GB2106914A

GB2106914A - Multi stage graft polymerisation process

Info

Publication number: GB2106914A
Application number: GB08214853A
Authority: GB
Inventors: Joseph Michael Schmitt; Richard James Quinn
Original assignee: CY RO IND; Cy/Ro Industries
Current assignee: CY RO IND; Cy/Ro Industries
Priority date: 1978-09-18
Filing date: 1982-05-21
Publication date: 1983-04-20
Also published as: FR2455066A1; FR2491931A1; GB2106120A; GB2030154A; GB2106120B; FR2491930A1; GB2030154B; GB2107329A; GB2106914B; JPH02138323A; GB2107329B; DE2937718A1; FR2455066B1

Abstract

Non-agglomerating, readily-dispersible mixtures of grafted rubber are prepared by a series of grafting polymerization reactions in which one or more monomers is (are) grafted onto a rubber, the or each later said grafting reaction being performed in the presence of the products of the preceding grafting reaction or reactions, and, in Examples, of separately introduced rubber.

Description

1 GB 2 106 914 A. 1

SPECIFICATION

Preparing non-agglomerating grafted rubber It has been known to prepare thermoplastic molding compositions from various polymers and rubber latices by blending the polymers with the grafted rubber or by polymerizing the monomers used to produce the polymer in the presence of the rubber.

For example, U.S. Patent No. 3,354,238 discloses such a molding composition wherein the resinous phase is composed of methyimethacrylate, styrene and acrylonitrile, and the rubber phase is composed of polybutadiene grafted with methyl m ethacryl ate, styrene and acrylonitrile. Similarly, U.S. Patent No. 3,261,887 discloses a molding composition substantially identical to that of the above- discussed patent except that the acrylonitrile is omitted therefrom. Also, similarly, U.S. Patent No. 4,085,116 discloses molding compositions wherein the acrylonitrile has been replaced by ethylacryiate.

These products exhibit acceptable properties when utilized as colored molding compositions, but have deficiencies when used in the absence of a coloring agent. In their uncolored states the products 90 are not sufficiently transparent and, as a result, their use in such as packaging applications has been restricted.

Research has indicated that the optical properties of the molding compositions improve when the rubbery reinforcing elastomer, ie the polybutadiene phase in the above patents, is more uniformly distributed in the resinous polymer phase and the agglomerations of the elastomer, if any, are smaller than the wavelength of visible light. The smaller the agglomerations, the better are the optical properties.

While the wavelength of visible light is about 4000 to 7000 Angstroms and the polybutacliene previously used has generally had a diameter on the order of less than 2000 Angstroms, the resultant products have still not been entirely satisfactory due to relatively poor haze and gloss characteristics.

We have now discovered a new procedure for preparing the grafted rubber which leads to a non-agglomerating readily dispersible grafted rubberfrom which improved molding compositions may be prepared.

The method in accordance with the present invention comprises performing a series of grafting polymerization reactions, the or each later reaction being performed in the presence of the products of the preceding reaction or reactions.

Examples of the rubbers to which the present grafting method is applicable include such as poly- butadienes, poly(styrenelbutadienes), poly(methyl120 methacrylate / butadienes), polyisoprenes, polyisobutylenes, poly(isobutylene - isoprene) copolymers, poly(acrylonitrile 1 butadienes), polyacrylates, polyurethanes, neoprene, silicone rubbers, chlorosulfonated polyethylene, ethylene - propylene rub- 125 bers and other such rubbery materials.

Examples of monomers which may be grafted onto the rubber by the method of this invention include: acrylates, methaerylates, nitriles, styrenes, vinyl ethers, vinyl halides, and other similar mono- vinyl compounds. Particularly suitable monomers include methylacrylate, ethylacrylate, propylacrylate, methyl methaerylate, ethyl m eth acrylate, polymethacrylate, acrylonitrile, methacrylonitrile, styrene, a-methylstyrene, butyl vinyl ether, and vinyl chloride.

Preferably, the rubber is polybutacliene onto which is grafted methyl methacrylate and styrene, and optionally a third monomer selected from methy- lacrylate, ethylacrylate or acrylonitrile. Most preferably, the overall ratio of polybutadiene to said graft monomers ranges from 1: 1 to 6:1 by weight, with the graft monomers being used in a weight ratio of from 60 to 85 parts of methylmethacrylate, 15 to 30 parts of styrene and 0 to 15 parts of either methylacrylate, ethylacrylate or acrylonitrile.

