CA2028784A1 - Basic functionalized polyethylene - Google Patents

Abstract

Abstract of Disclosure Basic functionalized polyethylene has been produced, by melt grafting of polyethylene with a monomer selected from vinyl pyridines allyl ureas and amino methacrylates such as secondary and tertiary alkyl amino ethyl methacrylates in the presence of a peroxide initiator. The grafted polyethylene can be melt blended with various maleic anhydride modified polymers to produce composites having superior properties.

Description

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Field of Invention This invention relates to the production of functionalized polymers and more particularly to the production of basic functionalized polymers such as polyethylene and polymer blends containing the same.

Backqround of Invention Functionalization of commercially available polymers has been recognized as one route to obtaining new kinds of macromolecules. Such modified polymers containing functional groups are used as adhesives and for blending to obtain composites, including polymer blends and alloys, with improved properties. Heretofore, most such functional groups have been acidic in nature and very few basic functionalized polymers have been produced. Amine terminated nylon and polystyrene with oxazoline groups (OPS) are among the few commercially available basic functional polymers. OPS has been used in reactive blending with polyethylene containing carboxyl groups to obtain polymer alloys with improved mechanical properties.

Grafting reactions have been extensively used to obtain acid functionalized polyolefins containing controlled amounts of reactive groups. On a reduced scale basic :
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functionalized polyolefins can be obtained by grafting of amino monomers. Modified chlorinated rubber can be obtained by grafting it with ethyl ll-aminoundecanoate in toluene solution and recently basic: functionalized ethylene-propylene rubber (EPR) with amino groups has been prepared by grafting 2-dimethyl amino ethyl methacrylate ~DMAEMA) onto EPR in a solution of chlorobenzene using dicumyl peroxide as an initiator. Heretofore it has not been possible to produce basic functionalized polymers in a melt although direct functionalization of molten polymers has considerable economic advantages over solution grafting reactions since production of a functional polymer can be carried out in an extruder without the re~uirement of an entirely new facility and, further, the costs of solvent recovery are eliminated.

Object of Invention It is, therefore, an object of the present invention to provide a process for preparing basic functionalized polymers in a melt.

Another object of the invention is to provide novel basic functionalized polymers.

Statement of Invention Thus by one aspect of this invention there is provided a method for preparing basic functionalized polyethylene polymers comprising mixing particulate linear low density polyethylene with a selected c~ount of a monomer selected from vinyl pyridine allyl ureas and secondary and tertiary alkylamino methacrylate and a peroxide initiator; heating said mixture to a temperature up to about 275 and preferably in the range 90C-190C in a mixer-extruder and intensively mixing for a selected time so as to produce a grafted polyethylene product containing up to about 3.0 wt %
of said monomer.

By another aspect of this invention there is provided a basic functionalized polyethylene having a monomer selected from vinyl pyridine, alkyl ureas and secondary and tertiary alkyl amino methacrylates grafted thereto.

By yet another aspect of this invention there is provided a composite polymer comprising a polymer having maleic anhydride grafted or copolymerized herewith and having up to about 50% by weight of a basic functionalized polyethylene polymer substantially completely miscibly blended therewith.

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Brief Description of Drawinqs Fig. 1 is graph illustrating variations of the degree of grafting, DG, and monomer conversion x, with the average reaction temperature at 6 minutes reaction time; 40g LDPE, 12g DMAEM~ and 0.6g L130;

Fig. 2 is a graph illustrating variations of torque TQ
and temperature T with reaction time for Run HB-6 at 85C;

Fig. 3 (a) is an electron micrograph 2,500X of a 30/70 blend of PE 5105/S-MA;

Fig. 3 (b) is an electron micrograph 2,5Q0 X of a 30/70 blend of G-PE5101/S-MA;

Fig. 4 (a) is an electron micrograph 2,500 X of a S0/50 blend of PE5105/S-MA;

Fig. 4 (b~ is an electron micrograph 2, 500 X of a 50/50 blend of G-PE5101/S-MA; and Fig. 4 (c) is an electron micrograph 20,000 X of a 50/50 blend of G-PE5101/S-MA.

