thereof.

It should be noted that for the purposes of this application the term hardener is considered to be a synonym for the term curing agent.

In one embodiment, the compositions of thiirane-functional polysulfide polymer and epoxide-functional polysulfide polymer have a weight ratio of these two compounds of between 4:1 and 1 :4. Preferably, the weight ratio of thiirane- functional polysulfide polymer to epoxide-functional polysulfide polymer is between 3:1 and 1 :1.

In one embodiment, the coating, sealant or adhesive composition of the invention further comprises bisphenol A/F resin.

In the coating, adhesive or sealant compositions of the invention, the amount of curing agent is chosen such that the molar ratio of reactive protons (i.e. the protons on the amine-, amide-, thiol-, or alcohol-functional group of the curing agent) to the total number of epoxide- and thiirane-functional groups of the polysulfide polymer resins is between 2:1 and 1 :2, preferably about equimolar.

Examples

Preparation Examples 1 a and 1 b

Acetonithle, oxalic acid, and ammonium thiocyanate were supplied by Aldrich.

1 a - Synthesis of thiirane-terminated polysulfides (TPS) with 45% thiirane termination

250 g Thioplast EPS 25 (an aliphatic epoxidized polysulfide polymer, ex Thioplast Chemicals GmbH und Co, hereinafter also referred to as "EPS 25") were dissolved in 2 I acetonitrile with great agitation. Next, 63.5 g ammonium thiocyanate and 7.5 g oxalic acid were added and the reaction mixture was vigorously stirred for 5 hours under reflux conditions. Afterwards the solvent mixture was removed via vacuum and the residue was dissolved in 1 I chloroform and washed four times with 1.7 I water, respectively. Following that the chloroform solution was dried over sodium sulfate and evaporated to give 220 g of a reddish polymer. Acetonitrile is ready for reuse after distillation. Elemental analysis determined a polymer with 45% thiirane termination.

1 b - Synthesis of thiirane-terminated polysulfides (TPS) with 70% thiirane termination

800 g EPS 25, an aliphatic epoxidized polysulfide polymer, were dissolved in 6.7 I acetonitrile with great agitation. Next, 24 g oxalic acid and 203 g ammonium thiocyanate were added and the reaction mixture was vigorously stirred for 15 hours under reflux conditions. Afterwards acetonitrile was removed via vacuum and the residue was dissolved in 3 I chloroform and washed four times with 5 I water, respectively. Following that the chloroform solution was dried over sodium sulfate and evaporated to give 700 g of a reddish polymer with 70% sulfur content. Acetonitrile is ready for reuse after distillation.

Elemental analysis determined a polymer with 70% thiirane termination.

(Application) Example 2 - Adhesion Tests

For the tests three different formulations were developed and used. Concrete, aluminium, stainless steel, and steel were used as substrates. Table 1 gives information regarding the used formulations. In all formulations the TPS polymer mixture presented in Example 1 b was used.

Table 1

Formulation A 50 wt% TPS mixture, 50 wt% DGEBA resin (Epilox A 19-00,

Leuna Harze) Formulation B 50 wt% TPS mixture, 50 wt% EPS 70 resin (aromatic EPS resin; Thioplast Chemicals) Formulation C 50 wt% TPS mixture, 50 wt% EPS 350 resin (aromatic EPS resin; Thioplast Chemicals)

The formulations further contained filler, pigment, and a diluent where necessary. Polypox H503 was used as curing agent. The adhesion was tested on an lnsistron Model 4467 of the lnsistron Company in accordance with DIN ISO 4624. The results are represented in Figure 1.

Example 2 demonstrates the good adhesion of compositions comprising thiirane-functional polysulfide polymer of the invention to several substrates.

As an explanation for the good adhesion results, one by which Applicant does not wish to be bound, in scheme 1 the curing mechanism of the above thiirane compounds with an amine curing agent is illustrated.

