Compositions – Liquid crystal compositions
Patent
1998-01-20
2000-01-04
Wu, Shean C.
Compositions
Liquid crystal compositions
25229961, 25229963, 25229964, 25229965, 25229966, 349183, 428 644, 528105, 528392, 528401, C09K 1938, G02F 1133, C08G 6702, C08G 6502
Patent
active
060106417
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the alignment of liquid crystal polymers in liquid crystal devices and the provision of novel liquid crystal polymers.
The unit that is the basic building block of a polymer is called a monomer.
The polymerisation process i.e. the formation of a polymer from its constituent monomers does not usually create polymers of uniform molecular weight, rather what is created is a distribution of molecular weights. In order to describe a sample of polymer it is necessary to state the average number of monomers in a polymer this is called the degree of polymerisation (D.P). By how much the majority of polymer molecules differ from this average value (or to describe the spread of molecular weight) is called the polydispersity.
A number of different average molecular weights can be drawn from gel permeation chromatography (GPC) for a given sample including: Mn--number average molecular weight and Mw--weight average molecular weight. The value used to calculate D.P. is usually Mn and polydispersity is usually defined as Mw/Mn.
Polymers can be made from different types of monomers, in which case the polymer is called a co-polymer. If two types of monomer join in a random fashion then the polymer is called a random co-polymer. If the two monomers form short sequences of one type first which then combine to form the final polymer then a block copolymer results. If short sequences of one of the monomers attach themselves as side chains to long sequences consisting of the other type of monomer then the polymer is referred to as a graft copolymer.
In liquid crystal polymers the monomers can be attached together in essentially two ways. The liquid crystal part or mesogenic unit of the polymer may be part of the polymer backbone resulting in a main chain polymer, alternatively the mesogenic unit may be attached to the polymer backbone as a pendant group i.e. extending away from the polymer backbone; this results in a side-chain polymer. These different types of polymer liquid crystal are represented schematically below. The mesogenic units are depicted by the rectangles. ##STR1##
The side chain liquid crystal polymer can generally be thought of as containing a flexible polymer with rigid segments (the mesogenic unit) attached along its length by short flexible (or rigid) units as depicted in the schematic representation below. It is the anisotropic, rigid section of the mesogzenic units that display orientational order in the liquid crystal phases. In order to affect the phases exhibited by the liquid crystal and the subsequent optical properties there are many features which can be altered, some of these features are particularly pertinent to side-chain liquid crystal polymers. One of these features is the flexible part that joins the mesogenic unit to the polymer backbone which is generally referred to as a spacer, the length of this spacer can be altered, its flexibility can also be altered. ##STR2##
A number of side-chain liquid crystal polymers are known, for example see GB 2146787 A.
Liquid crystal polyacrylates are a known class of liquid crystal polymer (LCP). LCPs are known and used in electro-optic applications, for example in pyroelectric devices. non-linear optical devices and optical storage devices. For example see GB 2146787 and Makromol. Chem. (1985) 186 2639-47.
Side-chain liquid crystal polyacrylates are described in Polymer Communications (1988), 24, 364-365 e.g. of formula: ##STR3## where (CH.sub.2).sub.m --X is the side-chain mesogenic unit and R is hydrogen or alkyl.
Side-chain liquid crystal polychloroacrylates are described in Makromol. Chem. Rapid Commun. (1984), 5,393-398 e.g. of formula: ##STR4## where R is chlorine.
A method for the preparation of polyacrylate homo- or co-polymers having the following repeat unit is described in UK patent application GB 9203730.8 ##STR5## R.sub.1 and R.sub.2 are independently alkyl or hydrogen, R.sub.3 is alkyl, hydrogen or chlorine, m is O or an integer 1-20, W is a linkage group COO or OOC or O and X is a mesogenic group.
One of the main p
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Beattie David R
Blackwood Keith M
Coates David
Sage Ian C
Verrall Mark A
The Secretary of State for Defence in her Britannic Majesty's Go
Wu Shean C.
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