WO2003054043A1

WO2003054043A1 - Grafted polymers with low cross-link density

Info

Publication number: WO2003054043A1
Application number: PCT/EP2002/014866
Authority: WO
Inventors: Wasil Maslow; Auke Gerardus Talma
Original assignee: Flexsys B.V.
Priority date: 2001-12-21
Filing date: 2002-12-20
Publication date: 2003-07-03
Also published as: AU2002360099A1

Abstract

The invention pertains to a grafted polymer having the formula R-X, X being: (I) wherein (a) P is a saturated polymer moiety, and R1 is selected from methyl, ethyl, phenyl, and halogen; or (b) P is a saturated polymer moiety connected through a methylene group with the 5-membered imide ring, and R1 is hydrogen; and in both (a) and (b) X is bonded at its nitrogen atom with group R, which is hydrogen or an organic radical that does not substantially react with a radical initiator, or a spacer comprising 1-3 moieties X that are bonded to the spacer through their nitrogen atom, wherein the cross-link density expressed as the amount of cross-linked product as measured via gel formation is less than 2 wt. %.

Description

GRAFTED POLYMERS WITH LOW CROSS-LINK DENSITY

The invention pertains to grafted polymers, to an intermediate for obtaining said polymers, and to a process for making the polymers. The invention further pertains to a method of using said process for modifying polymers.

Peroxide vulcanized rubber compositions comprising a biscitraconimide moiety are disclosed in EP 540,103, but these compositions comprise highly vulcanized (i.e. highly cross-linked) rubbers, which are not the subject of the present invention. Radical reaction of polymers with co-agents having activated olefinic bonds are well known in the art, see for instance E. Borsig, J.M.S. Pure Applied Chemistry A 36(11), pp 1699-1715 (1999) and references cited therein. When polymers comprising a hydrogen donor are brought into contact with a radical initiator, such as a peroxide, or with UV or daylight initiators, such as benzophenone or a halogen, respectively, a polymer radical is obtained that reacts with the activated olefinic compound, such as maleimide or maleic anhydride, to a radical intermediate of the polymer and the co-agent. A molecule of this radical intermediate invariably reacts further with another radical intermediate molecule to obtain oligomers and polymers, as has been disclosed in A. Hogt, Proceedings 2^nd International Congress on Compatibilizers and Reactive Polymer Alloying "Compallov '90". March 7-9, 1990, pp. 179-193. The molecular weight of the starting polymer is thereby substantially increased, and in fact a completely new molecule is obtained with properties that bear minimal or no relation with the starting polymers, whereas the efficiency of the aimed grafting reaction is far below 100%, especially at lower peroxide/maleic anhydride ratios. Such radical polymerization reaction cannot be prevented until now. However, it would be a substantial improvement if the radical reaction of the starting polymer and the co- agent could be stopped in the intermediate stage, also when low initiator/co-agent is used, in order to control further reaction thereof and to obtain products, the properties of which can be changed in a controlled manner. It is an object of the present invention to find conditions and reagents to perform such controlled reactions. It has now been found that using a specific co-agent enables a controlled radical reaction, and, dependent on the selection of the co-agent, grafted polymers can be produced.

The invention therefore pertains to a grafted polymer having the formula R-X, X being:

wherein

(a) P is a saturated polymer moiety, and R1 is selected from methyl, ethyl, phenyl, and halogen; or

(b) P is a saturated polymer moiety connected through a methylene group with the 5-membered imide ring, and R1 is hydrogen; and in both (a) and (b) X is bonded at its nitrogen atom with group R, which is hydrogen or an organic radical that does not substantially react with a radical initiator, or a spacer comprising 1-3 moieties X that are bonded to the spacer through their nitrogen atom, wherein the cross-link density expressed as the amount of cross-linked product as measured via gel formation is less than 2 wt.%.

These grafted polymers can be prepared by a process comprising the step of reacting a saturated polymer with a hydrogen donor in the presence of a radical initiator with a co-agent of the formula R-Y:

Y being

wherein:

R1 is selected from methyl, ethyl, phenyl, and halogen; and Y is bonded at its nitrogen atom with group R, which is hydrogen or an organic radical that does not substantially react with a radical initiator, or a spacer comprising 1-3 moieties Y that are bonded to the spacer through their nitrogen atom, wherein the ratio initiator/co-agent is less than 2, preferably less than 1.

