Ethylene/alpha-olefin copolymer and method for preparing the same

Abstract

The present invention provides an ethylene/alpha-olefin copolymer having narrow molecular weight distribution together with a low density and an ultra low molecular weight, minimized number of unsaturated functional groups, and particularly a small amount of vinylidene among the unsaturated functional groups to show excellent physical properties, and a method for preparing the same.

Claims

1. An ethylene/alpha-olefin copolymer satisfying the following conditions i) to iv): i) a viscosity: 6,000 cP to 40,000 cP, when measured at a temperature of 180° C., ii) a molecular weight distribution (MWD): 1.5 to 3.0, iii) a total number of unsaturated functional groups per 1000 carbon atoms: 0.8 or less, and 0.2 or more, and iv) a R.sub.vdvalue according to the following Mathematical Equation 1: 0.3 or less: $\begin{array}{cc}{R}_{\mathrm{vd}}=\frac{\left[\mathrm{vinylidene}\right]}{\left[\mathrm{vinyl}\right]+\left[\mathrm{vinylene}\right]+\left[\mathrm{vinylidene}\right]}& \left[\mathrm{Mathematical}\mathrm{Equation}1\right]\end{array}$ in Mathematical Equation 1, the vinyl, vinylene and vinylidene mean the number of each functional group per 1000 carbon atoms, measured through nuclear magnetic spectroscopic analysis.

2. The ethylene/alpha-olefin copolymer according to claim 1, wherein a density is 0.85 to 0.89 g/cc, measured according to ASTM D-792.

3. The ethylene/alpha-olefin copolymer according to claim 1, wherein a weight average molecular weight is 17,000 to 40,000 g/mol.

4. The ethylene/alpha-olefin copolymer according to claim 1, wherein the viscosity is 8,500 to 35,000 cP, when measured at a temperature of 180° C.

5. The ethylene/alpha-olefin copolymer according to claim 1, wherein the alpha-olefin comprises one or more selected from propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, or 1-eicocene.

6. The ethylene/alpha-olefin copolymer according to claim 1, wherein the alpha-olefin is one or more selected from 1-buene, 1-hexene or 1-octene.

7. The ethylene/alpha-olefin copolymer according to claim 1, wherein the alpha-olefin is comprised in an amount of from greater than 0 and 99 mol % or less, with respect to a total weight of the copolymer.

8. The ethylene/alpha-olefin copolymer according to claim 1, further satisfying the following conditions v) to vi): v) a number average molecular weight (Mn): 9,000 to 25,000, and vi) a melt index (MI) at 190° C., 2.16 kg load by ASTM D1238: 200 to 1,300 dg/min.

9. The ethylene/alpha-olefin copolymer according to claim 1, wherein the ethylene/alpha-olefin copolymer has a crystallization temperature (Tc) of 45° C. to 60° C., and a melting temperature (Tm) of 60 to 80° C., wherein both the crystallization temperature and the melting temperature are measured by a differential scanning calorimetry (DSC).

10. A method of preparing the ethylene/alpha-olefin copolymer according to claim 1, comprising a step of polymerizing ethylene and an alpha-olefin-based monomer by injecting hydrogen in 45 to 100 cc/min in the presence of a catalyst composition including a transition metal compound of Formula 1: ##STR00007## wherein, R.sub.1 is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms, R.sub.2a to R.sub.2e are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; or aryl of 6 to 20 carbon atoms, R.sub.3 is hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkyl amido of 1 to 20 carbon atoms; aryl amido of 6 to 20 carbon atoms; or phenyl which is substituted with one or more selected from the group consisting of halogen, alkyl of 1 to 20 carbon atoms, cycloalkyl of 3 to 20 carbon atoms, alkenyl of 2 to 20 carbon atoms, alkoxy of 1 to 20 carbon atoms and aryl of 6 to 20 carbon atoms, R.sub.4 to R.sub.9 are each independently hydrogen; silyl; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; or a metalloid radical of a metal in group 14, which is substituted with hydrocarbyl of 1 to 20 carbon atoms; where among the R.sub.6 to R.sub.9, adjacent two or more are optionally connected with each other to form an aliphatic ring of 5 to 20 carbon atoms or an aromatic ring of 6 to 20 carbon atoms, wherein the aliphatic ring or the aromatic ring is optionally substituted with halogen, alkyl of 1 to 20 carbon atoms, alkenyl of 2 to 12 carbon atoms, or aryl of 6 to 12 carbon atoms, Q is Si or C, M is a transition metal in group 4, and X.sub.1 and X.sub.2 are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms.

