Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Plastics technology. Часть 2. Учебное пособие.pdf
121
Table 7 – Selected properties of PC-ABS and PC-PBT alloys
PC-ABS
High
Low
GF-reinforced
(20% glass)
Vicat softening point, °C
111
130
130
125
O C
CH
3
CH
3
O
C
O
O
C
CH
3
CH
3
O
C
O
O
C
Grade
ABS
ABS
Low ABS
PC-PBT
basic
grade
Specific gravity
Water absorption, %
Oxygen index, %
Tensile strength, MPa
Elongation at break, %
Flexural modulus, MPa
Ball hardness, N/mm
2
1.1
0.7
21
40
60
2000
80
1.16
0.6
24
50
85
2200
90
1.2
0.6
24
75
2
6000
125
1.22
0.35
<21
55
75
2200
96
Yet another recent development has been the alloying of
polycarbonates with liquid crystal polymers. These alloys are notable for
their very good flow properties and higher strength and rigidity than
conventional bisphenol A polycarbonates.
1.4.6 Polyester Carbonates and Block Copolymers
In the 1980s a number of copolymers became established, known
as polyester carbonates, which may be considered as being intermediate
between bisphenol A polycarbonates and the polyarylates.
These materials have the general structure shown in Figure 34 and
are prepared by reaction of bisphenol A with iso- and/or terephthalic acid
and a carbonate group donor (e.g. phosgene or diphenyl carbonate).
Because of the irregular structure the copolymers are amorphous
and transparent. The higher the polyester component the higher the
softening point, typical grades having values in the range 158-182°C
compared with 148°C for unmodified polymer. On thermal aging the
polyester carbonates also show a lower tendency to embrittlement than
Figure 34
122
polycarbonate. This is, however, at the cost of a reduction in notched Izod
HO
C
OH
R
R
1
impact strength (35-28 kJ/m2, compared to 45 kJ/m2 for unmodified
polymer) and increased melt viscosity. As with the poly(co-carbonates)
based on bisphenol A and bisphenol S, the polyester carbonates have a low
level of notch sensitivity. The polyester carbonates are easier to process
than the polyarylates.
Block copolymers of polycarbonates and silicone polymers have
also been commercially marketed (e.g. Makrolons KU 1-1198 and KU 1-
1207). These block copolymers show a marked increase in toughness at
low temperatures coupled with reduced notch sensitivity. (They show little
improvement in toughness at normal ambient tem perat ures. )
1.4.7. Miscellaneous Carbonic Ester Polymers
Unless the hydroxyl groups have such proximity that cyclization
takes place, polycarbonates will normally be produced whenever phosgene
or a carbonate ester is reacted with a polyhydroxy compound. This means
that a very large range of polycarbonate resins are possible and in fact
many hundreds have been prepared.
Aliphatic polycarbonates have few characteristics which make
them potentially valuable materials but study of various aromatic
polycarbonates is instructive even if not of immediate commercial
significance. Although bis-phenol A polycarbonates still show the best allround properties other carbonic ester polymers have been prepared which
are outstandingly good in one or two specific properties. For example,
some materials have better heat resistance, some have better resistance to
hydrolysis, some have greater solvent resistance whilst others are less
permeable to gases.
It is particularly interesting to consider the influence of the
substituents R and R1 in diphenylol alkanes of the type shown in Figure 35.
Such variations will influence properties because they affect the flexibility
of the molecule about the central C-atom, the spatial symmetry of the
molecule and also the interchain attraction, the three principal factors
determining the physical nature of a high polymer.
Figure 35
123
Thus where R and R1 are hydrogen the molecule is symmetrical,
the absence of bulky side groups leads to high intermolecular attraction and
the flexibility of the molecule enables crystallization to take place without
difficulty. The resultant material is highly crystalline, with a melting point
of above 300°C, and is insoluble in known solvents.
Where R is hydrogen and R1 a methyl group the molecule is less
symmetrical and less flexible and the intermolecular attraction would be
slightly less. The melting point of this polymer is below 200°C. In the case
where R and R1 are both methyl groups the molecule is more symmetrical
but the flexibility of the molecule about its central carbon atom is reduced.
The higher aliphatic homologues in this series show lower melting
points, the reduction depending on symmetry and on the length of the side
group. The symmetrical methyl, ethyl and propyl disubstituted materials
have similar glass transition temperatures presumably because the
molecules have similar degrees of flex ibil i ty .
Introduction of aromatic or cycloaliphatic groups at R and/or R1
gives further restriction to chain flexibility and the resulting polymers have
transition temperatures markedly higher than that of the bis-phenol A
polycarbonate.