Detailed Description of Preferred Embodiments It has been found that vinyl pyridines, allyl ureas and secondary and tertiary alkyl amino methacrylates can be ., . . ~ .

v grafted to linear low density polyethylene (LLDPE) in the melt in the presence of an initiator and that the resulting functional pol~mer is one oE the rare examples of a saturated hydrocarbon based polymer containing a small number of basic sites.

Example 1 Production of grafted LLDPE.

Materials: linear low density polyethylene, supplied by Esso Chemical Company Canada under the trademark ESCORENE, was employed. ESCORENE 5101 is an ethylene-butene copolymer with a density of 0.9225g/Cm3, a melt flow index of 4.2 g/10-min, a weight average molecular weight of approximately 85,000 and an Mw/Mn of about 4. Proton NMR analysis indicated a comonomer content of 3.6 mol% butene. About 150 ppm of hindered phenol antioxidant was also present.

For the experiments described below 2-(dimethylamino) ethyl methacrylate (DMAEMA), Aldrich reagent grade was used as the monomer.

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An initiator selected from: Lupersol R 130 (L130), obtained from Pennwalt Corp., as a 90 wt % solution of 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3; Benzoyl peroxide (BPO) Fisher reagent grade; cumene hydroperoxide (CPO);
tert-butyl hydroperoxide (TBHPO) and tert-butyl peroxide tTBPo) obtained from Matheson Coleman & Bell Company, was employed as noted below.

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Methods 40g of LLDPE was mixed with preweighed quantities of DMAEMA and a selected initiator and fed in a preheated 65ml Haake Buchler Rheomix 600 mixer and allowed to react for a selected ,time at 100 rpm and at different selected temperatures.

Grafting reactions were carried out at different set temperatures using Lupersol 130 as initiator. Chemical grafting was confirmed by the following purification and characterization techni~ue. The reaction product was removed from the mixer and dissolved in refluxing toluene ~BDH, reagent grade) at a maximum concentration of 4% w/v.
The product was precipitated dropwise, with stirring, in 10 volumes of methanol (BDH, reagent grade), filtered, stirred with more methanol, refiltered, and dried in a vacuum oven at 80 for several days.

The DMAEMA content.of the purified graft polymer was obtained using FTIR and confirmed with proton NMR. the reaction conditions and the grafting results are summarized in Table 1.
The influence of reaction temperature on the degree of grafting is shown in Fig. 1. In general, the DG for the reactions completely carried out in the melt state ~ ~b G,~

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(temperature greater than 100C) increases with increasing temperature until at about 140C and then decreases slightly as temperature is further increased. Grafting may be accomplished at temperatures up to about 275 but at such temperature excessive degradation and homopolymerization may occur. The preferred temperature range is therefore 90-190 and more particularly 100-160.

The degree of grafting depends on both the number of grafts and the graft length. The degree of grafting increased with increasing temperature in the lower temperature range (Fig. 1) because larger number of grafts were produced at higher temperature for the same reaction time. The degree of grafting probably decreased with increasing temperature in the high temperature range because faster chain termination at high temperature led to short graft length. This explains the maximum shown in Fig. 1.

Reaction runs carried out at temperature below 100C
are complicated because the reacting system changed from one physical state (powder) to another state (melt) during the reaction period. High grafting degree was obtained for Run HB-6 at a set temperature of 85C. Thus, the reaction of Run HB-6 progressed in powder state first. After about 4 minutes, the polymer began to melt after the temperature r?g ~

increased above 93C. The beginning of the polymer melting is indicated by the dramatic increase in torque as shown in Fig. 2. Fig. 2 also shows that the temperature increased aftPr the polymer is melted. The increase in temperature may be a result of viscous dissipation or possibly the polymerization reaction heat.

