Biodegradable polymers, preparation thereof and use thereof...

Details Biodegradable polymers, preparation thereof and use thereof... Biodegradable polymers, preparation thereof and use thereof...

2000-07-07

2001-10-16

Yoon, Tae H. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S047000, C524S601000, C524S603000, C525S437000, C525S450000, C525S938000

Reexamination Certificate

active

06303677

ABSTRACT:

The present invention relates to biodegradable polyesters P1 obtainable by reaction of a mixture consisting essentially of
(a1) a mixture consisting essentially of
from 35 to 95 mol % of adipic acid or ester-forming derivatives thereof or mixtures thereof,
from 5 to 65 mol % of terephthalic acid or ester-forming derivatives thereof or mixtures thereof, and
from 0 to 5 mol % of a sulfonate compound,
the sum of the individual mole percentages being 100 mol %, and
(a2) a dihydroxy compound selected from the group consisting of C
2
-C
6
-alkanediols and C
5
-C
10
-cycloalkanediols,
the molar ratio of (a1) to (a2) being chosen within the range from 0.4:1 to 1.5:1, with the proviso that the polyesters P1 have a molecular weight (M
n
) within the range from 5000 to 50,000 g/mol, a viscosity number within the range from 30 to 350 g/ml (measured in 50:50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight of polyester P1 at 25° C.) and a melting point within the range from 50 to 170° C. and with the further proviso that the polyesters P1 are prepared using from 0.01 to 5 mol %, based on the molar quantity used of component (a1), of a compound D having at least three groups capable of ester formation.
The present invention further relates to polymers and biodegradable thermoplastic molding compositions as claimed in dependent claims, processes for their preparation, their use for producing biodegradable moldings and adhesives, biodegradable moldings, foams and blends with starch obtainable from the polymers or molding compositions of the present invention.
Polymers which are biodegradable, ie. decompose under environmental influences in an appropriate and demonstrable time span have been known for some time. This degradation usually takes place by hydrolysis and/or oxidation, but predominantly by the action of microorganisms such as bacteria, yeasts, fungi and algae.
Y.Tokiwa and T. Suzuki (Nature, 270, (1977) 76-77 describe the enzymatic degradation of aliphatic polyesters, for example including polyesters based on succinic acid and aliphatic diols.
EP-A 565,235 describes aliphatic copolyesters containing [—NH—C(O)O—] groups (urethane units). The copolyesters of EP-A 565,235 are obtained by reacting a prepolyester, which is obtained by reacting essentially succinic acid and an aliphatic diol, with a diisocyanate, preferably hexamethylene diisocyanate. The reaction with the diisocyanate is necessary according to EP-A 565,235 because the polycondensation alone results only in polymers with molecular weights displaying unsatisfactory mechanical properties. A crucial disadvantage is the use of succinic acid or ester derivatives thereof to prepare the copolyesters because succinic acid and derivatives thereof are costly and are not available in adequate quantity on the market. In addition, the polyesters prepared using succinic acid as the only acid component are degraded only extremely slowly.
WO 92/13019 discloses copolyesters based on predominantly aromatic dicarboxylic acids and aliphatic diols, where at least 85 mol % of the polyester diol residue comprises a terephthalic acid residue. The hydrophilicity of the copolyester is increased, and the crystallinity is reduced, by modifications such as the incorporation of up to 2.5 mol % of metal salts of 5-sulfoisophthalic acid or short-chain ether diol segments such as diethylene glycol. This is said in WO 92/13019 to make the copolyesters biodegradable. However, the disadvantage of these copolyesters is that biodegradation by microorganisms has not been demonstrated, on the contrary only the behavior toward hydrolysis in boiling water or, in some cases, also with water at 60° C. has been carried out.
