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New trends in high polymer synthesis and structural characteristics of the new materials.

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Die Angewandte Makronzolekulare Chemie 22 (1972) 87-105 ( N r . 298)
From the Universiteit te Leuven, Laboratorium voor Macromoleculaire
Scheikunde, Belgium
New Trends in high Polymer Synthesis, and structural
Characteristics of the new Materials
By G. SMETS*
(Eingegangen am 3. Juni 1971)
SUMMARY:
The development of the polymer chemistry during the last decade is characterized by the existence of several new methods of polymerization, e. g. the isomerization polymerization of aliphatic hydrocarbons, the oxidative catalytic polymerization of aromatics, the photochemical polyaddition, the 1.3 and 1.4 dipolar polycycloadditions, the two step polycondensation processes. Some of these methods
have already been applied on an industrial scale. Simultaneously new catalytic
procedures were discovered, some of which permit stereoregular copolymerization,
and very recently stereo-elective polymerization. These different aspects will be
considered successively.
The isomerization polymerization in which the chain growth is characterized by
alternate addition isomerization steps, is illustrated by several examples, and compared to the polymerizations with previous monomer isomerization, as in the case
of B-olehs.
The stepwise oxidative coupling of different 2.6 disubstituted phenols, with
oxygen in the presence of amine complexes of copper salts is considered from kinetic
and structural point of view and compared with the oxidative FRIEDEL-CRAFTS
reaction on aromatic hydrocarbons.
Two types of photochemical polyadditions are considered on the basis of the
cyclomerization reaction, in which cyclobutane rings are formed by dimerization
of olefins (in solution and in the solid state), and of the reductive dimerization, e. g.
of bisarylketones into polypinacols.
The use of 1.3 dipolar cycloaddition for the synthesis of heterocyclic rings containing polymers is illustrated and some properties of these polymers are described.
Similarly the 1.4 DIELS-ALDER
cycloaddition is exemplified by the synthesis of
polyphenylenes as described from biscyclopentadienones or (and) bis-phenylenebispyrones and diethinylbenzene.
Only short mention will be made on the synthesis of thermally stable polymers
by polyheterocyclization, e. g. single strand benzoxazole- and benzthiazole-imide
copolymers and Kapton fibre, and double strand ladder polypyrrolone-anthrachinone fibres. New catalytic procedures are finally briefly commented as far as they
*
Presented at the Scientific Symposium “The Physics and Chemistry of Fibre
Materials”, Miinchen, 3rd and 4th June 1971.
87
G. SMETS
offer possibilities for the synthesis of new polymers and regular copolymers. Some
properties of these new polymers are reported.
ZUSAMMENFASSUNG :
I n den letzten 10 Jahren sind auf dem Gebiet der Polymer-Chemie einige neue
Polymerisationsmethoden entwickelt worden, z. B. die Isomerisierungs-Polymerisation von aliphatischen Kohlenwasserstoffen, die oxidative katalytische Polymerisation von Aromaten, die photochemische Polyaddition, die 1,3-und 1,4-dipolaren Polycycloadditionen und die Zwei-Stufen-Polykondensationen.
Einige dieser Methoden sind schon industriell angewandt worden. Gleichzeitig
wurden neue katalytische Prozesse entdeckt, die eine stereoregulierte Copolymerisation erlauben und seit kurzem sogar stereoselektiv verlaufen.
Die Isomerisierungs-Polymerisation,bei der das Kettenwachstum durch alternierende Additions-Isomerisierungs-Schrittecharakterisiert ist, wird an einigen
Beispielen aufgezeigt. Diese Methode wird verglichen mit Polymerisationen, der
eine Isomerisierung am Monomeren vorausgeht, wie es z. B. der Fall mit B-Olehen
ist.
Die stufenweise oxidative Kupplung von verschiedenen 2,6-disubstituierten
Phenolen mit Sauerstoff in Gegenwart von Aminkomplexen von Kupfersalzen
wird aus kinetischer und struktureller Sicht betrachtet. Es wird ein Vergleich mit
der oxidativen FRIEDEL-CRAFTS-Reaktion an aromatischen Kohlenwasserstoffen
angestellt .
