FR2658826A1 - ACTIVE COMPOSITIONS IN NONLINEAR OPTICS MATERIALS AND DEVICES CONTAINING SAME. - Google Patents

Abstract

These compositions are of the type comprising a matrix formed from a polymer base and at least one hyperpolarisable compound, the main constituent of the matrix being a thermosetting polymer containing an imide group, preferably a maleimide group.

Description

COMPOSITION ACTIVE IN NONLINEAR OPTICS
MATERIALS AND DEVICES CONTAINING SAME
The present invention relates to materials having nonlinear optical activity and devices containing them.

 It relates more particularly to materials of the type comprising a matrix consisting of a polymer in which is incorporated a hyperpolarizable compound.

 Many optical or electro-optical devices, such as switches, modulators, directional couplers, bistables use the property of certain materials to be active in non-linear optics.

Thus, the devices use as active element in nonlinear optics inorganic crystalline compounds such as LiNbO3, hydrogen phosphates such as (KDP, ADP, KTP) or organic compounds.

These organic compounds may be single crystals, Langmuir Blodgett type ordered molecular layers, active polymers.

In the latter, the activity in nonlinear optics is generally provided by a hyperpolarizable compound ordered non-centrosymmetrically in a polymerizable matrix.

There are two classes in active polymerized materials
functionalized polymers in which the hyperpolarizable compounds are covalently grafted onto the backbone of the polymer; and
the materials in which the hyperpolarizable compound is incorporated, for example by dissolution, into the polymerizable or polymerized matrix. These latter materials are sometimes called "Guest / host" materials. As an example of hyperpolarizable compound include the "Disperse Red One" marketed by the company Aldrich under the name "DR1".

 European Patent No. 218938 describes such a material and cites numerous hyperpolarizable organic compounds and compatible polymers to form the matrix, Thus, the polymers mentioned are acrylates, methacrylates, transparent epoxies, styrene or polycarbonates.

 The material is activated by orientation of hyperpolarizable compounds under the effect of an electric field, electromagnetic or magnetic.

The polymer generally used is polymethyl methacrylate (PMMA).

 However, the matrix is a material whose rigidity is imperfect, variable depending on the temperature and not completely preventing the movements of the contained compounds, which will tend to disorient, in other words to return to a position of equilibrium dipoles in the material.

 This disorientation, of course, results in an often erratic decrease in nonlinear optical activity.

 In addition, the above materials have certain disadvantages. Indeed, hyperpolarizable matrices and compounds must be miscible. More particularly, the hyperpolarizable compound should have the highest possible solubility in the matrix polymer and in common solvents to thereby obtain the highest possible optical activity.

 The present invention is intended in particular to remedy these drawbacks by proposing a new material of the type comprising a matrix based on polymer (s) and at least one hyperpolarizable compound, having a higher nonlinear optical activity due mainly to better solubility of the hyperpolarizable compound and a decrease in the loss of activity over time.

 For this purpose, the invention proposes a material of the type comprising a matrix formed based on polymer (s) and at least one hyperpolarizable compound characterized in that the main constituent of the matrix is a thermosetting polymer with imide groups.

 This polymer makes it possible to substantially increase the solubility of hyperpolarizable compounds, and especially, by way of example, those which contain cyano radicals in their molecule, nitro- radicals.

 Thus, the nonlinear optical activity of these materials is substantially higher than that of materials made with other polymers as a matrix, such as polymethylmethacrylate.

 In addition, the hyperpolarizable compound concentration will be as high as possible, its upper limit being limited by the solubility of the compound in the polymer (i.e., a formation of a second phase beyond).

 Advantageously, the concentration of hyperpolarizable compound is about 1 to 20% by weight.

 Another advantage of the material of the invention lies in the exceptional stability of the activity in nonlinear optics as a function of time.

 Indeed, it has been found that the phenomenon of disorientation of active groups in linear optics was significantly slower than in the so-called "guest / host" conventional systems.

 In addition, their very high stability over time, the polymers according to the invention have the advantage of being very film-forming.

dans laquelle : les radicaux R représentent indépendamment un atome d'hydrogène ou des radicaux alcoyle ou alcoylidène de bas poids moléculaire (de 1 à C6) éventuellement substitué.The best results are obtained using as polymer those obtained by a reaction, at a temperature ranging from 50 ° C. to 1800 ° C., between - (a) one or more bis-maleimide (s) corresponding to formula (I) and
definitions given above with respect to this formula, a N, N '-Bis-imide of formula

wherein: the R radicals independently represent a hydrogen atom or optionally substituted lower molecular weight (1 to C6) alkyl or alkoylene radicals.