During the first 4 minutes, the reacting system is in the powder state. The LLDPE powder was swollen wit~ DMAEMA
monomer at the relatively high temperature. The monomer swollen LLDPE powder can be a good environment for polymerization. The gel effect will be significant which will increase the graft length and lead to higher grafting degree. This gel effect may also enhance crosslinking of the polymer as indicated by the lower melt flow index of the grafted LLDPE obtained from this run (Table 1). The monomer swollen LLDPE powder shows a lower than expected melting point as the low molecular weight monomer likely serves as a plasticizer. Independent experimental test has shown that the LLDPE can be dissolved in hot DMAEMA. This may explain why the reacting system began to melt at about 93C which is far below the melting point (120C). Grafting occurring on the surface of the LLDPE powder may also make some contribution to the degree of grafting obtained.

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The degree of grafting is determined both by the number of grafts on PE backbone and by the graft chain length.
Note that reaction temperature increased with time. The decrease in DG after 4 minutes can be a result of degradation of longer grafts which were formed at lower temperature. During this degradation period, the degree of grafting decreased from the maximum value of about 4% to about 2%. This suggests that graft length has decreased to half of its original length. Oxygen may play an important role in the degradation of the polyDMAEMA side chains since the reactor used in this study is open to the air. After about 10 minutes as the reaction temperature became relatively constant, the graft length remains the same and the number of grafts (and thus DG) increases slowly with time.

During the reaction, monomer is converted either to grafts on the LLDPE backbone or to homopolyD?MAEMA. The fraction of the monomer converted to grafts on the PE
backbone, based on the total converted monomer, is an indication of how efficient the grafting polymerization is and is defined as grafting efficiency (GE). The GE
decreases rapidly at first and then levels off. Most of the grafts are obtained during the initial reaction period.

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Example 2 Influence of different initiators.

Five organic peroxides were used in this investigation.
The half-life times of the peroxides used range from 0.1 to 1500 minutes. Two levels of initiator concentration were used for each initiator. All grafting reactions were carried out at set temperature of 160C for 6 minutes. The reaction conditions and results are summarized in Table 2.

As can be seen, the monomer conversion increased with increasing half-life time of the initiators. The grafting efficiency decreased slightly with increasing half-life time for initiators with tl/2 above 16 minutes at 160C.

The organic peroxides used in these reactions were designed to initiate grafting rather than oxidizing DMAEMA
monomer. The brown color of the reaction product can be taken as an indication of oxidization of DMAEMA by peroxide initiators. The shorter the tl/2 of a peroxide, the stronger the apparent oxidizing effect of the peroxide. TBPO
has the shortest tl/2 of the peroxides used in this study.
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consumed in the oxidization side reaction and more was utilized in initiating polymerization and grafting of the monomer. This is consistent with the observation that the monomer conversion increases with increasing t1/2 of the initiators.

Example 3 The procedures of Example 1 were repeated using two different monomers, butyl amino ethyl methacrylate (BAEMA) and allyl urea in place of DMAEMA. The monomers were reagent grade from Pflat3and Bauer, and Aldrich respectively. The polyethylene was the same Escorene and the initiator was Lupersol 130 used at a concentration of from 0.005 to 0.011 gm/gm of polyethylene. The grafting reactions were conducted in the same Haake Buchler Rheomix 600 mixer at 160C. For the butyl amino ethyl methacrylate the degree of grafting was 3.1% and the grafting efficiency was 35% while for the allyl urea the degree of grafting was observed to be 1.2% and the grafting efficiency was 100%.

Example 4 Production of styrene-maleic anhydride (SMA) copolymer blends with polyethylene or DMAEMA grafted polyethylene.

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Dylark R 132, crystal grade, a styrene-maleic anhydride copolymer containing about 6% maleic anhydride was employed as the styrene phase. The polyethylene phase was selected from ~a) Escorene R 5101, a linear low density polyethylene with a melt index of 5 grams/10 min, (b) Escorene R 5105, a similar polymer having a melt index of 1 gram/10 min and (c) a DMAEMA grafted polyethylene produced as in Example 1 from Escorene 5101 and having a melt index of about 2 grams/10 min. (G-PE) Samples containing 10%, 30%, and 50~ by weight of the polyethylene phase (the remainder Dylark 132) were prepared by melt blending premixed powders in a Rheomix 600 mixer at 190C and 100 rpm for 10 minutes. Fournier transform infrared (FTIR) analysis and differential scanning colorimetry (DSC) was performed on all samples. Sample morphology was observed using a JEOL 840 scanning electron microscope (SEM). Subsequent to freezing under liquid nitrogen and fracture, the samples were coated with a thin film of gold to prevent charging. Blends were examined at 2,500, 10,000 and 20,000 X magnification using an accelerating voltage of 10 keV.

