WO1994020552A1

WO1994020552A1 - Enhanced processing of ultrahigh molecular weight polymers

Info

Publication number: WO1994020552A1
Application number: PCT/US1994/001423
Authority: WO
Inventors: Jan Vleggaar; Ki-Soo Kim; Sophia Dashevsky; Jian-Lin Liu; Stanley W. Palmaka; Johannes A. Juijn
Original assignee: Akzo Nobel N.V.
Priority date: 1993-03-05
Filing date: 1994-02-08
Publication date: 1994-09-15

Abstract

Polymer blends of an ultrahigh molecular weight polymer, such as ultrahigh molecular weight polyester, for example, polyethylene terephthalate, or polyamide, and a liquid crystalline polymer, oligomer, or mixture thereof have improved melt processing characteristics due to the presence of the liquid crystalline additive.

Description

ENHANCED PROCESSING OF ULTRAHIGH MOLECULAR WEIGHT POLYMERS

BACKGROUND OF THE INVENTION

It is well known that ultrahigh molecular weight (UHMW) thermoplastic polymers, such as polyester (for example, polyethylene terephthalate) and polyamide (such as polyamide 6 and polyamide 6,6) are very difficult to process, especially in melt spinning (for example, of fibers) because of their molecular weight. Representative molecular weight ranges for certain of the more significant polymers of this type from a commercial perspective are 70,000 to 100,000 for polyester, such as polyethylene terephthalate (PET) . UHMW PET, for example, requires high temperature and pressure to process due to its high melt viscosity which leads to high pressure conditions in the spinneret and extrusion regions of melt spinning apparatus. Furthermore, UHMW PET is also susceptible to undesired hydrolytic and thermal degradation to lower molecular weight under the temperature and moisture conditions often present in such melt spinning procedures. It would therefore be advantageous to develop compositions containing a major portion of such UHMW polymers that have enhanced processing characteristics (e.g., they can be processed at lower temperatures and/or can be processed using less energy) with the avoidance of some of the degradation problems also encountered with certain of these polymer types, such as UHMW PET, for example.

SUMMARY OF THE INVENTION

The present invention relates to a polymer blend which comprises an ultrahigh molecular weight polymer, such as polyethylene terephthalate, and an effective amount for improved melt processing of a liquid crystalline polymer, oligomer, or mixture thereof.

DETAILED DESCRIPTION OF THE INVENTION

Ultrahigh molecular weight polymers which can be used as the predominant or "matrix" for blends in accordance with the present invention include the ultrahigh molecular weight polyester materials known to persons of ordinary skill in the art. As described above, polyethylene terephthalate of molecular weight 70,000 to 100,000 are representative. This invention is also considered to be applicable to UHMW polya ides. The liquid crystalline additive which is used for melt processing improvement can be added at from about 0.5% to about 5% by weight of the matrix polymer.

Liquid crystalline oligomers of the type described in U.S. Ser. No. 891,502, filed May 29, 1992, are preferred. The type of mesogenic unit for the rod portion of the LC oligomer can be appropriately selected from known mesogenic units in main chain thermotropic liquid crystal polymers, with the proviso that the molecular weight be controlled to yield an oligomer rather than a polymer. Included are those of the general structure:

[-A-Y-X-Z-]_m (I)

as set forth in U.S. Patent No. 4,952,334, for example, which is incorporated herein by reference. In the above formula, for example, in preferred embodiments, X (the "alkylene" spacer) can be (CH₂)_n and (CH₂CH₂0)_n, where n is an integer of from 2 to 10, m can range from about 2 to about 10, and Y and Z can each be -C(0)0- or -C(0)NH- or can be a single bond between two carbon atoms, and A can be p-phenylene, 1,4-, 2,6-, or 1,5-naphthylene, monosubstituted phenylene with methyl, chloro, or phenyl substitution; -ArCH=CHAr-, where Ar is a phenyl ring, -Ar-C(0)OAr-, -Ar-C(0)NHAr-, or -ArOC(0)-Ar-C(0)0-Ar-, as more fully depicted in the aforementioned patent. In addition, another mesogenic unit which can be employed has the structure -Ar-C(0)-NH-Ar-NH-C(0)-Ar-. Yet another mesogenic unit can have the formula -ArC(0)OAr'OC(0)Ar- where Ar' can be unsubstituted or substituted (e.g., alkyl or alkoxy) phenyl (derived from hydroquinone) or biphenyl (derived from biphenol) and Ar can be derived from terephthalic or the mesogenic-producing naphthylenic starting materials. The commercial rod polymers based on oxybenzoate units, 4,4^,-biphenylene terephthalate units, and oxynaphthalene carboxylate units (the latter two including copolymers with the oxybenzoate units) can be especially preferred.