In the preferred procedure of this invention, at least two graft stages are run in succession by the addition of the rubber and grafting monomers, followed by more rubber, and more grafting monomers. The grafting procedure used in each stage is either a rubber with equilibrated monomer, as in U.S. Patent 4,085,166, or a controlled addition of monomers as described in our co-pending Ap plication No. which, like the present applica tion, is divided out of Application No. 7926433 (hereafter the "SCAM" process for short. To the first stage graft product is added about 0.5-1.0% (based on second stage rubber latex weight) of a stabilizer such as potassium lauryl aryll sulfonate to ensure latex stability during the second stage polymerization. For further stages, further stabilizers may be added. The ratios of monomers, preferably methylmethacrylate, styrene and either methylacrylate, ethyl acrylate or acrylonitrile used in the individual grafting stages are the same as given above in the overall graft composition. The ratio of rubber to monomer in the individual grafting stages is bounded by the overall graft compositions given above, ie from 1: 1 to 6:1 by weight. The prime restriction on stage compositions is that each stage graft product by weight be at least as large as the earlier produced grafted rubbers. In a two stage system, the second stage preferably is at least 60% by weight of the product and most preferably, 65 to 95% by weight. When calculating the subsequent stage graft rubber product weight, the subsequent stage monomer are assumed to be equally distributed among the previous and new stage rubbers and the previous stage resin (graft monomer).

As already noted, in the method of this invention each stage may be either a conventional grafting process or a controlled addition of monomer (SCAM) process. Preferably, at least one of the stages is a SCAM process, and most preferably two stages are used with each being a SCAM process. While graftings may be done in a series of reactors, it has been found convenient to use a single reactor with the graftings done in succession.

If the SCAM procedure forms part of the grafting procedure of this invention, the monomer(s) being controllably added should be added over a period of at least 15 minutes, preferably at least 1 hour, and most preferably about 1 to 3 hours, with the grafting reaction occurring during the addition and prefer- 2 GB 2 106 914 A 2 ably allowed to continue thereafterfor about one hour. The initiatorwhich is preferably a redoxtype may be included in the reactor initially, it may be added simultaneously as the monomer being added either in the same stream or in a separate stream; or ultraviolet light may be used. Generally, the initiator is used in an amount up to about four times the standard amounts as used in U.S. Patent 4,085,166. When a redox initiator is to be controllably added, (as opposed to being in the reactor initially) either the oxidant or reductant portion may be placed in the reactor initially and only the other portion need be controllably added. The reaction is conducted at a pH range of about 6.0 to 8.5 and in the temperature range of about 20'to 65'C, though neither has been found to be critical to the present invention.

Examples of suitable redox initiator systems include: t-butyl hydroperoxide, cumene hydroperoxide, hydrogen peroxide or potassium persulfate-so- dium formaldehyde sulfoxylate-iron; hydroperoxides-tetra ethylene pentamine or dihydroxyacetone; hyd rope roxides-bisu Ifite systems; and other such well known redox initiators.

The rubber-to-monomer ratios of the graft polymerizations, be they conventional or SCAM, may be varied as desired to control the rubber-tomonomer ratios so as to produce the desired balance of properties in the final product. Hence, it is the desired final product which determines the actual ratios to be used in making the graft polymerizations. Generally, the rubber-to-monomer ratios should be in the range of 1: 1 to as high as 6: 1, with the lower ratio materials providing the better optical properties and the higher ratio materials the better physical properties. Preferably, one portion of the graft procedure has a rubber-to-monomer weight ratio of at least 2.5: 1, and the other less than 2: 1. Most preferably, one has a weight ratio of 2.5A to 4: 1, and the other from 1: 1 to 2: 1.

The procedure of the present invention provides a more intimate blending of different rubber-to-monomer ratio rubbery phases than was heretofore possible. Different rubber-to-monomer ratios are readily obtained even when the same ratio of rubber to monomer is added in each stage, due to the first grafted rubber being in the reactor when the next graft is performed.

