WO1996034024A1

WO1996034024A1 - Modified polyolefins

Info

Publication number: WO1996034024A1
Application number: PCT/GB1996/001026
Authority: WO
Inventors: Anthony Francis Johnson; Malcolm William Reid Brown
Original assignee: University Of Bradford
Priority date: 1995-04-28
Filing date: 1996-04-29
Publication date: 1996-10-31
Also published as: GB9508740D0; AU5653996A

Abstract

A method of preparation of a graft propylene polymer functionalised with an isocyanate group comprising the steps of mixing in the melt or solid phase a mixture of a propylene polymer, a radical initiator and α, α'-dimethyl-1,3-isopropenyl benzyl isocyanate, and extruding the mixture to form a graftable macromer.

Description

MODIFIED POLYOLEFINS

This invention relates to preparation of polyolefins which are functionalised with isocyanate groups, particularly but not exclusively to polyolefins with blocked isocyanate functionality. The invention also relates to the modified polyolefins and to products made from such polymers.

Polyolefins such as polypropylene are non-polar polymers which are usually partially crystalline. Although these materials have a large number of uses, a major disadvantage for many applications is their poor adhesion to other materials such as glass fibres, metals, polar polymers, printing materials and dyes. Polar compounds for example for maleic anhydride, acrylic acid and vinyl silanes have been grafted with polyolefins. Grafting reactions may be carried out by various methods but use of a continuous melt reactor or extruder is preferred commercially. A modified polyolefin may be obtained by feeding a polyolefin, polar monomer and an organic peroxide into the extruder. The resulting mixture is extruded at a temperature higher than the melting point of the polymer.

Grafted polymers derived from isopropenyl-α, a ' - dimethylbenzyl isocyanate (TDI) are disclosed in US-A-5231137. Polypropylene cografts with methyl methacrylate prepared by refluxing with polypropylene, TDI and a peroxide initiator are also disclosed. This process resulted in a copolymer of TDI and methylmethacrylate, which copolymer is then reacted with the polypropylene under reflux. Grafting of a polypropylene homopolymer of propylene-polyolefin copolymer is not disclosed.

According to a first aspect of the present invention a method of preparation of a graft propylene polymer functionalised with an isocyanate group comprises the steps of: mixing in the melt or solid phase a mixture of a propylene polymer, a radical initiator and an isocyanate for formula (1) ,

wherein R_x, R₂, R₃ and R₄ are independently cyclic, straight or branched chain alkyl or alkylene groups optionally containing nitrogen, oxygen, sulphur or phosphorus heteroatoms, m is an integer between 1 and 10 and n is an integer between 1 and 100; and extruding the mixture to form a graftable macromer.

The isocyanate (1) has the advantage that it is sterically blocked and does not homopolymerise under the conditions of the grafting reaction. The isocyanate gives a blocked functionalised polymer which is thermally reactive but which does not react with water.

A preferred isocyanate is a, a' -dimethyl-1,3 -isopropenyl benzyl isocyanate (also referred to as dimethyl meta- isopropenyl benzyl isocyanate or TMI) (2) .

TMI

The propylene polymer of this invention may comprise a homopoly er, copolymer with ethylene or other alpha olefin having the formula H₂C=CHR wherein R is an alkyl radical comprising 1 to 10 carbon atoms. Preferred alpha olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-l- pentene, 1-heptene, 1-octene and 1-decene. Conjugated dienes may be employed. However, this invention also extends to terpolymers, and multi-component polymers incorporating non- conjugated polyenes in which at least one component has an active methine proton, such as that which stems from propylene monomer.

The isocyanate functionalised propylene polymer of the present invention is characterised in being dyeable, printable or paintable although the mechanical properties of the unmodified polymer may be substantially retained.

According to a second aspect of the present invention a dyeable, printable or paintable polymer composition comprises a graftable monomer of formula (3) ;

CH₂=C(CH₃)R₁-C(R₃) (R -U-P (3)

wherein R_, R₂, R₃ and R₄ are as defined above;

U is an urethane or urea group; and

P is a propylene polymer with a molecular weight between 100 and 1000.

A preferred macromer resultant from use of the isocyanate (2) has the formula (3) wherein R₃ and R₄ are both methyl groups. P is any polymer group which might be attached to TMI through a reaction with the NCO group. For blending purposes the preferred group has a molecular weight in the range 100 - 1000, and this stems from the reaction of TMI with appropriate non-functionalised oligomers of the general structure shown in X-R-X where X is a reactional functionalised group such as - OH,-NH₂ or other reactive group. R may be an aliphatic aromatic .

Hitherto polypropylene has been notoriously difficult to dye, making it necessary to use pigments.

Introduction of functionality into a propylene polymer in accordance with this invention confers a wide range of advantages. Blending with polar materials is facilitated. For example blends with ethylene-vinyl alcohol copolymers have been prepared. It has been found that although- the domain sizes of unfunctionalised polypropylene blends with ethylene-vinyl alcohol copolymers are coarse (30 to 40 microns) , blends in accordance with the invention may have domain sizes of 5 microns or less, preferably 2 or less. Yarns and filaments may be prepared. Printable films and other packaging materials including printable or recyclable gas impermeable thermoplastic barrier materials may be prepared. Materials in accordance with this invention may be formulated with fibre reinforcing agents for example glass or carbon fibres. Cross linked polypropylene compositions may also be prepared.