A particularly preferred oligomer has the repeat unit

-[ (CH₂)_nOC(O)ArOC(O)ArC(O)OArC(O)O]-

where n can range from 2 to 10, preferably 4, and Ar are para-phenylene.

The oligomers of the present invention can be synthesized, for example, by reacting the appropriate building blocks for the desired mesogen (e.g., a terephthaloyl halide and an α,ω-bis(p-hydroxybenzyl- oxy)alkane) with a slight molar excess of one building block over the other using single digit molar amounts of each, e.g., 4/3 to 7/6. The use of substantially equal molar amounts of reagent will yield excessively large molecular weight materials (i.e. polymers) as will the use of high molar amounts of reagents. In general, such oligo ers will have a molecular weight of no higher than about 7,000 to about 8,000. The preferred liquid crystalline polymer is a thermotropic liquid crystalline segmented block copolymer of the type described in PCT International Publication No. W093/13172 in which the blocks are "rod" and "flexible coil" blocks, respectively. The liquid crystalline segmented block copolymer which is intended to be added to the ultrahigh molecular weight polymer matrix can be envisioned to have the general formu1a:

-[[Rod]_x-[Coil]_y]_p-

where "Rod" indicates the mesogenic block with x, normally from 2 to 15, indicating the number of mesogen repeats, "Coil" indicating the block comprising the flexible coil polymer segment, with y, normally from about 2 to about 25, indicating the number of repeat units in the flexible coil polymer block, and p representing the repeat units of Rod and coil blocks. The mole % rod in the total polymer can range from about 4% to about 80%. The repeat unit p can range from about 1 to about very large numbers such as 50-500 for high molecular weight segmented block copolymers. Polyethylene terephthalate and polybutylene terephthalate are representative coils. The rod length, which is responsible for liquid crystalline properties for the block copolymer additive and the % block in the matrix/block copolymer combination need to be appropriately balanced within the general ranges given above.

The type of mesogenic unit for the rod portion of the LC copolymer can be appropriately selected from known mesogenic units (main chain thermotropic liquid crystal polymers) including those of the general structure:

(I) as set forth in U.S. Patent No. 4,952,334, for example, which is incorporated herein by reference. In the above formula, for example, in preferred embodiments, X can be (CH₂)_n, where n is an integer of from 2 to 10, m can range from about 5 to about 15, and Y and Z can each be -C(0)0- or -C(0)NH- or can be a single bond between two carbon atoms, and A can be p-phenylene, 1,4-, 2,6-, or 1,5-naphthylene, monosubstituted phenylene with methyl, chloro, or phenyl substitution; -ArCH=CHAr-, where Ar is a phenyl ring, -AR-C(0)0Ar-, -Ar-C(0)NHAr-, or -ArOC(O)-Ar-C(0)0-Ar-, as more fully depicted in the aforementioned patent. In addition another mesogenic unit which can be employed has the structure -Ar-C(0)-NH-Ar-NH-C(0)-Ar-. The commercial rod polymers based on oxybenzoate units, 4,4 '-biphenylene terephthalate units, and oxynaphthalene carboxylate units (the latter two including copolymers with the oxybenzoate units) can be especially preferred.

A particularly preferred structure for the "Rod" or mesogenic unit is of the general type described by Ober et al. in Polymer Journal, Vol. 14, No. 1, pp. 9-17 (1982) and, in view of its presence in a block copolymer as contrasted to the Ober et al. ho opolymer, has the structure:

-[-OArC(O)O(CH₂)_nOC(O)ArOC(O)ArC(O)-]-_x

where Ar represents phenyl with para- bond sites, n can range from 2 to 10, e.g., 4 and x can range, for example, from about 5 to about 15. These mesogenic units can be characterized as aromatic ester mesogenic units containing a flexible alkylene spacer. The "triad" structure comprising three linearly-aligned aromatic rings, the bis(p-carboxy- phenyl) terephthalate moiety, and a flexible spacer of varying length (n) , which can be alkylene or alkylene with heteroatom (e.g., oxygen) interruption, is particularly preferred as depicted above. The mesogenic units contain "diad" or "dyad" linkages, -OC(0)ArOC(0)ArC(0)-, at either end adjacent the connection points with the coil block segments. In general the block copolymers described herein will have a molecular weight of no less than about 7,000 to about 8,000.