R 'independently represents an optionally substituted C1-C5 acyl group or an optionally substituted and / or unsaturated C1-C6 acylidene group.

R and R 'being advantageously connected together to form a 5- to 7-membered heterocyclic ring
A is quoted below.

dans laquelle
. les symboles Y représentent indépendamment H, CH3 ou Cl
. le symbole A représente un radical divalent de préférence choisi
dans le groupe constitué par les radicaux : cyclohexylènes
phénylènes ; méthyl-4 phénylène-1,3 ; méthyl-2 phénylène-1,3
méthyl-5 phénylène-1,3 ; méthyl-6 phénylène-1,3 ; diéthnyl-2,5
méthyl-3 phénylène-1,4 ; et les radicaux de formule

dans laquelle T représente un lien valentiel simple ou un groupement

Preferably, the radicals R and R 'are chosen so that the formula (I) becomes the formula (I')

in which
. the symbols Y represent independently H, CH3 or Cl
. the symbol A represents a divalent radical preferably chosen
in the group consisting of radicals: cyclohexylenes
phenylenes; 4-methyl-1,3-phenylene; 2-methyl-1,3-phenylene
5-methyl-1,3-phenylene; 6-methyl-1,3-phenylene; diéthnyl-2,5
3-methyl-1,4-phenylene; and the radicals of formula

where T represents a simple valency bond or a grouping

and X represents a hydrogen atom, a methyl, ethyl or
isopropyl; - reagent (s) (b) and / or (c)
(b) consisting of one or more substituted heterocycle (s)
especially by unsaturated short chains (C2-C6) such as
vinylpyridines, N-vinylpyrrolidone-2, isocyanurate
of allyl, vinyltetrahydrofuran
(c) consisting of a styrene compound, such as by
for example, α-methylstyrene, divinylbenzene or ethylvinylbenzene.

The ratio b + c may vary from 1/20 to 1, preferably from 1/10 to 1.

a - and if necessary to improve the rheology one or more reagents acrylate (d) consisting of one or more
compound (s) of general formula (CH2 = CR6 - CO - O) n B (11)
in which
. the symbol R6 represents a hydrogen atom or a
methyl radical; nn is a whole or fractional number at least
equal to 1 and not more than 8;
. the symbol B represents an organic radical of valence n
derivative: of a saturated aliphatic residue, linear or branched,
having 1 to 30 carbon atoms and which may contain one or
several oxygen bridge (s) and / or one or more function (s)
free hydroxyl (s); an aromatic residue (of type
aryl or arylaliphatic) having from 6 to 150 carbon atoms
carbon constituted by a benzene ring, which can be
substituted with one or three alkyl radicals having from 1 to 5
carbon atoms, or by several benzene rings,
possibly substituted as indicated above, connected
between them by a simple valency bond, an inert group
or an alkylene radical having 1 to 3 carbon atoms,
said aromatic residue being able to contain at various places
of its structure one or more bridge (s) oxygen and / or one or
several free hydroxyl function (s), the
valence (s) free (s) aromatic B radical can be
range (s) by a carbon atom of an aliphatic chain
and / or by a carbon atom of a benzene ring.

The amount of reagent being such that the mass ratio
d / a may vary from 0 to 1/10.

dans laquelle le radical allyloxy ou méthallyloxy est en position ortho, métha ou para par rapport à l'atome de carbone du cycle benzénique relié à l'azote ;

- Optionally
one or more monomers of formula III, IV, V

in which the allyloxy or methallyloxy radical is in the ortho, metha or para position with respect to the carbon atom of the benzene ring connected to the nitrogen;

 In the abovementioned compound, the proportions of the various constituents of the mixture of the products of formulas (III) (IV) and optionally (V) may vary within wide limits.

