ENHANCED THERMAL STABILITY POLYALKYLENE CARBONATE COMPOSITION AND A PREPARATION METHOD THEREOF

TECHNICAL FIELD OF THE INVENTION This invention relates to chemical engineering, particularly to an enhanced thermal stability polyalkylene carbonate composition and a preparation method thereof.

BACKGROUND OF THE INVENTION

Recently, carbon dioxide (C0 ₂ ) utilization has attracted a great deal of attention due to the persistent increase of concentrated C0 ₂ emission into the atmosphere, leading to a global warming phenomenon and problems associate therewith. Transformation of C0 ₂ waste into a new product is one of popular paths to minimize the aforementioned concern as well as allowing new low-carbon and resource-efficient industries to flourish. In 1968, Inoue and colleagues were among the first to invent a technique for making plastic out of C0 ₂ . Their methods involved mixing equal molar portion of C0 ₂ and epoxide to form polymer compound, hereafter called polyalkylene carbonate (PAC).

To date, the synthesis of PAC, including polyethylene carbonate (PEC) and polypropylene carbonate (PPC) has been intensively reported by several studies. Both PEC and PPC possess excellent gas barrier properties, printability, biodegradability, melt strength and transparency. However, one of the drawbacks for PEC and PPC polymers is their poor thermal processability which limits their application ranges. PAC including PEC or PPC has a low thermal decomposition temperature range of 200-250 °C, resulting in the narrow processing range. Therefore, enhancement of thermal stability of PAC including PEC and PPC is desirable to broaden its applications.

Thermal decomposition of PAC mainly occurs through two mechanisms; chain backbiting and chain scission. At a processing temperature of below 200 °C, chain backbiting by the terminal hydroxyl group occurs and subsequently leads to thermolysis of PAC backbone in convergent manner. The resultant main product is cyclic carbonate which becomes a plasticizer causing polymer pellets to stick together and is very difficult to separate. At an elevated processing temperature (>200 °C), chain scissions ignited by radical process have irreversibly set in which results in random decomposition in PAC chain. However, the mechanism of radical deterioration has not been well established.

In order to improve the thermal stability, both chain-backbiting and chain scission must together be prevented. Several approaches to enhance thermal stability of PAC have been proposed. For example:

U.S. Patent No. 4,066,630, U.S. Patent No. 4, 104,264 and U.S. Patent No. 4, 145,525 disclosed polycarbonates, of the type formed by reacting an aliphatic or cycloaliphatic 1 ,2- monoepoxide with carbon dioxide and having substantially alternating units of epoxide and carbon dioxide, that are improved in thermal stability by reacting the free hydroxyl groups thereon with a hydroxyl reactive organic compound, a hydroxyl reactive sulfur compound, and a hydroxyl reactive phosphorus compound, respectively.

JP 1 1263904A disclosed peroxy-reactive compounds or radical scavengers to inhibit random chain scission process, specifically, polyalkylene carbonate resin composition comprising of polyalkylene carbonate resin and a thermal stabilizer selected from a group consisting of a compound containing in a molecule at least two kinds selected from sulfur, phosphorus and phenolic hydroxyl group, a triaryl phosphite containing at least one phenyl group substituted by a substituent having at least five carbons, and a compound containing an aryl group substituted at least by hydroxyl group and having an ester structure. However, there remains a need for alternative solution to provide polyalkylene carbonate, which possesses advantageous property such as enhanced thermal stability over those known in the art so as to broaden the processing and application window of this polymer

SUMMARY OF THE INVENTION

In a first aspect of the invention, the present invention provides an enhanced thermal stability polyalkylene carbonate composition. In one embodiment, the enhanced thermal stability polyalkylene carbonate composition comprises polyalkylene carbonate, one or more end-capping agents and one or more antioxidants. The enhanced thermal stability polyalkylene carbonate composition according to this invention has a decomposition temperature ranging of about 250 to 320 °C.