Zwei Typen von photochemischen Polyadditionsreaktionen, die auf einer Cyclopolymerisation beruhen, werden betrachtet. Cyclobutan-Ringe werden einmal
durch Dimerisation von Olehen gebildet (in Losung und im festen Zustand) und
zum anderen durch reduktive Dimerisation, wie z. B. von Bis-arylketonen zu
Polypinakolen.
Die Anwendung der 1,3-dipolaren Cycloaddition zur Synthese von heterocyclischen Ringen in Polymeren sowie einige Eigenschaften dieser Polymeren werden
beschrieben. So wie die 1,4-DIELS-h~ER-Cy~loaddition
beispielhaft fiir die Synthese von Polyphenylen ist, wird dies bei Cyclopentadienonen oder/und Bis-phenylbis-pyronen und Diiithinylbenzol beschrieben.
Kurz erwiihnt wird die Synthese von thermisch stabilen Polymeren durch Polyheterocyclisierung, z. B. einfache Ketten- Benzoxazol- und Benzthiazol-imid-Copolymere und Kapton-Fasern, ebenso doppelkettige Leiter-Polypyrrolon-Anthrachinon-Fasern.
SchlieBlich wird kurz uber neue katalytische Prozesse sowie deren Moglichkeit
zur Anwendung zu Synthesen von neuen Polymeren und regelmaBigen Copolymeren berichtet. Einige Eigenschaften dieser neuen Polymeren werden beschrieben.
The most important progresses in vinyl polymerization, and especially in aolefin polymerization are originated in the discovery of new catalytic systems by
ZIEGLER~
and N A T T A
3, ~
which
~
are able t o influence basically the monomer additions during the chain propagation. These new methods of stereoregular polymerization, based mainly on the use of heterogeneous coordination catalyst,
have been rapidly generalized and applied t o most varied monomers. On the
88
N e w Trends in Polymer Synthesis and Characteristics
other hand, a progressively better knowledge of the basic principles of coordination catalysis in polymer chemistry made possible an important development
in the domain of the polymerization kinetics concerning the nature of the catalytic systems (heterogeneous, homogeneous, coordination anionic and cationic),
their use for several monomers, olefins, dienes, vinyl ethers, ring compounds etc.
Although a review of these progresses reaches far beyond the scope of this
lecture, it is however unthinkable to omit to stress again their deep influence on
the development of the chemistry and the physics of high polymers.
A, N e w Aspects of Polymerization
From the organic chemical point of view, some new aspects of these polymerizations should be however pointed out, and will be considered successively,
namely,
a ) the isomerization polymerization, in which each chain growth step alternates
with an intramolecular rearrangement,
b) the polymerization with previous monomer isomerization (/?-olefines),
c) ring opening polymerization.
I n the isomerization polymerization several a-olefhes undergo an hydrogen
shift rearrangement a t each propagation step. Such intramolecular rearrangement occurs extensively, for example, in the cationic polymerization of 3-methylbutene-14 and 4-methylhexene-15, involving a 1.2 and 1.3hydride shift respectively :
R @X'
+ CH2
=
CH-CHMe2
12add.
+
1.2 hydride
0
R-CH2-CH-CMe2
shift
I
>
XG H
Me
0
R-CH2-CH2--CMe2
--+
X@
R-
CH2-CH2-C-
I
I
0
X@
Me
1.3 polymer
(2)
R-CHz-CH2-CH2-C-Et
0
I
X@+ R-
Me
1.4 polymer
89
G. SMETS
Low polymerization temperatures favour such rearrangements, for the activation energy for hydride shift is lower than that of propagation.
Methyl shift can also occur e.g. in the boronfluoride polymerization of
3.3-dimethylbutene-16 (3) and 3-phenylbutene-17.
The growing neopentyl carbonium rearranges to tert.-amyl carbonium, the
last being 10 to 15 Kcal more stable than the former. The temperature dependence of the rearrangement is again important, the extent being about 50%
a t 45°C while complete a t -130”.
The resulting polymers, so called “phantom polymers” present three or more
carbon repeating units, instead of the usual two carbon one corresponding to
the monomer.