11. The method of preparing the ethylene/alpha-olefin copolymer according to claim 10, wherein the transition metal compound of Formula 1 comprises a compound represented by any one among the structures below: ##STR00008## ##STR00009## ##STR00010##

12. The method of preparing the ethylene/alpha-olefin copolymer according to claim 10, wherein the catalyst composition further comprises a promoter for activating the transition metal compound of Formula 1.

13. The method of preparing the ethylene/alpha-olefin copolymer according to claim 12, wherein the promotor comprises an organometal compound including a metal in group 13.

14. The method of preparing the ethylene/alpha-olefin copolymer according to claim 12, wherein the promotor comprises one or more selected from a compound of the following Formula 2, a compound of the following Formula 3, or a compound of the following Formula 4:
R.sub.41—[Al(R.sub.42)—O].sub.n—R.sub.43  [Formula 2] in Formula 2, R.sub.41, R.sub.42 and R.sub.43 are each independently any one selected from hydrogen, halogen, a hydrocarbyl group of 1 to 20 carbon atoms, or a halogen-substituted hydrocarbyl group of 1 to 20 carbon atoms, and n is an integer of 2 or more,
D(R.sub.44).sub.3  [Formula 3] in Formula 3, D is aluminum or boron, and each R.sub.44 is each independently any one selected from halogen, a hydrocarbyl group of 1 to 20 carbon atoms, or a halogen-substituted hydrocarbyl group of 1 to 20 carbon atoms,
[L—H].sup.30[Z(A).sub.4].sup.− or [L].sup.+[Z(A).sub.4].sup.−  [Formula 4] in Formula 4, L is a neutral Lewis base or Brønsted base, H is a hydrogen atom, [L].sup.30 is a cationic Lewis acid, [L—H].sup.+ is a cationic Brønsted acid, Z is an element in group 13, and A is each independently a hydrocarbyl group of 1 to 20 carbon atoms or a hydrocarbyloxy group of 1 to 20 carbon atoms, wherein the hydrocarbyl group or the hydrocarbyloxy group is unsubstituted or substituted with one or more substituents selected from halogen, a hydrocarbyloxy group of 1 to 20 carbon atoms, or a hydrocarbylsilyl group of 1 to 20 carbon atoms.

15. The method of preparing the ethylene/alpha-olefin copolymer according to claim 10, wherein the transitional metal compound of Formula 1 is in a supported state on a support, and a weight ratio of the transitional metal compound of Formula 1 to the support is 1:10 to 1:1,000.

16. The method of preparing the ethylene/alpha-olefin copolymer according to claim 15, wherein the support is silica, alumina, magnesia or a mixture thereof.

17. The method of preparing the ethylene/alpha-olefin copolymer according to claim 10, wherein the polymerization is performed at 80° C. to 200° C., and under a pressure of about 1 to about 100 gf/cm .sup.2.

Description

MODE FOR CARRYING OUT THE INVENTION

EXAMPLES

(1) Hereinafter, preferred embodiments will be suggested to assist the understanding of the present invention. However, the embodiments are provided only for easy understanding of the present invention, and the contents of the present invention is not limited thereto.

Synthetic Example: Preparation of Transition Metal Compound

(2) Step 1: Preparation of Ligand Compound (1a-1)

(3) To a 250 mL schlenk flask, 10 g (1.0 eq, 49.925 mmol) of 1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene and 100 mL of THF were put, and 22 mL (1.1 eq, 54.918 mmol, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature for 3 hours. A stirred Li-complex THF solution was cannulated into a schlenk flask containing 8.1 mL (1.0 eq, 49.925 mmol) of dichloro(methyl) (phenyl)silane and 70 mL of THF at −78° C., followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out and extraction with 100 ml of hexane was carried out.

(4) To 100 ml of an extracted chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl) (phenyl)silane hexane solution, 42 mL (8 eq, 399.4 mmol) of t-BuNH.sub.2 was injected at room temperature, followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out and extraction with 150 ml of hexane was carried out. After drying the solvents, 13.36 g (68%, dr=1:1) of a yellow solid was obtained.

(5) ##STR00005##

(6) .sup.1H NMR(CDCl.sub.3, 500 MHz): δ 7.93(t, 2H), 7.79(d,1H), 7.71(d,1H), 7.60(d, 2H), 7.48(d, 2H), 7.40-7.10(m, 10H, aromatic), 3.62(s, 1H), 3.60(s, 1H), 2.28(s, 6H), 2.09(s, 3H), 1.76(s, 3H), 1.12(s, 18H), 0.23(s, 3H), 0.13(s, 3H)

(7) Step 2: Preparation of Transition Metal Compound (1a)

(8) To a 100 mL schlenk flask, 4.93 g (12.575 mmol, 1.0 eq) of a ligand compound of Formula 1a-1 and 50 mL (0.2 M) of toluene were put and 10.3 mL (25.779 mmol, 2.05 eq, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature overnight. After stirring, 12.6 mL (37.725 mmol, 3.0 eq, 3.0 M in diethyl ether) of MeMgBr was added thereto dropwisely, 13.2 mL (13.204 mmol, 1.05 eq, 1.0 M in toluene) of TiCl.sub.4 was put in order, followed by stirring at room temperature overnight. After stirring, drying in vacuum and extraction with 150 mL of hexane were carried out, the solvents were removed to 50 mL, and 4 mL (37.725 mmol, 3.0 eq) of DME was added dropwisely, followed by stirring at room temperature overnight. Again, drying in vacuum and extraction with 150 mL of hexane were carried out. After drying the solvents, 2.23 g (38%, dr=1:0.5) of a brown solid was obtained.

(9) ##STR00006##

(10) .sup.1H NMR(CDCl.sub.3, 500 MHz): δ 7.98(d, 1H), 7.94(d, 1H), 7.71(t, 6H), 7.50-7.30(10H), 2.66(s, 3H), 2.61(s, 3H), 2.15(s, 3H), 1.62(s, 9H), 1.56(s, 9H), 1.53(s, 3H), 0.93(s, 3H), 0.31(s, 3H), 0.58(s, 3H), 0.51(s, 3H), −0.26(s, 3H), −0.39(s, 3H)

(11) [Preparation of Ethylene/Alpha-Olefin Copolymer]

Example 1

(12) Into a 1.5 L autoclave continuous process reactor, a hexane solvent (5.0 kg/h) and 1-octene (1.00 kg/h) were charged, and the top of the reactor was pre-heated to a temperature of 150° C. A triisobutylaluminum compound (0.05 mmol/min), the transition metal compound (1a) (0.40 μmol/min) prepared in the Synthetic Example as a catalyst, and a dimethylanilium tetrakis(pentafluorophenyl) borate promoter (1.20 μmol/min) were injected into the reactor at the same time. Then, into the autoclave reactor, ethylene (0.87 kg/h) and a hydrogen gas (50 cc/min) were injected and copolymerization reaction was continuously carried out while maintaining a pressure of 89 bar and a polymerization temperature of 125° C. for 60 minutes or more to prepare a copolymer.

(13) Then, a remaining ethylene gas was exhausted out and the copolymer-containing solution thus obtained was dried in a vacuum oven for 12 hours or more. The physical properties of the copolymer thus obtained were measured.

Examples 2 to 5 and Comparative Examples 1 to 7

(14) Polymers were prepared by carrying out the same method as in Example 1 except that the reactant materials were injected in amounts listed in Table 1 below.

(15) TABLE-US-00001 TABLE 1 Catalyst Promoter 1-C8 H.sub.2 injection injection injection Polymerization injection amount amount amount TiBAl temperature amount (μmol/min) (μmol/min) (kg/h) (mmol/min) (° C.) (cc/min) Example 1 0.40 1.20 1.00 0.05 125 50 Example 2 0.40 1.20 1.00 0.05 125 75 Example 3 0.40 1.20 1.00 0.05 125 80 Example 4 0.40 1.20 1.00 0.05 125 95 Example 5 0.20 0.60 1.10 0.05 125 85 Comparative Example 1 0.70 2.10 2.00 0.05 150 0 Comparative Example 2 0.40 1.20 1.00 0.05 125 0 Comparative Example 3 0.40 1.20 1.00 0.05 125 10 Comparative Example 4 0.40 1.20 1.00 0.05 125 15 Comparative Example 5 0.40 1.20 1.00 0.05 125 130 Comparative Example 6 0.26 0.78 1.20 0.05 125 35 Comparative Example 7 0.65 1.95 2.20 0.05 160 0 * In Comparative Examples 6 and 7, [Me.sub.2Si(Me.sub.4C.sub.5)NtBu]Ti(CH.sub.3).sub.2 was used as a catalyst.

(16) [Evaluation of Physical Properties of Olefin Polymer]

Experimental Example 1

(17) With respect to the ethylene/alpha-olefin copolymers prepared in the Examples and the Comparative Examples, physical properties were measured according to the methods described below and are shown in Table 2.

(18) 1) Density (g/cm.sup.3): measured according to ASTM D-792.

(19) 2) Viscosity (cP): measured using a Brookfield RVDV3T viscometer and according to the method described below. In detail, 13 ml of a specimen was put in a specimen chamber and heated to 180° C. using Brookfield Thermosel. After the specimen was completely dissolved, a viscometer equipment was lowered to fix a spindle to the specimen chamber, the rotation speed of the spindle (SC-29 high temperature-melt spindle) was fixed to 20 rpm, and viscosity values were deciphered for 20 minutes or more, or until the value was stabilized, and a final value was recorded.

(20) 3) Viscosity change rate (%): measured using a Brookfield RVDV3T viscometer and according to the method described below. In detail, 13 ml of a specimen was put in a specimen chamber and heated to 180° C. using Brookfield Thermosel. After the specimen was completely dissolved, a viscometer equipment was lowered to fix a spindle to the specimen chamber, the rotation speed of the spindle (SC-29 high temperature-melt spindle) was fixed to 20 rpm, and viscosity values were recorded once per hour for 72 hours. A difference between an initial viscosity and a viscosity after 72 hours was converted into a percentage, and the viscosity change rate was calculated.

(21) 4) Melting temperature (Tm, ° C.): The melting temperature of a polymer was measured using a differential scanning calorimeter (DSC, apparatus name: DSC 2920, manufacturer: TA instrument). Particularly, the polymer was heated to 150° C., kept for 5 minutes, and cooled to −100° C., and then, the temperature was elevated again. In this case, the elevating rate and decreasing rate of the temperature were controlled to 10° C./min, respectively. The maximum point of an endothermic peak measured in a second elevating section of the temperature was set to the melting temperature.

(22) 5) Crystallization temperature (Tc, ° C.): performed by the same method as that for measuring the melting temperature using DSC. From a curve represented while decreasing the temperature, the maximum point of an exothermic peak was set to crystallization temperature.

(23) 6) Weight average molecular weight (g/mol) and molecular weight distribution (MWD): a number average molecular weight (Mn) and a weight average molecular weight (Mw) were measured, respectively, by gel permeation chromatography (GPC, PL GPC220) under the conditions below, and molecular weight distribution was calculated through dividing the weight average molecular weight by the number average molecular weight: Column: PL Olexis Solvent: trichlorobenzene (TCB) Flow rate: 1.0 ml/min Specimen concentration: 1.0 mg/ml Injection amount: 200 μl Column temperature: 160° C. Detector: Agilent High Temperature RI detector Standard: Polystyrene (calibrated by cubic function)

(24) 7) Total number of unsaturated functional groups (per 1000 C): the numbers of vinyl, vinylene, and vinylidene per 1000 carbon atoms were measured from the NMR analysis results.

(25) In detail, first, in order to remove remaining 1-octene which may be present in a specimen, the polymer was prepared by reprecipitation prior to conducting NMR analysis. In detail, 1 g of the polymer was completely dissolved in chloroform of 70° C., and the polymer solution thus obtained was slowly poured into 300 ml of methanol while stirring to reprecipitate the polymer. The reprecipitated polymer was dried in vacuum at room temperature. The above-described process was repeated once more to obtain a polymer from which remaining 1-octene was removed.

(26) 30 mg of the specimen of the polymer obtained above was dissolved in 1 ml of a chloroform-d (w/TMS) solution. Measurement was performed 16 times at room temperature with an acquisition time of 2 seconds and a pulse angle of 45°, using an Agilent 500 MHz NMR equipment. Then, the TMS peak in 1 H NMR was calibrated to 0 ppm, a CH.sub.3-related peak (triplet) of 1-octene at 0.88 ppm and a CH.sub.2-related peak (broad singlet) of ethylene at 1.26 ppm were confirmed, respectively. An integration value of the CH.sub.3 peak was calibrated to 3 to calculate the contents. The numbers of vinyl, vinylene and vinylidene could be calculated based on the integration values of each functional group in 4.5-6.0 ppm region. For reference, the viscosity of Comparative Example 5 was not measured because the viscosity is too low.

(27) 8) R.sub.vd: R.sub.vd value was calculated according to the following Mathematical Equation 1 from the numbers of vinyl, vinylene and vinylidene, measured through the NMR analysis:

(28) $\begin{array}{cc}{R}_{\mathrm{vd}}-\frac{\left[\mathrm{vinylidene}\right]}{\left[\mathrm{vinyl}\right]+\left[\mathrm{vinylene}\right]+\left[\mathrm{vinylidene}\right]}& \left[\mathrm{Mathematical}\mathrm{Equation}1\right]\end{array}$

(29) (in Mathematical Equation 1, vinyl, vinylene and vinylidene mean the number of each functional group per 1000 carbon atoms, measured through nuclear magnetic spectroscopic analysis).

(30) TABLE-US-00002 TABLE 2 Viscosity change Number of unsaturated functional groups (per 1000 C) Molecular Density Tc/Tm Viscosity rate Total weight (g/cc) (° C.) (cP) (%) amount vinyl vinylene vinylidene R.sub.vd Mw distribution Example 1 0.873 50.6/66.5 35000 18 0.40 0.05 0.27 0.08 0.20 34900 1.98 Example 2 0.875 52.0/68.1 17000 15 0.35 0.04 0.24 0.07 0.20 24400 1.96 Example 3 0.876 52.3/68.9 13500 14 0.32 0.03 0.22 0.07 0.22 22400 1.98 Example 4 0.877 53.2/69.7 8500 11 0.29 0.03 0.20 0.06 0.21 19500 1.77 Example 5 0.875 52.2/68.3 17000 12 0.30 0.02 0.21 0.07 0.18 24500 1.96 Comparative 0.872 49.7/66.0 >50000 N/A 1.36 0.20 0.78 0.39 0.29 46800 2.14 Example 1 Comparative 0.874 51.5/67.6 >50000 N/A 0.54 0.06 0.38 0.10 0.19 75400 2.08 Example 2 Comparative 0.874 51.3/67.8 >50000 N/A 0.45 0.04 0.32 0.09 0.20 57700 2.09 Example 3 Comparative 0.873 50.5/66.3 >50000 N/A 0.42 0.04 0.29 0.09 0.21 48700 2.08 Example 4 Comparative 0.879 55.7/72.7 3500 N/A 0.29 — — — — 14600 1.97 Example 5 Comparative 0.876 56.1/73.2 13900 22 0.32 0.03 0.10 0.20 0.63 22800 1.94 Example 6 Comparative 0.875 55.3/73.1 15800 41 1.38 0.19 0.79 0.40 0.29 26700 2.24 Example 7 In Table 2, “—” means not measured, and “N/A” means unmeasurable.

(31) Referring to Table 2, the ethylene/alpha-olefin copolymers of Examples 1 to 5, which were prepared by using the catalyst composition including the transition metal compound according to the present invention and injecting hydrogen during polymerization, showed a low density, at the same time, an ultralow molecular weight (evaluated by viscosity), narrow molecular weight distribution when compared with Comparative Examples 1 to 7, and the total number of unsaturated functional groups was 0.5 or less per 1,000 carbon atoms and at the same time, a R.sub.vd value was 0.5 or less, particularly, 0.22 or less.

(32) Particularly, in case of Comparative Examples 1 to 4, in which hydrogen was not injected or injected in an amount not more than a certain amount, copolymers with a quite high molecular weight were prepared, and molecular weight distribution was broad and thus, inferior physical properties were expected. In addition, the viscosity was high and the viscosity and its change rate were unmeasurable using the SC-29 high temperature-melt spindle (5000-45000 cP), and the application to a hot melt adhesive composition is unsuitable. In addition, in case of Comparative Example 2, the R.sub.vd value was similar to that of the Examples, but the total number of unsaturated functional groups was grater than 0.5, and the deterioration of physical properties thereby is expected.

(33) In addition, in case of Comparative Example 5, in which an excessive amount of hydrogen was injected, the polymerization was terminated at an early stage due to hydrogen and a copolymer having a very small molecular weight was prepared. In addition, the viscosity was low and the measurement of the viscosity change rate using the SC-29 high temperature-melt spindle (5000-45000 cP) was impossible.

(34) In addition, in case of Comparative Example 7, in which hydrogen was not injected and a catalyst other than the catalyst according to the present invention was applied, molecular weight distribution was relatively broad, and the total number of unsaturated functional groups was 1.38 and was confirmed significant. In case of Comparative Example 6, in which hydrogen was injected, molecular weight distribution and viscosity properties were similar, and the total number of unsaturated functional groups was markedly decreased, but the R.sub.vd value was relatively increased.

(35) This could be affected by the compound used as the catalyst. From the view of beta-hydride elimination of the production process of the unsaturated functional groups, if the polymerization is terminated after 1,2-insertion of octene, vinylidene is produced, if the polymerization is terminated after 2,1-insersion, vinylene is produced, and if the polymerization is terminated after the insertion of ethylene, vinyl is produced. If the copolymerization properties of the catalyst are excellent, 2,1-insersion may also be increased, and accordingly, the vinylene content may tend to increase and the vinylidene content may tend to decrease.

(36) That is, the transition metal compound used as the catalyst composition in Examples 1 to 5 has better copolymerization properties than the catalyst used in Comparative Examples 6 and 7, and 2,1-insersion was increased, and accordingly, the vinylene content was increased and the vinylidene content was decreased. However, in case of Comparative Examples 6 and 7, the results showed that the vinylidene content was not decreased.

(37) In this regard, in view of viscosity change rate data, Comparative Example 7 had a relatively low vinylidene content ratio but high total amount of the number of unsaturated functional groups such as vinyl and vinylidene. Accordingly, viscosity change rate according to time was large, and through this, the stability at a high temperature may be expected to be inferior.

(38) On the contrary, in case of the copolymers of Examples 1 to 4, since the total amount of the number of unsaturated functional groups was small and the ratio of vinylidene was low, the viscosity change rate was small, and in this case, the stability at a high temperature is expected to be excellent.

(39) In addition, if Example 3 and Comparative Example 6, which had the same degree of the total number of unsaturated functional groups of 0.32/1000 C, are compared, Example 3 which had a low R.sub.vd value was confirmed to show smaller viscosity change rate by about two times when compared with Comparative Example 6 which had a high R.sub.vd value.

(40) Through this, it could be confirmed from the experimental data that the viscosity change is small in case where the total amount of the unsaturated functional groups is small as well as in case where the R.sub.vd value is small.