Although the particular thermotropic LCP block (e.g., triad with flexible spacer block and polyester block) of structure (I) , above, is not a true rigid-rod, it readily assumes an extended chain structure and forms nematic mesophases and consequently high modulus/strength structures. Ideally, the high strength chain extended block polymer molecules would be very finely dispersed in the PET matrix and would be expected to have potential as a high performance molecular composite material.

The foregoing type of thermotropic liquid crystal block copolymer can be synthesized by the process shown in PCT International Publication No. WO93/01238. In the initial step, oligomers of the mesogen are prepared in one reactor and oligomers of the selected polyester are prepared in a second reactor, each set of oligomers having appropriate complementary end groups for later reaction of each set of oligomers. Then, the previously formed oligomers are allowed to react to one another to form the desired block copolymer. In this type of procedure, the sizes of the respective oligomers controls the lengths of the respective blocks.

More preferably, it is synthesized by the one reactor process described and claimed in U.S. Patent No. 5,194,569. In this one reactor process an α,ω-bis(hydroxybenzoyloxy) alkane is the preferred reagent for reaction with an aromatic acid chloride to form a functionalized liquid crystal oligomer containing the desired mesogenic unit or units and then reacting this oligomer with either a chosen polyester oligomer or the reagents for synthesizing such a polyester oligomer.

The most preferred synthesis procedure is described in U.S. Patent No. 5,258,486 in which an α,ω-bis(hydroxy- benzoyloxy) alkane monomer is reacted with an aromatic acid chloride in the presence of a functionalized flexible coil oligomer under two differing temperature conditions to initially form an acid chloride-terminated bis(hydroxyalky1 terephthalate) oligomer at a first, lower temperature and the desired block copolymer at a second, higher temperature.

The following Examples further illustrate the invention.

COMPARATIVE EXAMPLE 1

This Example illustrates the change in relative viscosity (ΔR.V.) in melt processing chips of ultrahigh molecular weight polyethylene terephthalate (PET) into yarn at 300°C.

R.V. (chips) R R.. .VV.. r (vvaarrnn)) ΔR.V.

1.60 1. . 59 -0. . 01 2.00 1. . 82 -0. . 18<» 2.40 2 . . 04 -0 . , 36®

⁽¹ a pressure of 200 bar was employed,

(2) a pressure of 490 bar was employed.

Small levels of moisture (in the ppm range) lead to a decrease in molecular weight and tenacity of the PET. Higher molecular weight product and higher spinning or processing temperatures lead to a more pronounced reduction of molecular weight.

EXAMPLE 2

This Example shows melt flow rate (MFR) of control UHMW PET and its melt and dry blends with a liquid crystalline polymer (LCP) and liquid crystalline oligomer (LCO) . The MFR was measured with a KAYNESS GALAXY Melt Indexer apparatus (2160 g weight) with six minute residence time as described below with higher melt flow rates being more desirable:

Temp. ( °C) Melt Flow Rate (q/10 min)

UHMW PET (control) 300 15

MELT BLENDING

PET/LCP* (98/2) 285 30

PET/LCP (95/5) 285 30

PET/LCO** (98/2) 285 14 PET/LCO (95/5) 285 42

DRY BLENDING

PET/LCP (98/2) 285 7

PET/LCO (98/2) 285 7.5

* LCP — the thermotropic block copolymer of U.S. Ser. No. 812,606, filed December 23, 1991, comprising blocks of triad aromatic mesogenic units with flexible polyalkylene spacers and blocks of polybutylene terephthalate. ** LCO = the thermotropic triad aromatic mesogenic oligomer with flexible polyalkylene spacers of U.S. Ser. No. 891,502, filed May 29, 1992, was employed.

The above data indicate that addition of LCP and LCO to PET significantly increases the MFR of the PET. EXAMPLE 3

This Example sets forth fiber spinning conditions with LCP and LCO-containing blends of ultrahigh molecular weight PET (relative viscosity = 2.19).