These arrangements can be compared with those occuring in the base catalyzed polymerization of acrylamide899and maleimide 10 where intramolecular proton transfer reaction alternates with each 1.2 addition step :
CHz= CH-CO-RHz
/
R* ,/
J
R-CH~H-CORH~
1.2 addition
\ \,Be
I
0
B-CH~CH-CO-RH~
I
(4)
1.3 proton shift
B-CH~CH~-CO-EH
0
!
.I
R-(CHz-CH-)x
I -
CONHz
poly acrylamide
poly-,!?-ahnine
The polymerization of ,!?-olefinswith previous isomerizationsll might become a
very attractive method, because ,!?-olefins are available in large quantities e.g.
from cracking processes, olefin dimerization, dehydration of alcohols. It is based
New Trends in Polymer Synthesis and Characteristics
on the use of dual-site catalysts, which are responsible for two independent
steps, namely first the isomerization, secondly the polymerization.
Thusl2, butene-2 polymerizes very difficultly by steric hindrance compression,
and isomerizes t o butene-1. Although the concentration of butene-1 a t equilibrium is low (3 to 5 yo)on account of its lower stability than that of butene-2, it
polymerizes in the presence of ZIEGLER-NATTA
catalysts much faster, and is
thus removed from the dynamic equilibrium existing a t the catalyst site; on the
other hand, the rate of isomerization is sufficiently high in order to assure a sufficient monomer concentration and give high molecular weight homopolybutene-1.
Similarly 4-methylpentene-2 gives in the presence of AlEt3/TiCl3/CrCl3poly4-methylpentene-113 (5):
(CH~)ZCH-CH=CH--CH~
-
(CH~)ZCH-CHZ-CH=CHZ
-
polymer (5)
As suggested by K E N N E D Y
one
~ ~could imagine as well that a dualsite catalyst
could enhance dismutation of an olefin, followed by polymerization of the dismutation products; thus a mixture of butene-1 and butene-2 could afford ethylene-proyplene copolymers.
The driving force of a holocarbon ring opening polymerization is provided by
the strain caused by bond-angle distortion and the resulting strain in the rings
and double bonds. Ring opening instead of 1.2 addition by bond opening adjacent to double bond is strongly dependent of the nature of the catalyst149159 16.
Thus cyclobutene gives the two following possibilities (6):
“normal” 1.2 addition
(61
MoCl5
-CH2-CH=CH-CH2--
cis or trans 1.4 addition
in the exclusion of 1.2
butadiene units
Cyclopropane, and 1.l-dimethyl cyclopropane give in the presence of aluminium bromide and hydrogen bromide only low polymers17 with the same structure as poly-3-methylbutene
CH3
(-CHz-CHz-C-)
I
n
I
CH3
Similar ring opening can also occur during radical polymerization, e.g. in the
case of vinylcyclopropane derivativesl*919 (7):
91
G. SMETS
R -CH2-CH-
-
R -CH2 -CH =C H- CH2?!C
I
I
Very recently HALL^^^ 21922 has shown that the polymerization of bicyclocompounds (x. y. 0)with opening of a strained single bond may present new possibilities. For example, 1-bicyclobutane carbonitriles undergo readily free radical
and anionic homopolymerizations to form high polymers containing 1.3-cyclobutane links in the chains. The poly-1-bicyclobutane carbonitrile melts only at
370°C and is thermally a stable compound:
Similarly copolymerization with styrene, methylmethacrylate and with other
bridge-head-substituted bicyclobutanes gives a new class of high molecular
weight copolymers:(9, 10):
B. Step growth Polymerizations
Step growth polymerizations by radical coupling must be considered as a new
synthetic method of polyaddition. The formation itself of the radicals can be
achieved either by oxidative or reductive way, and both cases will be considered successively.