According to the statements of Y.Tokiwa and T.Suzuki (Nature, 270 (1977) 76-78 or J. of Appl. Polymer Science, 26 (1981) 441-448), it may be assumed that polyesters which are substantially composed of aromatic dicarboxylic acid units and aliphatic diols, such as PET (polyethylene terephthalate) and PBT (polybutylene terephthalate), are not enzymatically degradable. This also applies to copolyesters which contain blocks composed of aromatic dicarboxylic acid units and aliphatic diols.
Witt et al. (handout for a poster at the International Workshop of the Royal Institute of Technology, Stockholm, Sweden, Apr. 21-23, 1994) describe biodegradable copolyesters based on 1,3-propanediol, terephthalic ester and adipic or sebacic acid. A disadvantage of these copolyesters is that moldings produced therefrom, especially sheets, have inadequate mechanical properties.
It is an object of the present invention to provide polymers which are degradable biologically, ie. by microorganisms, and which do not have these disadvantages. The intention was, in particular, that the polymers according to the invention be preparable from known and low-cost monomer units and be insoluble in water. It was furthermore the intention that it be possible to obtain products tailored for the desired uses according to the invention by specific modifications such as chain extension, incorporation of hydrophilic groups and groups having a branching action. The aim was moreover that the biodegradation by microorganisms is not to be achieved at the expense of the mechanical properties in order not to restrict the number of applications.
We have found that this object is achieved by the polymers and thermoplastic molding compositions defined at the outset.
We have also found processes for the preparation thereof, the use thereof for producing biodegradable moldings and adhesives, and biodegradable moldings, foams, blends with starch and adhesives obtainable from the polymers and molding compositions of the present invention.
The polyesters P1 of the present invention have a molecular weight (M
n
) in the range from 5000 to 50,000, preferably from 6000 to 45,000, particularly preferably from 8000 to 35,000 g/mol, a viscosity number in the range from 30 to 350, preferably from 50 to 300 g/ml (measured in 50:50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight of polyester P1 at 25° C.) and a melting point in the range from 50 to 170, preferably from 60 to 150° C. The polyesters P1 are obtained according to the invention by reaction of a mixture consisting essentially of
(a1) a mixture consisting essentially of
from 35 to 95, preferably from 45 to 80 mol % of adipic acid or ester-forming derivatives thereof, in particular the di-C
1
-C
6
-alkyl esters such as dimethyl, diethyl, dipropyl, dibutyl, dipentyl and dihexyl adipate, or mixtures thereof, preferably adipic acid and dimethyl adipate, or mixtures thereof,
from 5 to 65, preferably 20 to 55, mol % of terephthalic acid or ester-forming derivatives thereof, in particular the di-C
1
-C
6
-alkyl esters such as dimethyl, diethyl, dipropyl, dibutyl, dipentyl or dihexyl terephthalate, or mixtures thereof, preferably terephthalic acid and dimethyl terephthalate, or mixtures thereof, and
from 0 to 5, preferably from 0 to 3, particularly preferably from 0.1 to 2, mol % of a sulfonate compound,
the sum of the individual mole percentages being 100 mol %,
(a2) a dihydroxy compound selected from the group consisting of C
2
-C
6
-alkanediols and C
5
-C
10
-alkanediols,
the molar ratio of (a1) to (a2) being chosen within the range from 0.4:1 to 1.5:1, preferably from 0.6:1 to 1.1:1.
The sulfonate compound which is normally employed is an alkali metal or alkaline earth metal salt of a dicarboxylic acid containing sulfonate groups, or the ester-forming derivatives thereof, preferably alkali metal salts of 5-sulfoisophthalic acid or mixtures thereof, particularly preferably the sodium salt.
The dihydroxy compounds (a2) employed according to the invention are selected from the group consisting of C
2
-C
6
-alkanediols and C
5
-C
10
-cycloalkanediols, such as ethylene glycol, 1,2- and 1,3-propanediol, 1,2- and 1,4-butanediol, 1,5-pentanediol or 1,6-hexanediol, in particular ethylene glycol, 1,3-propanediol and 1,4-butanediol, cyclopentanediol, cyclohexanediol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,

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