By way of specific examples of bis-imides (a) of formula (I), mention may be made in particular of the compounds indicated in French application 86/17918, that is to say
N, N'-metaphenylene-bis-maleimide,
N, N'-para-phenylene-bis-maleimide,
N, N'-4,4'-diphenylmethane-bis-maleimide,
N, N'-4,4'-diphenyl ether-bis-maleimide,
N, N'-4,4'-diphenylsulphone-bis-maleimide,
N, N'-cyclohexylene-1,4-bis-maleimide,
N, N'-4,4'-diphenyl-1,1 cyclohexane-bis-maleimide,
N, N'-4,4'-diphenyl-2,2-propane-bis-maleimide,
N, N'-4,4'-triphenylmethane-bis-maleimide,
N, N '-methyl-2-phenylene-1,3-bis-maleimide,
N, N'-methyl-4-phenylene-1,3-bis-maleimide,
N, N'-methyl-5-phenylene-1,3-bis-maleimide.

 These bis-maleimides can be prepared according to the methods described in US Pat. No. 3,018,290 and British Patent No. 1,137,290. N, N'-4,4'-diphenylmethane-bis-maleimide, taken alone or as a mixture with N, N '-methyl-2-phenylene-1, is preferably used for carrying out the present invention. 3-bis-maleimide, N, N'-methyl-4-phenylene-1,3-bis-maleimide and / or N, N'-methyl-5-phenylene-1,3-bis-maleimide.

dans laquelle le symbole U représente un lien valentiel simple ou un groupement :

As the acrylate reagent (d) which is suitable, mention may be made of (d1) the mono (meth) acrylates corresponding to formula (II)
in which
nn = 1, and
BB represents a monovalent organic radical of formula
- (CH2 CH2O) m ---- B1 (VI)
in which: B1 represents an alkyl radical,
linear or branched, having from 1 to 6 carbon atoms or
a phenyl radical;
and m is an integer equal to zero, 1 to 9 (d2) di (meth) acrylates corresponding to the formula (IV) in
which :
nn = 2, and
BB represents a divalent organic radical of formula
- (CH 2 CH 2 O) p B2 (OCH 2 CH 2) q (VII)
in which: B2 represents a divalent alkylene radical,
linear or branched, having from 2 to 9 carbon atoms and
which may contain one or more oxygen bridges or
radical of formula

in which the symbol U represents a simple valency bond or a grouping:

the symbols p and q, which are identical or different, represent
each an integer equal to zero, 1, 2, 3, 4 or 5 (d3) the tri- and tetra (meth) acrylates corresponding to formula (VI)
in which
nn = 3 or 4, and
BB represents a trivalent or tetravalent organic radical
derived from a saturated aliphatic residue, linear or branched, having 3
to 20 carbon atoms and may contain one or more bridge (s)
oxygen and / or one or more free hydroxyl function (s) (d4) epoxy novolac (meth) acrylates which, while corresponding
in formula (IV), are represented hereby by the following formula

in which
. the symbol R6 has the meaning given above about
of formula (II)
the symbol Rii represents a hydrogen atom or a
methyl radical; tt is an integer or fractional number lying in
the range from 0.1 to 7 (d5) of mixtures of several acrylates and / or methacrylates of the same
type
[(dl), (d2), (d3) or (d4)] between them or mixtures of one or
several acrylate (s) and / or methacrylate (s) of the same type with
one or more acrylate (s) and / or methacrylate (s) from another
type.

 As specific examples of acrylate reagent (d1) which are particularly suitable, mention may be made in particular of: methyl mono (meth) acrylates 1 mono (meth) acrylates of phenol (mono-oxyethyl) 7 mono (meth) phenol (di-oxyethyl) acrylates.

et p = q = 1 ou 2 ]
A titre d'exemples spécifiques de réactif acrylate (d3) qui conviennent bien, on peut citer en particulier : les tri(méth)acrylates de butanetriol-1,2,4 ; les tri(méth)acrylates d'hexanetriol-1,2,6 ; les tri(méth)acrylates de triméthylolpropane ; les tri(méth)acrylates de pentaérythritol ; les tétra(méth)acrylates de pentaérythritol.As specific examples of acrylate reagent (d2) which are suitable, mention may be made of: ethylene glycol di (meth) acrylates 1,4-butanediol di (meth) acrylates; the di (meth) acrylates of hexanediol-1,6 1 tripropylene glycol di (meth) acrylates 1 di (meth) acrylates of diphenols, di (mono- or poly-oxyethyl) or not following: dihydroxy-4,4 ' diphenylmethane, bisphenol A, 4,4'-dihydro-diphenyl ether and in particular di (mono-oxyethyl) bisphenol A di (meth) acrylates or di (di-oxyethyl) bisphenol A di (meth) acrylates) [cf. formula (VII) in which B2 represents the radical

and p = q = 1 or 2]
As specific examples of acrylate reagent (d3) which are well suited, there may be mentioned in particular: butanetriol-1,2,4 tri (meth) acrylates; 1,2,6-hexanetriol tri (meth) acrylates; tri (meth) acrylates of trimethylolpropane; pentaerythritol tri (meth) acrylates; pentaerythritol tetra (meth) acrylates.