2.6-Disubstituted phenols, f. e. 2.6-dimethylphenol23, can be easily oxidized
already a t room temperature in homogeneous medium by bubbling oxygen in
the presence of tertiary amine, very often pyridine, and a copper I-salt (Py/Cul
> 10). When the substituents are small, carbon-oxygen coupling prevails and
high molecular weight polyarylene ethers are obtained (11)
> 200). Their
softening points are higher than 240 '(324. Only minor amounts of diphenoquinone are formed :
(xn
92
(7)
New Trends in Polymer Synthesis and Characteristics
On the contrary, with bulky groups as tert.-butyl carbon-carbon coupling occurs exclusively and diquinone derivatives are obtained (12):
R = t .C&
Though the carbon-oxygen versus carbon-carbon coupling is depending on the
ratio amine/copper, very likely on account of the formation of (at least) two
copper-pyridine complexes25, one admits the reaction scheme (13), in which
two phenoxy radicals give oxygen carbon cross-coupling:
Chain growth26 results then from coupling of oligomeric radicals to give quinol
ethers as intermediates (14). The polymer chain grows only a t the phenoxy end
group, and corresponds to
^..
p'
0
It
0'
I
P'
cH3w
0
' V
I
93
G. SMETS
a step growth polymerization, both because of the equal reactivity of all species
and of the continuous generation of new species by hydrogen atom transfer27.
Oxidative coupling of acetylenic units by copperI1-salts is also a well known
reaction in organic synthesis28 (15):
-
R-C-C-Cu+II
2R-CAP
R-C-Cx
CuI
(15)
R-C-C-R
4
and was applied to m- and p-diethinylbenzene with formation of poly ethinylaryl derivatives results29 (-C-G-CGH~-C-C)~.
The so called polyrecombination reaction described by KORSHAK
must be considered as a radical coupling reaction of bifunctional monomers capable of
forming benzylic type radicals30931 a t both sides. A typical example is given by
heating p-diisopropylbenzene in the presence of a large excess (5 to 10%) of
tert.-butylperoxide a t relative high temperature. Schematically, one assumes
a-hydrogen abstraction by the radicals (tert.-C4HgO. or methyl radicals,
CH3COCH3 * CH3) produced by homolytic scission of the peroxide, and coupling of the resulting cumyl radicals (16):
+
Rs
+ MezCH-@HMe2
--L
RH
+
Me2CH-@Me2
Although very attractive and quite general in its basic principles, it is likely
that the detailed structure of these polymers are still not firmly established.
Indeed, recombination between cumyl type radicals with primary radicals, originating from the initiator, disproportionation between sterically hindered radicals a t high temperature, as well as chain branching seem difficult to be avoided
in the drastic conditions used in these experiments.
The formation of polydisulfides by oxidation of bisthiols (17) with ironm chloride32 or with air 33 in soap emulsion systems as described by MARVELand COworkers must also be ranged in this general class of radical coupling polyadditions :
HS-R-SH
94
+ [O]
- H20
-(S-R-S),
(17)
New Trends i n Polymer Synthesis and Characteristics
Mention should also be made of the oxidative FRIEDEL-CRAFTS
reaction described by KOVACIC
and coworkers349359 36 in which polyphenylenes are obtained
by oxidation of aromatic compounds in the presence of a LEWISacid and an oxidizing agent. Though polymers are dark coloured and insoluble, the main structure is mainly characterized by para-aromatic linkages.
It is assumed that the reaction is related to the reaction of SCHOLL
and proceeds through the formation of a phenonium ion, that initiates an electrophilic
aromatic substitution followed by a n oxidative dehydrogenation37:
The photoreductive dimerization of bisarylketones into polybenzpinacols
afyords another nice example of radical coupling polyaddition growth. Indeed, by
ultraviolet irradiation of arylketones in the presence of isopropylalcohol in dichloromethane, it is indeed possible to obtain in very mild reaction conditions
benzpinacols3*,39940. The same reaction principle has recently been applied to
bisarylketones following the overall reaction scheme4174% 43 :
[
Ar-S-M-R-
Arf-C-
II
0
Ar
1
xCH3-cHOH-c,
hV
[
+
-~~Ar’-R-Ar’-~~]
OH
(19)
OH x
x CH3CO-CH3
If the corresponding bisbenzhydrol derivative is used as reducing agent instead
of isopropanol, secundary reactions due to the (CH3)2&OH small radicals44
are avoided, and the overall reaction becomes :
H
-C-Ar’-R-Ar‘-C-Ar
II
0
II
0
I
+ Ar-C-Ar‘-R-Ar‘-C-Ar
I
OH
r h
H
I
--+
OH
I
1
Ar
I
I
-C-Ar’-R-Ar’-C-
I
H
!
