(Co)polymers by photopolymerization

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...

Reexamination Certificate

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C522S042000, C522S064000, C522S177000, C522S178000, C522S182000, C526S193000, C526S208000, C526S328000, C526S328500, C526S329000, C526S329100, C526S329200, C526S329300, C526S329700, C526S330000

Reexamination Certificate

active

06251962

ABSTRACT:

The invention is directed to a process for selectively preparing acrylate-, methacrylate- or vinylacetate-homo- and copolymers of specific molecular weight ranges.
In the DE-A-32 19 121 an emulsion polymerization process, which is conducted in a specific reactor and which process is initiated by irradiation with ultraviolet light, is described. A process for continuously preparing an acrylic polymer gel (in the form of a film) by irradiating the monomer on a moving support is disclosed in U.S. Pat. No. 5,004,761. In JP-A Hei 04 248802 and JP-A Hei 04 248803 a polymerization process initiated by ultraviolet light, wherein the rate of polymerization is controlled by adjusting the light irradiation and speed of reaction solution supply, is disclosed and additionally specifically designed reactors are described.
For specific technical uses it is important to obtain oligomers or polymers with defined properties. Desirable are, for example, a specific range of the number average molecular weight, as well as specific values for the polydispersity. Further, with respect to the structure of the oligomers and polymers for specific technical uses special requirements are to be fulfilled. So, for many applications it is necessary to employ straight chain oligomers.
It is therefore the object of the present invention to provide a process for manufacturing polymers with a specific molecular weight, polydispersity and conversion.
It has been found that this can be achieved by employing specific photoinitiators and process parameters.
Object of the instant application is a process for the preparation of acrylate- or methacrylate-homo- or acrylate- or methacrylate-co-oligomers with a weight average molecular weight (Mw) from 1000 to 20000,
a polydispersity≦3
and a conversion of the monomers to polymers greater than or equal to 70%,
characterized in that
at least one acrylic or methacrylic monomer or a mixture of said acrylic monomers with styrene or with vinylacetate, butadiene, acrylamide, acrylonitrile, vinylidene chloride or vinyl chloride
is irradiated in the presence of at least one &agr;-hydroxyketone photoinitiator or at least one phosphorus containing photoinitiator or a mixture of an &agr;-hydroxyketone photoinitiator with a phosphorus containing photoinitiator, said photoinitiator or photoinitiator mixture having a molar extinction coefficient &egr; from 0.1-2000 and at least one maximum of absorption, useful for the generation of radicals, in the range from 305 to 450 nm,
at a temperature from −20 to 70° C.
in a solvent or solvent mixture,
with light of a wavelength from 305 to 450 nm,
where the concentration of the polymer in the final solution is up to 80%.
A further object of the invention is a process for the preparation of polyvinylacetate and its hydrolysis product polyvinylalcohol with a weight average molecular weight (Mw) from 1000 to 30000,
a polydispersity≦3
and a conversion of the monomers to polymers greater than or equal to 70%,
characterized in that
vinylacetate or a mixture of said vinylacetate with other vinylic monomers is irradiated in the presence of at least one &agr;-hydroxyketone photoinitiator, at least one phosphorus containing photoinitiator or a mixture of an &agr;-hydroxyketone photoinitiator with a phosphorus containing photoinitiator, said photoinitiator or photoinitiator mixture having a molar extinction coefficient &egr; from 0.1-2000 and at least one maximum of absorption in the range from 305 to 450 nm,
at a temperature from −20 to 70° C.
in a solvent or solvent mixture,
with light of a wavelength from 305 to 450 nm,
where the concentration of the polymer in the final solution is up to 80%.
The photoreactor used is fabricated in Rodoxal, an aluminum alloy, but suitable reactors can also be constructed, for example in stainless steel or in any material compatible with the monomers employed, as for example teflon, brown glass etc. The reactor possesses a glass window allowing transmission of the UV-light. The overall irradiation surface of the reactor used to prepare some of the examples of the instant application is 13 cm
2
and the cell thickness is 1 cm. In this connection the “overall irradiation surface” of the reactor means the surface of the irradiated part of the reactor, namely the window and the “cell thickness” is the thickness of the internal path (diameter) of the reactor at the irradiated part. The process can also be carried out using an optical bench and a UV-cell for absorption spectra fitted with a septum to allow reactions under argon and a magnetic stirrer. This UV-cell, similar to those used to measure UV-spectra, is irradiated through a 2 cm
2
window with homogeneous light from a Philips 100 W medium pressure mercury lamp and the cooling is effected through the side walls of the cell.
But also bigger reactor dimensions are possible, as for example an overall irradiation surface (window size) of 26 cm
2
with a cell thickness (diameter) of 1 cm. In this case, lamps of higher output and bigger irradiation surfaces such as, for example, Fusion Curing lamps F200 to F600 are used. As those commercially available lamps have a bulb length of 6 inches (about 15.5 cm; F200 lamp) or 10 inches (about 25 cm; F600 lamp), the reactor should not exceed this height. The irradiation surface can thus be adapted to the necessary reaction conditions. Naturally, for the instant process it is also possible to employ reactors with other dimensions. The crucial point is to guarantee a controlable and homogenic generation of radicals of the photoinitiator throughout the reactor, which is achieved, by controling the flow of the mixture and the distribution of radicals in the mixture by stirring and appropriate irradiation. This not dependant on the size of the reactor or the irradiation surface.


REFERENCES:
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patent: 4501868 (1985-02-01), Bouboulis et al.
patent: 4721734 (1988-01-01), Gehlhaus et al.
patent: 4758642 (1988-07-01), Yezrielev et al.
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patent: 5942290 (1999-08-01), Leppard et al.

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