 Epoxy novolac (meth) acrylates (d4) are known products some of which are commercially available. They can be prepared by reacting (meth) acrylic acids with a novolak type epoxy resin, the latter being the reaction product of epichlorohydrin and of phenol / formaldehyde polycondensates in formula (VIII) given above. a hydrogen atom or polycondensates cresol / formalin in the formula R 1 is then a methyl radical. These oligomeric polyacrylates (e4) and a process for their preparation are described, for example, in US Pat. No. 3,535,403.

 As specific examples of acrylate reagent (e4) which are particularly suitable, mention may be made in particular of novolak epoxy acrylates of formula (VIII) in which R 6 and R 11 represent a hydrogen atom and t is an integer or fractional in the range of 0.1 to 5.

 By way of specific examples of acrylate reagent (e5) which are suitable, mention may be made of mixtures of epoxy novolac (meth) acrylates (e4) with at most 30% by weight, relative to the weight of the mixture (e4) + (e3), a triacrylate and / or a trimethacrylate meeting the definitions given above with regard to the reagent acrylate (e3) and in particular the mixtures of epoxy novolac acrylates that are suitable, just mentioned above with not more than 25% by weight, based on the weight of the mixture, of a suitable triacrylate and / or trimethacrylate of those just mentioned above.

 The acrylate reagent (e) which is used very preferably is taken from the group formed by: di (meth) acrylates of di (mono-oxyethyl) bisphenol A; the epoxy novolak di (meth) acrylates of formula (VIII) in which R 6 and R 11 represent a hydrogen atom and t is an integer or fractional number ranging from 0.1 to 5, these compounds being taken alone or in admixture with at most 25% by weight, relative to the weight of the mixture, of tri methyl methyl propane triacrylate.

 The acrylate reagent (e), formed from one or more compound (s) of formula (IV), is used in amounts generally representing from 1% to 60% and, preferably, from 5% to 30% of the total weight of the reagents (a) + (b) + optionally (c) + (e).

 Advantageously, the above polymers having a melt viscosity measured under the conditions defined hereinafter between 0.1 Pa.s and 500 Pa.s.

 According to another characteristic of the invention, the hyperpolarizable compound is chosen from hyperpolarizable compounds comprising cyano and / or nitro radicals.

By way of example, suitable compounds may be
those described in the article by HE Katz et al published in Mol.

- le "Disperse Red One" ou "DR1" commercialisé par la société Aldrich
ayant comme formule

- ceux décrits dans la demande de brevet français n" 88 12028, publiée sous le N 2 636 441 et ayant pour formule générale

dans laquelle A et A1 représentent des groupements accepteur d'électrons et
D des groupements donneur d'électrons comme par exemple, le composé suivant de formule (A)

Cryst. Inc Non linear Opt. Flight. 157, p. 525-533 (1988) having the
following formulas

the "Disperse Red One" or "DR1" sold by the company Aldrich
having as formula

those described in French Patent Application No. 88 12028, published under No. 2,636,441 and having the general formula

wherein A and A1 represent electron acceptor moieties and
D electron donor groups such as, for example, the following compound of formula (A)

This list is not exhaustive. In fact, any hyperpolarizable compound that is soluble in the styrene / acrylonitrile copolymer is suitable for the invention. Any non-centrosymmetric compound having at least one donor group and at least one acceptor group interconnected by at least one bonding system (s). (s), possesses more or less the property of being active in nonlinear quadratic optics.

 The material of the invention can be used in any form such as films, moldings, extrusions, etc.

 It is also possible, without departing from the scope of the invention, to add different components or additives in the material to improve these mechanical properties or shaping, for example ignufigeants, antistatic, antioxidants, stabilizers or the like .

