WO1991009909A1

WO1991009909A1 - Polymeric composition having orthopedic utility

Info

Publication number: WO1991009909A1
Application number: PCT/US1989/005704
Authority: WO
Inventors: Speros Peter Nemphos
Original assignee: Polysar Financial Services S.A.
Priority date: 1989-12-27
Filing date: 1989-12-27
Publication date: 1991-07-11

Abstract

Polymer blends comprising 60 to 90 wt % of polycaprolactone having an Mw from 20,000 to 100,000 and from 10 to 40 weight % of a terpolymer comprising 60-80 wt % styrene; 10-30 wt % maleic anhydride and optionally from 0 to 15 wt % of a C1-2 ester of acrylic or methacrylic acid are useful in orthopedic applications. The polymer blends are moldable and clear at temperatures of about 70 °C and opaque at temperatures of less than 50 °C and rigid at temperatures of less than 40 °C. The polymer blends have orthopedic utility.

Description

POLYMERIC COMPOSITION HAVING ORTHOPEDIC UTILITY FIELD OF THE INVENTION The present invention relates to thermoplastic polymer blends which, among other things, are suitable for use in orthopedic splint material. More particularly, the present invention relates to polymer blends of poly(epsilon caprolactone) and a terpolymer of a vinyl aromatic monomer, maleic anhydride, and a C. _ alkyl ester of acrylic or methacrylic acid.

BACKGROUND OF THE INVENTION It is known to compound poly(eρsilon caprolactone) with various other thermoplastics and/ or elastomers to prepare thermoplastic compounds which are useful in a number of applications including thermoplastic orthopedic casts. Representative of this art are U.S. Patents 4,274,983 and 4,144,223 issued June 23, 1981 and March 14, 1979 respectively to Polysar Limited. These patents relate to blends of ρoly(epsilon caprolactone) and conjugated 1 ,4-diolefins . While these compounds have useful strength and a Tg to permit ther mo forming at relatively low temperatures of about 60°C, they are opaque.

In some instances , particularly where there are wounds to the skin, it would be desirable if the cast material could be made transparent under some circumstances. The compounds of the present invention have a softening temperature from 50-55°C which is comparable to existing medicast material of trans - polyisoprene. The compounds of the present invention have a good molding time in the order of at least 3 minutes and have good rigidity and tensile strength. Most importantly, the compositions of the present invention become transparent when heated above 50-55°C. The present invention provides a thermoplastic material which is transparent at a temperature in excess of 50°C preferably from 50-55°C and which is suitable as an orthopedic cast material.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a polymer blend consisting of:

(A) 60-90 weight percent of poly(epsilon caprolactone) having a molecular weight from 20,000 to 100,000; and

(B) from 10-40 weight percent of a terpolymer comprising (i) from 60-80 weight percent of one or more C_Q vinyl aromatic monomers which are unsubstituted or substituted by a C , alkyl radical or a chlorine atom;

(ii) from 10-30 weight percent of maleic anhydride; and

(iii) from 0-15 weight percent of a C _ alkyl ester of acrylic or methacrylic acid.

DETAILED DESCRIPTION

Poly(eρsilon caprolactone) has a structure indicated in Formula 1. Formula 1

[- 0 -CCH₂)₅ - C -]-_p 0 wherein P is not less than 200, and not more than 3000, preferably- from 250 to 450. Thus, the polymers have a molecular weight from about 20,000 to about 1,000,000 preferably from 20,000 to 100,000 most preferably from 20,000 to 50,000.

In the blends of the present invention the poly(eρsilon caprolactone) is present in an amount from 60 to 90, preferably from 60 to 80 weight percent. The terpolymers useful in accordance with the present invention are present in the blend in an amount from 40 to 10, preferably 40 to 20 weight percent. The terpolymers comprise:

(i) from 60 to 80, preferably from 70 to 80, most preferably 75 weight percent of one or more Co , ~ vinyl aromatic monomers which are unsubstituted or substituted by a C- , alkyl radical or a chlorine atom;

(ii) from 10 to 30, preferably from 10 to 20, most preferably 15 weight percent of maleic anhydride; and

(iii) from 0 up to 15, preferably from 5 to 15, most preferably 10 weight percent of a C, „ alkyl ester of acrylic or methacrylic acid.

Suitable C₀ . vinyl aromatic monomers include o- 1-. styrene, alpha methyl styrene, and para-methyl styrene. Suitable esters of acrylic and methacrylic acid include methyl methacrylate .

The compositions of the present invention may optionally contain fillers and may further comprise antioxidants , and other processing aids such as mold release agents. It should be noted however, that highly filled compounds may be opaque at temperatures above 50-55°C.