For example, an intimate blend of a 3:1 and a 1: 1 rubber: monomer may be prepared from two 2:1 graftings as follows:

Graft 1 uses a total of three parts by weight reactants- 2 parts rubber and 1 part monomers to produce a 2:1 product. Thereafter, a second graft is performed using nine parts reactants - 6 parts rubber and 3 parts monomers -together with the first graft product. In the second graft, the new monomers will be attracted to the first product and the newly added rubber essentially in the ratio in which these are present in the reactor. Hence, in this example, 6/9 of the 3 parts newly added monomers will graft onto the new rubber, ie 6 parts rubber to 2 parts monomer- a 3:1 ratio, and 319 will graft onto the previous graft, ie 2 parts rubber to 1 part first monomers plus 1 part new monomer- a 1: 1 ratio.

Thus, the resultant mixed graft will contain 4 parts of a 1:1 graftand 8 parts of a 3:1 graftwhich are intimately admixed.

As has been indicated above, the graft rubbers obtainable by the method of this invention are useful in the production of molding compositions of improved properties. More specifically, and as described in our co-pending Application No. the present invention can produce grafted rubbers which when blended with a major proportion of a resinous polymeric phase, result in molding compositions in which there are present a large number of individual grafted rubber particles with essentially no agglomeration andlor aggregation of the rubber particles. The molding compositions therefore lead to molded products exhibiting improved optical properties and having reduced taste and odor characteristics.

The invention is illustrated by the Examples which follow and in which all parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1

A graft rubber composition is prepared by a two-stage grafting polymerization as follows:

A first grafted rubber composition is prepared by blending 100 parts of polybutadiene in latex form with 40 parts of methyl methacrylate and 10 parts styrene. The rubber to monomer ratio is 2 to 1. The monomers are then grafted onto the polybutadiene by a redox initiated polymerization using, based on monomer, 0.1 part of t-butylhydroperoxide, 0.23 part sodium formaldehyde sulfoxylate, 27 ppm ferric chloride. 6 H20 and 127 ppm ethylene diamine tetraacetic acid - 4 Na salt at room temperature of 1 to 5 hours.

The second graft is prepared by placing the first graft of above in a reactor, adding 6.7 g of potassium lauryl aryl sulfonate, and then blending in 300 parts of polybutadiene in latex form, 120 parts of methylmethacrylate, 30 parts of styrene, and the like amounts of the initiator system of above. The second rubber to second monomer ratio in this stage is 2: 1. The grafting reaction is run at room temperature for 1-5 hours with constant agitation.

In this example, the mixed grafted polybutadiene phase contains, by calculation, 1 part of a 1:1 graft for every 2 parts of a 3:1 graft wherein the grafts are intimately mixed. The overall rubber to monomer ratio is 2: 1.

As described in Example 1 of Application No.

supra, the resulting graft rubber can be blended with a 71.5123.515.0 methyl methacrylate l styrene 1 ethylacrylate terpolymer composition to provide molding compositions having superior optical properties as compared to a conventionally prepared product wherein the grafted rubber is prepared from a 3:1 rubber- to-monomer single stage reaction as disclosed in U.S. Patent No. 4,085, 166.

EXAMPLE2

A first grafted rubber composition is prepared by blending 325 parts of polybutadiene in latex form with 133 parts of methyl m ethacryl ate and 33 parts of styrene. The rubber to monomer ratio is 1.963: 1. The J# 1 3 GB 2 106 914 A 3 monomers are then grafted onto the polybutadiene by a redox initiated polymerization using, based on monomer, 0.33 part of t-butyihydroperoxide, 0.66 part of sodium formaldehyde sulfoxylate, 88 ppm ferric chloride. 6 H20, and 408 ppm of ethylene diamine tetraacetic acid 4Na salt at room temper ature overnight. The maximum exotherm was reached in 36 minutes. The solids content of the first stage is 45.1 %.

The first grafted product is placed in a reactor 75 along with. 17.48 parts of sodium lauryl aryl sulfon ate and then 1646 parts of polybutadiene in latex form (44.8% solids, 737 parts polybutadiene) and deionized water. The pH is adjusted to about 8.3 with 1.5% aqueous ammonia. To this is charged 56 parts of styrene with stirring and the equilibrating mixture is purged with nitrogen to provide a near oxygenfree atmosphere. Then 37 parts of sodium formaldehyde sulfoxylate chelate solution of the following is added:

96.25% deionized water 3.51% sodium formaldehyde sulfoxylate 0.19% ethyienediamine tetraacetic acid tetra sodium salt 0.04% % After five minutes and continuing the stirring, 222 parts of methyl methacrylate and 32.8 parts of tert-butyl hydroperoxide solution 1.7% t-butyl hydroperoxide and 98.3% deionized water are pumped into the reactor. The methyimethacrylate rate is 1.85 part per minute for 2 hours. The t-butylhydroperox- ide solution rate is 1.64 part per minute for 10 minutes, then 0.1367 part per minute for 120 minutes. The second rubber to second monomer ratio in this second stage is 2.666: 1. One hour after the monomer addition is completed the conversion to polymer is 98-99%. The final solids are about 47%.

