Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-08-19
2001-11-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S150000, C522S153000, C522S183000, C522S184000, C522S188000, C522S187000, C522S064000, C522S018000, C522S028000
Reexamination Certificate
active
06316519
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of synthesizing linear acrylic polymers and copolymers having controlled molecular weight based on photo-initiated free radical polymerization of vinyl monomers in the presence of chain transfer agents.
Synthesis of vinyl polymers by free radical initiated polymerization is known in the art. The ability to assemble linear vinyl polymers is complicated by several reaction pathways that are available to the initiation and propagating species. Radical polymerization of vinyl monomers is particularly sensitive to these reactions and are discussed in detail in “Radical Chain Polymerization” in Principles of Polymerization, 2nd Ed., G. Odian, John Wiley & Sons, Inc. (1981). Under certain circumstances, particularly at elevated temperatures, these side reactions can be used very effectively to control vinyl polymer molecular weight (e.g., chain transfer and chain terminators). However, these same processes are the source of defects which alter the properties of the polymer. Their impact on polymer properties is amplified as the molecular weight of the polymer decreases. Therefore, control of these side reaction is desirable. T. Corner in “Free Radical Polymerization: The Synthesis of Graft Copolymers”, Adv. Polym. Sci., 1984, C2. 95, discusses how one can produce polymers with fewer defects. Low reaction temperature is a predominant factor in reducing the unwanted chain transfer and chain termination processes.
Thermal-initiated polymerization require initiators which decompose upon heating. There is a lower temperature limit for any thermal initiator below which it becomes ineffective in initiating polymerization. Very low temperature thermal initiators are not practical because of safety concerns relating to their instability under polymerization conditions.
Redox initiators are used at low temperature to polymerize vinyl monomers. Ionic redox initiator are ineffective for organic solution processes due to solubility issues. The organic soluble redox initiators contain chemical moieties which cause yellowing of the polymer or make the polymer more susceptible to oxidation, e.g., amines and metal accelerators. It is therefore desirable to conduct vinyl polymerizations at temperatures lower than conventionally achievable by these techniques.
Photoinitiated vinyl polymerizations work well at temperatures which are impractical for thermal initiators. The photoinitiators have the organic compatibility needed for effectiveness in solution processes and contain moieties which do not alter the performance of the polymer as do the organic soluble redox systems. Photoinitiators which work effectively at low temperature also produce polymers with fewer defects by virtue of the depression of undesirable transfer and termination reactions.
Control of molecular weight in vinyl polymerizations can be achieved with the minimum of undesirable side reactions by use of specifically designed chain transfer agents (CTAs). In free radical polymerizations, compounds which contain a sulfur-hydrogen (commonly known as a thiol moiety) are good CTAs for moderating molecular weight. They control the polymer molecular weight by hydrogen atom abstraction from the mercaptan by the propagating radical center. See, “Radical Chain Polymerization” in Principles of Polymerization, 2nd Ed, G. Odian, John Wiley & Sons, Inc. (1981). The deficiencies of this class of CTAs are well known to one skilled in the art. Offensive odor and deleterious effects to weathering properties has resulted in a search for other classes of CTAs.
The use of addition-fragmentation agents to control molecular weight are known. These chain transfer agents are effective at controlling molecular weight of vinyl polymers but copolymerize with monomers thus being ineffective as CTAs. As pointed out in “Addition-Fragmentation Processes in Free Radical Polymerization”, Colombani, et al., Prog. Polym. Sci., Vol. 21, 439, 1996, and references therein, the chain transfer reaction is favored at elevated temperatures whereas copolymerization is favored at low temperatures. It is then anticipated that this class of CTAs would not be effective in low temperature polymerizations.
It is therefore surprising to find that addition-fragmentation CTAs provide good molecular weight control in acrylic polymerizations initiated by irradiating a photoinitiator and that photoinitiated vinyl monomer polymerization can be employed at relatively low temperatures to synthesize linear polymers.
SUMMARY OF THE INVENTION
This invention is directed to an improved method for photopolymerizing one or more mono-ethylenically unsaturated monomers having the following general structure:
where Q=H, halogen or CH
3
and Y=any group which activates the double bond toward radical addition, by:
i) contacting the monomer with a photoinitiator,
ii) contacting the monomer/photoinitiator of step (i) with actinic radiation, and
iii) forming a polymer of controlled molecular weight;
where Y is selected from the group consisting of COOR, CONR
2
, OCOR, CN, Cl, OCO
2
R
1
, OR
1
, and aryl;
R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl and alkaryl;
R
1
is selected from the group consisting of alkyl, aryl, aralkyl and alkaryl; and wherein each of said groups is optionally substituted with one or more functional groups selected from the group consisting of hydroxy, epoxy, isocyanato, acid, amino, and silyl;
the improvement which comprises employing an addition-fragmentation chain transfer agent along with the photoinitiator in step (i).
Contemplated addition—fragmentation chain transfer agents include the following:
or a vinyl terminated compound of Formula VII:
wherein
Y
1
is any group which activates the double bond toward radical addition and is the same or different from Y;
X′ is an element other than carbon selected form Groups IV, V, VI or VII of the Periodic Table or a group consisting of an element selected from Groups IV, V or VI to which is attached one or more oxygen atoms; and
Y
2
is halogen or C(R)
2
R
4
;
m is a number from 0 to 3, such that the valency of the group X′ is satisfied and, when m is greater than 1, the groups represented by R are the same or different;
Z is hydrogen, SR
1
, S(O)R, S(O)
2
R, R, R
2
, R
3
;
R
2
is derived from initiator fragments;
R
3
is a chain transfer agent-derived radical selected from the group consisting of alkyl cycloalkyl, aryl, aralkyl, alkaryl, organosilyl, alkoxyalkyl, alkoxyaryl, and —P(R)
2
, each of said groups being optionally substituted with a member selected from the group R, COOR, CONR
2
, OCOR, CN, halogen, OCO
2
R, OR;
R
4
is chlorine or bromine; and
n≧1.
The actinic radiation includes single or multiple wavelengths in the ultraviolet region of the electromagnetic spectrum. The irradiation of the reaction mixture includes wavelengths from 305 nm to 450 nm, preferably from 335 nm to 400 nm. The polymer formed has a DP of about 2000 or less, preferably a DP of 2 to 200. The term “polymer” as used herein includes copolymers as well.
Preferred monomers are one or more of the following: methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, alpha methyl styrene, methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, functional methacrylate, acrylates and styrene selected from glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), diethylaminoethyl methacrylate, triethyleneglycol methacrylate, itaconic anhydride, itaconic acid, glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), diethylaminoethyl acrylate, triethyleneglycol acrylate,
Berge Charles Thomas
Desobry Vincent
Costello James A.
Deshmukh Sudhir G.
E. I. Du Pont de Nemours and Company
McClendon Sanza L.
Seidleck James J.
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