Chemistry Reference
In-Depth Information
stability of PETP and polymethylterephthalate does not differ very much, and thermal
stability of polybutylene terephthalate is less, than that of PETP and polymethylterephthalate.
On the basis of the results of investigations [192, 193] it was proved in the work [194]
that thermal stability of polyester will depend on one of the initial reagents (alcohol) taken for
polymer synthesis.
Decrease of polymer molecular mass takes place during the process of destruction. In the
work [195] there has been shown linear behaviour of the dependence of lg(da/dt) on t (time),
which speaks about the fact that the quantity of broken bonds α at any moment of time is
defined by the equation α=1-e
kt
, hence, decrease of molecular mass at PETP destruction
happens as a results of bonds decay according to the law of randomness. This conclusion is
proved by PETP destruction in nitrogen flow at 280ºC which does not lead to the change of
the character of molecular - mass distribution (MMD) [196].
R
C=O
O
R
C=O
O
R
C=O
O
CH CH CH CH CH CH
O
R C O CH=CH
2
2
2
O
R C O CH CH CH=CH CH=CH R C OH
O
+
2
During thermal destruction colourless PETP-fibre is dyed into cream-colour, then it turns
yellow and further becomes brown. It was shown earlier that darkening of decomposed PETP
is connected with polymer product dyeing and is not caused by the presence of dyed low-
molecular compounds. Vinyl ester groups in decomposed PETP even at temperatures up to
300
0
C are able to come into reactions of polymerization [197].
Besides there appear branched chains, containing sections of polyvinylbenzoate type,
which may again decompose through ester bonds with hydrogen atom break in β-position
regarding ester bond end forming and carboxyl groups: R-C
6
H
4
.
So, there appear systems of conjugated double bonds which cause polymer dyeing.
It should be noted that some authors [198, 199] connected polymer dyeing at thermal
destruction with aldehyde polymerization:
nCH
3
CHO CH
3
(CH=CH)
n-1
+(n-1)H
2
O
There has been also voiced a supposition about simultaneous proceeding of both
processes [200].
In the work [201] it was supposed that chemical behaviour of PETP thermal
decomposition both in inert medium and in atmosphere is defined by the mechanism
assuming formation and decay of intermediate cyclic compounds, catalyzing the process.
Prokopchuk N.P. [199] with his research workers suggested the scheme of radical
mechanism of PETP thermal destruction with initiation by the way of C-H bond break:
-C
6
H
4
-COO-CH-CH
2
-OOC-C
6
H
4
-
Æ
-C
6
H
4
-COOCH=CH
2
+-OOC-C
6
H
4
-
Search WWH ::
Custom Search