In this example, the mixed grafted polybutadiene phase contains by calculation 1 part of a 1.13:1 graft for every 2 parts of a 4:1 graft which are intimately mixed. The overall rubberto monomer ratio is 2.451.

As described in Example 2 of Application No.

supra, the resulting graft rubber can be blended with methyl m ethacryl ate / styrene 1 ethylacrylate terpolymer (having the proportions indicated in Example 1 hereinabove), to give a molding composition of advantageous properties. EXAMPLES 3-6 The procedure of Example 1 is repeated except that in the second grafting polymerization 0.4 part of sodium formaldehyde sulfoxylate, 89 ppm ferric chloride. 6 H20 and 407 ppm ethylene diamine tetraaacetic acid -4Na are used and the first grafting polymerization is performed by a SCAM procedure as follows:

A graft rubber composition is prepared by charg- 125 ing 225 parts of polybutacliene latex (44.5% solids, parts of polybutacliene) and 25 parts of deio nized water to a reactor, and adjusting the pH to about 8.3 with 1.5% aqueous ammonium. To this is charged 10 parts of styrene with stirring and the 130 equilibrating mixture is purged with nitrogen to provide a near oxygen- free atmosphere. Then 6.6 parts of sodium formaldehyde sulfoxylate chelate solution of Example 2 is added. After five minutes 70 and continuing the stirring, 40 parts of methyl methacrylate and 4.69 parts of tert-butyl hydroperoxide solution (2.13% t-butyl hydroperoxide and 97. 87% deionized water) are pumped into the reactor. The methyl methacrylate rate is 0.6667 part per minute for 1 hour. The t-butylhydroperoxide solution rate is 0.235 part per minute for 10 minutes, then 0.0391 part per minute for 60 minutes.

The above procedure is repeated except that the styrene is pumped in together with the methyl80 methacrylate.

Examples 3-6 of Application No. supra, give properties of molding compositions prepared from the grafted rubbers obtained by these procedures.

EXAMPLE 7

A grafted rubber is prepared asfollows:

Afirst graft rubber composition is prepared by charging 151 parts of polybutadiene latex (44.8% solids, 67.65 parts of polybutadiene) and 19.5 parts of deionized water to a reactor and adjusting the pH to about 8.3 with 1. 5% aqueous ammonia. To this is charged 6.8 parts of styrene with stirring and the equilibrating mixture is purged with nitrogen to provide a near oxygen-free atmosphere. Then 4.48 parts of the sodium formaldehyde sulfoxylate chelate solution of Example 2 is added. After five minutes and continuing the stirring, 27.1 parts of methyl meth acryl ate and 10 parts of tert-butyl hydroperoxide solution (0.678% t-butylhydroperoxide and 99.322% deionized water) are pumped into the reactor. The methyl methacrylate rate is 0.3985 part per minute for 66 minutes. The t-butyl hydroperoxide solution rate is 0.5 part per minute for 10 minutes and then 0.0833 part per minute for 60 minutes. The rubber to first monomer ratio is 2: 1. This product is about 46% solids.

To the first grafted product are added 18.5 parts of a 23% aqueous solution of potassium iauryl aryl su Ifonate and 36 parts of deionized water with stirring, then 453 parts of polybutadiene latex (44.8% solids, 203 parts of polybutacliene). The pH is adjusted to about 8.3 with 1.5% aqueous ammonia. To this is charged 20.3 parts of styrene with stirring and the equilibrating mixture is purged with nit- rogen to provide a near oxygen-free atmosphere. Then 13.4 parts of sodium formaldehyde sulfoxylate chelate solution of Example 2 is added. After five minutes and continuing the stirring, 81.2 parts of methyl m eth acryl ate and 10 parts of t-butyl hyd- roperoxide solution (2.03% t-butyl hydroperoxide and 97.9% deionized water) are pumped into the readtor. The methyl methacrylate rate is 1. 3533 part per minute for 1 hour. The t-butyl hydroperoxide rate is 0.5 part per minute for 10 minutes, then 0.033 part per minute for 1 hour. The second rubber to second monomer ratio in the second stage is 2: 1. The final solids are 47.5%.

