WO1996005253A1

WO1996005253A1 - Melt viscosity reduction of polycarbonate containing liquid crystalline block copolymer

Info

Publication number: WO1996005253A1
Application number: PCT/US1995/010252
Authority: WO
Original assignee: Akzo Nobel Nv; Kim, Ki-Soo; Dashevsky, Sophia
Priority date: 1994-08-15
Filing date: 1995-08-11
Publication date: 1996-02-22

Abstract

The melt viscosity of a polycarbonate resin which is being subjected to shearing in the melt can be reduced by adding to the polycarbonate resin an effective amount, for such molecular weight characteristic retention, of a thermotropic segmented liquid crystalline block copolymer containing rod blocks, containing a flexible spacer therein, and flexible polyester coil blocks.

Description

MELT VISCOSITY REDUCTION OF POLYCARBONATE CONTAINING LIQUID CRYSTALLINE BLOCK COPOLYMER

BACKGROUND OF THE INVENTION

It is known to add liquid crystalline polymers (LCPs) to various resins, including those of polycarbonate, to achieve certain desired characteristics including: improved flow; reinforcement; and blend toughness. See D.J. Williams, "Applications for Thermotropic Liquid Crystal Polymer Blends", Advances in Polymer Technology, Vol. 10, No. 3, 173-184 (1990) and D. Dutta et al.,

"Polymer Blends Containing Liquid Crystals: A Review", Polymer Engineering and Science, Mid-September 1990, Vol. 30, No. 17, 1005-1018.

Representative U.S. Patents which demonstrate the viscosity reduction effects known for LCPs when added to polycarbonate resins include U.S. Patent Nos. 4,386,174 and 4,438,236 to F.N. Cogswell et al. A publication in the scientific literature which discusses polycarbonate- LCP blends is A. Kohli et al., Polymer Science and Engineering, Mid-May 1989, Vol. 29, No. 9, 573-580.

A thermotropic segmented liquid crystalline block copoly er containing rod blocks, with a flexible spacer therein, and flexible polyester coil blocks is described as a novel composition which is suitable for blending with certain flexible coil polymers in PCT WO 93/01238. The flexible coil polymers to which this LCP can be added can be "selected from known polyester and polyamide polymer" (see page 4, lines 19-20). The flexible coil block units of the LCO need to be "substantially similar to the matrix material" (see page 5, lines 13-14) . Therefore, this patent publication teaches away from blends of a polycarbonate, rather than either a polyamine or polyester, and this block copolymer additive. SUMMARY OF THE INVENTION

The present invention relates to a process for reducing the melt viscosity of a polycarbonate resin which is being subjected to shearing in the melt which comprises adding to the polycarbonate resin an effective amount for such reduction of the melt viscosity of the resin of a thermotropic segmented liquid crystalline block copolymer containing rod blocks with a flexible spacer therein and flexible polyester coil blocks.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is applicable for use conventionally known polycarbonate resins.

The liquid crystalline copolymer additive which, when added to the forgoing type of polycarbonate resin, reduces the melt viscosity of the resulting blend, as compared to the neat polycarbonate resin, under the shearing conditions of melt processing. The liquid crystalline polymer which is added is the type of liquid crystalline segmented block copolymer that is described in U.S. Ser. No. 53,838, filed April 28, 1993 and in PCT International Publication No. WO 93/01238, January 21, 1993 in which the respective blocks in the copolymer are "rod" and "flexible coil" blocks, respectively. The liquid crystalline segmented block copolymer which is intended to be added to the polycarbonate resin can be envisioned to have the general formula:

-[[Rod]_s-[Coil],]_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 a flexible coil polyester segment, with y, normally from about 2 to about 25, indicating the number of repeat units in the flexible polyester 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 or polybutylene terephthalate comprise the preferred coil segments. 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.

Generally speaking, the amount of the liquid crystalline copolymer which can be added in accordance with the present invention will be up to about 10 %, by weight of the polycarbonate resin, preferably from about 0.1 % to about 5 %.

The type of mesogenic unit for the rod portion of the LCP can be appropriately selected from known mesogenic units (main chain thermotropic liquid crystal polymers) including 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 can be (CH₂)_B, 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- naphthalene, 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(O) -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. homopolymer, 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-carboxyphenyl) 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(O)ArOC(O)ArC(O)-, 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 U.S. Serial No. 53,838, filed April 28, 1993. 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, which is incorporated herein by reference. In this one reactor process an c.,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(hydroxybenzoyloxy) 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(hydroxyalkyl terephthalate) oligomer at a first, lower temperature and the desired block copolymer at a second, higher temperature.