H

R' N-CH ₂ -CH R . R' N CH ₂ -CH R

R" Sθ R" SH

H H R' N-CH ₂ -CH R + CH, — CH R R' N-CH ₂ -CH R

\ /

R" Sθ S R" S

CH ₂ -CH — R

Scheme 1 : Curing mechanism

During curing the thiirane ring undergoes ring opening, which results in a thiol group. It is known that a thiol group has a higher affinity to react with metals than the hydroxyl group which is developed in epoxide curing (these reactions may result in a coordinative bond).

(Comparative) Examples 3a-c - Pot life tests

To compare the polysulfide polymers of the invention with the state of the art epoxy-terminated polysulfide polymers, pot life measurements (apparatus: Bohlin Rheometer CS50 of Bohlin Instruments) were performed using the TPS mixture from Preparation Example 1 b (70% thiirane termination) and aliphatic polyamines and commercial amine mixtures as curing agents. For pot life measurements the polymer was mixed with the curing agent and the viscosity was monitored over a certain time range.

a) Pot life measurement with TPS polymer mixture of Example 1 b and EPS 25 using thethylene tetramine (D. E. H™ 24 from DOW) as curing agent. 0.375 g triethylene tetramine was mixed with 10 g polymer.

The results are represented in Figure 2.

b) Pot life measurement with TPS polymer mixture of Example 1 b and EPS 25 using a modified aliphatic amine (Ancamine ^® 1768 from Air Products) as curing agent. 1.6 g Ancamine 1768 were mixed with 10 g polymer.

The results are represented in Figure 3.

c) Pot life measurement with TPS polymer mixture of Example 1 b and EPS 25 using several commercial Polypox ^® agents (from UPPC AG) as curing agent. The results are represented in Figure 4.

These Examples 3a to 3c show that the thiirane-functional polysulfide polymers according to the invention give an improved reactivity to curing agents while still having a sufficiently low viscosity.

(Comparative) Examples 4 - Tensile Properties

To compare the polysulfide polymers of the invention with the state of the art epoxy-terminated polysulfide polymers and to ensure that the polysulfide polymers of this invention do not exhibit reduced tensile properties, several measurements were carried out. In all formulations the TPS polymer mixture presented in Example 1 b was used.

Table 2

Formulation A 10 wt% TPS mixture, 65 wt% DGEBA resin (Epilox A 19-00,

Leuna Harze) Formulation B 20 wt% TPS mixture, 55 wt% DGEBA resin (Epilox A 19-00,

Leuna Harze) Formulation C 30 wt% TPS mixture, 45 wt% DGEBA resin (Epilox A 19-00,

Leuna Harze) Formulation D 40 wt% TPS mixture, 35 wt% DGEBA resin (Epilox A 19-00,

Leuna Harze) Formulation A' 10 wt% EPS 25, 65 wt% DGEBA resin (Epilox A 19-00, Leuna

Harze) Formulation B' 20 wt% EPS 25, 55 wt% DGEBA resin (Epilox A 19-00, Leuna

Harze) Formulation C 30 wt% EPS 25, 45 wt% DGEBA resin (Epilox A 19-00, Leuna

Harze) Formulation D' 40 wt% EPS 25, 35 wt% DGEBA resin (Epilox A 19-00, Leuna

Harze)

The formulations further contained filler, pigment, and a diluent where necessary. Aradur 2964 (from Huntsman) was used as curing agent. The tensile strength was tested on a TIRAtest 2410 of Tira Maschinenbau GmbH. The results are represented in Figures 5 and 6.

Figures 5 and 6 demonstrate the good tensile properties of the thiirane- functional polysulfide polymer of the invention in comparison to state of the art polysulfide polymers. In formulation A the thiirane polymer even has superior tensile properties.

(Comparative) Example 5 - Thermoanalvsis

Figure 7 shows the thermogravimetric analysis (TGA) of the TPS polymer of Preparation Example 1 b and EPS 25. The results found demonstrate that the thiirane-functional polysulfide polymers of the invention have a higher or prolonged thermal stability in comparison with the corresponding epoxy- functional polysulfide polymers.

% weight loss of EPS 25 was detected at 153°C, 1 % weight loss of TPS with0% thiirane termination was detected at 168°C.