 The invention also relates to an optical or optoelectric device comprising at least one element constituted by the material according to the invention.

 The thermoplastic material obtained is brought to a temperature greater than or close to its glass transition temperature. A continuous electric field is applied to the film and directs the active molecules.

 The material is then cooled to a temperature below its glass transition temperature (Tg) to thereby freeze the oriented position of the active molecules.

 The process described above is given by way of example only and in no way limits the invention.

An example of a method of manufacturing such materials is also European Patent No. 218,938.

 It is also easily understandable that the material conforms to the desired use form preferably before performing the orientation of the molecules.

 The activity of materials in nonlinear optics is determined by the measurement of second, third or nth order susceptibilities.

 The susceptibilities of a material are directly related to the polarization of the material by the following fundamental relationship P = Po + tC 1. E + zC 2 E.E + t 3 E.E.E + .....

in which: P and Po represent the polarization respectively in the presence and absence of electromagnetic field.

 E represents the electromagnetic field.

 X, X, X represent the linear and nonlinear susceptibilities of the material.

Preferably, the hyperpolarizable compound is solubilized in the copolymer in the molten state or in the dissolved state in a solvent.

 The polymer is then heated to a temperature above its glass transition temperature (Tg), then subjected to an intense electric field to guide the hyperpolarizable molecules.

 In general, the following operating sequence is used, using both the good solubility of the active molecule with polymers according to the invention and the crosslinking of the matrix polymers according to the invention.

1) Dissolve a resin in a solvent, 2) Dissolve the active molecule in the preparation obtained in 1), 3) Evaporate the solvent, 4) Make a film
5) It is oriented under electric field E at a temperature at least
equal to that of glass transition waste (generally Tg
greater than or equal to 50 ° C).
ambient.

6) It is cross-linked under electron beam e, which gives a film of which
the glass transition temperature Tg is greater than 300 ° C.

The electric field can be cut after step 5).

In steps 1 and 2 the role of the active molecule and that of the resin can be reversed.

The technique of the synthesis of host resins is described in particular in the published patent applications Nos. 2,628,111, 1,555,564 and 2,612,195.

The following nonlimiting examples illustrate the invention
Example 1
Synthesis of Resin:
In a 100 ml casting reactor preheated to 165 ° C., a mixture of 21 g of N, N'-4-4'-diphenylmethane bis-maleimide + 9 g of N, N '2,4 tolylene bis is charged with stirring. -maléimde.

Duration of the casting 5 mn; 5 g of (N.Vinylpyrrolidone) are added and added over 0.5 min.

Let react 4.5 min.

Then added in 0.5 minutes the acylate mixture
EBECRYL 150: (7.5 g) Polyoxyethyl biphenol A Diacrylate
EBECRYL 629: (7.5 g) mixture of 20% trimethylolpropane triacrylate and 80% epoxy novolac acrylate. Homogenize in 2 minutes; after cooling, a resin is obtained.

Examples 2 to 4
Solubilization of active molecules
Blends are made according to the following process
Active substance: 0.315 g
NVP. ig
Acetone (or DMF): 4 g
Previous resin: 5 g
(example 1)
10, 315 g
The active substance is first dissolved in the NVP + solvent mixture at room temperature; the mixture is then added to the hot resin (60ex); it is homogenized for 3 minutes; This produces collodions that can be filmed; prepared films are very good qualities; the percentage of active molecule in the polymer is about 5%.

It is possible to crosslink this film under an electron beam.

Active molecules

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<tb><SEP> a
<tb><SEP> P
<tb><SEP> AT
<tb> HOU <SEP> OH
<Tb>
Fluid collodion + homogeneous-fluid resin
Example 3

Fluid collodion + homogeneous-fluid resin
Example 4

Fluid collodion + fluid homogeneous resin
Measurement of the activity of the film of Example No. 3
The measurement of the coefficients 113 and 333 of electrooptic quadratic susceptibility is carried out by an interferometric method described in the article by R. MEYRUEIX et al. Fall Meeting of The Material
Research Society - Boston MA (USA) - Nov. 28 - Dec. 2 1989 - entitled "Rotationnal diffusion of Chromophores inside a glassy polymeric film studied by electrooptical interferometry".

Gold electrodes (thickness 100 Å (10 nm) are deposited on the 2 faces of the film which is polarized under a field of 25 volts / m according to the procedure described above.