Polycarbonates have also been prepared from diphenyl compounds
where the benzene rings are separated by more than one carbon atom. In
the absence of bulky side groups such polymer molecules are more flexible
and crystallize very rapidly. As is to be expected, the more the separating
carbon atoms the lower the melting range.
Polymers have been prepared from nuclear substituted di-(4hydroxyphenyl)-alkanes, of which the halogenated materials have been of
particular interest. The symmetrical tetrachlorobis-phenol A yields a
polymer with a glass transition temperature of 180°C and melting range
of 250-260°C but soluble in a variety of solvents.
Crystallizable polymers have also been prepared from diphenylol
compounds containing sulphur or oxygen atoms or both between the
aromatic rings. Of these the polycarbonates from di-(4hydroxyphenyl)ether and from di-(4-hydroxyphenyl)sulphide crystallize
sufficiently to form opaque products. Both materials are insoluble in the
usual solvents. The diphenyl sulphide polymer also has excellent
resistance to hydrolysing agents and very low water absorption. Schnell
quotes a water absorption of only 0.09% for a sample at 90% relative
humidity and 250°C. Both the sulphide and ether polymers have melting
ranges of about 220-240°C. The di-(4-hydroxyphenyl)sulphoxide and the
124
di-(4-hydroxyphenyl)sulphone yield hydrolyzable polymers but whereas
the polymer from the former is soluble in common solvents the latter is
insoluble.
Further variations in the polycarbonate system may be achieved
by copolymerization. The reduced regularity of copolymers compared
with the parent homopolymers would normally lead to amorphous
materials. Since, however, the common diphenylol alkanes are identical
in length they can be interchanged with each other in the unit cell,
providing the side groups do not differ greatly in their bulkiness.
Christopher and Fox have given examples of the way in which
polycarbonate resins may be tailor-made to suit specific requirements.
Whereas the bis-phenol from o-cresol and acetone (bis-phenol C) yields a
polymer of high hydrolytic stability and low transition temperature, the
polymer from phenol and cyclohexanone has average hydrolytic stability
but a high heat distortion temperature. By using a condensate of o-cresol
and cyclohexanone a polymer may be obtained with both hydrolytic
stability and a high heat distortion temperature.
1.5 Polyamides and Polyimides
Whilst by far the bulk of polyamide materials are used in the form
of fibres, they have also become of some importance as speciality
thermoplastics of particular use in engineering applications. The fibreforming polyamides and their immediate chemical derivatives and
copolymers are often referred to as nylons. There are also available
polyamides of more complex composition which are not fibre-forming and
are structurally quite different. These are not normally considered as
nylons.
The early development of the nylons is largely due to the work of
W.H.Carothers and his colleagues, who first synthesized nylon 66 in 1935
after extensive and classical researches into condensation polymer ization.
Commercial production of this polymer for subsequent conversion into
fibres was commenced by the Du Pont Company in December 1939. The
first nylon mouldings were produced in 1941 but the polymer did not
become well known in this form until about 1950.
For a variety of reasons the aromatic polyamides were slow in their
development. A glassy aromatic polymer, poly(trimethylhexamethylene
terephthalamide) became available in the early 1960s as Trogamid T, and
this was followed by a series of other glassy aromatic polyamides in the
1970s and 1980s. During the same period several aromatic polyamides of
125
more regular structure than the glassy polymers became important as fibres
nHOOCRCOOH + nH2R1NH
COO
COOH
nR
H3N
R
1
NH
2
OCRCONHR
1
NH
n
+ 2nH2O
nNH
2
RCOOH
(NHRCO)
n
+
nH
2
O
NH
nR
CO
(NHRCO)
n
because of their exceptional strength in some cases or because of their fireretarding properties in others. In the latter part of the period polyamides
became available which might be classified as thermoplastic rubbers.
There thus exists a very wide range of materials–fibres, cr ystalli ne
plastics, amorphous plastics, adhesives and rubbers–which are classified as
polyamides. They have the common feature that the amide (–CONH–)
group occurs repeatedly in the polymer. Such an amide group can increase
resistance to swelling and dissolution in hydrocarbons, increase interchain
attraction and hence stiffness and heat deformation resistance, reduce
electrical insulation resistance, particularly at high frequencies, and
increase water absorption. However, as with other condensation polymers
which are classified by the group formed during the condensation reaction,
the amide groups form only a small proportion of the molecule, and other
chemical groups may also have an important influence on the properties.