Grafting of DMAEMA on PE 5101 resulted in a decrease in melt index, so control samples of PE 5105 whose melt index .,., ~ . :

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is more comparable to that of the grafted material were also studied.

No torque or temperature rise of the melt was observed during blending either reactive (DMAEMA-grafted) or non reactive polyethylene ~PE 5101 or PE 5105) with the Dylark 132. This implies that little or no covalent bonding has taken place during processing of the samples.

The DSC scans for the blends of the G-PE with the S-MA
did not differ significantly from those of the blends containing PE 5101 or PE 5105 in the polyethylene phase.
Similarly, the FTIR spectra of the blends were only the sum of the two blend components. No shifts of the peaks to different wavenumber or change in their relative intensity was observed. The spectra of the blends containing DMAEMA
grafted polyethylene were very "busy", however, and the difficulty of obtaining sufficiently thin films meant that only major changes in the spectra could have been detected.

Therefore, the behaviour of the melt blends during processing, the thermal analysis data, and the infrared spectra do not indicate any significant difference between blends of S-MA with PE 5101 or PE 5105, and those containing the DMAEMA grafted polyethylene.

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In contrast to the preceding methods, scanning electron microscopy revealed that grafting of 2.5 wt% of DMAEMA onto PE 5101 results in a dramatic improvement in compatibility with S-MA. Figures 3 a and b show the micrographs obtained for blends containing 30% by weight of the polyethylene phase, at a magnification of 2,500 times. Figure 3a shows the morphology for a blend of PE 5105 with S-MA, while figure 3b is a micrograph of a blend of the G-PE with the same S-MA copolymer. In the blend containing the non reactive polyethylene, there is a wide distribution of sizes of the phase-separated polyethylene regions, with many of them over 10 microns in diameter. Clearly, the DMAEMA - :
grafted polyethylene is much more compatible with the styrene phase, in that it is distributed uniformly throughout in domains seldom over 1 micron in diameter.
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Similar behaviour is exhibited by the blends containing 50% by weight of the polyethylene phase, shown in figure 4.
Figure 4a shows that the non reactive PE 5105/S-MA blend possesses a co-continuous two-phase morphology. The blend of S-MA with the DMAEMA grafted PE 5101 shown in figure 4b does show phase separation, but the si2e of the domains of the dispensed phase is greatly reduced. The difference in the type of fracture obtained for the two blends is also significant. AS can be seen in Figure 4a, the non-reactive blend could only be broken along the boundaries of the co-continuous phases. However, the fracture of the blend containing the G-PE appears to have occurred right through the phase boundaries.

It is believed that the improvement is compatibility observed and the change in behaviour during fracture can be attributed to improved adhesion between the polyethylene and polystyrene phases brought about by chemical interaction between the acidic anhydride groups in the polystyrene phase and the basic DMAEMA groups grafted onto the polyethylene.
This is supported by the observation under high magnification of a "corona"-like structure around some of the regions of DMAEMA-grafted polyethylene in the SEM
micrographs, which was not observed in the non-reactive blends, as well as the fracture behaviour of the 50 wt %
polyethylene phase blends. Figure 4c, which is an enlargement of the micrograph in figure 4b to 20,000 times magnification, shows the corona structure.

While the invention has been illustrated by reference to styrene-maleic anhydride copolymer blends with DMAEMA
grafted polyethylene, it will be appreciated that the invention is not limited to this particular series of blends. As previously noted the monomer grafted to the ~, . . . . . . .