At room temperature, the film is subjected to an alternating voltage of 50 volts-500 Hertz, and crossed at a 45 "incidence by a light beam of wavelength 830 nm.The measurement of the transmittance modulation of the film for the polarizations TE and TM give the following values for E / O susceptibility at 830 nm X113 = 0.3 × 10-12 mv -1 and X 333 = 1.0 × 10-12 mv -1.

Of course, a more intense polarization field would induce high values for the X

Claims (6)

1) Composition of the type comprising a matrix formed based on polymer (s) and at least one hyperpolarizable compound characterized in that the main constituent of the matrix is a thermosetting polymer imide group, preferably maleimide groups. 2) Composition according to claim 1, characterized in that the concentration of hyperpolarizable compound is between 1 to 20% by weight of copolymer. for example, α-methylstyrene, divinylbenzene or ethylvinylbenzene. (c) consisting of a styrene compound, such as N-vinylpyrrolidone-2, allyl isocyanurate, vinyltetrahydrofuran; taken from the group consisting of: vinylpyridines, (b) one or more substituted heterocyls (s) a (or) reagent (s) (b) and / or (c) and X represents an atom hydrogen, a methyl, ethyl or isopropyl radical; wherein T represents a single valency bond or 1,4-phenylene group; and radicals of the formula phenylene-1,3; 6-methyl-1,3-phenylene; 2,5-diethyl-3-methyl-4-methyl-1,3-phenylene; 2-methyl-1,3-phenylene; methyl-5 group consisting of the radicals: cyclohexylenes; phenylene; . the symbol A represents a divalent radical chosen from the. the symbols Y independently represent H, CH3 or Cl in which an N, N'-bis-imide of formula C at 180 ° C between - (a) one or more bis-maleimide (s) corresponding to the formula (I ') 3) Composition according to claim 1 or 2, characterized in that said polymer can be obtained by a reaction, at a temperature of 50 and / or by a carbon atom of a benzene ring. range (s) by a carbon atom of an aliphatic chain valence (s) free (s) aromatic B radical may be more free hydroxyl function (s), the (or) structure one or a plurality of oxygen and / or aromatic bridges capable of containing at various locations its alkylene having from 1 to 3 carbon atoms, said single valency remainder, an inert group or a radical as indicated above, connected to one another by a plurality of benzene rings, optionally substituted with alkyl radicals having from 1 to 5 carbon atoms, or by benzene, which may be substituted with one or three to 150 carbon atoms constituted by an aromatic ring (of the aryl or arylaliphatic type) having several free hydroxyl function (s); a remainder containing one or more oxygen and / or branched bridge (s) having from 1 to 30 carbon atoms and possibly derived from: a linear saturated aliphatic radical or the symbol B represents an organic valence radical n equal to 1 and at most equal to 8 methyl radical; nn represents an integer or fractional number at least the symbol R6 represents a hydrogen atom or one in which: (CH2 = CR6 - CO - O -B several compound (s) of general formula - and one or more acrylate reagents (d) ) consisting of one or 4). Composition according to one of Claims 1 to 3, characterized in that the said hyperpolarizable compound has a non-linear quadratic susceptibility. 5). Composition according to Claim 4, characterized in that the said hyperpolarizable compound is a non-centrosymmetric compound having at least one donor group A, at least one acceptor group connected by a linking system (s) at least double (s). 6). Material characterized in that it comprises at least partly poly-imide according to claims 1 to 5. 7). Material according to Claim 6, characterized in that it is used in the form of a film. 8). Material according to one of claims 1 to 7, characterized in that it is used as a coating. 9). Device containing at least one active element in nonlinear optics, characterized in that said element is constituted by the material according to one of claims 1 to 8, preferably 7 and 8. 10). Process for the preparation of film according to one of claims 7 and 8, characterized in that said material according to a process comprising the following steps  1) The constitive resin of the matrix is dissolved in a solvent  2) The active molecule is dissolved in the preparation obtained in 1)  3) The solvent is evaporated  4) A film is made  5) It is oriented under electric field E at a temperature at least  equal to that of glass transition waste.  Let cool with E until ambient.  6) It is cross-linked under electron beam e, which gives a film  whose glass transition temperature Tg is greater than 300 ° C. The electric field can be cut after step 5).