The polyalkylene carbonate may be selected from polyethylene carbonate, polypropylene carbonate or mixtures thereof. The end-capping agent is hydroxyl-reactive compound with large molecule. As an exemplary embodiment, the end-capping agent is selected from aromatic anhydride, aromatic acyl chloride, aromatic sulfonyl chloride or aromatic isocyanate or any combinations thereof. Preferably, the end-capping agent is selected from phthalic anhydride, benzoyl chloride, biphenyl-4-sulfonyl chloride, phenyl isocyanate or any combinations thereof. The antioxidant is selected from one or more compound from hindered phenol or phosphite or any combinations thereof. Preferably, the antioxidant is selected from such compounds which are compatible with polyalkylene carbonate.

Preferably, a weight ratio of the polyalkylene carbonate to the end-capping agent is in a range of 100 to 0.5-2. More preferably, the weight ratio of the polyalkylene carbonate to the end- capping agent is 100 to 1 . And, a weight ratio of the polyalkylene carbonate to the antioxidant is in a range of 100 to 0.2-1 . More preferably, the weight ratio of the polyalkylene carbonate to the antioxidant is 100 to 0.6.

Yet, another embodiment, the enhanced thermal stability polyalkylene carbonate composition further comprises an additive or a combination thereof, such as a plasticizer, a lubricant, a surface modifier, an anti-blocking agent, a reinforcement agent, inorganic filler or a pigment.

In another aspect, the invention provides a method for preparing an enhanced thermal stability polyalkylene carbonate composition. In one embodiment, the method for preparing the enhanced thermal stability polyalkylene carbonate composition comprises the steps of adding one or more end-capping agents to polyalkylene carbonate; and adding one or more antioxidants to polyalkylene carbonate. The polyalkylene carbonate composition prepared according to the method of this invention has a decomposition temperature ranging of about 250 to 320 °C. In another embodiment, the method for preparing the enhanced thermal stability polyalkylene carbonate composition further comprises a step of adding an additive or a combination of additives. The additive may be selected from a plasticizer, a lubricant, a surface modifier, an anti-blocking agent, a reinforcement agent, inorganic filler or a pigment.

The method for preparing the enhanced thermal stability polyalkylene carbonate composition of this invention may be performed in a solvent or solventless system, the solvent system such as a solution blending and the solventless system such as a melt blending

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the thermal decomposition temperatures (Td) of the samples made from comparative PEC and the PEC compositions according to this invention.

FIG. 2 shows the thermal decomposition temperatures (Td) of the samples made from comparative PPC and the PPC compositions according to this invention.

DETAILED DESCRIPTION OF THE INVENTION In the following description, reference is shown by way of illustration specific exemplary embodiments in which the present teachings may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present teachings and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present teachings. The following description is, therefore, merely exemplary.

Technical terms and scientific terms used herein have definitions as understood by those having an ordinary skill in the art, unless stated otherwise.

The use of singular noun or pronoun when used with the term "comprising" in the claims and/or specification means "one", and also includes "one or more", "at least one", and "one or more than one". Throughout this application, the term "about" used to identify any values shown or appeared herein may be varied or deviated. The variation or deviation may be caused by errors of devices and methods used to determine a variety of values.

The terms "comprise", "have", and "include" are open-ended linking verbs. One or more forms of these verbs such as "comprise", "which comprise", "have", "which have", "include", "which include" are also open-ended. For example, any methods, which "comprise", "have", or "include" one or more steps, are not limited to possess only the one or those more steps, but also cover all unidentified steps.

The present invention relates to, in a first aspect of the invention an enhanced thermal stability polyalkylene carbonate composition, and in a second aspect of the invention, a method for preparing an enhanced thermal stability polyalkylene carbonate composition. By way of exemplary example, the following description will respectively discuss each aspect of the invention and its related embodiments.

In the first aspect of the invention, the present invention disclosed an enhanced thermal stability polyalkylene carbonate composition using a synergistic combination of an end-capping agent or any combinations thereof and an antioxidant or any combinations thereof. The derived composition illustrates enhanced thermal stability. More specifically, from the test results which will be discussed in detail later on, it was found that the thermal decomposition temperatures of the enhanced thermal stability polyalkylene carbonate composition, including PEC and PPC compositions according to the present invention are in a range of about 250 to 320 °C in comparison to the thermal decomposition temperatures of unmodified PEC and PPC which are 239 and 253°C respectively. The combination of polyalkylene carbonate with one or more end- capping agents and one or more antioxidants decreases chain backbiting by the terminal hydroxyl group and also decreases chain scissions ignited by radical process resulting in an enhancement of the thermal decomposition temperature of polyalkylene carbonate composition.