Melt spinning was conducted on a Randcastle Microtruder apparatus with a 1/4 inch screw extruder and a single spinning hole having a diameter of 0.5 mm and a length/diameter ratio of 20. A CSI take-up unit was employed using a velocity in the range of 70-75 m/min. Drawing of the as-spun fibers was performed on a pin (at 76°C) and a hot plate (at 220-225°C) :

— -PET- — —Melt : Blend- — —Dry Blend—

LCP. % Wt 0 2 5 2* 2

Temperature, C

Zone l 304 264 264 280 282

Zone 2 310 281 281 293 294

Zone 3 315 292 292 300 298

Die 315 264 264 300 290

Output (g/min) 0. 8 0. 78 0. 73 0. 7 0.7

Winding speed (m/min) 75 75 74 77 73

Torque (amps) 3. 2 1. 8 1. 3 2. 8 2.0

* LCO was used instead.

The melt blend (the samples containing 2% and 5% additive) were prepared by extrusion of the dry blend in a CSI mixing extruder in the temperature range of 280° to 290°C depending on blend composition. The dry blends were formed by the process described in U.S. Patent No. 5,266,658 in which the ultrahigh molecular weight PET and LCO or LCP were blended together for four hours at a temperature (175°C) above their respective glass transition temperature but below their respective melting temperatures.

The Table indicates that UHMW PET blends can be spun at lower temperature with lower torque as compared to the unmodified PET.

EXAMPLE 4

The data set forth below illustrates the characteristics for a variety of ultrahigh molecular weight PET monofilament samples, some containing LCP and LCO additives, which have been melt spun at various die temperatures:

Die temp IM^® _BT ⁽³⁾ E_AB⁽⁴⁾ (°C) DR¹> N/tex (ro-N/tex) (%)

PET (Control) 313 6.6 12.5 780 10.5

2% LCP* 290 5.7 11.8-13 780 16.6 2 2%% LLCCPP**** 2 25544 6 6..00 1 122..77 780 15.6

5% LCP** 254 6.9 15.7 710 10.3

5% LCO** 292 6.9 15.2 864 12.7

* Dry blend ** Melt blends ^d) DR = total draw ratio. ^® IM = initial modulus. ⁰⁾ BT = breaking tenacity. ⁽⁴⁾ EAB = elongation at break.

EXAMPLE 5

This Example illustrates the change in relative viscosity (R.V.) due to reduction in the molecular weight of the ultrahigh molecular weight PET during spinning described in Example 3. Lower R.V. reduction was observed for the LCP containing blend sample as compared to the control.

Initial Post-spun R.V. R.V. Δ R.V.

PET (Control) : 2.21 1.80 -0.41 (-18.5%)

PET + 2% LCP: 2.18 1.91 -0.27 (-12%) (Dry Blend)

The foregoing Examples are presented for illustrative purposes only and, for this reason, should not be construed in a limiting sense. The scope of protection sought is set forth in the claims which follow.

Claims

We Claim:

1. A polymer blend of improved melt processibility which comprises an ultrahigh molecular weight thermoplastic polymer, as substrate, and an effective amount of a liquid crystalline polymer, oligomer, or mixture thereof for improved melt processing of the substrate.

2. A blend as claimed in Claim 1 wherein the liquid crystalline polymer is a thermotropic segmented block copolymer comprising mesogenic and flexible coil polymer blocks.

3. A blend as claimed in Claim 2 wherein the mesogenic block comprises aromatic ester units and a flexible alkylene spacer.

4. A blend as claimed in Claim 2 wherein the flexible coil block comprises polyalkylene terephthalate.

5. A blend as claimed in Claim 3 wherein the flexible coil block comprises polyalkylene terephthalate.

6. A blend as claimed in Claim 1 wherein the liquid crystalline oligomer comprises a mesogen comprising aromatic ester units and a flexible alkylene spacer.

7. A blend as claimed in Claim 1 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.

8. A blend as claimed in Claim 2 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.

9. A blend as claimed in Claim 3 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.

10. A blend as claimed in Claim 4 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.

11. A blend as claimed in Claim 5 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.

12. A blend as claimed in Claim 6 wherein the ultrahigh molecular weight polymer is selected from the group consisting of polyester and polyamide.