The grafted polymer of the invention wherein R1 is hydrogen and P is a saturated polymer moiety connected through a methylene group with the 5-membered imide ring is formed by a recombination of a polymer radical that is formed by hydrogen abstraction from the saturated polymer, and a radical of group R1 when R1 is a methyl group, and that is formed by hydrogen abstraction from the methyl group. The selectivity of the reaction can be improved by the addition of a small amount of a stable nitroxile radical. Addition of a stable nitroxile radical effectively traps the aggressive alkyl radicals, especially methyl radicals that may be formed as part of the decomposition of the peroxide as a side reaction. Methyl radicals are known to be very efficient in adding to a double bond and by doing so, may initiate unwanted side reactions. The alkoxy radicals formed are not affected by nitroxile radicals, do not react with double bonds, and will only abstract hydrogen atoms. The polymer radicals will be formed by hydrogen abstraction when too much nitroxide is used, these polymer radicals will be trapped as well be forming alkyl nitroxides which are known to dissociate at high temperatures, and are known as so called initers. The amounts of stable nitroxide radicals would be less than 50 wt.% of the peroxide intake, preferably less than 20 wt.% of the peroxide intake and most preferably less than 10 wt.% of the peroxide intake.

It was found that this reaction did not lead to substantial amounts of oligomers and polymers, obtained by the further polymerization of the radical intermediate. Less than 10 wt.%, and usually less than 5 wt.% of such oligo- and/or polymers are comprised in the end product as a contaminant. Preferably, these contaminants comprise less than 2 wt.% of the product. It is also part of this invention to use the intermediate radical for making the grafted polymer of the instant invention. To this end the intermediate radical has the structure:

wherein R, R1 , and P have the previously given meanings.

The saturated polymer with a hydrogen donor that can be used for making the grafted polymers of the invention can be represented as P-H, wherein P stands for a saturated polymer moiety and H is the hydrogen donor. In principle any polymer P-H can be used, as long as a radical initiator can abstract the hydrogen donor, so as to obtain a polymer moiety P radical. Preferred polymers that are suitable in the present invention are selected from polyethylene, polypropylene, polybutylene, polyisobutylene, polypropylene glycol, silicon rubber, PVC, polystyrene, and copolymers thereof.

The radical initiators that can be used are the common radical initiators that are known in the art. Suitable initiators are peroxides and UV and daylight initiators. Examples of peroxides are hydrogen peroxide, ketone peroxides, diacyl peroxides, diallyl peroxides, peroxydicarbonate, hydroperoxides, peresters, perketales, (cyclic) peracetals, and the like. A suitable UV initiator is benzophenone, and halogens are suitable daylight initiators.

Group R1 in moiety X and co-agent moiety Y is preferably a methyl group, which leads to a maximum yield of desired product with a minimum amount of oligomeric or polymeric contaminants. The selection of group R in X and Y is not decisive for the present process. R is selected to control and direct the properties of the end product. Although group R in principle can be any group, it should not substantially react with the radical initiator, i.e. it should be stable under the reaction conditions used. A group R is considered to be stable, i.e. does not substantially react with the radical initiator, when the reaction rate of group R with the initiator is at least ten times less than the reaction rate of the initiator with the hydrogen donor of the saturated polymer. If R does not contain further groups X in the end product and further groups Y in the co-agent, the resulting polymer will be a grafted polymer without any cross-links. It is required to obtain a polymer with as low as possible cross-linking. Preferably, the cross-link density expressed as amount of cross-linked product as measured via gel formation is less than 2 wt.%, more preferably less than 1 wt.%, most preferably there is no gel formation at all.

Examples of co-agents R-Y are:

and the like.

Preferably, R is selected from hydrogen, alkyl, cycloalkyl, alkenyl, aryl, aralkyl, alkaryl, which may be unsubstituted or substituted with one or more carboxy, cyano, halogen, ester, oxirane, ether, nitro, alkoxy, alkylcarbonyl groups, or moieties with formula Y, wherein R1 is selected from methyl, ethyl, phenyl, and halogen. The synthesis of these co-agents is known in the art, and described in EP 495,545.