In accordance with preferred aspect of the present invention there is provided a method of controlling molecular weight degradation of a polyolefin during extrusion comprising the step of addition of an effective amount of an isocyanate of formula (1) .

Peroxide induced molecular weight degradation of polypropylene has caused difficulties during reactive extrusion. A compound (1) , preferably TMI (2) can be used to moderate peroxide induced degradation to give products with desired molecular weights and molecular weight distributions.

Use of an amount of 0.1 to 4% of TMI is preferred. The addition of TMI and peroxide the extruder in a pulsed manner has been found to be particularly efficacious. This method of controlling degradation is particularly amenable to automatic control. Controlled degradation is already in commercial use and use of a compound (1) preferably TMI may extend the range and utility of existing commercial processes.

The polyolefin which may be employed in accordance with this invention may comprise a homopolymer of a C_: - C₄ alkene, for example ethylene, propylene. Use of polypropylene copolymer or copolymers as described above is preferred.

Classical organic chemistry (Wood, TCI Polyurethanes; 2nd Ed, 1990) could be used to convert the isocyanate group into a range of different organic groups such as alcohols, acids, amines, thiols etc by reacting the isocyanate with compounds such as ammonia, diamines, diacids, diols, triols and others as appropriate.

The invention is further described by means of example but not in any limitative sense.

In the following examples an APV2030 30 mm diameter screw, 40:1 L/D co-rotating twin screw extruder was employed. The extruder was instrumented to make in-line measurements of the die pressure and the torque of the extruder.

Polypropylene pellets, KY6100 (Shell Chemicals) with MFI=3.0 at 230^*C were employed.

EXAMPLE 1

Peroxide (Trigonox 101 added as polypropylene master batch, containing 7.5% w/w) was fed into the extruder at the hopper. The TMI was injected into a sealed zone down the barrel and a nitrogen blanket was placed over the hopper. The apparatus was run with a screw speed of 250 rpm.

The temperature profile of the extruder was as follows (zone 1 = hopper, zone 6 = die) .

Table 1

Zones 1 2 3 4-5 6-7 8-13 14 15 16

Temp/^*C 40 73 135 185 200 220 200 180 180

Various peroxide and TMI concentrations were used. The dye pressure and torque measurements during the process were used to monitor changes in the material during processing. Increases in both die pressure and torque were observed on addition of TMI to the peroxide/polymer system. These are shown in Figure 1. Figure 1 illustrates reactive grafting of polypropylene using in-line rheometry with 0.07% peroxide added to the polypropylene at the hopper and 4% monomer added at the injection port. The graphs show torque and die pressure variations with peroxide and TMI addition. Trace 1 is the pressure at transducer 1, trace 2 is the pressure at transducer 2 and trace 3 is the torque (%) . High temperature GPC and FT-

SUBSTJTUTESHEET(RULE26) IR techniques were used to analyse the polymer. The polymer was found to have a higher molecular weight and broader molecular weight distribution than material produced from an equivalent system containing only polypropylene and peroxide as shown in Figures 2, and 3. Figure 2 is a plot showing the effect of increasing peroxide content on the molecular weight of polypropylene in the presence of varying TMI concentrations. Figures 3a and 3b show the molecular weight distribution (MWD) variation of polypropylene with various peroxide and TMI concentrations. Figure 3a shows the MWD profile of polypropylene with various peroxide and TMI contents and Figure 3b is a graph showing variation of MWD grafted polypropylene with peroxide and TMI content. Grafting was found to increase with increasing peroxide and TMI concentrations as shown in Figures 4 and 5. Figures 4a and 4b are FT-IR spectra showing peroxide and TMI of isocyanate grafting of polypropylene in a twin screw extruder. Figure 4a is a FT-IR spectrum of TMI grafted polypropylene produced from addition of 4% TMI and 4% peroxide to polypropylene. Figure 4b is a FT-IR spectrum showing the effect of increasing peroxide content on the amplitude of the TMI grafted isocyanate peak produced from 4% TI and polypropylene in a twin screw extruder. Figure 5 shows the effect of peroxide and TMI concentration on isocyanate grafting content of polypropylene in a twin screw extruder using Trigonox 101 as the peroxide.

EXAMPLE 2

A Brabender batch mixer was heated to 175^*C. Polypropylene (30 g, KY6100, MFI = 3 at 230^*C) was added to the reaction chamber. A TMI peroxide mixture was added to the polypropylene melt over a two minute period and the polymer mixture was processed for a further 10 minutes. The final torque was recorded. Final process torque values are shown in Table 2. Table 2

% Peroxide 0% TMI 1% TMI 2% TMI 4% TMI

0 1000 1000 1000 1000

0.5 260 470 570 750

1 190 280 400 625

2 85 130 175 375

4 -100 90 105 145

The polymer was found by high temperature GPC and FT-IR analysis to have a higher molecular weight and broader molecular weight distribution than the material produced from an equivalent system containing only polypropylene and peroxide as shown in Figure 7. Figure 7 shows the effect of increasing peroxide content on molecular weight of polypropylene in the presence of varying TMI concentrations using a Brabender mixer. Grafting was found to increase with increasing peroxide and TMI concentrations as shown in Figure 6. Figure 6 shows the effect of peroxide and TMI concentration on isocyanate grafting content on polypropylene in a Brabender at 175^*C. The graphs show a variation of grafting with increase in peroxide at a given TMI concentration.

