Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
  • C08F255/02—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00 on to polymers of olefins having two or three carbon atoms

Definitions

• This invention relates to a method of free radical grafting of monomers onto polypropylene resins. More particu ⁇ lar the invention relates to a method of the simultaneous grafting of two different monomers, preferably an allylepoxy compound and a styrenic compound, onto a polypropylene poly ⁇ mer, and the material obtained in said method.
• EP 0.280.454 discloses a method for the grafting of at least two different monomers onto molten hydrocarbon poly ⁇ mer.
• the polymer is a homopolymer of pro- pylene, a high density polyethylene or linear low density polyethylene, and the monomers are styrene or maleic anhydride.
• the process is operated in the absence of an initiator for the grafting reac ⁇ tion and in the substantial absence of antioxidant in the polymer, by the use of an extruder at extrusion conditions.
• US 5.079.295 relates to a thermoplastic composition comprising a polyphenylene ether resin, a modified propylene polymer and a rubbery substance.
• the polypropylene component is grafted with a styrene-based monomer and an unsaturated carboxylic acid or its derivative. A number of grafting pro- Fallss are described.
• 100 parts by weight of polypropylene are mixed with one part of maleic an ⁇ hydride (MAH), one part of styrene and one part of peroxide in a mixer, and subsequently extruded at 220 ⁇ C.
• MAH maleic an ⁇ hydride
• styrene and MAH in water is allowed to react at 120°C.
• the MAH of said dispersion is replaced by glycidyl methacrylate or glycidyl acrylate.
• NO patent application no. 924786 relates to poly ⁇ propylene compositions grafted with glycidyl acrylate or gly- cidyl methacrylate (GMA) using an organic peroxide as a radi ⁇ cal-generating agent, performed by kneading the melted mix ⁇ ture, preferably in an inert atmosphere.
• GMA glycidyl acrylate or gly- cidyl methacrylate
• the virgin polypropylene resin should be maintained to retain its desired physical and mechanical properties. If only one type of monomer, such as a monomeric allylepoxy compound, is used in a polypropylene grafting method, the achieved grafting efficiency is poor and accompanied by a heavy degradation of 0 the polymer by chain scission in the ⁇ -position and simultane ⁇ ous homopolymerization of the added monomer. Such a degrada ⁇ tion of the polypropylene will inevitably result in polypropy ⁇ lene compositions having a reduced molecular weight, and con ⁇ sequently articles manufactured therefrom will have mechanical s properties inferior to those of articles made from virgin polypropylene resins.
• a monomeric allylepoxy compound such as a monomeric allylepoxy compound
• the problem of chain scission would be avoided if the grafting could be performed in the presence of a compound having a stabilizing effect on the intermediate polymeric radicals created during the grafting process.
• the o composition would then maintain its high molecular weight and its highly valued physical properties.
• the present invention thus provides a method of free radical grafting of monomers onto a polypropylene resin having 5 a melt flow index of 0.2 to 100 g/10 minutes, preferably 0.2 to 50 g/10 minutes (measured according to ASTM D 1238 at 230°C/2.16 kg), comprising the steps of:
• n is an integer of 1 to 4; a styrenic compound having the formula: -
• R 2 in which R 2 is H, OH, CH 3 or allyl; and a peroxide as an initiator,
• the invention also provides a grafted polypropylene composition being obtained by the method described above.
• composition of the present invention may be used as a compatibilizer in the manufacturing of a polymer blend, as a polymer adhesion promotor, and in articles which require an improved printability.
• the polypropylene resins that may be used in the grafting method of the present invention comprise polypropy ⁇ lene homopolymers and copolymers of propylene with ethylene and/or butadiene, in particular resins having a weight average molecular weight of 150,000 to 500,000 and a melt flow index of 0.2 to 100 g/10 minutes, preferably 0.2 to 50 g/10 minutes, determined at 230°C and 2.16 kg load according to the method of ASTM D 1238.
• Copolymers may contain up to 20 % by weight, preferably 2 to 12 % by weight, of ethylene.
• the monomeric allylepoxy compound to be grafted onto the polymer chains must contain polar or" functional substi- tuents.
• Said monomers are preferably chosen from the group comprising allylepoxy compounds having the formula:
• R is H or a C ⁇ alkyl and ⁇ is -(CH 2 ) n -; -C(0)0-(CH 2 ) n -; or -(CH 2 ) n -0-; and n is an integer of 1 to 4.