In one embodiment, the end-capping agent is selected from one or more hydroxyl- reactive compound which is comprised of the following formula:

R G wherein R group is an aliphatic or aromatic hydrocarbon or hydrocarbon derivatives. Preferably, R group is a large molecule or aromatic hydrocarbon. Examples of R such as:

whereas G group is a functional group that is reactive toward hydroxyl (-OH) group content in polyalkylene carbonate. Examples of G group such as carboxylic anhydride, carboxyl halide, sulfonic anhydride, sulfonyl halide, phosphoryl halide, epoxides and isocyanate, shown below.

The end-capping agent in an exemplary example may be selected from aromatic anhydride, aromatic acyl chloride, aromatic sulfonyl chloride, aromatic isocyanate or any combinations thereof. Preferably, the aromatic anhydride is phthalic anhydride; the aromatic acyl chloride is benzoyl chloride; the aromatic sulfonyl chloride is biphenyl-4-sulfonyl chloride; and the aromatic isocyanate is phenyl isocyanate.

In one embodiment, the antioxidant is selected from one or more compound from hindered phenol or phosphite.

Said hindered phenol corresponds to the following formula: O 0

. II II

R-C ₂ H ₄ -COCH _{2 /} CH ₂ OC-C ₂ H ₄ -R

C

/ \

R-C ₂ H ₄ -COCH ₂ CH ₂ OC-C ₂ H ₄ -R

II II

0 O wherein R is aromatic phenol containing at least 1 tert alkyl group. The hindered phenol optionally corresponds to the following formula:

O

II

R-C ₂ H ₄ -CO-R _x -R _y wherein Rx and Ry are each independently chosen from the group consisting of optionally substituted alkyl preferably optionally straight, branched or alicyclic alkyl, alkenyl, alkynyl, alkoxyl, aryl group of 5 to 32 carbon atoms, and optionally containing hetero atom in a molecule R is aromatic phenol containing at least 1 tert alkyl group.

Said phosphite corresponds to the following formula:

OH,C _/ CH ₂ 0 _N

/ \

R _y -R _x -0- P C P -0-R _x -R _v

/ \ / wherein Rx and Ry are chosen from the group consisting of optionally substituted alkyl preferably optionally straight, branched or alicyclic alkyl, alkenyl, alkynyl, alkoxyl, aryl group of 5 to 32 carbon atoms, and optionally containing hetero atom in a molecule.

Said phosphite optionally corresponds to the following formula:

lO-R ; n = 3 wherein R is aromatic containing at least 1 tert alkyl group.

Said phosphite optionally corresponds to the following formula

wherein Rx and Ry are each independently chosen from the group consisting of optionally substituted alkyl preferably optionally straight, branched or alicyclic alkyl, alkenyl, alkynyl, alkoxyl, aryl group of 5 to 32 carbon atoms, and optionally containing hetero atom in a molecule R is an aromatic containing at least 1 tert alkyl group.

Preferably, the antioxidant is selected from such compounds which are compatible with polyalkylene carbonate.

In another embodiment, the enhanced thermal stability polyalkylene carbonate composition further comprises one or more additives, such as a plasticizer, a lubricant, a surface modifier, an anti-blocking agent, a reinforcement agent, an inorganic filler or a pigment.

Now, turning to the second aspect of the invention, the present invention provides a method for preparing an enhanced thermal stability polyalkylene carbonate composition.

In one embodiment, the method comprises the steps of adding one or more end-capping agents to polyalkylene carbonate; and adding one or more antioxidants to the end-capped polyalkylene carbonate. The polyalkylene carbonate composition prepared according to the method of this invention has a decomposition temperature ranging of about 250 to 320 °C.