Of the many possible methods for preparing linear polyamides five
are of commercial importance:
(1) The reaction of diamines with dicarboxylic acids, via a “nylon
salt”:
(2) Self-condensation of an ω-amino acid:
(3) Opening of a lactam ring:
(4) The reaction of diamines with diacid chlorides.
(5) The reaction of di-isocyanates with dicarboxylic acids:
OCNRNCO + HOOCR'COOH → –OCNHRNHCOR'– + CO2
This route has only been developed during the 1980s and has
proved of particular interest in the manufacture of thermoplastic polyamide
rubbers.
126
An example of the first route is given in the preparation of nylon
OH
OH
O
HOOC(CH2)4COOH
66, which is made by reaction of hexamethylenediamine with adipic acid.
The first “6” indicates the number of carbon atoms in the diamine and the
second the number of carbon atoms in the acid. Thus, as a further example,
nylon 6.10 is made by reacting hexamethylenediamine with sebacic acid
(HOOC(CH2)8COOH). (In this context the numbers 10, 11 and 12 are
considered as single numbers: the need to use two digits results simply
from the limitations of the decimal system.)
Where the material is denoted by a single number, viz nylon 6 and
nylon 11, preparation from either an ω-amino acid or a lactam is indicated.
The polymer nylon 66/6.10 (60:40) indicates a copolymer using 60 parts of
nylon 66 salt with 40 parts of nylon 6.10 salt.
Closely related to the polyamides are the polyimides and
derivatives such as polyamide-imides and polyether-imides.
Intermediates for aliphatic polyamides
Adipic acid
It is possible to produce adipic acid by a variety of methods from
such diverse starting points as benzene, acetylene and waste agricultural
products. In practice, however, benzene is the favoured starting point and
some of the more important routes for this material are illustrated in Figure
36
A typical route is that via cyclohexane, and cyclohexanol.
Hexamethylenediamine
Hexamethylenediamine may be conveniently prepared from adipic
acid via adiponitrile
Figure 36
127
HOOC(CH2)4COOH
NC(CH
2)4
CN
H2N(CH2)6NH
2
CH
2
CH
CH
CH2
+ HCN
Mixed mononitriles
Ni
Separation and
isomerisation
Pentenenitriles
HCN
Dinitriles
Separetion
Adiponitrile
Hexmethylenediamin
Hexamethylenediamine is also prepared commercially from
butadience. The butadiene feedstock is of relatively low cost but it does
use substantial quantities of hydrogen cyanide. The process developed by
Du Pont may be given schematically as:
Another process using butadiene as the starting material was
developed by Esso. This involved the reaction of butadiene with iodine and
cuprous cyanide to give the cuprous iodide complex of
dehydroadiponitrile. This is further reacted with HCN to give a high yield
of dehydroadiponitrile and regeneration of the iodine and cuprous iodide.
Commercial routes from acrylonitrile and from caprolactam have
also been developed. This diamine may also be prepared from furfural and
from butadiene.
Sebacic acid and azelaic acid
Sebacic acid is normally made from castor oil, which is essentially
glyceryl ricinoleate. The castor oil is treated with caustic soda at high
temperature, e.g. 250°C, so that saponification, leading to the formation of
ricinoleic acid; is followed by a reaction giving sebacic acid and octan-2-ol
(Figure 37).
Because of the by-products formed, the yield of sebacic acid is
necessarily low and in practice yields of 50-55% (based on the castor oil)
are considered to be good.
128
Castor Oil
Glycerol
+
CH
3
(CH2)5CHCH2CH
CH(CH
2)7
COOH
OH
NaOH
NaOH + H
2
O
CH3(CH2)5CHCH3 + HOOC(CH2)8COOH +H
2
OH
Figure 37
CH3(CH
2
)5CHCH
2
CH
CH(CH
2)7
COOH
O
2
, O
3
, H
2
O
Solvent
CH
3
(CH
2)7
COOH + HOOC(CH
2
)
7
COOH
Azelaic acid is made by the ozonolysis of another natural product,
oleic acid:
Sebacic acid is used for nylon 610 and azelaic acid for nylon 69.
Caprolactam
Caprolactam is preferred to co-aminocaproic acid for the
manufacture of nylon 6 because it is easier to make and to purify. Over the
years many routes for the manufacture of caprolactam itself have been
developed and major commercial routes are summarized in Figure 38. Of
these routes the bulk of manufacture is via cyclohexanone and
cyclohexanone oxime.