OH
(20)
Self-evidently the reaction mechanism can be varied depending the reaction
partners and on this way copolybenzpinacoles are easily accessible.
C. Photochemical Step Growth
I’hotochemical step growth has been developed very recently and simultaneously in our laboratories by DE SCIIRYVER
and coworkers 45146, and by HASE96
G. SMETS
and coworkers47*48~
49. The reaction principle consists in the cyclodimerization of olefines into cyclobutane derivatives50.
I n these experiments, the coupling reaction consists in the photocyclodimerization of bischromophoric derivatives, e.g. bismaleimides, biscoumarines, bisaacryl-, biscinnamoyl derivatives and results in cyclobutane ring closure. A typical example of these cyclomerization is given by the bismaleimides :
GAWA
Remarkably high are the stabilities of these cyclobutane ring containing polymers, even when R represents a polymethylene chain (Tdecomp > 300°C). It
may be also worth-while to mention that where these reactions are carried out
in the solid state, highly crystalline polymers are obtained without appreciable
contraction ; their solubility and stability properties are different of those obtained in solution and are related with a different endolexo structure ratio of
the cyclobutane rings, as a consequence of a different reaction mechanism.
D. Cycloaddition
Cycloaddition constitutes another attractive method of synthesis of new
polymers. A priori, distinction should be made between 1.3- and 1.4-cycloaddition.
1.3 dipole i b c reacts with a dipolarophile(d = e)51
d-e
Considering that these reactions are usually carried out in very mild conditions and very often proceed with high yields, they give many possibilities if
one uses dipoles and bis-dipolarophiles, (A-A B-B polyaddition), or a compound containing both a dipole and dipolarophile (A-B A-B). Several examB-B type will
ples are now available, and only two examples of the A-A
be given as illustration. The reader should refer t o the abundant literature available in this domain.
+
96
+
+
N e w Trends in Polymer Synthesis and Characteristics
The cycloaddition of bis-p-cyano benzonitrile oxide with 1.4 diethinylbenzene52 gives a yellowish polymer, infusible up to 500 "Cin an inert atmosphere ;
its structure corresponds to an alternation of 1.4-benzene and 3.5-isoxazole
rings :
Similarly cycloaddition of 1.4-diazidobenzene with bismaleimides and other
bisdipolarophiles53 can be easily carried out and gives e. g. polytriazolines polymers; these polymers, on heating a t 60"C, loose nitrogen and give polymers
containing aziridine rings in the main chain. Further ring opening (thermally
or photochemically) of such aziridine rings affords evidently new reaction possibilities :
The 1.4-cycloaddition can be best examplified by the DIELS-ALDER
reaction
and coworkers. The reaction of bistetracyclones
as described by J. K. STILLE
with m- and p-diethinylbenzene in toluene a t 225°C affords high yellow amorphous phenylated polyphenyls54155with outstanding thermal stability and soluble in common organic solvents (up to 10 weight %) ; on the .contrary, the
97
G . SMETS
polyphenylene prepared by oxidative FRIEDEL-CRAFTS
reactions (see above)
are brown to black, and insoluble in any solvent.
Thermal decomposition of these polymers involves the loss of side phenyl
groups, and causes cross-linking of the film, without appreciable main chain
degradation. Similar products have been obtained from 1.4-cycloaddition reaction of bispyrones with bisacetylenes56~
573 58.
E. Ladder Polymers
The synthesis of ladder polymers constitutes another high light of polymer
syntheses in which very important advances have been realized during the last
decade. An excellent review on these problems was published recently by OVERBERUER and MOORE59.
Several reaction principles can be imagined to form ladder systems; the
two most important methods will be considered here :
a ) ladder formation based on “zipping u p ” of side reactive functional
groups, as carbonyl groups (polyacroleine60f61, polymethylvinylketone62*63),
nitriles (Black Orlon)649 659 6% 67, vinyl68 and acetylenic groups69 and isocyanates70.
The reaction for polyacroleine (26) and polyacrylonitrile (27) can be schematized as follows :
98
New !l’rends in Polymer Synthesis and Characteristics
or
Black Orlon is obtained by a regulated pyrolysis of polyacrylonitrile; in a
first step the nitrile groups “zipp u p ” with very little formation of volatile
products, thereafter aromatization occurs into a polyquinizarine or a partially hydrogenated polyquinizarine.
The major difficulty in this “zipp up” method is, besides a selective first polymerization step through one functional group, to limit the ladder formation
along and within a single chain in order to avoid insolubilization by cross-linking, and nevertheless preserve a sufficient ladder length.
The second method, named polyheterocyclization, is usually a two step polycondensation reaction in which the ladder is completed in a second condensation reaction.
The ladder formation is strongly favoured versus cross-linking (due to intermolecular condensation) by the formation of conjugated aromatic rings, and
by the great tendency for 5- and 6-membered ring closure.
Particular mention should be deserved to the ordered copolyamides and benand
zoxazole and benzthiazole-imide copolymers developed by PRESTON
13LACK71-77.
These heterocyclic units containing imide copolymers have unusually high
thermal decomposition temperatures in the range of 560-625 “C.
Most polyheterocyclization products present however some disadvantages
which make difficult their technological use; indeed, they do not melt below
400-500 “C and are poorly soluble (only in concentrated HzS04, methane sulfo99
G. SMETS
nic acid) ; consequently, they must actually be fabricated in a prepolymer form,
and then converted to the heat resistant material.
C. S. MARVELapplied the general principles of anthraquinone vat-dyes to
the synthesis of thermally stable polymers, i. e. reduction of anthraquinone
systems with sodium dithionite into soluble anthrahydroquinones, which will
reoxidize in the air into the stable products789 79*80.
Most satisfactory product was recently obtained from 1.2.5.6-tetraaminoanthraquinone with 1.4.5.8-naphthalene tetracarboxylic bis-anhydride 81.
A polypyrrolone with an inherent viscosity of 2,7 was obtained; it has been
wet spun (10% in methanesulfonic acid) into a dark green flexible fibre, that
is stable up to about 550 "C in air :
\o
/
H2N
DMAc
160°
0
P. Optically Active Polymers
A last very attractive and important field of research is in our opinion the
synthesis of optically active polymersgz. Such polymers can of course be syn100
N e w Trends in Polymer Synthesis and Characteristics
thesized by polymerization of corresponding optically active monomers, or by
chemical transformation of a preexisting polymer with an optically active substance.
Two other methods of synthesis have however been used, and will be commented briefly.
Optically active polymers have been obtained from monomers that do not
present optical stereoisomerism using a catalytic process responsible for asymmetric synthesis ; such polymers contain asymmetric (non-compensated)carbon
atoms only in the main chain, e. g. polybenzofurane prepared in the presence
of an aluminium halide and optically active p-phenyl alanine catalyst83284.
Another method is based on the selective polymerization of one optical antipode from the racemic mixture in the presence of stereospecific catalysts.
N ATTA, PINOand coworkers demonstrated that poly-4-methyl hexene obtained
in the presence of Et3Al-TiC13catalyst can be separated in two antipode polymeric fractions859 86,879 88.
Similarly (R) (S) 3-methyl-pentene-1 was polymerized in optically active
polymer in the presence of Tic14 di [(S) 2-methyl butyl] zinc, and the residual monomer was itself active.
Such a stereo elective polymerization was also obtained by TSURUTA
and his
coworkers89~9% 91 in the case of propylene oxide ; using a asymmetric catalyst
consisting of diethylzinc and d-borneol, (+) propylene oxide was incorporated
into the polymer chain in preference to its optical antipode.
It was shown91 that the enantiomorphic nature of the catalyst site and not
the asymmetry on the growing polymer chain end is responsible for the stereocontrol.
Similar results were also reported for propylene sulfide92, for N-carboxy-a
amino-acid anhydride93, e. g. DL-alanine NCA gives an optically active polypeptide in the presence of an optically active alcohol in combination with trietlhylaluminium.
Undoubtedly the stereoelection of one optical antipode with respect to the
other one constitutes one of the most fascinating problems in the organic and
coordination chemistry. Applied to polymer synthesis, it may once contribute
very fundamentally to a better understanding of enzymatic syntheses and
properties of biological systems.
+
Discussion
H. RINGSDORF,
Mainz : Do you run your photopolymerization of bis-maleimides
in the solid state or in solution? Is it a topochemical reaction?
G. SMETS:
Both polymerizations have been carried out. The polymers obtained in
solution have a ratio exo/endo of the cyclobutane rings of about 4 or more; contra-
101
G. SMETS
ril y the polymers irradiated in the solid state polymerize apparently without appreciable contraction and are mainly exo.
H. RINGSDORF,
Mainz: What about the configuration of these polymers? Are they
exo or endo ? And how are the properties influenced by the configuration ?
G. SMETS
: The solubility and thermostability properties have been compared and
will describe the melting
differ markedly; a forthcoming paper of Dr. DE SCHRYVER
points and the TGA behavior.
P. SIGWALT,
Paris : Could Professor SMETSgive us some information about the
mechanism involved in the polymerization of cyclobutane carbonitrile.
G. SMETS
: The polymerizations and copolymerizations described recently by Professor HALLand Du Pont’s coworkers (J. Amer. Chem. SOC. 1971) for dicyclobutane carbonitriles and -esters, were carried out in the presence of radical initiators as AIBN, and proceed without difficulties.
H. HERRLINGER,
Stuttgart : Are the KOVACIC
polymers n-8-complexes? n-&Cornplexes would cause colour and would cause an insolubility by chain interaction.
G. SMETS
:Though difficult to control, it is evident that such interactions should
intervene as well in the discolouration and solubility properties. A treatment of Prof.
STILLE’S
polyphenylenes with AlC13 could possibly afford a definitive answer to that
problem.
L. BONNARD
: Vous avez par16 des possibilites de polymerisation de l’acrylamide
donnant soit le polyacrylamide soit le nylon 3 et des maleimides donnant des cycles
cyclobutanes mais il est impossible en fait d’obtenir un seul type de rBaction. Dans le
premier cas on ne peut pas obtenir le nylon 3 seul par exemple etdans le second cas
il n’est pas possible d’obtenir uniquement la formation de cycles cyclobutane sans
reaction parasites de la double liaison. Pour que ces diverses reactions puissent
avoir des applications ne pensez-vous pas qu’il est necessaire que les Btudes des
prochaines ann6es portent sur la spBcificit6 des ces rbctions?
G. SMETS
: The formation of poly-/I-alanine was described by BRESLOW,
and is based on a base-catalyzed isomerization. The strong alkaline medium is evidently not
as selective as one should like to have ;moreover, some alkaline hydrolysis is difficult
to avoid.In the case of maleimides, the reaction can proceed very nicely and without insolubilization, likely due to the greater stability of the -CO-N-CO- anion and
the higher stability of the imide towards alkaline hydrolysis.
@
With respect to the photochemical cyclomerization (cyclobutane ring formation)
it is indeed necessary to have substitution (f. e. halogenes) on the maleic double bond,
if one would avoid photo cross-linking.
H. W. SCHNECKO,
Hanau : I n case of vinyl cyclopropanes you have only shown one
mode of polymerization i. e. involving the ring-opening of the strained ring. In this
has shown that various structures with ring-opening are obtained.
case, PINAZZI
However, polymerization of the vinyl double bond only is also possible a t least with
the unsubstituted ring (OVERBERGER).
On the other hand, at least one case is
known where 3-ring opening cannot be avoided : vinyl episulfide. Even with radical
catalysts polymerization occurs with participation of the heterocyclic ring. (J.
Polym. Sci. A 1 8 (1970)).
G. SMETS:I do agree entirely with the remarks.
102
New Trends i n Polymer Synthesis and Characteristics
K. ZIEGLER,E. HOLZKPMP,
H. BREIL,and M. MARTIN,Angew. Chem. 67 (1955)
541.
2 G. NATTA,
Atti Accad. Naz. Lincei, C1. Sci. Fis. Mat. Nat. Rend. 4 (1955) 61.
3 G.NATTA,
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