In this Example the mixed grafted polybutacliene phase contains by calculation 1 part of a 1:1 graftfor every 2 parts of a 3:1 graftwhich are intimately 4 GB 2 106 914 A 4 mixed. The overall rubber to monomer ratio is 2A.

The advantageous properties of a molding composition prepared from the graft rubber of this Example can be seen from Example 7 of Application No. , supra.

EXAMPLEB

The procedure of Example 7 is repeated except thatthe first rubberto first monomer ratio is 1.963:1 and the second rubberto second monomer ratio is 2.666: 1. Therefore, the mixed polybutadiene phase contains, by calculation, 1 part of a 1.13:1 graftfor every 2 parts of a 4:1 graft which are intimately mixed. The overall rubber to monomer ratio is 2.45A.

Example 8 of Application No. supra, 80 gives properties of a molding composition prepared from the graft rubber obtained by this procedure.

EXAMPLE 9

The procedures of Examples 1-7 were repeated, except that the ethylacrylate in the resin portion is 85 replaced by methylacrylate. Similar results are observed.

EXAMPLE 10

The procedures of Examples 1-7 are repeated except that the ethylacrylate in the resin portion is omitted and the ratios of the monomers is varied to compensate for the resultant change in refractive index. Similar results are noted.

EXAMPLE 11

The procedures of Examples 1-7 are repeated except that the polybutadiene latex is replaced by a polyisaprene latex, and the monomer ratios in both the graft and the resin phases are varied to compensate forthe difference in the rubber refractive index.

Comparable results are achieved.

EXAMPLE 12

The procedures of Examples 1-7 are repeated except that 3 parts of methyl m eth acrylate on the graft polymerizations are replaced by 3 parts of

Claims

ethylacrylate. Similar results are observed. CLAIMS

1. A method of preparing a non-agglomerating, readily-dispersible mixture of grafted rubber, which comprises performing a series of grafting polymerization reactions in which one or more monomers is(are) grafted onto a rubber, the or each later said grafting reaction being performed in the presence of the products of the preceding grafting reaction or reactions.

2. A method according to Claim 1, wherein at least one of the grafting polymerizations is conducted with a controlled addition of monomer over a period of at least 15 minutes during which time the graft polymerization occurs.

3. A method according to Claim 1 or Claim 2, wherein the grafting polymerization is conducted in two stages.

4. A method according to any preceding claim, wherein said rubber is polybutadiene.

5. A method according to any preceding claim, wherein methylacrylate, styrene and, optionally, a monomer selected from methacrylate, ethylacrylate and acrylonitrile are grafted onto said rubber.

6. A method according to Claim 5, wherein the weight proportions of said grafted monomers are 60-80 parts of methyl methacrylate, 15 to 30 parts of styrene and 0-15 parts of said optional monomer.

7. A method according to any preceding claim, wherein the rubber-tomonomer ratio is from 1:1 to 6:1 by weight.

8. A method according to Claim 7 when dependent upon Claim 3, wherein two stages of grafting are used to form a mixture of two rubbery phases, one of the rubbery phases having a rubber-to-mo- nomer ratio of at least 2.5:1 by weight while the other of said rubbery phases has a rubber-to-mo nomer ratio of less than 2.0:1 by weight, wherein the rubbery phase having the higher rubber-to-monom er ratio is present in excess of the one having the lower rubber-to-monomer ratio.

9. A method according to Claims 2-8, wherein both stages of the grafting polymerization are con ducted with a controlled addition of monomer over a period of at least 15 minutes, and wherein the monomer being controllably added is methyl methacrylate.

10. A method according to Claim 9, wherein said controllable addition is over a period of at least 1 hour.

11. A method according to Claim 9 or Claim 10, wherein, during said controllable addition, a pH of from 6-8.5 and a temperature of from 20-65'C are used.

12. A method according to Claim 2, or anyone of Claims 3-11 when dependent upon Claim 2, wherein a redox initiator is used and eitherthe reductant or the oxidant portion of the initiator is controllably added atthe same time as the monomer which is controllably added.

13. A method of preparing a non-agglomerating, readily-dispersible mixture of grafted rubbers, according to Claim 1 and substantially as described in any one of the Examples herein.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1983. Published at the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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