Tải bản đầy đủ - 0 (trang)
1 Characterization of PSPA, PSTMA, PSTHPA, PSPMDA

1 Characterization of PSPA, PSTMA, PSTHPA, PSPMDA

Tải bản đầy đủ - 0trang

272



GANGULY



are insoluble in organic solvents including aliphatic and aromatic hydrocarbons in

which PS is freely soluble. Table 1. compiles the elemental analysis data based on



SYNTHESES, CHARACTERIZATION



273



suggested structures of Figure l.The IR spectra of PSPA, PSPMDA and PSTMA

indicate the stretching bands at

typical of aromatic carboxylic acids. At

and

peaks correspond to aromatic C=C stretching and due to

diaryl ketone respectively. The IR spectrum of PSTHPA is otherwise same; expect

the alicyclic carboxylic acid peak at



The total capacities of PSPA, PSTMA, PSPMDA and PSTHPA are found to

be 0.96, 1.89, 1.60, and 2.72meq/g (dry) polymer respectively. It has been

observed from Table 2. that almost all of the four anhydride modified polystyrenes

show a higher pK value compared with the literature value for COOH (25). In

addition, both PSPA and PSTHPA show one pK value whereas PSPMDA and

PSTMA show two and three pK (Figure 6) values respectively which is in

accordance with the proposed structure. It is apparent from the proposed structure

for PSPMDA and PSTMA that due to ortho, meta and para effect the exchange of

Na+ ion in all the –COOH groups are not same. In contrast, considering the case

of Matheison and Shet (27), it is not surprising to expect that due to high

crosslinking in PSPMDA some –COOH groups will be H-bonded resulting in low

degree of dissociation or higher pK values.



Comparison of TGA analysis of PSPA, PSPMDA, PSTMA and PSTHPA in

air and in nitrogen have been replotted in Figure 7.(a and b). The thermal stability

of PSPMDA is observed to be more or less the same as that of PSTMA up to

approximately 390°C, though the ultimate stability of the trend in the variation of



274



GANGULY



the thermal stability reveals that PSTMA is thermally more stable. It is possible

that additional crosslinks in the network are introduced in a non-facile way in

PSTMA in which the –COOH groups are exposed during the course of weak bond

formation, while in PSPA only one –COOH group will be available per pendent

ring.



PSPMDA has greater stability PS, PSPA and PSTMA.The higher thermal

stability is apparently consistent with a more rigid network of PSPMDA resulting

from interchain crosslinking involving PMDA moieties. About the cross-linked

structure of PSPMDA, it has been reported that like the conventional cross-linking

process, a small part of PMDA molecules involve at early stage (28). The

remaining molecules of pyromellitic dianhydride react at first by only one of their

functional groups and wait for favorable conformation of the neighboring

polystyrene chain. Ultimately, the other group will react to give least unstrained

structure. Hence, macrosyneresis will not stop even when the network becomes

sufficiently rigid.



SYNTHESES, CHARACTERIZATION



275



The Tg values as observed from Table 4. appear to be rather consistent with

what is to be expected from consideration of the copolymerisation effect coupled

with the addition of rigid side groups(29), followed by branching and crosslinking

on the polystyrene network and formation of stiff bonds. These effects tend to

decrease the flexibility causing hindrance to rotation and hence



increase Tg. In PSTHPA, the hydrogen bonding is much higher for the aliphatic

–COOH group, than that observed for PSPA, PSTMA, whereas in PSPMDA, the

crosslinking due to PMDA results in highest Tg. Therefore, the order of Tg of the

four anhydride modified polystyrene is justified.

PS
During the optimization reaction of PSPMDA, we have observed the

interesting feature for the reaction is the reduction of gelation time from 40 h to 1530 min with the change of reaction temperature 40 °C to 100 °C (Figure 8).



We have controlled the morphology of PSPA using in a (1) nonsolvent for

modified polymer, i.e., nitrobenzene medium and (2) in 1,2-dichloroethane

medium, which is a solvent as well as a reactant for the reaction(Figures 9&10).



276



GANGULY



Nitrobenzene medium shows large number of holes, which are created by the

removal of nitrobenzene due to the solvent action of benzene. PSPA synthesized

in 1,2 dichloroethane medium; rather it shows a corrugated surface because of high

substitution on the benzene ring of polystyrene due to competitive Friedel Crafts

acylation and alkylation reactions.



Reproduced Author’s work from J. of Appl. Polym.(5).



3.2 Novel Membrane from Pyromellitic dianhydride Modified

Polystyrene with controlled pore size on Micro- and Macrolevels

On the basis of the acquired data, we have fabricated a novel membrane from

PSPMDA.The membrane was characterized by TGA, DTA and

solid

state NMR.The cross-section morphology is spectacular. The membrane is

generally viewed as a honeycomb structure as shown in Figures 11 and 12. The

pore size is approximately

It appears that the mean diameter of the pores

increases from the surface. The magnification in Figure 13 shows the interior of the

large holes. The walls of those cavities and boundaries are also porous. The

average pore size is

Figure 14 shows covered and uncovered holes side by

side. Based on our technique of membrane fabrication and the feature of the above

morphology, a possible mechanism has been proposed.



3.3 Structural Characterization of Sulfonic acids resins PSPAS,

PSTMAS, PSTHPAS and PSPMDAS

The sulfonic acid resins, PSPAS, PSTMAS, PSTHPAS and PSPMDAS, are

brittle and black in colour and insoluble in organic solvents . However, the resins

swell considerably in organic solvents due to gel nature . The sulfonation of

PSPMDA results in the presence of a polyquinonic structure in between the



SYNTHESES, CHARACTERIZATION



277



polyethylene chain which posses the most rigid cross-links, hence a highly limited

conformational mobility. The sodium salt of the resins are brittle and brownish

black in color and exhibit the same solubility characteristics of H-form of resins.



Reproduced Author’s work from J. of Appl. Polym.(9).



Table 5. summarizes the pertinent IR absorptions in PSPAS, PSTMAS,

PSTHPAS and PSPMDAS, and their assignments. Significantly, no stretching

band due to –COOH group appears in the IR spectra.

Incorporation of sulfonic acid group is also endorsed by the results of sulfur



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

1 Characterization of PSPA, PSTMA, PSTHPA, PSPMDA

Tải bản đầy đủ ngay(0 tr)

×