OH
+H
O
H
CH
3
OH
2
2
O
2
H
OH
H
COOH
-H
2
+
NOCl hν
H
O
H
2
CH3COOH
(CH
3
O
(NH2OH)|H2SO
COOH
H
CHO +O
2)
CO O
(CH2)
3
NOH
4
HNOSO4-CO
NH
3
4
CO NH
Caprolactan
(CH
2)3
H2SO
H
3
Figure 38
129
The alternative route involves the air oxidation of cyclohexane and
Castrol Oil
CH
3
(CH
2
)
5
CHCH
2
CH
CH(CH2)7COOR
OH
CH
2
CH(CH
2
)
8
COOR C
6H13
CHO
+
Pyrolysis
500
0
C
Hydrolysis
CH
2
CH(CH
3)8
COOR C
6
H
13
CHO
+
Bromination
CH
2
CH
2
(CH
2)8
COOH
+
CH
3
CH(CH
2)8
COOH
Br
Br
NH
3
NH
2
(CH
2
)10COOH
proceeds via the production of a mixture of cyclohexanol and
cyclohexanone often known as KA oil.
Of the other routes the photonitrosation process involving nitrosyl
chloride is in use in Japan. This avoids, at the expense of complicated
purification processes, the high yields of ammonium sulphate unavoidably
produced in the route involving the Beckmann rearrangement.
ω-Aminoundecanoic acid
The starting point for this amino acid, from which nylon 11 is
obtained, is the vegetable product castor oil, composed largely of the
triglyceride of ricinoleic acid. This is first subjected to treatment with
methanol or ethanol to form the appropriate ricinoleic acid ester.
Cracking of the ester at about 500°C leads to the formation of the
undecylenic acid ester together with such products as heptyl alcohol,
heptanoic acid and heptaldehyde. Undecylenic acid may then be obtained
by hydrolysis of the ester. Treatment of the acid by HBr in the presence of
a peroxide leads to ω-bromoundecanoic acid together with the 10-isomer,
which is removed. Treatment of the ω-bromo derivative with ammonia
leads to ω-aminoundecanoic acid, which has a melting point of 50°C:
This amino acid may also be produced via telomerization reactions
(see below).
ω-Aminoenanthic acid
Interest in this material as an intermediate for nylon 7 arises largely
from the development by Russian scientists of the process of
telomerization, a process yielding low molecular weight polymers of
simple unsaturated compounds, the polymers possessing useful reactive
end-groups. Of greatest interest to date is the reaction of ethylene with
carbon tetrachloride initiated by a peroxide such as benzoyl peroxide. The
130
reaction proceeds by the following stages.
I- + CCl
4
ICl + CCl
3
-
Initiator
Radical
Inert
Compount
Radical
CCl
3
+ CH
2
=CH
2
Cl
3
CCH
2
CH
2
Cl
3
CCH
2
CH
2
+ CH
2
CH
2
Cl
3
CCH
2
CH
2
CH
2
CH
2
etc
Cl
3
C(CH
2
CH
2
)
n
+ CCl
4
ClC
3
C(CH
2
CH
2
)
n
Cl
+ CCl
3
Cl(CH
2
)6CCl
3
Cl(CH
2)6
COOH
NH
2
(CH
2
)6COOH
+NH
4
Cl
H
2SO4
NH
3
Because of the random nature of the occurrence of the chain
transfer reaction which terminates molecular growth, polymers varying in
molecular weight will be formed. For reaction at about 100°C, 100
atmospheres pressure and with an ethylene-carbon tetrachloride ratio of
about 4:1, about 60% of the telomers have 7, 9 or 11 carbon atoms in the
molecule. The individual telomers may be fractionated at reduced
pressures. ω-Amino acid may be obtained from the isolated telomers by
hydrolyzing the –CCI3 group on heating the telomer with concentrated
sulphuric acid for one hour at 90-100°C and then treating the product with
an aqueous solution of ammonia under pressure. As an example, for ω-
aminoenanthic acid the following reactions occur
The amino acid and the ammonium chloride may conveniently be
separated by passing through a column of ion-exchange resins. The amino
acid melts at 195°C.
ω-Aminopelargonic acid (for nylon 9) and ω-aminoundecanoic
acid may also be prepared by this route.
Dodecanelactam
Nylon 12 first became available on a semicommercial scale in
1963. The monomer, dodecanelactam, is prepared from butadiene by a
multistaged reaction. In one process butadiene is treated with a Zieglertype catalyst system to yield the cyclic trimer, cyclododeca-1, 5, 9-triene.
This may then be hydrogenated to give cyclododecane, which is then
subjected to direct air oxidation to give a mixture of cyclododecanol and
cyclododecanone. Treatment of the mixture with hydroxylamine yields the
corresponding oxime, which on treatment with sulphuric acid rearranges to
form the lactam: