Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-10-04
2002-03-19
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C525S241000
Reexamination Certificate
active
06359094
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a styrenic polymer, more precisely to that having a syndiotactic structure, syndiotactic polystyrene having good melt flowability and improved moldability and melt tension and still having excellent mechanical strength, heat resistance and solvent resistance.
BACKGROUND ART
It has heretofore been known that a styrenic polymer having a syndiotactic structure, syndiotactic polystyrene (hereinafter referred to as SPS) has excellent mechanical strength, heat resistance and solvent resistance, and the polymer has many applications. However, since conventional SPS is produced by the use of a single-site catalyst, its molecular weight distribution is narrow and its melt tension is low. Therefore, its moldability especially in expansion molding, inflation molding or blow molding is poor, and the practical use of the polymer is often problematic.
On the other hand, Japanese Patent Laid-Open No. 119006/1991 discloses a method for producing SPS having an expanded molecular weight distribution, by the use of a catalyst comprising two or more different types of titanium compounds. This is for improving the moldability of the polymer. However, the molecular weight distribution (Mw/Mn) of the SPS products produced in Examples in the laid-open publication is 10 or more and is too broad. In addition, the number-average molecular weight (Mn) of the polymer is tens of thousands or so and is low. The polymer contains a large quantity of low-molecular-weight components, and its moldability could not be improved to the intended degree. In addition, still another problem with the polymer is that the strength of its moldings is low.
The present invention is to solve the problems noted above, and its object is to provide a styrenic polymer having a syndiotactic structure, syndiotactic polystyrene having good melt flowability and improved moldability and melt tension and still having excellent mechanical strength, heat resistance and solvent resistance.
DISCLOSURE OF THE INVENTION
We, the present inventors have assiduously studied to attain the object as above, and, as a result, have found that a syndiotactic polystyrene, of which the elastic modulus change to shear rate change satisfies a specific requirement, has good melt flowability and improved moldability and melt tension. Based on this finding, we have completed the present invention. Specifically, the invention provides a styrenic polymer mentioned below.
1. A styrenic polymer having a syndiotactic structure, of which the ratio P of the angular frequency, &ohgr;
3000
(unit: rad/sec), when its storage elastic modulus G′ measured through dynamic viscoelastometry is 3000 (Pa), to the angular frequency thereof, &ohgr;
30
(unit: rad/sec), when its storage elastic modulus G′ is 30 (Pa), P=[&ohgr;
3000
/&ohgr;
30
] satisfies the following formula (1):
P=[&ohgr;
3000
/&ohgr;
30
]≧25 (1).
2. The styrenic polymer of above 1, which satisfies the following (1) and (2):
(1) The ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the polymer measured through gel permeation chromatography (GPC), Mw/Mn, is at most 5;
(2) The ratio of the Z-average molecular weight (Mz) to Mn of the polymer measured through GPC, Mz/Mn, is at least 3.5.
3. The styrenic polymer of above 1, of which the molecular weight distribution measured through GPC satisfies the following (1), (2) and (3):
(1) The proportion of the component having a molecular weight of at most 50,000 of the polymer, C
50
, falls between 1 and 30% by weight;
(2) The proportion of the component having a molecular weight of at least 1, 000,000 of the polymer, C
1000
, falls between 1 and 30% by weight;
(3) The weight-average molecular weight, Mw, of the polymer falls between 100,000 and 2,000,000.
4. The styrenic polymer of above 3, of which the proportion of the component having a molecular weight of at most 50,000, C
50
, and the weight-average molecular weight, Mw, satisfy the following:
log(C
50
)≧−1.48×log(Mw/1000)+4.44.
5. The styrenic polymer of above 1, of which the melt tension, MT, and the melt index, MI, satisfy the following formula (2):
log(MT)≧−0.887×log(MI)+0.654 (2).
6. Moldings of the styrenic polymer of any of above 1 to 5.
BEST MODES OF CARRYING OUT THE INVENTION
The styrenic polymer [1] and its moldings [2] of the invention are described in detail hereinunder.
1 Styrenic Polymer
The styrenic polymer [1] of the invention has a syndiotactic structure, of which the ratio P of the angular frequency, &ohgr;
3000
(unit: rad/sec), when its storage elastic modulus G′ measured through dynamic viscoelastometry is 3000 (Pa), to the angular frequency thereof, &ohgr;
30
(unit: rad/sec), when its storage elastic modulus G′ is 30 (Pa), P=[&ohgr;
3000
/&ohgr;
30
] satisfies the following formula (1):
P=[&ohgr;
3000
/&ohgr;
30
]≧25 (1).
The styrenic polymer having a syndiotactic structure is meant to include polystyrenes, poly(alkylstyrenes), poly(halogenostyrenes), poly(halogenoalkylstyrenes), poly(alkoxystyrenes) and poly(vinyl benzoates) having a degree of racemi-diad syndiotacticity of generally at least 75%, but preferably at least 85% or having a degree of racemi-pentad syndiotacticity of generally at least 30%, but preferably at least 50%, and their hydrogenated polymers and their mixtures, or copolymers comprising, as the essential ingredient, any of them. The poly(alkylstyrenes) include poly(methylstyrenes), poly(ethylstyrenes), poly(isopropylstyrenes), poly(tert-butylstyrenes), poly(phenylstyrenes), poly(vinylnaphthalenes), poly(vinylstyrenes), etc.; and the poly(halogenostyrenes) include poly(chlorostyrenes), poly(bromostyrenes), poly(fluorostyrenes), etc. The poly(halogenoalkylstyrenes) include poly(chloromethylstyrenes), etc.; and the ply(alkoxystyrenes) include poly(methoxystyrenes), poly(ethoxystyrenes), etc.
Of those styrenic polymers, especially preferred are polystyrenes, poly(p-methylstyrenes), poly(m-methylstyrenes), poly(p-tert-butylstyrenes), poly(p-chlorostyrenes), poly(m-chlorostyrenes), poly(p-fluorostyrenes), hydrogenated polystyrenes, and copolymers containing any of these structural units.
P in formula (1) is the ratio of the angular frequency, &ohgr;
3000
(unit: rad/sec) of the polymer, when its storage elastic modulus G′ measured through dynamic viscoelastometry mentioned below is 3000 (Pa), to the angular frequency thereof, &ohgr;
30
(unit: rad/sec), when its storage elastic modulus G′ is 30 (Pa), P=[&ohgr;
3000
/&ohgr;
30
].
<Dynamic viscoelastometry>
For dynamic viscoelastometry, used is Rheometric Scientific FE's ARES. Briefly, a polymer sample sheet of 1 mm thick formed by the use of a press-molding machine is sandwiched between a cone and a disc in the device, and heated up to 300° C. to have a strain of 20%, and the storage elastic modulus of the sample sheet is measured with varying the angular frequency &ohgr; (rad/sec) of the sample sheet. On the curve indicating the relationship between &ohgr; and the storage elastic modulus G′ of the sample sheet thus measured, &ohgr;
3000
and &ohgr;
30
are read, from which is obtained the ratio P. In case where the sample sheet could not be measured within the range up to 300° C., it may be measured at different temperatures to prepare a master curve at 300° C. according to the temperature-time conversion rule. On the master curve thus prepared, the data may be read to obtain the intended ratio P.
P indicates the degree of elastic modulus change to shear rate change, and a smaller value of P indicates that the elastic modulus change to shear rate change of the polymer is smaller. P of the styrenic polymer of the invention must be at least 25 in order that the polymer retains good melt flowability and has improved moldability and melt tension. Preferably, it is at least 30, more preferably
Sera Masanori
Shouzaki Hajime
Idemitsu Petrochemical Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Teskin Fred
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