EXAMPLE 3 : TMI Grafting of polyethylene

30g of PE (MFI=4) was added to a Brabender mixer set at 190"C. The polymer was allowed to melt and mix. A TMI/peroxide mixture was added to the melt in four equal aliquots over a two minute period. The polymer was processed for ten minutes and then recovered for analysis. FT-IR was used to show the presence of grafted TMI (isocyanate peak at 2256 cm^"1) . GPC analysis of TMI grafted PE has shown that the polymer has a lower molecular weight and molecular weight distribution than the equivalent polymer produced from a PE/peroxide system (see Table 3) . Table 3

Variation of molecular weight and molecular weight distribution of PE with various peroxide and TMI ratios.

Polymer system MW MWD

PE 42000 7.8

E/0.5% peroxide 51000 8.2

PE/0.5 peroxide/4% TMI 45000 7.7

PE/1.0% peroxide 68000 9.9

PE/1.0% peroxide/1% TMI 43000 8.5

EXAMPLE 4 : Macromer grafting in polyolefin

A TMI capped polyether macromer was synthesised in kg quantities from TMI and polyether glycol monomethyl ether using a conventional glass batch reactor.

TMI capped polyether macromer/peroxide mixture was added to a Brabender mixer containing a PP melt (at 190^*C) . The material was processed for 10 minutes and then recovered for analysis. A Fourier transform infra red spectrum of the reactively processed PP showed the presence of a carbonyl group (1740cm^"1) confirming the presence of grafted polyether macromer. Figure 8a is a FT-IR spectrum of TMI grafted polyethylene produced from addition of 4% TMI and 1% peroxide. Figure 8b is a FT-IR spectrum showing the effect of increasing TMI content on the amplitude of the TMI grafted isocyanate produced from 1% peroxide and polyethylene in a Brabender mixer.

EXAMPLE 5 : Use of isocyanate functionalised PP in the manufacture of polymer blends and alloys

Polypropylene/poly(ethylene vinyl alcohol, EVOH) (composition 80:20) was fed into a APV 2030 co-rotating twin screw extruder at 5kg/h, melt mixed at 250 rpm and extruded through an in-line rheological die to give an immiscible blend with domain sizes of approximately 30μm. A blocked isocyanate (TMI) was used to compatibilise the system by:- i. adding PP-g-TMI (TMI content of 0.8%) to the PP/EVOH blend at the hopper. A PP/EVOH blend containing 0.1% TMI was found to be homogeneous with good mechanical properties and domain sizes of less than 3μm. ii. adding peroxide (0.3%) and TMI (4%) to the polymer melt to give an homogeneous polymer alloy with domain sizes of less then 5μm.

Claims

1. A method of preparation of a graft propylene polymer functionalised with an isocyanate group comprising the steps of : mixing in the melt or solid phase a mixture of a propylene polymer, a radical initiator and an isocyanate for formula (1) ,

wherein R_1# R₂, R₃ and R₄ are independently cyclic, straight or branched chain alkyl or alkylene groups optionally containing nitrogen, oxygen, sulphur or phosphorus heteroatoms, m is an integer between 1 and 10 and n is an integer between 1 and 100; and extruding the mixture to form a graftable macromer.

2. A method as claimed in claim 1, wherein the isocyanate is a , a' -dimethyl-1, 3 -isopropenyl benzyl isocyanate.

3. A method as claimed in any preceding claim, wherein the propylene polymer is a homopolymer, copolymer with ethylene or other alpha olefin having the formula H₂C=CHR wherein R is an alkyl radical comprising 1 to 10 carbon atoms.

4. A dyeable, printable or paintable polymer composition comprising a graftable monomer of formula (3) ; -l'O- CH₂=C(CH₃)R₁-C(R₃) (R₄) -U-P (3)

wherein R_x, R₂, R₃ and R₄ are as defined above; U is an urethane or urea group; and

P is a propylene polymer with a molecular weight between 100 and 1000.

5. A composition as claimed in claim 3, wherein R₃ and R₄ are both methyl .

6. A method of controlling molecular weight degradation of a polyolefin during extrusion comprising the step of addition of an effective amount of an isocyanate of formula (1) .

7. A method as claimed in claim 6 wherein the isocyanate is a, a' -dimethyl-1, 3 -isopropenyl benzyl isocyanate.

8. A method as claimed in claim 7, wherein an amount of 0.1 to 4% by weight of isocyanate is employed.

9. A method as claimed in claim 7 or 8, wherein the TMI and peroxide are added to the extruder in a pulsed manner.