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polyethylene may be selected from vinyl pyridine, allyl ureas and secondary and tertiary alkyl amino methacrylates.
A particularly suitable monomer is t-butyl amino ethyl methacrylate.

The polymer blended with the grafted polyethylene is preferably a polymer having maleic anhydride grafted to or copolymerized therewith or acrylic acid copolymerized ~ -therewith such as styrene-maleic anhydride copolymer or acrylonitrile butadiene acrylic acid terpolymer, but alternative polymers include graft copolymers in which maleic anhydride is grafted onto polypropylene, polystyrene, acrylonitrite-butadiene styrene polymer or ethylene vinyl acetate copolymers. ;~

Claims (19)

1. A method for preparing basic functionalized polyethylene polymers comprising mixing particulate linear low density polyethylene with a selected amount of a monomer selected from vinyl pyridine allyl ureas and amino-methacrylates and a peroxide initiator;

heating said mixture to a temperature up to about 275° in a mixer-extruder and intensively mixing for a selected time so as to produce a grafted polyethylene product containing up to about 3.0 wt % said monomer.

2. A method as claimed in claim 1 wherein said mixture is heated to a temperature between 90° and 190°.

3. A method as claimed in claim 2 wherein said monomer is selected from secondary and tertiary alkyl amino ethyl methacrylates.

4. A method as claimed in claim 3 wherein said monomer is selected from 2-(dimethylamino) ethylmethacrylate, methylamino ethyl methacrylate, and t-butyl amino ethyl methacrylate.

5. A method as claimed in claim 4 wherein said temperature is in the range 100°C-140°C.

6. A method as claimed in claim 4 wherein said peroxide initiator is selected from the group consisting of 2,5-di(t-butyl-peroxy) hexyne-3, cumene hydroperoxide, tert-butyl hydroperoxide and tert-butyl peroxide.

7. A method as claimed in claim 3 wherein said monomer is t-butyl amino ethylmethacrylate.

8. A method as claimed in claim 7 wherein said intensive mixing is effected in a twin screw extruder.

9. A basic functionalized polyethylene polymer having a monomer selected from vinyl pyridine allyl ureas and amino methacrylates grafted thereto.

10. A polyethylene polymer as claimed in claim 8 containing up to about 3.0 wt % of methacrylate selected from secondary and tertiary alkyl amino ethyl methacrylates.

11. A polyethylene polymer as claimed in claim 10 wherein said ethyl methacrylate is selected from 2 methylamino ethyl methacrylate, 2 (dimethylamino) ethyl methacrylate and t-butyl ethyl methacrylate.

12. A polyethylene polymer as claimed in claim 10 wherein said ethyl methacrylate is melt grafted to said polyethylene.

13. A polyethylene polymer as claimed in claim 11 containing up to about 3.0 wt % of t-butyl amino ethyl methacrylate.

14. A polyethylene polymer as claimed in claim 13 wherein said t-butyl amino ethyl methacrylate is melt grafted to said polyethylene.

15. A composite polymer comprising a polymer having maleic anhydride grafted to or copolymerized therewith and up to about 50%, by weight of said composite, of a basic functionalized polyethylene polymer substantially completely miscibly blended therewith.

16. A composite polymer as claimed in claim 15 wherein said basic functionalized polyethylene polymer comprises linear low density polyethylene containing up to about 3.0 wt % of a melt grafted monomer selected from vinyl pyridine, allyl ureas and secondary and tertiary alkyl amino methacrylates dimethly is a tertiary/secondary alkyl amino eltyl methacrylates.

17. A composite polymer as claimed in claim 16 wherein said melt grafted monomer is a secondary or tertiary alkyl amino ethyl methacrylate.

18. A composite polymer as claimed in claim 17 wherein said amino ethyl methacrylate is selected from 2 methyl amino ethyl methacrylate, 2(dimethyl amino) ethyl methacrylate and t-butyl amino ethyl methacrylate.

19. A composite polymer as claimed in claim 18 wherein said amino ethyl methacrylate is t-butyl amino ethyl methacrylate.