The polymerization reaction of the saturated polymer with a hydrogen donor in the presence of the radical initiator with the co-agent of the formula Y can be performed in any manner that is commonly used for radical polymerization reactions. A suitable manner, for instance, is to mix these ingredients and to heat the mixture, for instance for 1 to 3 min in an extruder. In another suitable manner the ingredients are dissolved in a solvent, heated, or irradiated with UV or daylight. The present method is advantageously used for controlled changing the properties of polymers. By the suitable selection of the co-agent soluble polymers, such as polyethylene, polypropylene, poly(iso)butylenes, polypropylene glycol, silicon rubber, etc. are modified by using bi- or multi-functional co-agents. Alternatively, these polymers can also be changed to soluble functionalized polymers by using mono-functional co-agents. In this manner apolar polymers can be rendered into polar polymers. Particularly, rheological properties of polymers can be changed by the present method by introducing long-chain branching into the polymer, thereby rendering the polymer from low-melt strength to high-melt strength. The present method of modification of polymers can also be used for increasing the paintability of polymers, such as polypropylene, polyethylene, and copolymers thereof.

The cross-link density of the composition expressed as the amount of cross-linked product as measured via gel formation (insoluble product) is limited to maximal 2 wt.%, preferably to maximal 1 wt.% or less, or not measurable.

The invention is further illustrated by the following Examples.

Example 1 10 g of PP Hostalen 0180P mol weight 180000 (polymer powder) were mixed at room temperature with 1 g of dicumylperoxide and 1 g of N-benzyl citraconimide (co-agent) using a mechanical stirrer. The mixture was heated in an oil bath that was already preheated to 220°C for 3 min with intimate mixing. The final reaction product was transferred partly into an NMR tube and dissolved/swollen in tetrachloro-ethane D-2 and analyzed at high temperature (~120°C) by DOSY NMR [D.A.Jayawickrama, C.K.Larive, E.F.McCord and D.C.Rose, Magnetic Resonance in Chemistry, 36, (1998) 755]. The NMR spectrum shows that a major part of the N-benzyl-citraconimide is grafted to the polymer. Example 2

10 g of PP Hostalen 0180P mol weight 180000 were mixed at room temperature with 1 g of dicumylperoxide and 1 g of N-benzyl citraconimide and 0.1 g of TEMPO (2,2,6,6-tetramethylpiperidinooxy free radical) using a mechanical stirrer. The mixture was heated in an oil bath that was already preheated to 220°C for 3 min with intimate mixing. The final reaction product was transferred partly into an NMR tube and dissolved/swollen in tetrachloro-ethane D₂ and analyzed at high temperature (~120°C) by DOSY NMR. The NMR spectrum shows that a major part of the N-benzyl-citraconimide is grafted to the polymer.

Example 3

1 kg of PP Hostalen 0180P mol weight 180000 was pre-mixed with 5 g of dimyristyl peroxydicarbonate (Perkadox 26), 0.5 g of TEMPO, and 10 g of metaxylylene biscitraconimide, and the mixture was fed in a twin-screw-extruder at 180-220°C with a rate of 40 g/min. The product was completely soluble in xylene (see method below). The modified polymer had a melt flow index of 2.5 g/10 min, and a melt strength of 2 cN.

Method of determining the cross-link density

The xylene-soluble part of polymer in cross-linked polymer gives a direct relationship to the degree of vulcanisation (cross-linking).

This method can also be extended to attain comparative results for filled or unfilled compounds, when: 1) the filler is unsoluble in xylene.

2) the quantity of filler in the compound is known.

3) the compound is sufficiently vulcanized so that migration of filler during the extraction is prevented. Apparatus

1. The extraction apparatus should be of the following general type: a) round 2 I quick-fit flask in which a maximum of 15 samples can be extracted in 1.5 I of solvent. b) fitting cover with 2 ground openings for reflux condensers. c) 2 reflux condensers. d) heating jacket for flask. e) stand with sufficient clamps.

2. Suitable equipment (scissors, punch}, to reduce the test samples to a maximum thickness of 2 mm and a maximum dimension of 2 x 2 x 1 mm.

3. lOO-mesh capper wire gauze.

4. Hot air oven.

5. Reagents: xylene p.A.; acetone, technically pure grade.

Procedure

Fundamentally, all determinations should be carried out in three-fold.

1. Preparation of the specimen holders a) Cut the copper gauze to the dimensions 4.5 x 7.5 cm. b) Fold the cut gauze along the middle. c) Fold in approx. 0.5 cm along two open edges. Clamp these securely to form a pouch for the test specimen.

2. Preparation of the specimen a) Reduce the sample to the afore-mentioned dimensions. b) Weigh the pouch before addition of specimen (= W1 , in mq). Add approx. 0.3 g to the pre-weighed pouch.

Weight of pouch + specimen (= W2, in mg). c) Close the remaining open side of the pouch by folding along the edge and clamp securely to form a basket. d) Weigh the closed basket (= W3, in mg). e) Secure the specimens on a wire, which is sufficiently long to be hung in the reflux condenser. Three samples per wire should be attached. 3. Extraction a) Set the samples attached to wire in the 2 I flask. b) Close the flask with the cover and draw the wires through the reflux condensers so that they can be hung respectively through the cylinders. c) Fill the 2 I flask with 1.5 I of xylene and check that all samples are adequately immersed. d) Position the heating jacket around the flask and heat the xylene until a good reflux is ensured. e) Extract for 16 hours.

4. Washing a) After extraction, let the flask cool before removing the wires singularly. b) Wash the samples in acetone in a 600 ml beaker immersing approximately 5-fold (time = 2 min).

5. Drying a) After washing, dry the samples 2 hours at 125°C in a hot air oven. b) Cool the samples. c) Weigh sample in holder (= W4, in mg) Note: If the substance is hygroscopic then it should be laid in a desiccator to cool.

6. Calculation

Soluble portion (S) = (loss in weight during extraction) x 100

(original weight of sample) - (weight of filler)

W3 -W4 x 100

(W2-W1) - F.(W2-W1)

W3-W4 x 100

(1-F).(W2-W1)

Cross-link density (%) = 100 - S

W1 = Weight of 100 mesh copper pouch with one side open. W2 = Weight of 100 mesh copper pouch + sample with one side open.

W3 = Weight of sample + 100 mesh basket, closed.

W4 = Weight of sample + 100 mesh basket after extraction and drying.

F = Proportion of the xylene insoluble filler in the polymer. e.g. 80 Polymer

20 Filler gives F = 0.25.

If the proportion of filler in the sample is unknown, then this can be determined by methods ASTM D 1603-76 or ASTM D 297-79.

Claims

Claims:

1. A grafted polymer having the formula R-X, X being:

wherein

2. The grafted polymer of claim 1 wherein R1 is methyl.

3. The grafted polymer of claim 1 or 2 wherein R is selected from hydrogen, alkyl, cycloalkyl, alkenyl, aryl, aralkyl, alkaryl, which may be unsubstituted or substituted with one or more carboxy, cyano, halogen, ester, oxirane, ether, nitro, alkoxy, alkylcarbonyl groups, or moieties comprising formula Y:

wherein: R1 is selected from methyl, ethyl, phenyl, and halogen.

4. The grafted polymer of any one of claims 1-3 wherein P is selected from polyethylene, polypropylene, polybutylene, polyisobutylene, polypropylene glycol, silicon rubber, PVC, polystyrene, and copolymers thereof.

5. The grafted polymer of any one of claims 1-4 wherein the cross-link density wherein the cross-link density expressed as the amount of cross-linked product as measured via gel formation is less than 1 wt.%.

6. A grafted polymer obtainable by reacting a saturated polymer with a hydrogen donor in the presence of a radical initiator with a co-agent of the formula R-Y, Y being:

wherein: R1 is selected from methyl, ethyl, phenyl, and halogen; and

Y is bonded at its nitrogen atom with group R, which is hydrogen or an organic radical that does not substantially react with a radical initiator, or a spacer comprising 1-3 moieties Y that are bonded to the spacer through their nitrogen atom, wherein the ratio initiator/co-agent is less than 2, and wherein the cross-link density expressed as the amount of cross-linked product as measured via gel formation is less than 2 wt.%.

7. A process for making the grafted polymer of claim 1 comprising the step of reacting a saturated polymer with a hydrogen donor in the presence of a radical initiator with a co-agent of the formula R-Y.Y being:

wherein:

8. The process according to claim 7 wherein the reaction step is performed in the presence of a nitroxide radical.

9. A method of converting a saturated thermoplastic polymer comprising a hydrogen donor to a saturated apolar polymer comprising a hydrogen donor to a polar polymer, or a saturated polymer comprising a hydrogen donor with a low-melt strength to a polymer with a high-melt strength, by applying the process of claim 7 or 8 to the saturated polymer comprising a hydrogen donor.