Vinylcyclohexane-based polymers

Details Vinylcyclohexane-based polymers Vinylcyclohexane-based polymers

2002-03-04

2003-11-18

Choi, Ling-Siu (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348000, C526S335000, C526S346000

Reexamination Certificate

active

06649723

ABSTRACT:

Compared with polycarbonates, which are currently used for the production of optical data storage media, polymers based on vinylcyclohexane which exhibit satisfactory mechanical properties have a higher viscosity at the same temperature over a broad range of low shear rates.
The accurate moulding of pits which are smaller and disposed more closely together than those cited in EP-A 317 263 and U.S. Pat. No. 4,911,966, and of the grooves which are possible nowadays, is essential for high densities of data storage of >5 Gbytes, particularly >10 Gbytes.
The method of producing polymers based on vinylcyclohexane which is described in EP-A 317 263 and the use thereof as substrates for optical discs result in a molecular weight which is too low compared with that which would ensure the operationally reliable production thereof (comparative example 1). The mechanical properties of the homopolymers described there are not very suitable for the production of optical data storage media.
The method described in U.S. Pat. No. 4,911,966 only results in partially hydrogenated products (<97%), and most of the examples comprise degrees of hydrogenation of <86%. According to the prior art, partially hydrogenated systems exhibit inadequate transparency (DE-AS 11 31 885 (=GB 933 596)). The partially hydrogenated systems which are disclosed are turbid, and are unsuitable for applications as optical substrates which are penetrated by a laser beam. Partially hydrogenated systems also have the disadvantage that their glass transition temperature depends on the degree of hydrogenation. In an industrial process, an adjustment of the degree of hydrogenation and thus of the thermal properties of the optical substrate can only be reproducibly implemented by expending considerable engineering effort and at considerable cost.
Moreover, for the most part the partially hydrogenated products which are cited in U.S. Pat. No. 4,911,966 have a molecular weight which is far too low for the operationally reliable production of substrates for optical data storage media.
The aforementioned patent specifications do not mention the quality of moulding of pit and groove structures or their existence in principle by means of the substrates cited there.
Optimised molecular weights and molecular weight distributions are essential for satisfactory mechanical properties, and at the same time good melt flow properties are essential for the moulding of pit and groove structures of high-density optical data storage media.
A molecular weight which is possibly too high can lead to problems with the moulding of pits and grooves, as a consequence of too high a viscosity.
The substrates according to the present invention, which comprise a polymer based on vinylcyclohexane with a narrow molecular weight distribution or a mixture thereof with a low molecular weight component, are distinguished by their good level of mechanical properties and by their good melt flow properties.
It is thereby possible to produce optical discs in an operationally reliable manner by injection moulding, and the discs can subsequently be handled without their bending or breaking.
Thinner substrates can be produced which have layer thicknesses less than 1.1 mm, of 0.6 mm thickness for example, and which at the same time exhibit satisfactory mechanical properties.
On account of these properties, the materials can be used very satisfactorily as substrates for optical data storage media.
Satisfactory mechanical properties are also required for other optical substrates which do not require mechanical indentations in the form of pits and grooves, for example, and have to be accompanied by a low level of birefringence, a low moment of inertia, a high level of dimensional stability when hot, a high modulus of elasticity, low water absorption and low density. These requirements are also met by the substrates according to the invention.
The present invention relates to polymers of vinylcyclohexane with an absolute molecular weight M
w
from 100,000 to 450,000 g/mol or a mixture thereof with a low molecular weight component with an absolute molecular weight from 1000 to less than 100,000 g/mol, wherein the molecular weight distribution is characterised by a polydispersity index (PDI=M
w
/M
n
) of 1 to 3 and the maximum melt viscosity is 1000 Pa·s, as measured at 300° C. and at a shear rate of 1000 sec
−1
.
Any oligomeric fraction with a molecular weight M
w
of up to 3000 g/mol which may possibly be present is not taken into account in the calculation of the polydispersivity index.
Any oligomeric fraction with a molecular weight of up to 3000 g/mol which may be present amounts to less than 5% of the weight of the polymer.
The molecular weight M
w
of the high molecular weight polymer (homopolymer) preferably ranges from 200,000 to 450,000 gmol
−1
, and ranges in particular from 200,000 to 400,000 gmol
−1
.
The molecular weight M
w
of a high molecular weight copolymer or block polymer preferably ranges from 100,000 to 400,000 gmol
−1
, and ranges in particular from 100,000 to 250,000 gmol
−1
.
The molecular weight M
w
of the low molecular weight component generally ranges from 1000 to 100,000 gmol
−1
, preferably from 7000 to 90,000 gmol
−1
, most preferably from 10,000 to 90,000 gmol
−1
.
The molecular weight distribution of the respective component is characterised by a polydispersity index (PDI=Mw/Mn) from 1 to 3.
In the case of mixtures, the proportion of low molecular weight component with respect to the weight of the mixture of high molecular weight and low molecular weight polymers generally amounts to up to 70% by weight, preferably 5 to 60% by weight, most preferably 10 to 50% by weight.
A polymer based on vinylcyclohexane is preferred both for the high molecular weight and for the low molecular weight component. This polymer comprises a recurring structural unit of formula (I)
wherein
R
1
and R
2
, independently of each other, denote hydrogen or a C
1
-C
6
alkyl, preferably a C
1
-C
4
alkyl,
R
3
and R
4
, independently of each other, represent hydrogen or a C
1
-C
6
alkyl, preferably a C
1
-C
4
alkyl, particularly methyl and/or ethyl, or R
3
and R
4
jointly represent an alkylene, preferably a C
3
or C
4
alkylene (comprising a condensed-on 5- or 6-membered cycloaliphatic ring),
R
5
represents hydrogen or a C
1
-C
6
alkyl, preferably a C
1
-C
4
alkyl,
R
1
, R
2
and R
3
, independently of each other, represent hydrogen or methyl in particular.
Apart from stereoregular head-to-tail linkages, the concatenation of the above structural units can comprise a small proportion of head-to-head linkages. The vinylcyclohexane-based polymer can be branched via centres, and can have a star configuration structure for example.
Comonomers can be contained in an amount which generally ranges from 0 to 80% by weight, preferably from 0 to 60% by weight, most preferably from 0 to 40% by weight, with respect to the finished polymer. Polymers are preferred which comprise recurring structural units of formula (I) and which are formed from one monomer or from a mixture of monomers.
The following substances can preferably be used as comonomers and incorporated in the polymer during the polymerisation of the starting polymer (a polystyrene which is optionally substituted): olefines which generally comprise 2 to 10 C atoms, such as ethylene, propylene, isoprene, isobutylene or butadiene for example, C
1
-C
8
, preferably C
1
-C
4
alkyl esters of acrylic or methacrylic acid, unsaturated cycloaliphatic hydrocarbons, e.g. cyclopentadiene, cyclohexene, cyclohexadiene, norbomene which is optionally substituted, dicyclopentadiene, dihydrocyclopentadiene, tetracyclodecene which is optionally substituted, styrenes with alkylated nuclei, &agr;-methylstyrene, divinylbenzene, vinyl esters, vinylic acids, vinyl ethers, vinyl acetate, vinyl cyanides such as acrylonitrile or methacrylonitrile, maleic anhydride, and mixtures of these monomers.
The polymers can have a linear chain structure, or can also c

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