• R is H or CH 3 , and more preferably CH 3 .
• R ⁇ is prefe ⁇ rably -C(0)0-(CH 2 ) n -.
• the most preferred compound is gly ⁇ cidyl methacrylate.
• Suitable styrenic compounds are those having the for- mula:
• R 2 is H, making styrene the most preferred styrenic compound.
• the styrenic compound is assumed to stabilize by delocalization the free radical species being present during the grafting process.
• any free radical generating peroxide compound known in the art having a suit ⁇ able decomposition temperature may be used.
• DHBP 2,5-bis(tert-butylperoxy)-2,5-dimetylhexane
• Perkadox- 14 bis(tert-butylperoxyisopropyl)benzene
• Trigonox-145" 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne
• Intimate mixing of the polypropylene resins, the initiator and the grafting monomers at a temperature higher than both the melting point of the polypropylene resin and the peroxide decomposition temperature is a prerequisite for achieveing a desired degree of grafting in the present method.
• the required grafting conditions can be accomplished both in a s batch process and a continuous process.
• any suitable, closed batch mixer of a conventional type equipped with a con ⁇ tinuous stirring device can be used, for example a Haake mixer.
• the polypropylene resin is introduced along with the styrenic compound, the allylepoxy compound and the initiator into the preheated mixer operated at a mixing speed of 10 to 200 rpm and at a temperature of 150 to 200 ⁇ C. Normally an acceptable degree of grafting is accomplished within a time s period of less than 15 minutes at said temperatures.
• the grafting is performed in a continuous manner, and an extruder may be used for the purpose.
• the graf ⁇ ting conditions are adapted to the type of extruder used, as will be well known to a man skilled in the art.
• the most o important features of the process are to secure adequate mixing and a uniform temperature of the polymer melt, as well as a sufficient dwell time to ensure the completion of the grafting reactions.
• a double screw extruder having co-rotating intermeshing screws is preferably used, for example a ZSK 5 Werner & Pfleiderer machine.
• the components may be fed to the mixing machine in any practical way.
• the sequence of adding the components is not critical.
• the components o may optionally be premixed, which may be done by the use of any conventional mixer and mixing method known in the art.
• grafting 100 parts by weight of polypropylene resin is mixed with up to 10 parts by weight of the styrenic compound and up to 10 parts by weight 5 of the allylepoxy compound.
• the initiator is usually added in an amount of up to 0.25 % by weight of the starting polypropylene resin, but higher amounts may also be used.
• a problem connected with the grafting method is a possible contamination of the reagents with oxygen from the 5 surrounding air. Oxygen will react spontanously with the gene ⁇ rated radicals, giving oxy-radicals which are particularly active agents in polymer chain scissions; Therefore, the graf ⁇ ting method is preferably carried out under an inert atmos ⁇ phere, most preferably in an atmosphere of nitrogen. °
• the polymer chain scissions and the molecular weights of the present compositions can be controlled by the use of the comonomer system described herein. In the grafting re ⁇ actions taking place the styrenic compound will function as a chain transfer agent.
• the degradation of the polypropylene backbone chain by ⁇ -scission will be sig ⁇ nificantly lower than what can be achieved in traditional gra ⁇ fting processes without the use of a chain transfer compound.
• the grafting efficiency of glycidyl methacrylate increases when the styrene concentration increases, while the incorporation efficiency of styrene is substantially constant.
• the glycidyl methacrylate grafting level increases more than two times compared with the case of styrene not being present.
• a composition obtained by the present method will comprise an amount of glycidyl methacrylate of 0 to 10% by weight, preferably 2 to 5% by weight, and an amount of styrene 0 of 0 to 10% by weight, preferably 2 to 5% by weight, said weights being calculated on the basis of the starting, neat polypropylene resin.
• the styrenic compound also acts as a comonomer, reac ⁇ ting with the allylepoxy monomers giving random copolymers.
• the side chains grafted onto the polypropylene backbone are random copolymers of said two species.
• the bulky benzene groups of said copolymers will exert a sterical effect making the reactive sites more accessible to the polymerizing mono ⁇ mers of the reaction mixture, and as a consequence a higher amount of glycidyl methacrylate can be copolymerized and graf ⁇ ted onto the polypropylene resin.