The following Examples further illustrate the invention. EXAMPLE 1

This illustrates the process used to synthesize a thermotropic liquid crystalline block copolymer analogous to the preferred structures shown in PCT International Publication No. WO93/01238 containing five arylene groups in the mesogen with a butylene spacer and a polybutylene terephthalate (PBT) block. This copolymer is referred to below as "Pentad-4/PBT". It was synthesized in a single reactor from a mixture of bis(4-hydroxybutyl terephthalate) oligomer (BHBT oligomer) having a degree of polymerization of 5.5, the so-called "TR-4 monomer" (1,4- bis(p-hydroxybenzoyloxy) butane, and 4,4'- (terephthaloyldioxy)dibenzoyl dichloride ("TR diacid dichloride) . The TR-4 monomer (2.97 g, 0,009 mole), TR diacid dichloride (5.31 g, 0.012 mole), BHBT oligomer (2.97 g, 0.00297 mole) and 70 ml of 1-chloronaphthalene solvent were placed in a 250 ml flask equipped with a stirrer and were heated at 170°C. under nitrogen for one hour. The temperature was then slowly increased to 250°C. and was kept at that temperature for twenty-two hours. To the resulting reaction medium was then added 0.1 g of 1,4- butanediol. After one hour the reaction was terminated. After cooling methanol (80 ml) was added, the product was collected by filtration. The polymer was purified in boiling acetone five times and was vacuum dried at 110°C. overnight. The yield was about 94% by weight of the theoretical. The polymer had an inherent viscosity of 0.45 dl/g in p-chlorophenol/tetra-chloroethane (6/4 wt/wt) at 25°C. , a melting point of 220°C. (by DSC), and a clearing temperature of greater than 350°C (by POM) . EXAMPLE 2

This Example shows the melt flow index (MFI) properties of neat polycarbonate (PC) , and two samples containing thermotropic liquid crystalline (LC) block copolymers of the general type shown in PCT International Publication No. WO93/01238.

Blends of the PC and the liquid crystalline block copolymers were prepared by dry blending at 175°C for four hours under nitrogen and melt blending in a CSI mixing extruder at 277°/270°C. As-received PC (LEXAN LX 105 Brand) was extruded through the CSI extruder under the same conditions and was used as a control. As shown in the Table given below, the melt indices of the PC containing the LC block copolymers are higher than that of the control PC:

MFI.α/10 min; Load = 1200 σ

LC.% 300C 320C

Neat PC 0 10 25 TR-4/PBT* 2 15 26 TR-4/PBT* 5 19 Pentad-4/PBT** 2 11.5 31

* TR-4/PBT: the thermotropic liquid crystalline block copolymer of 0.5 dl/g inherent viscosity comprising a "triad" mesogenic block unit with C₄ alkylene spacer and a polybutylene terephthalate (PBT) flexible coil block as described as a preferred embodiment in PCT International Publication No. WO93/01238.

** Pentad-4/PBT: a copolymer of 0.45 dl/g inherent viscosity, as made in Example 1 which is analogous to the TR-4/PBT copolymer. It comprises a mesogen unit of the structure

[OArC(0)OC₄H₈OC(0)ArOC(O)ArOC(O)ArC(O)OArC(0) ] and a unit of PBT of the formula

[OC₄H₈OC(0)ArC(0) ].

Addition of the LC block copolymer reduced the melt viscosity of the PC. Scanning electron microscopy

(SEM) analysis of the PC containing 2% TR-4/PBT showed a single phase morphology. Addition of the LC block copolymers somewhat broadened the glass transition region of the two blend component at the given concentration level.

The foregoing Examples are provided to merely illustrate certain embodiments of the present invention and, for that reason, should not be construed in a limiting fashion. The scope of protection desired is set forth in the claims which follow.

Claims

We Claim:

1. A process for reducing the melt viscosity of a polycarbonate resin which is being subjected to shearing in the melt which comprises adding to the polycarbonate resin an effective amount for such reduction of the melt viscosity of a thermotropic segmented liquid crystalline block copolymer containing rod blocks with a flexible spacer in the mesogenic units contained therein and flexible polyester coil blocks and subjecting the resulting blend to shearing in the melt to achieve such reduction.

2. A process as claimed in Claim 1 wherein the block copolymer comprises up to 500 unit(s) of the general formula:

-[[Rod]_x-[Coil]_v]-

where "Rod" indicates the mesogenic block, with x ranging from 2 to 15 and indicating the number of mesogen repeats, "Coil" indicating the block comprising a flexible coil polyester segment, with y ranging from about 2 to about 25 and indicating the number of repeat units in the flexible polyester block.

3. A process as claimed in Claim 2 wherein the mesogenic unit in the block copolymer is of the general formula:

-[-OArC(0)O(CH₂)_nOC(O)ArOC(O)ArC(O) -]-_x

where Ar represents phenyl with para- bond sites, n can range from 2 to 10, and x can range from about 5 to about 15.

4. A process as Claimed in Claim 1 wherein the flexible coil blocks comprise polybutylene terephthalate.

5. A process as Claimed in Claim 2 wherein the flexible coil blocks comprise polybutylene terephthalate.

6. A process as Claimed in Claim 3 wherein the flexible coil blocks comprise polybutylene terephthalate.