The compositions of the present invention may be prepared by well known techniques such as melt blending or solution blending. For melt blending, the materials are heated and mixed in a suitable apparatus such as a

Brabender at a temperature of about 230°C under shear. For solution blending both components may be dissolved in a suitable solvent such as methylene chloride. The resulting solutions are blended in a ratio to provide the required weight ratio of polymers. The solvent is then evaporated from the solution to yield the polymer blend. The resulting polymer blend is clear at temperatures of at least 50-55°C; flexible at temperatures which range from 65 to 70°C and are rigid at temperatures up to about 40 °C. The higher the content of terpolymer in the blend, the longer the moldable time of the blend at temperatures below 65 °C. It may take from 1/4 to 1 hour for the blend to crystalize and cool and become opaque at temperatures below 55°C.

The present invention will now be illustrated by the following examples in which, unless otherwise indicated, parts are parts by dry weight (e.g. pounds). Experiment 1

A series of polymers were melt blended with a poly(epsilon caprolactone) in a weight ratio of poly(eρsilon caprolactone) to polymer of 80:20. In the examples the rubber was a 70:30 butadiene: styrene block copolymer. The polymers and their composition (weight ratio) were as follows:

A) Styrene/Butyl acrylate/ rubber (graft) 65/30/5

B) Styrene/Methyl methacrylate/Butyl rubber/rubber (graft) 30/57/7/6

C) Styrene/methyl methacrylate 75/25

D) Styrene/methyl methacrylate/ rubber (graft) 24/71/5

E) Styrene/methyl methacrylate/Butyl acrylate/ rubber 40/40/11/9

F) Styrene/ aleic anhydride /me hyl methacrylate 75//15/10

G) Styrene/maleic anhydride 92/8 - sold under the trade mark DYLARK. 131

H) Styrene/maleic anhydride 83/17 - sold under the trade mark DYLARK. 331 I) PVC J) Styrene/ alpha methyl styrene/maleic anhydride

78/12/10 The poly(eρsilon caprolactone) had a molecular weight of 50,000. The compounds were prepared by solution blending in dichloroethane (CH Cl -CH Cl ) solvent and also by blending in a Brabender (trademark) mixer at 230°C for 10 min.

Of the blends prepared, only the blend of ρoly(eρsilon caprolactone) and the terpolymer of styrene/maleic anhydride/ methyl methacrylate 75/15/10 (polymer F) provided a clear blend at temperatures over 50-55 °C.

The blend was unique as it was clear at temperatures over 50-55°C then became opaque as the blend crystalized. Experiment II

A series of blends of terpolymer of styrene: maleic anhydride: methyl methacrylate (75:15:10) (F from Example 1) and poly(eρsilon caprolactone) having a molecular weight of 50,000 were blended in various weight ratios. The polymers were blended using a Brabender mixer at 230°C and 100 rpm for 10 minutes . The blends were then extruded as sheets and cooled. Then samples of the resulting sheets were heated to 70 °C. The workability and time of easy workability as the samples cooled in air from 20°C to room temperature was measured. (These are subjective tests).

The results are set forth in Table II.

TABLE II

Terpolymer 20 15 10 25 30 35 40 45 50 55

Caprolactcne 40 45 50 35 30 25 20 15 10 5

Clarity clear

Workability at 70°C sltly very sltly stiff stiff stiff stiff stiff none ncne stiff good soft Εasy Working Time from

70°C (min .) 5 4 1.2 less than 1

* sltly = sli^itly

In a weight ratio of terpolymer to ρoly(epsilcn caprolactone) of 20:40 to 10:50 (e.g. 33; 25; 12.5 weight percent of terpolymer) the blends have a useful working time at 70°C.

Claims

CLAIMS :

1. A polymer blend consisting of:

(A) 60-90 weight percent of ρoly(epsilon caprolactone) having a molecular weight from 20,000 to 100,000; and

(B) from 10-40 weight percent of a terpolymer comprising

(i) from 60-80 weight percent of one or more

C_{0 ι} vinyl aromatic monomers which are unsubstituted or substituted by a C , alkyl radical or a chlorine atom;

(ii) from 10-30 weight percent of maleic anhydride; and

(iii) up to 15 weight percent of a C _ alkyl ester of acrylic or methacrylic acid.

2. A polymer blend according to Claim 1 wherein the poly(epsilon caprolactone) has a molecular weight from 20,000 to 50,000.

3. A polymer blend according to Claim 2 wherein the poly(epsilon caprolactone) is present in an amount from 60 to 80 weight percent.

4. A process according to Claim 3 wherein said terpolymer comprises from 70 to 80 weight percent of said vinyl aromatic monomer; from 10 to 20 weight percent of maleic anhydride; and from 5 to 15 weight percent of a C ₉ alkyl ester of methacrylic acid.

5. A polymer blend according to Claim 4 wherein said vinyl aromatic monomer is selected from the group consisting of styrene, alphal methyl styrene, p -methyl styrene and a mixture thereof.

6. A polymer blend according to Claim 5 wherein said

C alkyl ester of methacrylic acid is methyl methacrylate .

7. An orthopedic splint comprising a polymer blend of Claim 1.

8. An orthopedic splint comprising a polymer blend of Claim 6.