• the increased amount of incorporated glycidyl methacrylate increases the number of polar groups in the polypropylene composition, enhancing its compatibilizing effect.
• the styrenic compound has a combina ⁇ torial effect in that it is both participating as a comonomer in the copolymerization reactions and it is simultaneously acting as a chain transfer compound in said reactions.
• the polymeric composition obtained in the grafting method of the present invention will have a higher amount of allylepoxy compound and styrenic compound grafted onto the polymer chain than what is obtainable by any other known process, while the extent of polypropylene chain scissions is substantially reduced compared to other grafting processes.
• composition obtained in the method of the present invention is particularly suitable as a compatibilizing pre ⁇ cursor in polymer blends of various types. Typical amounts to be used in such blends are within the range of 0.1 to 15 % by weight, preferably 1 to 5 % by weight, based on the weight of the final blend.
• the grafted polypropylene composition of the present invention may also be used as a polymer adhesion promotor, in bonding layers, and being utilized in coating processes. More ⁇ over, the increased polarity of the grafted polypropylene com ⁇ position will improve the paintability of articles manufactured therefrom.
• Polypropylene resin, styrenic monomer, glycidyl meth ⁇ acrylate (GMA) and peroxide, are introduced into a conventio ⁇ nal closed Haake mixer equipped with a stirring device.
• the mixer is running at a constant speed of 64 rp during the entire grafting process. Samples of hot, grafted polymer are withdrawn and cooled in air of ambient temperature or in liquid nitrogen.
• the screw rotating speed is 150 rpm in all the presented exam- o pies.
• the polypropylene material premixed with styrenic, GMA and initiator, is fed to the extruder at a constant rate of 3.5 kg/h of polypropylene material.
• the present temperature profile in the extruder is:
• the polypropylene polymer is extruded as strands, cooled by water and then pelletized.
• MWD M ⁇ -
• Polypropylene resin in the form of powder is intro ⁇ quizzed into the mixer stirred at 64 rpm and heated to 200 ⁇ C. After 15 minutes of reactive mixing at 200°C, hot samples are collected and cooled in air of ambient temperature. The measu- 0 red molecular weight and the calculated molecular weight di ⁇ stribution are presented in Table 1.
• the mixing and sampling conditions are as in com ⁇ parative example A.
• the obtained molecular weight and molecu ⁇ lar weight distribution of the sample are presented in Table 1. 0
• the mixing and sam- s pling conditions are as in comparative example A.
• the obtained molecular weight, the molecular weight distribution and the amount of grafted GMA of the polypropylene composition are presented in Table 2 below.
• Polypropylene powder premixed at ambient temperature with 5.82% by weight of GMA and 8.73% by weight of styrene are introduced into the mixer. Mixing and sampling conditions are as in comparative example G.
• the obtained molecular weight, 5 molecular weight distribution, amounts of grafted GMA and sty ⁇ rene of the polypropylene composition are presented in Table 3 below.
• Examples 5 - 8 Polypropylene powder premixed at ambient temperature with 5.82% by weight of GMA, 8.73% by weight of styrenic and from 0 to 0.44% by weight of "Perkadox-14" peroxide is intro ⁇ quizd into the mixer.
• Mixing and sampling conditions are as in comparative example H.
• the obtained molecular weights, olecu- 5 lar weight distributions, and amounts of grafted GMA and styrene of the obtained polypropylene compositions are presen ⁇ ted in Table 3 below. Continuous grafting at extrusion conditions.
• the extrusion condi ⁇ tions are as given above. Samples are collected at the extru- o sion die and the amounts of grafted GMA and styrene in the obtained compositions determined. The obtained results are presented in Table 4.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Graft Or Block Polymers (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

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Citations (2)

• 1994
  • 1994-08-26 BR BR9408610A patent/BR9408610A/pt not_active Application Discontinuation
  • 1994-08-26 JP JP8508640A patent/JPH09511276A/ja not_active Withdrawn
  • 1994-08-26 WO PCT/NO1994/000140 patent/WO1996006872A1/en not_active Application Discontinuation
  • 1994-08-26 EP EP94930368A patent/EP0783539A1/en not_active Withdrawn

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