In a further embodiment, the method for preparing an enhanced thermal stability polyalkylene carbonate composition further comprises a step of adding one or more additives such as a plasticizer, a lubricant, a surface modifier, an anti-blocking agent, a reinforcement agent, an inorganic filler or a pigment. More specifically, the step of adding one or more additives is performed after completion of the steps of adding one or more end-capping agents and adding one or more antioxidants. The method for preparing the enhanced thermal stability polyalkylene carbonate composition of this invention may be performed in a solvent or solventless system.

As an exemplary embodiment of using a solvent system, the method for preparing the enhanced thermal stability polyalkylene carbonate composition may be performed by way of solution blending, the method comprising the steps of:

- dissolving polyalkylene carbonate in a solvent to obtain a PAC solution;

- adding one or more end-capping agents to the PAC solution;

- adding one or more antioxidants to the end-capped PAC solution; and

- removing the solvent to obtain the enhanced thermal stability PAC composition. In the step of removing the solvent, the solvent may be removed by way of evaporation.

Further, in an embodiment in which one or more additives are added, the additives may be added prior to the step of removing the solvent.

As an exemplary embodiment of using a solventless system in which the polyalkylene carbonate composition is prepared by way of melt blending, the method comprising the steps of: - melting the polyalkylene carbonate polymer to obtain a melted PAC;

- adding one or more end-capping agents to the melted PAC under melt blending; and

- adding one or more antioxidants to the end-capped PAC under melt blending.

Further, in an embodiment in which one or more additives are added, the additives may be added at the last step.

EXPERIMENTS AND EXAMPLES

Materials Commercial polyethylene carbonate (PEC) and polypropylene carbonate (PPC) marketed by Empower Materials were used in this experiment. Phthalic anhydride (PA) and biphenyl-4- sulfonyl chloride (PH2SOC1), commercially marketed by Sigma-Aldrich, were used as end- capping agents. Hindered phenol (AO50) and phosphites (21 12, PEP8, HP I O) commercially marketed by Adeka were used as antioxidants.

Sample preparation procedure

The following examples below show the present invention without limiting the scope of the invention.

Control samples A (PEC and B (PPC):

PEC and PPC were used without any modification.

Comparative sample A 1 (PEC-PA):

2 g of PEC was dissolved in a 15 ml of solvent, including but not limited to dichioromethane, tetrahydrofuran, chloroform or a mixture thereof. Then, 0.03 g of end-capping agent of phathalic anhydride, PA was added. The mixture was stirred at a room temperature for at least 6 hours. The solvent was then evaporated.

Comparative sample A2 (PEC-PH2SOC1):

A2 was prepared in the same manner to Al except using biphenyl-4-sulfonyl chloride (PH2SOC1) instead of PA as the end-capping agent.

Comparative sample A3 (PEC-AO50&HP 10):

2 g of PEC was dissolved in a 15 ml of solvent, including but not limited to dichioromethane, tetrahydrofuran, chloroform or a mixture thereof. Then, 0.002 g of AO50 and 0.01 g of HP 10 were added. The mixture was stirred at a room temperature until well-dispersed. The solvent was then evaporated.

Sample Aa (PEC-PA-AO50): 2 g of PEC was dissolved in a 15 ml of solvent, including but not limited to dichloromethane, tetrahydrofuran, chloroform or a mixture thereof. Then, 0.03 g of end-capping agent of phathalic anhydride, PA was added. The mixture was stirred at a room temperature for at least 6 hours. After that, 0.002 g of antioxidant, AO50 was added and the mixture was stirred at a room temperature until well-dispersed. The solvent was then evaporated.

Sample Ab fPEC-PH2SOCl-AO50 :

Ab was prepared in the same manner to Aa except using biphenyl-4-sulfonyl chloride (PH2SOC1) instead of PA as the end-capping agent.

Sample Ac rPEC-PA-AO50&PEP8): Ac was prepared in the same manner to Aa except using a combination of antioxidants, including AO50 and PEP8, as the primary and secondary antioxidants, respectively instead of AO50.

Sample Ad (PEC-PA-AO50&HP10):

Ad was prepared in the same manner to Aa except using a combination of antioxidants, including AO50 and HP 10, as the primary and secondary antioxidants, respectively instead of AO50

Sample Ae ( ^• pEC-PH2SOCl-AO50&HP10 ):

Ae was prepared in the same manner to Ad except using PH2SOC1 instead of PA as the end-capping agent. Sample Af (PEC-AO50&HP 10-PA):

Af was prepared in the similar manner to Ad except the sequence of adding end-capping agent and adding antioxidants were changed in alternate with one another.

Comparative sample B l (PPC-PA):

B l was prepared in the same manner to A l except using PPC instead of PEC. Comparative sample B2 (PPC-PH2SOC1): B2 was prepared in the same manner to A2 except using PPC instead of PEC.

Sample Ba fPPC-PA-AOSO :

Ba was prepared in the same manner to Aa except using PPC instead of PEC. Sample Bb rPPC-PH2SOCl-AO50 ):

Bb was prepared in the same manner to Ab except using PPC instead of PEC. Sample Be fPPC-PA-AO50&PEP8):

Be was prepared in the same manner to Ac except using PPC instead of PEC. Sample Bd ( PC-PH2SOC1-AO50&PEP8 :

Bd was prepared in the same manner to Be except using PH2SOC1 instead of PA- Testing method

PAC composition prepared from the above-mentioned explanation was analyzed by using thermogravimetric analysis (TGA) to determine the thermal decomposition temperature (Td) of each sample.

Experimental results

Table 1 shows the thermal decomposition temperatures of the samples. Each sequence name shows the types of one or more end-capping agents and/or one or more antioxidants and the sequences of the steps for preparing the PEC and PPC samples.

Table 1

Type of The ratio of antioxidant primary

The ratio of

Type of end- (primary antioxidant sec T„rc]

Sample Sequence Name end-capping

capping agent antioxidant/seco ondary

agent to PAC

ndary antioxidant to antioxidant) PAC Control samples

A PEC - - - - 239

B PPC - - - - 253

Comparative samples: PAC+end-capping agent or antioxidants

Al PEC-PA Phthalic anhydride 1 : 100 - - 24 ₆

Biphenyl-4-

A2 PEC-PH2SOCI 1 : 100 - - 258 sulfonyl chloride

A3 PEC-AO50&HP I0 - - AO50/HPI 0 0.1/0.5: 100 233

B l PPC-PA Phthalic anhydride 1 : 100 - - 237

Biphenyl-4-

B2 PPC-PH2SOCI 1 : 100 - - 269 sulfonyl chloride

Samples: PAC+end-capping agent/antioxidant or antioxidants

Aa PEC-PA-AO ₅ 0 Phthalic anhydride 1 : 100 AOS0 0. 1 : 100 255

Biphenyl-4-

Ab PEC-PH2SOCI-AO ₅ 0 1 : 100 AO50 0.1 : 100 272 sulfonyl chloride

Ac PEC-PA- AO50&PEP8 Phthalic anhydride 1 : 100 AO50/PEP8 0.1/0.5: 100 283

Ad PEC-PA-AO ₅ 0&HP 10 Phthalic anhydride 1 : 100 AO ₅₀ /HP10 0.1/0.5: 100 298

Biphenyl-4-

Ae PEC-PH2SOCI-AO50&HP10 1 : 100 AO50/HP10 0.1/0.5: 100 279 sulfonyl chloride

Af PEC-AO50&HP10-PA Phthalic anhydride 1 : 100 AO50/HP 10 0.1/0.5: 100 255

Ba PPC-PA-AO50 Phthalic anhydride 1 : 100 AO ₅₀ 0.1 : 100 269

Biphenyl-4-

Bb PPC-PH2SOCI-AO ₅ 0 1 : 100 AOS0 0. 1 : 100 287 sulfonyl chloride

Be PPC-PA-AO ₅ 0&PEP8 Phthalic anhydride 1 : 100 AO ₅ 0/PEP8 0.1/0.5: 100 283

Biphenyl-4-

Bd PPC-PH2SOCI- AOS0&HP 10 1 : 100 AO50/HP10 0.1/0.5: 100 293 sulfonyl chloride

We will now discuss the experimental results. First we will be discussing the group of PEC samples, wherein the samples starting with "A". As can be seen in Table 1 and Figure 1 , the sample A is a control sample where no end-capping agent or antioxidant is added. The thermal decomposition temperature of the sample is 239 °C. In the comparative sample A l and A2, where the samples are reacted with the end-capping agents without any antioxidant, the samples illustrate slight improvement of thermal decomposition temperatures at 246 and 258 °C, respectively. On the other hand, sample Aa, prepared from a combination of end-capping agent, PA and antioxidant, AO50, illustrates the thermal decomposition temperature at 255 °C, which is much higher than that of the comparative sample A l prepared from the same type of the end- capping agent. Similarly, the sample Ab illustrates much higher thermal decomposition temperature than that of the comparative sample A2, which is also prepared from using PH2SOC1 as an end-capping agent.

This may be concluded that the samples with a combination of an end-capping agent with an antioxidant possess enhanced thermal stability of the PEC composition.

Further, comparing between the comparative samples Al , A3 and samples Ad, Af, it is obviously seen that the thermal decomposition temperature of the samples Ad and Af are much higher than those shown in the comparative samples. The sample Ad and Af comprises an end- capping agent and a combination of primary and secondary antioxidants. From this, it can be concluded that the polyalkylene carbonate composition, comprising PEC, an end-capping agent, and one or more antioxidants, prepared according to the present invention, enhances thermal stability of the polyalkylene carbonate. Moreover, as apparently seen when comparing between the samples Ad and Af, the orders or sequences of adding the sample with end-capping agent and one or more antioxidants affect the thermal decomposition temperature of the attained PEC composition. Therefore, the polyalkylene carbonate composition, comprising PEC, prepared from the subsequently steps of reacting the PEC with the end-capping agent prior to mixing with one or more antioxidants, obviously shows the improvement to such the thermal decomposition temperature reaching nearly 300°C.

Under this theory, the same conclusion can also be drawn for a polyalkylene carbonate, comprising PEC, one or more end-capping agents, and one or more antioxidants, enhance thermal stability of the composition. We will now discuss the second group of the experiment as shown in Figure 2, PPC wherein the samples starting with "B". The samples are prepared in the same way as with the preparation of the samples using PEC. Sample B is a control sample where no end-capping agent and no antioxidant are added. Similarly, the samples with added end-capping agent, and added one or more antioxidants, for example, the samples Ba-Bd demonstrate higher thermal decomposition temperature. The sample Bd is among the sample with highest thermal decomposition temperature.

The sample Bd is prepared by solution blending as described above. PPC is reacted with the end-capping agent, biphenyl-4-sufonyl chloride. Then the end-capped PPC is mixed with a mixture of a combination of antioxidants, hindered phenol AO50 and phosphite HP10. Once again, the results of the experiment, confirm that a combination between one or more of end- capping agents and antioxidants provides synergic effect on enhancement of thermal stability of PEC and PPC prepared according to the present invention.

In addition, it can be obviously seen that the appropriate sequence for thermal enhancement process should be considered. To achieve the higher thermal decomposition temperature of PAC, the reaction with one or more end-capping agents should first be completed and followed by the addition of one or more antioxidants. Under the principle of the present invention, an end-capping reaction between OH-terminated PEC or PPC and reactive end- capping agent can be deteriorated or competed by other reactive compounds. To illustrate, antioxidants, which are hindered phenol and/or phosphite derivatives, would react with end- capping agent, leading to untreated PEC or PPC.

Accordingly, it can be concluded that thermal stability of PAC may be enhanced by the solution proposed by the principle of the present invention. The obtained PEC or PPC composition prepared by the method according to the invention shows enhanced thermal stability. Consequently, this allows PEC and PPC compositions having enhanced thermal stability with broadening processing range as set out in the objective of the invention.

The person skilled in the art would recognize that various modifications, adaptations, and variations may be brought to the previously presented specific examples without departing from the scope of the following claims.